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RIVERS AND ESTUARIES 
 
 OR 
 
 STREAMS AND TIDES 
 
 -*«c?^ 
 
RIVERS AND ESTUARIES 
 
 OR 
 
 STREAMS AND TIDES 
 
 AN ELEMENTARY STUDY 
 
 i;y 
 
 W. HENRY HUNTER, M.Inst.C.E., M.Am.Soc.C.E. 
 
 With diagrams 
 
 LONGMANS, GREEN, AND CO 
 
 39 PATERNOSTER ROW, LONDON 
 NEW YORK, BOMBAY, AND CALCUTTA 
 
 1913 
 
 All rights reserved 
 
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 0^ 
 
 &^^^s 
 
PREFACE 
 
 The Elementary Study which is contained in the ensuing pages, 
 is to a large extent based upon Lectures on the subject of " Eivers 
 and Estuaries," which were delivered in the beginning of 1911 at 
 the desire of the Council of the Institution of Civil Engineers, and 
 under the Vernon-Harcourt bequest, to the Students of the 
 Institution in various parts of Great Britain; and upon further 
 Lectures on the subject of " Streams and Tides," delivered in the 
 University of Manchester to the Students in the Department of 
 Engineering there, which is under the capable direction of 
 Professor Petavel, F.RS. 
 
 The object of the Lectures, which was kept in view during 
 their delivery, was to furnish to these young Students information, 
 and to offer to them counsel, which experience had taught the 
 lecturer would have been of lifelong service to him had he heard 
 and learned the same things in the remote period when he too was 
 young. 
 
 To youth pertains the inheritance of the ages, but to youth 
 also pertains a portentous faculty of forgetting ; for which reasons 
 amongst others, this Study is issued and is respectfully dedicated 
 to the Engineering Students of the present day. 
 
 W. H. HUNTER. 
 
 42, Speing Gardens, 
 Manchester. 
 October, 1912. 
 
 283562 
 
CONTENTS 
 
 CHAP. PAGE 
 
 I. Difficulties of the Subject 1 
 
 II. Physical Difficulties 5 
 
 III. The Pursuit of Information 11 
 
 IV. Flow round Beni>s 18 
 
 V. The Mouth of the River 25 
 
 VI. River Improvement Works 30 
 
 VII. Estuarial Works 37 
 
 VIII. Some Fatropean Examples 42 
 
 IX. Some American Examples 48 
 
 X. The Mersey 52 
 
 XL Estuarial Models 62 
 
 Index 67 
 
CHAPTEK I 
 
 DIFFICULTIES OF THE SUBJECT 
 
 Amongst the multitude of matters which engage the attention 
 and occupy the mind of the student of engineering, whether that 
 student is still in static pupillari or has reached more mature 
 years, there are none more difficult, none in which there is greater 
 liability to error, or in which the student is in greater peril of 
 failing to take all material points into consideration, than those 
 which relate to the subject of rivers and estuaries ; the difficulties, 
 as a matter of course, becoming particular when the study is 
 directed to the case of a special river and estuary, and has for its 
 objective the improvement of the waterway as a course for the 
 free passage of floods from the land and of the tidal column from 
 the sea, or for the purposes of navigation. 
 
 The reason for this is not far to seek. In dealing with ques- 
 tions relating to docks, canals, railways, and the like, men deal 
 with works which are graven by art and man's device, are created 
 by human minds and produced by human efforts, and which there- 
 fore can be controlled and maintained by the minds and efforts 
 which brought them into being ; while when attempt is made to 
 deal in a practical way with matters which pertain to the flow of 
 streams and the movements of tides, the attempt involves an effort, 
 first to understand and then to guide and to regulate the great 
 primeval forces to which such physical features as rivers and 
 estuaries owe their existence, and by which they are in a sense 
 maintained ; although in the great majority of cases the conditions 
 of their equilibrium are so unstable that endless change forms 
 part of the actual economy of the maintenance. 
 
 The uncertainty and attendant vagueness which beset the 
 subject may be illustrated (a) by propounding three questions of 
 apparently puerile simplicity, and (h) by searching for suitable 
 replies to these childish queries. 
 
2 h'lVFPS AND ESTUARIES 
 
 The questions are : (1) What is a river ? (2) What is an 
 estuary ? (3) Where does the one end and the other begin ? 
 
 Beginning with the first question. It will be found that 
 etymology can offer but little assistance to the student in his 
 quest. Our word " river " came to us from the Latin ri'pa, a 
 bank ; a derivative of which is riparius, a bank by which water 
 is confined (from which again came the familiar word " riparian," 
 an adjective which is frequently used with more hardihood than 
 discrimination, in order to denote what are alleged to be " riparian 
 rights" of "riparian proprietors" by owners of property whose 
 land does not at any point touch the bank of the stream or water- 
 course, in respect of which the rights of a bank owner are claimed), 
 but which has no direct connection with the water which flows by 
 or surges against that bank ; and it can hardly be deemed that a 
 definition of a river which excludes the fluid therein will satisfy 
 an engineering student : while if it be contended that a river is a 
 body of water confined between riparia then the Mediterranean 
 Sea is a river ! If etymology be abandoned as hopeless and the 
 precise phraseology of the jurist be prayed in aid, so far as 
 English law is concerned the result will be disappointing, as if the 
 Salmon Fishery Acts (1861 to 1866) be taken as an illustrative 
 example it will be found that the word " river " is defined 
 as including " such portion of any stream or lake with its tribu- 
 taries, and such portion of any estuary, sea, or sea coast " as may 
 be declared by the Secretary of State to belong to any particular 
 river.^ The phraseology of American law seems at first sight to 
 be more satisfactory, " As a general proposition wherever there is 
 a steady uniform current of water it constitutes a river," ^ but 
 reflection will show that though there is a " steady uniform 
 current " through the Lake of Geneva on the one hand, and 
 through many a tiny watercourse over which a boy can hop or a 
 cat jump on the other hand, yet neither of the phenomena would 
 be described by an engineer as a river. 
 
 The efforts of science have not been much more successful. 
 " The term river,'' said the late Professor Eobison, " is appro- 
 priated to a considerable collection of waters, formed by the 
 conflux of two or more brooks, which deliver into its channel the 
 united streams of several rivulets, which have collected the supplies 
 of several rills, trickling down from numberless springs, and the 
 
 » " The Law of Waters," by H. J. W. Coulson and U. A. Forbes, p. 385. 
 ' " American Law of Easements," by Emory Washburn. 
 
DIFFICULTIES OF THE SUBJECT 3 
 
 torrents which carry off from the sloping grounds the surplus of 
 every shower : " a definition which seems to be at once remi- 
 niscent of the nursery rhymes of early youth, and of the well 
 established principle in English law that if the drains from " two 
 or more " inhabited houses discharge into a " brook," that brook 
 becomes a sewer, and passes under the control of the local 
 Sanitary Authority. 
 
 The only answer to the question which presents itself is that 
 a river is the main course by which the run-off from a watershed 
 is borne to the sea, a definition which is open to the criticism that 
 tried by the letter of the proposition the Missouri is not a river, 
 the only possible reply to the criticism being that it is obvious 
 that the matter is one of degree. 
 
 The second question is, if anything, more difficult than the 
 first, as the minds of most people are in a more nebulous condition 
 about the estuary than about the river. The derivation is again 
 from the Latin: this time from the verb mstuo, to 'boil or to foam. 
 So that in strict speech the estuarial line is that on which the 
 incoming tide meets and foams against the fluvial stream of land 
 water struggling to make its way into the sea, to which "all the 
 rivers run." The estuarial line changes its position from moment 
 to moment during the period of flood, and changes its total stroke 
 from tide to tide, so that the only practical definition of an estuary 
 is, that it is an area on the sea coast, an indent into the land, in 
 which estuarial lines are formed at certain times and under certain 
 conditions; a definition about as precise as that offered by the 
 bewildered statesman in the old story, from whom information 
 was demanded as to the actual duties of an archdeacon, and who 
 replied that, so far as he understood the matter, an archdeacon 
 was an ecclesiastic " who from time to time performed archidiaconal 
 functions." 
 
 If such difficulty be found in formulating a description of 
 either river or estuary in terms which will stand the test of 
 criticism, it may be that at this point the student will be prepared 
 to avow himself of one mind with the distinguished law lord, 
 who possesses as astute a mind and as acute an intellect as any 
 man of his generation, and who on one occasion, first stated 
 frankly that he never could make out where the estuary ended 
 and the river began, and then tore to tatters every solution of 
 the problem which was presented to him. 
 
 This is by no means a mere matter of words, or of quibbling 
 
4 RIVERS AND ESTUARIES 
 
 about words. Cases might be cited in which engineering witnesses 
 have floundered, and learned judges have gone wrong because they 
 were not clear in their own minds as to what the word "river" 
 really means ; while the point at which the estuary ends and the 
 river begins must be authoritatively determined somehow ; as in 
 an estuary, the right-hand bank is on the starboard side of a vessel 
 which proceeds inland from the sea ; while, in a river, the right- 
 hand bank is, on the contrary, on the right of an observer who 
 stands looking in the direction in which the stream is flowing; 
 and any engineer who has been accustomed to the deposit of 
 plans for private Bills in Parliament, knows how many mistakes 
 are made in this respect in the " bank sections " which are required 
 to form part of the deposit, when a river and an estuary come 
 within its scope. 
 
 The suggestion to the student is that the point of division 
 between the river and the estuary should be determined by the 
 line which marks the limit of * the flow of the highest tide when 
 uninfluenced by the wind, except perhaps in such cases as those 
 in which the dividing line has been or is to be arbitrarily fixed 
 by artificial works. 
 
CHAPTER II 
 
 PHYSICAL DIFFICULTIES 
 
 We now turn from difficulties of term and description to difficulties 
 of a physical sort ; difficulties which have the quality of inherence 
 because they are native to the operation of the forces to which 
 the earth owes her form and value, and the streams and the tides 
 owe their existence. 
 
 The area of this planet, measured as an oblate spheroid at the 
 mean level of the sea, is about 192,000,000 square miles, of which 
 some 55,000,000 miles are land, and 137,000,000 are sea. 
 
 Excluding past periods of geological age, which are not within 
 the ambit of this study, the proportion between land and sea in 
 historic times seems to have been fairly constant : which implies 
 that the effects of the two great antagonistic forces of Nature 
 have, taken as a whole, balanced each other. 
 
 These two forces are gravitation, which leads to concentration 
 of material, and radiation (that is to say, dissipation of energy 
 in the form of heat), which tends to contraction. The one force, 
 aided by minor and subsidiary forces, leads to the lowering of the 
 level of the land and the deposit of the material thus won from 
 the land, in the bed of the sea. The other force causes irregular 
 contraction in the crust of the earth and produces as a consequence 
 of the contraction, serration, upheaval, lifting of the crust or of 
 parts thereof against gravity. This action, which shows itself in 
 what geologists describe as "folding, crushing, and overthrust 
 faulting," is the genesis of many of the mountain ranges, and is 
 also the cause of such processes as those of which the signs were 
 noted by Dr. Darwin on the coast of Chili in 1835, when measure- 
 ments which he made led him to conclude that in comparatively 
 recent times, a long strip of that coast has been upheaved by suc- 
 cessive movements, to heights of from 400 feet to 1100 feet above 
 the level of the sea. 
 
6 RIVERS AND ESTUARIES 
 
 The effect of such a movement upon the estuarial indents of 
 that coast and upon the rivers which drain into them can readily 
 be imagined, but it is in the local operation of the forces of gravity 
 and of radiation that the student who is concerned in the main- 
 tenance and improvement of rivers and estuaries is interested, 
 rather than in such remarkable phenomena as those described by 
 Dr. Darwin. 
 
 Gravity is of itself a static and conservative force ; but acting 
 in conjunction with Nature's carving tools, air, water, chemical 
 effect, extreme heat, severe cold, and such-like; the combined 
 effect of the whole, working as they do " without haste and without 
 rest," is change and transformation. Solid rocks are broken up 
 into ever diminishing fragments, parts are converted into particles, 
 masses are reduced to boulders, boulders to pebbles, pebbles to 
 sand, and sand to imponderable silt; while parts and particles 
 thus formed are seized by the flowing waters, and are hurled, 
 swept, rolled, or borne onwards and downwards until a new 
 resting-place is found for them as parts of low-lying and fruitful 
 lands, as encumbering banks in the bed of an estuary, or as ever- 
 increasing deposits in the marginal depths of the sea. 
 
 The sum of the whole matter may be expressed in two words. 
 Disintegration and Teansportation. The disintegrating effects 
 of the agencies described, subject refractory masses to the operation 
 of gravity, through which operation again water falls upon the 
 earth in the form of snow or rain, and under which it seeks a 
 plane of equilibrium at the sea level from whence it originally 
 proceeded, so that the great cycle may be completed; but the 
 point here is that the water does not return empty handed to the 
 source from whence it came, but bears with it, on its way, the 
 dehris of the mountains and of the hills. 
 
 At this point it is necessary to revert to the definition of a 
 river already suggested, as such will serve for the present purpose ; 
 that is to say, that a river is the main course through which the 
 run-off from the watershed is borne to the sea ; or, in other words, 
 is the line of least resistance to the discharge of the rainfall, as it 
 is obvious that this line of least resistance is the line upon which 
 the dehris from the earth will be transported until some more or 
 less stable resting-place is found for it. 
 
 The earth never becomes outworn, because its face is ever being 
 renewed. The process of renewal is one of disintegration and of 
 transportation; and beneficial as the process is when looked at 
 
PHYSICAL DIFFICULTIES 7 
 
 from one point of view, from another point of view it is big with 
 peril of injury to the river and of destruction to the estuary. 
 Failure to appreciate this fact, and consequent inability to 
 apprehend the potency of the forces which operate to the prejudice 
 of watercourses, have led to the irreparable injury of more than 
 one river and to the virtual ruin of more than one estuary, 
 through futile efforts for improvement and reclamation by means 
 of works which were unadapted to the conditions ; the fact being 
 that the conditions were not understood. 
 
 The locality where the river with its load of dhhris debouches 
 upon the coastline demands the special attention of the student, 
 as in many cases it is at that place that the conditions are 
 complicated by another phase of the operation of gravity. The 
 phase is that known as tidal action, an action which progresses in 
 two stages primary and secondary. The primary stage has its 
 most marked effect in the marine belt which girds the southern 
 portion of the globe, the effect of the secondary stage can be 
 observed on the greater part of the coastlines on the earth. 
 
 The primary stage is due to the direct attraction of the sun 
 and of the moon, which cause heaping-up of the mobile waters in 
 the ocean, sometimes at one and the same degree of longitude, 
 when the lines of attraction of sun and moon are co-incident, at 
 other times at degrees widely apart from each other, when the 
 lines of attraction are diverse in direction. 
 
 In the secondary stage gravity acts as a levelling and, 
 therefore, as a distributing force, through which the effect of the 
 heaping up in the Southern Ocean is spread over nearly all the 
 water areas connected with that ocean, causing rise and fall in 
 these areas generally speaking twice in each day, or in other 
 words producing the diurnal tides. 
 
 The heaping up in the great southern belt is of itself but small 
 in height, not more than two feet at most,^ when the attraction 
 of sun and moon are co-incident, at which time the spring tide 
 period follows the heaping up. It would be impossible, and is 
 unnecessary, to deal in an elementary study with this primary 
 stage of the operation of gravity, or with the intricacies of the 
 distribution of the wave, or with the almost infinite diversity of 
 
 * Sir George Airey calculated that the greatest tidal height in the Southern 
 Ocean is 1*95 feet, of which 1-34 feet are due to the attraction of the moon, and 
 0*61 foot is due to that of the sun. Such observations as have been taken, and 
 such measurements as have been made, have confirmed the calculation. " Tidal 
 Rivers," by W. H. Wheeler (Longmans, Green & Co.), p. 82. 
 
8 RIVERS AND ESTUARIES 
 
 form and circumstance which in some parts of the earth greatly 
 magnify the tidal oscillation, as in the Bay of Fundy, the deep 
 bight between New Brunswick and Nova Scotia, where the tidal 
 range is about fifty feet at springs; or obliterate it altogether 
 as in the Mediterranean, or produce regularly a range at spring 
 tides of nineteen feet in the Bay of Panama in the Pacific Ocean, 
 while in Limon Bay in the Atlantic, only forty-nine miles away, 
 there is but a fitful and irregular tide, which seldom exceeds two 
 feet in height, and frequently disappears altogether. 
 
 The effect of the tidal rise and fall at and upon the mouth of 
 any river is enormously influenced and complicated by wave 
 action, the occasion of which is the ceaseless variation of 
 barometric pressure on the surface of land and sea. This variation 
 is but another phase of the operation of gravity, but it leads to 
 vast atmospheric disturbances, now causing hurricanes and 
 tornadoes which lash the waters into fury, and again producing 
 soft breezes and gentle zephyrs which cajole them into languid 
 movement, the difference being mainly one of degree. Where 
 there is movement of marine waters first in the form of " waves 
 of oscillation" in the greater depths, subsequently in that of 
 " waves of translation " when the depths begin to diminish, and 
 finally in that of "rollers " or "breakers'* on the shore: there is 
 always movement of material, which is in fact an effort on the 
 part of the sea to cast up again on the land the terrigenous 
 material with which its bed is blanketed for a width of about three 
 hundred miles from every coastline which abuts upon an ocean or 
 a great sea. This belt of terrigenous deposit extends to an ocean 
 depth of about four miles and has at times been termed the 
 " transitional " or " critical " area. The importance of the belt 
 may be measured by two facts, (1) that it covers one-fourth of the 
 earth's surface (or in other words that the " critical " area is equal 
 in extent to two-thirds of the combined areas of all the lands on 
 the globe), and (2) that in it tides and currents produce their 
 maximum effect in the transport of material, this effect having 
 been traced in some instances to a depth of three hundred 
 fathoms.^ 
 
 ^ These facts were determined by the celebrated Challenger expedition 
 of 1872-6, through which also the existence of " Cosmic dust " (which after 
 the manner of fine rain falls upon the ocean floor, and accumulates thereon) was 
 detected. H.M.S. Challenger was commanded by Captain G. S. Nares, R.N. 
 (now Sir George S. Nares, K.C.B., F.R.S.), and the expedition was at the outset 
 led in a scientific way by the late Sir Wyville Thomson. 
 
PHYSICAL DIFFICULTIES 9 
 
 The combined effects of tidal and wave action are varied but 
 are sufficiently apparent in most places. There are few parts of 
 the east coast of England where cliff destruction may not be 
 studied ; many parts, such as the Norfolk coast, where that 
 destruction is proceeding on a disastrous scale, while collateral 
 mischief in the production of shoals and quicksands, such as 
 those which encumber the mouth of the Thames, is also proceeding. 
 On the other hand, practically the whole of the eastern coast of 
 North America, from Long Island in the north to the Bahama 
 Islands in the south, has been built up into fertile territory by 
 material first derived from the land, then deposited in the sea, and 
 finally disturbed by wave action and transported along the foreshore 
 by the combined influence of the winds, littoral currents, and tidal 
 streams, until the debris has found resting-places on the foreshore 
 above the level of the tidal range. Wherever this operation is in 
 progress it is obvious that the creeks, estuaries, and rivers by 
 which the coastline is interrupted and indented are in some cases 
 in danger of injury, in others in peril of destruction. It is true 
 that the process results in permanent advantage to the foreshore, 
 but it is equally true that it frequently results in detriment to the 
 creek, estuary, or river into which the unwelcome material has 
 been flung by the restless waters, so that works for the mainten- 
 ance and improvement of features of such material importance as 
 the indents in question, have usually for their objective the 
 remedying of injury caused by the deposit of materials within 
 their banks and the prevention, as far as such is possible, of further 
 injury by further deposit. 
 
 But this combined action of wind, wave, and tide, upon 
 materials which have been deposited in creeks and embayments 
 in coastlines is not always detrimental to the depths in or the 
 capacities of such indents. 
 
 On the shores of Bass' Strait which, in the Commonwealth of 
 Australia, divides the southern coast of Victoria from the northern 
 coast of Tasmania, there are several bays, of which Anderson's 
 Bay may be taken as an example ; into which the waters of many 
 rivers flow, bearing with them debris from the lands in the manner 
 already described. The debris is deposited within the shores of 
 the bay, it is hardly necessary to add that no attempt to remove 
 the material by artificial means has been or is ever made ; yet so 
 far as the available information goes, no shoaling of a material 
 sort can be detected in the indents; in the majority of the 
 
lo FIVERS AND ESTUARIES 
 
 cases the capacity below high-water mark seems to have suffered 
 no diminution. 
 
 The explanation of the apparent paradox is that under certain 
 conditions of exposure and of weather, materials derived from the 
 land which have been deposited in the embayments, are stirred up 
 again by wave action, and under the influence of the tides and of 
 strong and steady winds are hurled back by the sea upon the 
 shore, sometimes far above high water of the highest tides. The 
 materials thus hurled back by the sea, together with the shells 
 and other marine accessories which have been borne along with it, 
 are seized by the winds, are built into sand dunes and hills, and 
 are again slowly but surely borne inland in the track of the 
 prevailing winds, until large districts are overspread thereby ; 
 in some cases to the advantage of the affected districts, in 
 others with reverse effect; but always to the advantage of the 
 bays which are thus relieved from the incubus of the terrigenous 
 deposit. 
 
CHAPTEE III 
 
 THE PURSUIT OF INFORMATION 
 
 The assumption may now be made that a student who has taught 
 himself to appreciate the difficulties with which he will be 
 confronted, has been called to deal professionally with some 
 particular river or estuary with a view to the design of works and 
 the conduct of operations for the improvement and development 
 thereof; and the question will be what course is that student 
 to take. 
 
 The first essential, the fundamental requirement, is that he should 
 collect for himself information as to the regime of the stream and 
 the movements of material, (1) in its course and (2) at and about 
 its mouth. It will be found that the task is by no means light or 
 easily accomplished. The facts are frequently wrapped in 
 obscurity, the forces are mutable both in direction and duration, 
 and are incapable of accurate determination. Gradual changes 
 both in form and in meteorological conditions are taking place in 
 most watersheds, and the materials for the history of these changes 
 are usually meagre to the point of attenuation. 
 
 The regime (or regimen) of a river is a term which has some- 
 times afforded sport for dignitaries such as His Majesty's Judges, 
 Chairmen of Select Committees of Parliament, and other great 
 personages. Occasionally the interest in the sport has become 
 intense when some unhappy witness who has used the word as 
 terse and convenient, has found himself unable to define it 
 exactly when authoritatively required to do so. 
 
 The regime of a river may be described as the integration of 
 all the forces which maintain the river in the form in which it 
 exists. Changes in the river are of themselves evidence of 
 changes in the regime, from which it follows that though the 
 regime is an order to be studied, it is not a fetish to be worshipped 
 as though it were incapable of improvement. 
 
12 RIVERS AND ESTUARIES 
 
 It will be found that the information to be acquired, and 
 tabulated, as to the regimen of any river, is as varied as it is 
 voluminous. 
 
 The late Mr. David Stevenson divided rivers in a general way 
 into three parts,^ viz. 
 
 (1) The river proper. 
 
 (2) The tidal compartment {i,e. the estuary). 
 
 (3) The sea proper. 
 
 The division is not altogether exact, but Mr. Stevenson quoted 
 judicial authority for it, and it suggests a system of classification 
 of the data which are to be obtained and of the features which are 
 to be observed. 
 
 For the river proper, in the first instance the area of the 
 watershed should be ascertained and the general character of the 
 surface and of the nature of the sub-soil noted, the rainfall should 
 be measured and the maximum and the minimum quantities 
 which are discharged in flood times and in dry seasons respectively, 
 should be estimated as nearly as is practicable. In many cases 
 but little time or opportunity can be found for rain gauge and 
 other similar measurements and observations, as the matter in 
 hand must be brought to a conclusion of some sort too rapidly to 
 admit of protracted observation : in these cases such information 
 as has been obtained should be compared with the corresponding 
 figures in any known watershed in which the conditions are 
 similar or nearly similar to those in the area under investigation, 
 and a factor of comparison evolved which, applied to the tabulated 
 results in the watershed in which accurate information as to rain- 
 fall and run-off is available, will furnish particulars which are not 
 likely seriously to mislead the observer who is working in the 
 new ground. 
 
 When this assistance fails, help in estimating the quantities of 
 maximum run-ofiP may be obtained by observing and levelling 
 flood marks which can almost always be discovered, while for 
 minimum discharge when all other methods fail it is usual in this 
 country to assume an average run-off of 0*25 cubic foot per second 
 from an area of a 1000 statute acres ; a constant which is largely 
 used by waterworks engineers in preliminary inquiries relative to 
 the run-off which may be expected from comparatively unknown 
 catchment areas, but which, if employed for the purpose suggested 
 here, should be accepted subject to the qualification that even in 
 
 ^ *' Canal and River Engineering," p. 67. 
 
THE PURSUIT OF INFORMATION 13 
 
 a case in which the constant may be approximately correct for the 
 whole of the watershed of the river, it will vary considerably in 
 different parts of the watershed, being below the average in the 
 higher altitudes and perhaps much above it in the lower levels. 
 Eecent gaugings of an accurate sort have shown this conclusively. 
 
 The angle of inclination of the trees will show the direction of 
 the prevailing winds, while information will always be forthcom- 
 ing from the inhabitants of the district as to the severity and 
 duration of winter frosts, depth of snow, etc., as these are circum- 
 stances which impress themselves upon the memories of even the 
 least intelligent of natives ; but this information should be received 
 with caution, as the dramatic instinct which is innate in humanity 
 often leads a narrator, in an amiable desire to make his story 
 interesting, to sacrifice accuracy to picturesque detail. 
 
 Then, as the course of the river is followed downward, attention 
 should be paid to the bends in the more tortuous parts, the facts 
 that concavity is evidently increasing here and that shoaling is 
 takiog place there should be noted ; and particularly places where 
 Nature has pushed concavity so far as to indicate efforts for the 
 improvement of the watercourse by forcing it in a new direction 
 should be marked, for at these points the efforts of Nature may be 
 effectively aided by engineering knowledge and skill. 
 
 Cross-sections of the river are indispensable. It is essential 
 that the sections should extend sufficiently far on each side of the 
 stream to cover the range of the highest flood, and that the sections 
 should be spaced so as to show the transverse form of the river 
 at each bend. Subject to this provision it will be found in most 
 cases to be sufficient for the purposes of a preliminary survey if 
 the sections be taken at distances of about one mile apart. 
 
 On the line of each section a gauge must be fixed so that the 
 ever-varying levels of water at each point may be read and 
 recorded when the section is taken, and from time to time after- 
 wards. The whole series of gauges should be referred to one 
 horizontal datum, so that the inclinations of the surface of the 
 stream may be determined from the levels read on the gauges. 
 The inclinations are commonly described as the '* hydraulic 
 gradients " of the river, and upon them the velocities of the flow 
 of the stream depend in large measure. 
 
 Actual observations of the velocities of the flow, taken at 
 convenient parts of the stream, ought not to be omitted in the 
 investigation, as in conjunction with the areas of the cross- sections 
 
H RIVERS AND ESTUARIES 
 
 they render it possible to calculate the volume of water discharged 
 by the river with accuracy at different stages. Velocity of flow 
 is observed in various ways. Sometimes current meters, fitted 
 with a small screw or propeller, from which worm gear is driven 
 which records the travel of the stream in a given time, are used. 
 These meters are not suitable for use in silt-bearing streams, as 
 the friction due to the interposition of even a grain or two of silt 
 between the plates of the meter in use has a very sensible effect 
 upon the revolutions of the instrument, and consequently upon 
 the speed recorded thereby in any given time. Of late the 
 " Pitot " tube in which velocity is converted into energy ex- 
 pended in raising a column of water against gravity, and 
 the result measured in a graduated scale, has been success- 
 fully employed. For ordinary open streams no method of 
 measurement of velocity is superior to that in which rods of equal 
 diameter throughout, weighted so as to float at a depth as nearly 
 as practicable equal to the actual depth of the part of the stream 
 in which they are to travel, are used ; the times at which the rods 
 pass into and out of an accurately measured length of the stream 
 (which should not be too long) being carefully determined by 
 observers, one of whom should be equipped with a stop watch. 
 This was the method employed by Messrs. Humphreys and Abbot 
 in their classical investigation of the regime of the Mississippi 
 river. 
 
 Still proceeding downwards a zone will be reached in which 
 the first evidence of tidal action (observed through the checking 
 of the fluvial stream which becomes apparent there) will be 
 noted ; the significance of the evidence being that the head of 
 the tidal compartment, of the estuary of the river, has been dis- 
 covered, and that somewhere thereabouts the line which is to be 
 fixed as the boundary between the river and the estuary will be 
 found. 
 
 Below this line the gauges to be fixed will be tidal gauges, by 
 means of which the " Establishment of the Port," that is to say, 
 the normal rise and fall of the tides, the times and heights of high 
 and low water at springs and at neaps, the relationship between 
 the tides and the lunar phases, and the manner in which the tides 
 are affected by the direction and strength of the winds, is to be 
 determined, first tentatively, and after more extended observations, 
 with as near an approach to finality as possible. 
 
 For this purpose self-registering tide gauges such as are now 
 
THE PURSUIT OF INFORMATION 15 
 
 made by Sir W. H. Bailey and Co. and other well-known firms of 
 British Engineers offer overwhelming advantages. They are 
 worked by the tides themselves, their results are much more 
 reliable than those obtained from human observers, their records 
 are continuous, and if they receive proper attention they never 
 stop. 
 
 Two circumstances militate against the use of these gauges in 
 preliminary surveys, (1) their cost is considerable, and (2) it is 
 difficult to find sites for them at which the whole range of the tide 
 may be measured without thrusting the gauges too far out into 
 the estuary. 
 
 When tide gauges in the form of graded boards are used, this 
 difficulty is got over by stepping the boards on the shelving fore- 
 shore in such manner that as the tide rises and the observer is 
 driven inshore, he is able to continue his reading on one board 
 after another until he reaches the line of high water. 
 
 No problem in the whole series of proceedings requires for its 
 solution the exercise of greater care and judgment than that of the 
 selection of the sites for the tidal gauges. Estuarial tides are so 
 fitful and wayward, so given to form eddies here and backwaters 
 there, that experience has shown that it is possible to obtain 
 results from a series of observations of which each item is accurate 
 in itself, but which taken as a whole are absolutely inaccurate and 
 altogether misleading. 
 
 The gauges throughout, whether in the river proper or in the 
 tidal compartment, should be set at the same datum line, plus and 
 minus readings should be avoided for the sake of simplicity and 
 for the avoidance of error, from which it follows that the datum 
 line should be established at a level sufficiently low to permit of 
 all the observations being read upwards from zero, even on the 
 most seaward of the series of gauges. In this country a datum 
 line at a level of fifty feet below Ordnance Datum (which repre- 
 sents the mean level of the sea at Liverpool) will usually fulfil all 
 the conditions required. 
 
 The physical conditions in the tidal compartment must be 
 observed with even greater exactitude and if possible over a more 
 prolonged period than those in the river proper, as it is not only 
 that the tides in an estuary are fitful but that the ways of the 
 estuary itself are as whimsical and perverse, as apparently in- 
 subject to law and regardless of order, as if the indent were 
 seeking for a share in its own administration. 
 
i6 RIVERS AND ESTUARIES 
 
 Notwithstanding these difficulties the dictum laid down over 
 sixty years ago by the late Captain E. K. Calver, E.N. (who was 
 an authority on the subject) in his work on " The Conservation 
 and Improvement of Tidal Eivers " which was published in 1853, 
 that " Nature will answer faithfully if we interrogate her — not if 
 we interrogate ourselves," has been proved by the experience of 
 many men in many lands : while it was an aphorism of the late 
 Sir Benjamin Baker that "Nature never deceives you if you 
 watch her long enough." There is no other way for those who 
 would follow Nature's intricacies in an estuary, but to " watch her 
 long enough." 
 
 Positions of rocky reefs and of hard shelves are to be carefully ■ 
 noted and shown on the plan, as these will generally be found to 
 form nodal points on which the low water channels in the shifting 
 sands swing as they writhe to and fro. All possible information 
 should be obtained and all indications should be observed of the 
 manner and extent of this movement of the unstable channels in 
 the estuarial area. The influences which effect the movement are 
 of vital importance and should be carefully studied. The tidal 
 flow and ebb, the floods from the land, the varying winds all 
 combine to produce changes more or less gradual but mercilessly 
 continuous and sometimes destructive, while at time changes (to 
 which further reference will be made hereinafter) which may 
 almost be described as violent take place in the most unexpected 
 manner and from apparently incommensurate causes. 
 
 Attention should also be paid to the cliffs or banks by which 
 the tidal compartment is bounded, as if these are formed of friable 
 materials, as is usually the case, constant waste will add sensibly 
 to the masses of sand and silt which encumber the bed of the 
 estuary and will proportionately add to the difficulties attendant 
 upon any attempt to regulate and improve the channels. 
 
 In many cases the encumbering masses are swollen and the 
 difficulties are enhanced by the barbarous and filthy practice 
 which still obtains, of pouring crude sewage into tidal waters. 
 Unchecked by law, unhindered by public opinion, and unabated 
 by municipal effort, the pollution continues day and night through 
 all seasons and in all times, even in cities and amongst people to 
 whom it would be a deep affront if any question were raised as to 
 their status, or as to their claim to a place in an organized 
 civilization. 
 
 In respect of the movements of sand, silt, and sludge into, in, 
 
THE PURSUIT OF INFORMATION 17 
 
 and out of the estuary, and of the effect upon such movements of 
 any projected works, questions of great importance, upon which 
 much must depend, will arise as to the existence or otherwise of 
 periods of slack water at or about high tide at different points 
 during flood. Eeliable answers to these questions cannot be 
 obtained from the records derived from the tidal gauges. Nothing 
 but direct observations at regular periods made from a boat moored 
 in the tidal stream and by means of weighted rods and log-lines 
 will meet the case. Observations of this sort have shown again 
 and again that at places where deductions drawn from co-tidal 
 curves, laid down from readings from misplaced gauges, have led 
 to the conclusion that lengthened periods of slack water and of 
 consequent deposit, would be found to exist ; the change from flood 
 to ebb took place with such rapidity that the change actually 
 occurred within the very brief period covered by one observation, 
 that is to say that a float sent forth to measure the flood velocity 
 came back upon the observer under the influence of the first of 
 the ebb currents. 
 
CHAPTER IV 
 
 FLOW ROUND BENDS 
 
 While considering the questions relating to the bends of the 
 river, the student may be advised to take into account, as being 
 worthy of very careful consideration, principles which were 
 enunciated by Prof. James Thomson, F.R.S. (a brother of the 
 late Lord Kelvin), nearly forty years ago, to which little attention 
 has been paid by the majority of engineers, and which seem to 
 have been ignored by scientists. Prof. Thomson first stated as a 
 matter of hydro-kinetic law, and then showed experimentally, 
 that contrary to the opinion generally held, a stream flowing from 
 a straight into a curved channel flows along the bend with a 
 greater velocity on the inner or convex, than on the outer or 
 concave bank, something after the manner of a " whirlpool of free 
 mobility." Yet erosion takes place in the concave bank where 
 the velocity is least, and deposit occurs on the convex side where 
 the velocity is greatest. 
 
 His explanation of the apparent anomaly was, that on any 
 cross stream line of particles in a curved channel, water pressure 
 under the influence of centrifugal force increases from the inner 
 bank to the outer, thus causing a transverse inclination on the 
 surface of the stream, the angle of inclination being upward from 
 the inner to the outer bank. 
 
 But concurrently the lower laminae of water in motion will be 
 retarded by frictional resistance, and will therefore be less influenced 
 by centrifugal force than the laminae above ; hence the lower laminae 
 under the stress of the greater hydraulic pressure on the outer 
 bank will flow diagonally across the channel toward the inner 
 bank, and will expend the remainder of the energy stored in them, 
 in partially rising up that inner bank, and thus forming a sort of 
 cushion between the bank and the stream lines. This cushion 
 will protect the bank from erosion, while the material borne or 
 
FLOn^ ROUND BENDS 
 
 19 
 
 rolled along by the laminae of water in diagonal motion will (or 
 maT/, as Dr. Thomson put it) find a place of deposit there. On 
 the other hand, the surface water on the outer bank will under 
 the influence of gravity descend along that bank, eroding its face 
 in their descent, and providing material for transport by the lower 
 laminae in their diagonal progress across the channel. 
 
 The different lines of motion of the laminae of water are 
 illustrated in the annexed diagrams, of which Fig. 1 represents 
 
 I'l'i'i'i'i'i'iM'vi'm'Pi'iM'i'i'n'n'i'ri'Vi'TWPmnr ^ 
 
 Mu.i.i.i.i.i.i.i.i.irTrra.i,i.i,i.!,Ki,M.i.i.i.i,i,|,i,uT;i 
 Fig. 1. 
 
 a view in plan of part of the experimental tank in which Prof. 
 Thomson, by means of threads, of particles of aniline colours, and 
 of seeds, showed the lines of flow (marked CCCC), while Fig. 2 
 
 r, OUTER BANK 
 
 SECTION AT M-N. 
 Fig. 2. 
 
 represents a cross section of the channel in the tank in which DD 
 shows the surface of the water as raised by centrifugal force at 
 the outer bank, while DE and DF respectively represent the 
 descending laminae on the outer bank, and the ascending laminae 
 on the inner bank. The eddy action in the ascending laminae 
 near the surface of the water could be clearly seen in the experi- 
 mental tank. 
 
lo RIVERS AND ESTUARIES 
 
 A further protection to the inner bank is occasioned by the 
 tendency (which could also be readily observed) of the upper 
 laminae in the stream to flow in lines of greater radius than the 
 line of the curve of the inner bank, leaving space between the 
 inner bank and the line of flow. This space will be occupied by 
 water which has been moving along the bottom of the river, which 
 consequently is flowing at greatly reduced velocity, and which 
 therefore causes deposit of material which has been transported 
 by the stream from higher parts of its course. 
 
 The movements of the different lines of water which help to 
 make up the flow of the stream will be followed more readily if 
 
 Fig. 3 be examined. In 
 
 D ' '-"'-^ Fig. 3, which is derived 
 
 * -* ""-^^ ^\ from Prof. Thomson's 
 
 ^ B ^^^^v^s. \ diagram, the line AB 
 
 ^^^N^^,^\^ \ represents a vertical 
 
 \ \ \ \ film of water moving 
 
 \ \ \ I along and parallel to 
 
 E ie the straight bank of the 
 
 river. At B the com- 
 
 FiG. 3. I mencement of the curve 
 
 is reached, and under 
 the influence of well-known law the film diverges from the inner 
 bank of the curved channel and flows along the line BC. The 
 space between the inner bank and BC is left for occupation by 
 water which has moved down stream along the bottom of the 
 channel on some such line as that shown by DBE, and which 
 bears in suspension silt derived from a higher part of the course 
 of the river. 
 
 It will appear from the foregoing that Dr. Thomson held that 
 growth on the convex side of a river bend is due to material 
 derived from two sources, (1) from the neighbouring concave 
 bank of the stream, and (2) from banks and bends in "higher 
 parts " of the river course. 
 
 Some difference of opinion has arisen as to what the learned 
 Professor's view on this point really was; but it seems to be 
 fairly clear that the conclusion thus stated was that at which he 
 arrived, although he asserted it in somewhat hesitating and 
 tentative terms, to the effect that " ordinarily or very frequently " 
 in rivers in alluvial plains it will be found that detritus travels 
 down stream along the bottom seeking for resting places, and 
 
FLOJV ROUND BENDS 
 
 21 
 
 that in such plains deposit is on the average greater than erosion, 
 except when "geological changes" have occurred by which the 
 causes which produced the alluvial plains in question have been 
 rendered extinct. 
 
 The student who may have any doubt on the point may find 
 a solution for himself first, by spending a day on the banks of a 
 river in flood and secondly, by noting the rapidity with which a 
 bend, such as that shown in Fig. 4, becomes filled up by material 
 derived from " higher parts " of the river, when the bend is cut off 
 either artificially or by natural effect in the manner shown by the 
 hatched lines. There need be no doubt about the matter ; erosion 
 and transport of detritus by water are functions of velocity, and 
 
 Fig. 4. 
 
 when velocity is violently increased by flood action in a river, 
 both must take place, until the eroding and transporting powers 
 of the greatly increased volume of water passing over and through 
 the river's bed and banks are exhausted. 
 
 One reason why Prof. James Thomson's valuable contribution 
 to engineering knowledge in respect of the flow of water round 
 curves has never received the attention which it ought to have 
 commanded, is that the results of his interesting study were 
 published in an ineffective manner. These results were never 
 collected by him or by any one else, and even yet are only to be 
 found in what may, with the deepest respect, be described as the 
 catacombs of modern days ; that is to say, in the transactions of 
 Corporations so learned that the ordinary man, who is always 
 willing to " let the dead past bury its dead," will never venture 
 
22 RIVERS AND ESTUARIES 
 
 to attempt excavation amongst the relics, except under the stress 
 of peculiar and personal interest.^ 
 
 ISTotwithstanding the fact that the manner of the publication 
 of Dr. Thomson's results was not such as to assist inquiry, some 
 responsibility does lie upon scientists and upon engineers (not to 
 say, students) who undertake to deal with questions relating to 
 the flow of water, to make themselves acquainted with them. 
 
 The following quotations from well-known standard works — 
 one a charmingly told geological record of the development of the 
 earth, entitled, *' The Story of our Planet," ^ and the other an 
 engineering memoir of a great and successful American effort for 
 the improvement of the Mississippi Eiver, may serve to add 
 point to this suggestion. In the first of these standard works, the 
 author, whose status in the world of science may be gauged by the 
 
 fact that he is a Past- 
 President of the British 
 Association, says, "Sup- 
 pose, for instance, the 
 course of a stream repre- 
 sented by the lines PAE, 
 QBS, in the annexed dia- 
 gram (Fig. 5), to change 
 Fig. 6. ' at the points AB, from a 
 
 straight line to a curve, the 
 line of quickest motion which is parallel to AP, BQ will pass through 
 C, the middle point of AB. This line below C will not curve in 
 correspondence with the banks so as to divide the space between 
 
 ^ Short papers by Prof. James Thomson were included in the Proceedings 
 of the Royal Society, vols. xxv. (p. 5) and xxvi. (p. 356), and in the Proceedings 
 of the Institution of Mechanical Engineers for 1879 (p. 456). A brief paragraph 
 referring to his conclusions (erroneously attributed to his better-known brother, 
 Lord Kelvin) was published in 1908 by Mr. F. C. Lea, in his work on Hydraulics 
 (p. 520). The conclusions were also referred to by Prof. Unwin, F.R.S., in his 
 comprehensive article on " Hydraulics," in the eleventh edition of the Encyclo- 
 pcedia Britannica, vol. xiv. (p. 72). With these exceptions Prof. Thomson's work 
 seems to have been overlooked until quite recently when, on the completion of 
 the Collected Edition of Lord Kelvin's scientific work, "the idea impressed 
 itself on others that there should be available a full record of the work "of 
 Prof. James 1 homson also. As a result of that happy idea the Collected Papers 
 in Physics and Engineering, by Dr. Thomson, selected and arranged by Sir 
 Joseph: Larmor (the Secretary of the Boyal Society), and Mr. James Thomson, 
 M.A., have just been published in a>ingle volume by the Cambridge University 
 Press, and have been thus brought within the convenient reach of every 
 engineering student. 
 
 - By Prof. T. G. Bonney, F.R.S. (p. 124). 
 
FLOW ROUND BENDS 23 
 
 them equally ; but it will be nearer to the outer bank than the 
 inner bank, because, in conformity with the well-known law in 
 dynamics, " a body in motion will continue in motion uniformly 
 and in a straight line until acted upon by some external force." 
 So the line of quickest motion would continue to be a straight 
 one were it not for the resistance of the outer bank, and the 
 curve which it actually does follow lies rather on that side 
 of the channel. Thus beneath this bank the water flows more 
 swiftly t and its erosive effect is greater than on the opposite 
 side." 
 
 In the second work referred to, of which the title is " A History 
 of the Jetties at the Mouth of the Mississippi Eiver," ^ the author 
 quotes a long, carefully drawn letter (dated March 15, 1874), 
 addressed to the Hon. William Windon, United States Senate, 
 Chairman of Committee on Transportation Eoutes to the Seaboard ; 
 in which the late Mr. James B. Eads, a distinguished American 
 engineer, stated his views of river hydraulics as follows : " The 
 popular theory advanced in many standard works on hydraulics, 
 to wit, that the erosion of the banks and bottom of streams like 
 the Mississippi is due to the friction or impingement of the current 
 against them, has served to embarrass the solution of the very 
 phenomena presented in the formation of the delta of the Missis- 
 sippi. In the bends, the centrifugal force of the water makes the 
 current more rapid on the concave hank of the stream, and there it 
 usually gets its additional load, and the caving in of the bend 
 testifies to the rapacity of the water at that point of its course. 
 Once loaded, however, it can carry no more, and hence it may 
 sweep around half a score of other bends below with equal velocity 
 without injury to them." 
 
 In justice to the eminent men who wrote the words thus 
 quoted, it must be admitted that in many respects the opinions 
 which they expressed were well founded and were sound, and that 
 when these opinions were erroneous, such as that the maximum 
 velocity of the flow in the curved bend of a river will be found 
 along the outer bank (which both asserted), and that a current 
 once loaded to its maximum transporting power at a concave bank 
 might flow round " half a score " of concave banks below without 
 causing any erosion therein, as Mr. Eads thought and said, the 
 errors were due to lack of full acquaintance with the details of 
 the manner in which waters flow along and around bends, which 
 ' By E. L. Corthell, D.Sc. (p. 29). 
 
24 RIVERS AND ESTUARIES 
 
 lack they shared with the great majority of their compeers and 
 their contemporaries*. 
 
 The main channel of the Clyde abreast of Greenock presents 
 an excellent example of a bight in a tidal river in which the 
 flow of water round bends may be studied on a large scale, and it 
 is interesting to note that in a series of special observations carried 
 out in 1862, by Captain Calver, E.N"., for the purpose of a report 
 which he was instructed to make to the Lords of the Admiralty in 
 respect of certain dredging operations which were then proposed 
 in the interests of Glasgow, and to which the Greenock authorities 
 offered a strenuous opposition (subsequently shown by Captain 
 Calver's report to be well founded), that experienced hydrographer 
 noticed a movement '' of the filaments " of water which took him 
 " completely by surprise,'* and which, although described in terms 
 of a somewhat ambiguous sort, was almost beyond doubt, similar 
 to the movement which was apparent in Prof. James Thomson's 
 models and was shown by him on his diagrams. 
 
 Two practical conclusions may be derived from the considera- 
 tion of the subject which forms the heading of this chapter : one, 
 for the engineer, being that all concave bends in rivers should be 
 effectually protected against erosion ; the other, for the navigator, 
 that in steaming against the current along and around a bend in a 
 river the line of least resistance will be found in proximity to the 
 outer and not to the inner bank. 
 
CHAPTER V 
 
 THE MOUTH OF THE RIVER 
 
 If the course of the river be followed downward through the 
 estuarial area to the river's mouth, which is the line upon which 
 the combined volume of the upland and tidal waters is finally 
 discharged into the sea, the student will be confronted by a 
 new series of problems and perplexed by a new congeries of 
 questions. 
 
 Two outstanding questions must be determined at the out- 
 set, before any works are contemplated or any improvements 
 considered. 
 
 These questions are first, Is the river's mouth obstructed by a 
 bar ? and secondly. Are any sensible quantities of sand and silt 
 conveyed from the sea by the tidal column into the estuary ? 
 
 Before pursuing the investigation upon which the answer to 
 the query as to the existence or non-existence of the bar will 
 depend, the conditions and causes which lead to bar formation 
 should be recalled and reviewed. 
 
 In the case of a non-tidal river the existence and maintenance 
 of a bar is due principally to the conflict between the silt-bearing 
 river, which under the power of the kinetic law referred to in the 
 quotation from "The Story of our Planet" in the preceding 
 chapter, seeks to dispose of its burden upon the sea bed as it 
 loses its velocity in the wide and deep waters; and the sea 
 which, as has already been shown, seeks to throw back through 
 the agency of wave action, into the river or upon the foreshore 
 the incubus which was originally derived from the land. 
 
 The Danube discharging into the Black Sea, and the 
 Mississippi discharging into the Gulf of Mexico, furnish familiar 
 examples of bar-encumbered rivers of this class. 
 
 In the case of a tidal river with its waters rising or falling 
 in response to the movement of the tidal wave along a coast on 
 
26 RIVERS AND ESTUARIES 
 
 which the tidal range is considerable, and the drainage area 
 comparatively small, the existence of the bar will be found to 
 be almost wholly due to the marine wave action which tends, 
 except where held in check by the discharge of land water 
 reinforced by the scouring counteraction of the tidal ebb, to 
 form an unbroken beach upon the margin of the sea. 
 
 The outlets of such rivers as the Tyne on the east, and the 
 Mersey on the west of England, will serve as examples of this 
 action and counteraction. 
 
 If a bar be found to exist at the mouth of a river which 
 conveys the run-off from a great watershed to the sea and at 
 which the tidal rise is inconsiderable, it may be concluded that 
 the encumbrance is due to a combination of these causes. 
 
 Marine wave action is not only the occasion of the building 
 up of a bar at the mouth of a river in such instances as those 
 referred to, but in other cases operates in reducing depth by 
 producing a flattening of the slopes of the channel of the river, 
 thus increasing the area of the channel and correspondingly 
 diminishing velocity and scouring power. The harbours of 
 Pensacola and Galveston are both situated on the northern 
 shore of the Gulf of Mexico, their circumstances and surround- 
 ings, their tidal range, etc., are much the same, yet under natural, 
 i.e. unimproved conditions, the channel to Pensacola had a 
 depth of 20 feet, while that leading to Galveston had a depth 
 of 11 feet only, the difference being due in the main to the 
 greater exposure and consequent increased effect of wave stroke 
 at Galveston (Fig. 6). 
 
 Examination of the plans of the estuaries of the world will 
 show that the form of estuary which is best adapted for resistance 
 to the effort of the sea to block the entrance and thus to produce 
 a bar at the mouth, is that in which the banks gradually diverge 
 from the head to the seaward boundary in such manner that the 
 tidal compartment widens gradually as the sea is approached. 
 Estuaries of this form, even though obstructed in parts by sandbanks 
 and deposits of silt, are generally free from the bar encumbrance. 
 
 The estuary of the Thames will serve to exemplify this state- 
 ment, so will that of the Seine, and so, although the conditions are 
 different, will that of the Severn, while another more distant 
 but equally striking example is that of the river Tamar, which 
 drains about 4610 square miles of the northern part of Tasmania, 
 and discharges into Bass' Strait. 
 
THE MOUTH OF THE RIVER 
 
 27 
 
 The observation of the phenomena at the mouth of an estuary 
 is not business which should be entrusted either to amateurs or 
 to novices, and comparatively little need be said about it here, but 
 certain of the points to be considered may be noted. 
 
 First of all, the resultant direction in which the drift moves 
 along the coast should be ascertained (if it moves at all) and an 
 estimate made of the average rate of progress. By " resultant " is 
 meant the ultimate result of the movement, as sometimes it may 
 appear to be in one direction and at other times in another. Then 
 
 u, 
 
 
 ^ ^ M B X^/.-C-'O 
 
 
 Jil ' j -^ - 
 
 I' ' ^ ^ 
 
 Fig. 6. 
 
 the causes which produce the movement should be traced and 
 identified, however laborious the effort may be. The set of the 
 tides and their strength at various periods should be laid down, 
 and the direction and force of the prevailing winds noted ; if there 
 be any true littoral current its line should be laid down and its 
 effect upon the tidal currents observed. The student should be 
 warned that reflex action is not uncommon in the case of a littoral 
 current, and that in consequence of this action the line of the 
 current may not coincide with that of the prevailing winds ; 
 indeed the one may even be contrary to the other. The height of 
 
28 RIVERS AND ESTUARIES 
 
 the waves should also be measured, and particular attention 
 should be paid to the effect of the wave stroke on the cliffs 
 and beaches. 
 
 When no bar exists at the mouth of a river these difficult 
 enquiries become of comparatively small importance, and little 
 difficulty will ever be experienced even in the farthest parts of the 
 earth in deciding whether a bar exists at the mouth of the river or 
 not ; but determination of the question as to whether silt and sand 
 are carried by the flood tide into the estuary of the river is not so 
 simple a matter. Appearances are very apt to be misleading in 
 this respect, and a final conclusion cannot be safely reached unless 
 and until actual tests of the quality of the inflowing water have 
 been made. It is not necessary to incur the expense which would 
 be involved in attempts to test large quantities of the water, a 
 wooden box with an internal capacity of one cubic foot secured to 
 a pole and fitted with a small door controlled by a spring, will 
 furnish samples of bulk sufficient to supply the indication required. 
 The samples should be taken at least thrice during the period of 
 flood, beginning at about one hour after the turn of the tide, so 
 as to permit of the inertia of the outflowing waters being over- 
 come, and of the effect of the inflowing current upon the material 
 in the bed being felt. The samples should also be taken at two 
 points in the depth of the stream : one point within a few inches 
 of the bottom, so as to ascertain whether sand is being rolled 
 inwards by the stream, and another at about half depth, so that 
 if material in suspension is being borne into the estuary, a 
 sample of it may be trapped in the experimental box. 
 
 It is obvious that the answers to the two outstanding questions 
 propounded at the beginning of this chapter will have a profound 
 influence upon the design of works for the improvement of an 
 estuary and of the river to which the estuary owes its existence ; 
 but the other matters to which attention has hereinbefore been 
 directed must be considered in detail, as it is not until all possible 
 information has been collected and collated that the student may 
 safely begin the serious consideration of the problem before him ; 
 it being the first essential in such consideration that he should 
 place himself in a position in which he can do his duty to those 
 who are bearing the burden of the cost of the investigation, without 
 doing discredit to himself. 
 
 The experience of the past has shown clearly and frequently 
 that the lack of this patient and painstaking investigation of 
 
THE MOUTH OF THE RIVER 29 
 
 conditions and observation of phenomena has led, in the construc- 
 tion of works, to results of the most disappointing kind, both to 
 the engineers responsible for the works and to their employers ; 
 results which showed that instead of directing and regulating the 
 forces of Nature, a position of antagonism to these forces was, in 
 the design of the works, unwittingly taken up ; so that efforts at 
 improvement have been nugatory and expenditure futile ; or even 
 worse, the attempts to improve have made bad worse, and have 
 hastened the destruction of channel and waterway which Nature 
 was slowly accomplishing. 
 
 The jetties at the mouth of the Khone may serve as a warning 
 in the one case ; the land reclamation works and the groynes in the 
 estuary of the Dee below Chester in the other. 
 
 But human vision is limited, and human judgment is fallible ; 
 and even when the investigation of conditions has been under- 
 taken and the observation of phenomena has been completed, 
 errors may still be made, indeed not only have been made in the 
 past, but have, in some cases, been proved to be beyond remedy. 
 So that some method of experimental research by wliich con- 
 clusions may be checked and designs tested, has long been required 
 in such a matter as the projection of works for the improvement 
 of an estuary, or of the mouth of a river. 
 
 A method of research, such as that thus suggested, was 
 introduced by a man of original genius in the latter part of the 
 nineteenth century, was subjected to the criticism of a tribunal 
 of high scientific and practical attainment, was approved by that 
 tribunal, and will serve as the subject of a later chapter. 
 
CHAPTER VI 
 
 RIVER IMPROVEMENT WORKS 
 
 EiVER improvement works have generally an objective with a 
 major and a minor motive behind it ; the major being the provision 
 of facilities for navigation, and for the furtherance of trade and 
 commerce; and the minor the increase of the means for the 
 discharge of superfluous rainfall so as to prevent disastrous floods. 
 
 It is a question whether in a densely populated country like 
 Great Britain the order of motive should not be reversed, so that 
 the much neglected feature of flood prevention might have the 
 first place instead of the second ; but in any case, the fact that 
 operations for river improvement ought in the national interest 
 to be carried out so as to ensure flood prevention as well as to 
 provide direct commercial advantage, serves to condemn Brindley*s 
 maxim that " rivers are only useful to feed canals," and to require 
 a reversion to the original method of river canalization as against 
 the later system of canal construction on lines apart from rivers 
 which Brindley and his successors advocated as the only way of 
 escape from the difficulties attendant upon the working and 
 maintenance of the canalized river, and which arose out of the 
 fact that the river remained as the line of flood discharge, and 
 consequently, as the line of transport of material from the higher 
 levels to the lower. 
 
 The canalization methods of the eighteenth century, not only 
 did not diminish the effects of floods, they increased the effects ; as 
 the practice was to obstruct the flood channels by ill-designed 
 solid weirs, built at right angles to the course of the stream, and 
 approached by long paved slopes. In the earlier part of the 
 nineteenth century effort was made in such a case as that of the 
 Severn navigation, to improve upon the old method by building 
 weirs on diagonal lines across the watercourse in order to increase 
 discharging power by lengthening the crest line of discharge ; but 
 
RIVER IMPROVEMENT WORKS 31 
 
 the deflection of the stream lines as they flowed to and from the 
 weir with the consequent eddying and heaping up of level went far 
 to neutralize any advantage which was gained by the lengthened 
 weir crest ; at any rate the method was ineffective, and is obsolete. 
 Later on in the century, as the principles of hydraulic flow became 
 better understood, the paved sloping approaches were abandoned, 
 and weirs were built with vertical backs, and with crests formed 
 in approximate accordance with the lines of the flow. This change 
 was a distinct improvement, it was a step in the right direction. 
 
 One of the first and most important of the duties of an 
 engineer engaged in the regulation, or as continental engineers 
 would say the " normalization," of a river is to fix the areas of the 
 cross sections of that river. In the discharge of this duty regard 
 must always be had to the operation of the very obvious law that 
 " when the sections of a river vary, the quantity of water remain- 
 ing the same, the mean velocities are inversely as the areas of the 
 sections." Obvious as this law is it is sometimes forgotten and 
 its operation overlooked. 
 
 For the regulation of a river it is frequently necessary to 
 construct weirs at suitable points, but the solid type of weir is out 
 of date ; it is now essential that the weir by which the river is to 
 be controlled must itself be under control, and must be capable of 
 removal in times of flood, wholly or in part, according to the 
 volume of excess water to be discharged. 
 
 Many forms of removal weirs are in use, the majority being 
 remarkable rather for eccentricity than for either simplicity or 
 efficiency. The better known types are the "Needle" weirs, 
 much affected by French engineers; the "Bear's trap," largely 
 used in American waters; and the weir formed by a row of 
 vertically-lifted sluices, which is in use on several British rivers, 
 and which is the simplest, the safest, and the most easily 
 manipulated of all. 
 
 The substitution of a single row of flood sluices for two solid 
 weirs on the Weaver Navigation in Cheshire, furnished an interest- 
 ing example of the way in which river improvement for navigation 
 purposes may be combined with the abolition of destructive flood 
 effect. Prior to the construction of the sluices the town of 
 North wich, which is situated on the river Weaver, and of which 
 a considerable part is, owing to the subsidence caused by brine 
 pumping, only 3 or 4 feet above the ordinary level of the 
 river, was regularly inundated owing to flood rise in the stream, 
 
32 RIVERS AND ESTUARIES 
 
 even after the river channels had been deepened. The substitution 
 of the sluices at Button for the Acton and Pickering weirs took 
 place in 1881, since which time there has been no flooding in 
 North wich, even though the sluices are 8 miles below the town. 
 
 A similar effect though on a larger scale, has followed the 
 construction of the Manchester Ship Canal. Flood damage has 
 been eliminated from the city of Manchester, the borough of 
 Salford, the borough of Warrington, and from many miles of the 
 valleys of the Irwell and of the Mersey ; even from parts where 
 damage has been most severe, and from places where it had had 
 results which can only be described as ghastly. 
 
 In the higher reaches of the river the damage still continues, 
 but that is because the improvement has not been carried 
 sufficiently far inland, so that the watercourses are tortuous and 
 inefficient, and are still blocked by solid weirs, ill-designed bridges, 
 and other similar obstructions. 
 
 The markedly successful and yet incomplete character of the 
 flood-prevention work accomplished through the construction of 
 the Ship Canal leads to another consideration. The indirect 
 return on capital expended in river improvement for the prevention 
 of floods is enormous, but the direct return is small and seldom 
 accrues to the people who find the money for the improvement 
 works. It cannot therefore be expected that private enterprise 
 will provide the capital for such works, and it seems clear that 
 the improvement of rivers as flood courses should neither be left 
 to private companies nor to local corporations, but should be 
 undertaken by Drainage Boards with statutory powers of control 
 and regulation in the watersheds; authorized to acquire lands, 
 remove obstructions, regulate stream courses, cut off bends, pro- 
 tect banks, and last but not least, effectively safeguard the streams 
 in each watershed against pollution, whether caused by sanitary 
 authorities or by manufacturers. 
 
 It has been whispered that in the pigeon-holes in the office of 
 the President of the Local Government Board, there reposes the 
 embryo of a Bill which may not go as far in the direction here 
 suggested as engineering requirements and the needs of this 
 country demand, but which if enacted would be a step on the 
 way thereto ; and that when the more exciting political questions 
 of the day have burnt themselves out, an interesting event may 
 be expected, and the birth of the Bill for the establishment of 
 Eiver Boards in Britain may be hoped to take place. 
 
RIVER IMPROVEMENT WORKS 33 
 
 Great Britain is too small in area and too great in population 
 to be able to afford needless loss through flood damage such as was 
 experienced in the South and in the Midlands in the latter part 
 of 1910 (to take one example only out of many), when great areas 
 of autumn-sown wheat were destroyed, when the permanent way 
 at Loughborough Station on the main line of the Midland Eailway 
 was knee-deep in water, and when difficulty was experienced in 
 the supply of waggons at various ocean ports because goods stations 
 at great inland cities were inundated for days together. 
 
 It is much to be regretted that a valuable opportunity for 
 drawing public attention to questions relating to flood damage and 
 flood prevention was lost, when the Eoyal Commission on Canals 
 and Inland Navigations prepared and presented their Fourth and 
 Final Eeport, issued in 1909. The Commission seem to have 
 looked upon these vitally important matters as being beyond the 
 scope of their inquiry, and referred to them in the most meagre 
 of terms only ; such references as they made being confined to 
 bald statements as to interruptions to traffic on one or two navi- 
 gations by the passage of floods. 
 
 In the Final Eeport on Canals and Inland Navigations in 
 Ireland, issued in 1911, the Commission did take rather a bolder 
 line with regard to " questions of drainage " and to " the use of 
 rivers for the prevention of floods," and stated in an apologetic 
 way that they had been " obliged to take notice " of these questions, 
 as in certain rivers (they instanced the Barrow and the Bann) 
 interests affected by drainage " are at present, of greater and more 
 pressing importance than those of navigation." 
 
 If the Commission had felt '* obliged to take notice " of like 
 questions in England they would have been able, without difficulty, 
 to compile a much longer list of rivers concerning which the same 
 pronouncement might have been made. 
 
 The letting slip by the Commission of so great an opportunity 
 was the more unfortunate, as had they availed themselves of it 
 they might have saved their Eeport from the oblivion which now 
 seems likely to overtake it. Schemes for waterways proposed for 
 the purpose of competing with the railways and of reducing the 
 rates thereon, would, as a matter of course, be regarded by the 
 railway interests as an attack upon them, and railway com- 
 panies are not corporations who, when they are smitten upon one 
 cheek are disposed to turn the other ; on the contrary, promoters 
 of the schemes would find the whole of the great resources which 
 
 D 
 
34 RIVERS AND ESTUARIES 
 
 the railway companies control arrayed against them in one solid 
 phalanx of ruthless and determined opposition. It does not 
 require very keen vision on the part of the student of these 
 questions to enable him to see what a point of vantage would be 
 gained by the promoters if they could show that their schemes 
 comprised improved facilities, not only for navigation, but for the 
 passage of floods in times of storm and threatened disaster. 
 
 Works of the character suggested in this chapter would not 
 put an end to the transport of material from the uplands to the 
 estuary, but they would (1) check destruction and therefore 
 diminish the quantities of transported material and (2) facilitate 
 transport so as to lessen deposit in the channels of streams until the 
 point is reached at which, in the interest of navigation, the sectional 
 area must be so enlarged and velocity reduced to such an extent 
 that practically all the suspended matter will be deposited and 
 must therefore be removed by dredging. 
 
 Dredging silt and detritus (except in a heavy sea) is a simple 
 operation and is not costly. Apart from the provision of the plant 
 one penny per cubic yard should always cover the cost of dredging 
 soft material ; as the complexities arise, the difficulties are met, 
 and from 80 to 90 per cent, of the costs of the removal of the 
 deposits are incurred, in the transport and disposal of the material 
 after it has been raised by the dredger. 
 
 For this reason if circumstances bring the acquisition of low- 
 lying land at the head of the navigable part of the river within 
 the limits of reasonable expenditure, a proposal for further ex- 
 penditure for the widening and deepening of the channel to such 
 an extent as to compel deposit at a place where it can be dredged 
 and pumped ashore at a minimum of cost, and with an absence of 
 obstruction to navigation, will be justified and may be recom- 
 mended to Navigation Trusts and River Boards. 
 
 When a canalized river terminates in an estuarial channel the 
 continual expenditure on dredging for the maintenance of the 
 navigation can be viewed with some satisfaction, when it is 
 remembered that the destruction of the estuary is being postponed 
 through the interception and deposit elsewhere of the detritus 
 which would in the natural course have found a resting place 
 within the estuarial area. 
 
 Very little information is available upon which estimates ol 
 the quantities of material annually deposited in an estuary can be 
 based, as even in cases where the material is intercepted and 
 
RIVER IMPROVEMENT WORKS 35 
 
 dredged, and where the quantities dredged are measured with a 
 fair degree of accuracy, circumstances almost invariably compli- 
 cate each case and render the data uncertain. 
 
 In the case of the Manchester Ship Canal, practically the 
 whole of the detritus derived from the watershed for which the 
 canal is the " river," has for many years been intercepted in the 
 waterway, dredged therefrom and deposited either on low-lying 
 lands or at sea. The average quantities dredged annually have 
 been found to represent a mean denudation of about 1'97 cubic 
 yards per acre, or in other words, of about ^^ part of an inch 
 in depth over the whole drainage area, the average rainfall in the 
 area being about 38 inches. 
 
 The figures may be taken as furnishing some guidance for 
 estimating the quantities of dredging which will be required for 
 the maintenance of a river in a manufacturing district, which has 
 been regulated and controlled for navigation purposes ; but before 
 they can be applied for the determination of the quantities of 
 material, eroded from the land by natural operation and trans- 
 ported by the stream to the estuary ; a factor, which will vary in 
 varying districts, must be applied to them for the elimination of 
 the proportion of polluting and encumbering material dredged from 
 the waterway — and therefore included in the figure — the deposit of 
 which was not due to the operation of Nature, but to the unlawful 
 acts of men. 
 
 Where solid weirs are replaced by sluices, or where sluices are 
 employed in the first instance, the sluice sills should be laid at or 
 below the level of the bed of the reach which they are to control, 
 the sluice area should be calculated on the assumption that the 
 coefficient of contraction and of additional friction will, for sluices 
 from 30 to 50 feet in width, be '60, and the piers between the 
 sluices should be made of the minimum width required for 
 stability in times of heavy flood. 
 
 In determining the dimensions of flood sluices, which are of 
 course permanent works, account must be taken of the fact, that 
 as the population in any watershed grows and the proportions of 
 the areas thereof in which paved streets and yards, slated roofs, 
 and well drained properties, have been substituted for pervious 
 surfaces and undrained lands increase, the rate of run-off in- 
 creases also ; which means that floods will become more and more 
 concentrated, and therefore if not promptly discharged, will also 
 become more and more destructive ; or to put it in another way, 
 
36 FIVERS AND ESTUARIES 
 
 flood intensity will grow while flood duration will diminish. On 
 the other hand when sufficient provision is made for the discharge 
 of floods, growth of intensity should be welcomed in the interest 
 of the conservation of rivers, as in the words of the old formula, 
 " the force of water in deepening a channel is always proportional 
 to the quantity acting in a given time." 
 
 Protection of banks and slopes from the destructive effects of 
 erosion requires not only careful consideration in the first place, 
 but constant attention subsequently. It is only by such protection 
 against the undercutting action of floods that any sensible diminu- 
 tion in the quantities of solid matter brought down by the river 
 can be secured. Where the river is to be rendered navigable by 
 steamers, erosion due to the wave generated by the passage of 
 vessels must also be taken into account in designing protective 
 works. The effect of this wave action is nothing like so extensive 
 as it is frequently supposed to be, as the eye always greatly 
 exaggerates the range and extent of wave action. In a canalized 
 river with a width of say 200 feet at water level no damage will 
 be done by the wave action produced by a vessel steaming at the 
 rate of 8 miles per hour if the slopes be protected for vertical 
 distances of 3 feet below and 3 feet above water level re- 
 spectively, but as it is almost impossible to restrict the smaller 
 vessels (which cause the most damage) to that speed, prudence 
 requires that the belt of pitching should extend from 4 feet 
 below to 4 feet above water level. 
 
 Experiment and experience have alike demonstrated the 
 sufficiency of these figures, and have shown that limestone rubble, 
 hand-packed into place, and with an average thickness of fifteen 
 inches is, where available, an economical and effective material 
 for slope protection ; while systems such as those now in use in 
 Holland and on some of the rivers in this country (including the 
 Thames) of protection by means of small concrete slabs have 
 many advantages where limestone is not to be had at a reasonable 
 cost. The hand-packed rubble method of protection has been 
 adopted for the Kaiser Wilhelm Canal after exhaustive trials of 
 many methods and systems, and has, as has been the case on the 
 Manchester Ship Canal, been found to have special value where 
 the whiter limestones are used, as the bank protection serves to 
 pick out the lines of the banks for pilots when navigating vessels 
 by night. 
 
CHAPTER VII 
 
 ESTUARIAL WORKS 
 
 The next group of questions to be considered are those which 
 arise in connection with the improvement for navigation purposes 
 of the channel through the estuary of the river. 
 
 It may be well to recall here principles already enunciated 
 relating to the deposit and movement again of water-borne 
 sediment; and also to suggest, as a cautionary note, that, in 
 preparing designs for estuarial improvement works, prudence 
 requires that the difference of standpoint between the interests 
 which are established on the seaboard, and those which have 
 their centres further inland, should be kept in view. The estuary 
 is inter alia a natural provision by means of which the sea and 
 its advantages may be borne in to the dwellers on the " foothills " 
 (as the Americans call them), and those who think that the men 
 on the coast, who regard the sea and the advantages thereof as their 
 birthright, should look benevolently on proposals to improve the 
 estuarial channels in such way as to enable the hillmen to share 
 in what the coastmen consider to be their heritage, expect too 
 much from human nature. 
 
 In most estuaries the channels are essentially unstable, in 
 many they are diverse, the flood tide taking one course, and the 
 ebb the other ; while the upland waters, varying in volume from 
 day to day, pursue lines of their own, reinforcing here, baffling 
 there, and conducing generally to diversion and to change of 
 course. 
 
 In such cases modern efforts at improvement begin with works 
 for the regulation of the main channel in the estuary, and for the 
 concentration therein of all the conflicting streams ; the lines of 
 flood and ebb should be trained in such manner that they will 
 follow the same course, and into that course the lines of upland 
 water should be directed. For these purposes longitudinal " training 
 
38 RIVERS AND ESTUARIES 
 
 walls" or "dykes" are now most frequently employed, groynes 
 and spurs of varying kinds and sizes being made use of at the out- 
 set of the operations, first, because they can readily be extended or 
 reduced in length and so permit of the line of the channel being 
 finally determined by actual experience; and secondly, because 
 the cost of the groynes is, at the outset, much less than that of 
 training walls. 
 
 Training walls are in effect no more than the slope protection 
 works already described, but are somewhat different in form, being 
 generally deposited in place as a mound of rubble, or where stone 
 is difficult to obtain and unduly costly, of stone mixed with clay. 
 The lines of training walls should be carefully laid down, regard 
 being had to the paramount fact that to be successful their func- 
 tion should be to regulate and not to thwart the efforts of Nature. 
 The lines should diverge from the head of the estuary downwards, 
 the degree of divergence depending largely upon the proportion 
 between the volume of a land flood and the volume of tidal water 
 which passes into the estuary upon an average tide. Where the 
 upland water forms a considerable proportion of the combined 
 discharge the divergence should be greater, where the proportion 
 is inconsiderable, it should be less. In practice the variation in 
 divergence has not been very great, except in the case of the river 
 Seine, where the divergence as originally laid down, 1 in 200, 
 was found to be too small. In the regulated channel of the river 
 Weser, between Bremen and Bremerhaven, the divergence was 1 
 in 71 ; in the river Tyne and in the Nervion (from Bilbao to the 
 mouth) 1 in 75 ; in the river Clyde (from Glasgow to Dumbarton) 
 1 in 83; in the river Yire and in the Maas (from Krimpen to 
 Vlaardingen) 1 in 100; while in rivers in which the channels 
 are more or less in natural condition, such as the Thames, the 
 Humber, and the Scheldt, and in the Maas (below Vlaardingen) 
 the divergence is nearly 1 in 50. 
 
 Each curve should be of as large radius as practicable, straight 
 lines should be avoided even at the junction of two reverse curves. 
 The work of deposit should begin at the head of the estuary, and 
 the formation of the wall on the concave side should be undertaken 
 first, as in many estuaries where the tidal range is small, it will 
 be found that the concave wall or walls will fulfil the purpose 
 required, and that the formation of walls on the convex parts of 
 the channel may be dispensed with. 
 
 Dredging will, in most cases, be required at the outset ; one 
 
ESTUARIAL WORKS 39 
 
 of the first objects of the dredging being the lowering of the 
 inclined low water level. It is never possible to lower the low 
 water level at the head of the estuary to that of low water at the 
 seaward end, but much may be done to reduce the angle of inclina- 
 tion and to regulate the line of low water ; and it is important to 
 remember that the lowering of low water level has not only the 
 invaluable effect of inducing larger quantities of tidal water to 
 flow into and out of the estuary on each tide, and of thus com- 
 pensating whether altogether or in part, for any reduction of 
 capacity which may follow upon the construction of the training 
 wall or walls; but it has the further effect of concentrating a 
 greater part of the incoming and outgoing waters in the line of 
 the trained channel, and of thereby increasing the potentiality of 
 the flow as a scouring and transporting agency. 
 
 The questions relating to the problem as to whether reduction 
 of tidal capacity can or cannot be safely undertaken in estuarial 
 indents have been hotly debated by past generations of learned 
 counsel and of engineers of repute and of experience; the heat 
 imported into the discussions being, it must be admitted, due to 
 the circumstance that in most cases the disputants were engaged 
 as partisans and advocates for or against particular schemes 
 proposed in one interest or another : a condition of affairs which 
 did not lend itself to calmness of scientific contemplation, to 
 unemotional judgment, or to the expression of impartial and 
 unbiassed opinion. 
 
 No answers of a general sort can be suggested to these 
 questions, each case must be considered by itself and with regard 
 to the circumstances which are particular to itself, and to the 
 environment from which it derives its peculiar temperament — its 
 idiosyncrasy, so to speak. 
 
 It is however, well in the first place to consider whether any 
 true reduction of tidal capacity will follow upon what may be 
 admitted to be tidal displacement, as such displacement may be 
 merely diversion of tidal flow from one position in an estuary into 
 another position, a change out of which benefit may, and frequently 
 does accrue ; as in cases in which the filling up, or the closing, of 
 arms and pools on the sides of a tideway have led in the past, and 
 may lead in the future to an increase of the tidal height farther 
 inland, and thus had the effect and may become the occasion of 
 the replacing of almost useless waters by valuable flow. 
 
 The existence or non-existence of a bar at the mouth is an 
 
40 RIVERS AND ESTUARIES 
 
 important element in consideration of the questions; another 
 point of great importance in the study having relation to the 
 movement of sand and silt at and about the mouth of the estuary, 
 and particularly as to whether such sand and silt are borne into 
 the estuary from the sea or not. 
 
 The positions of the sites at which displacement of tidal water 
 may be contemplated are also of moment ; the distance from the 
 mouth of the river, and therefore the length of the channel through 
 which the displaced waters would flow, before being met and 
 checked by the flood tide, should be taken into account, while a 
 point which is frequently overlooked in these discussions is the 
 improvement which may be effected in the scouring force of land 
 floods by partially enclosing embayments, in which the great 
 volumes of water derived from these floods spend their force and 
 dissipate their efficiency as remedial agencies for the erosion and 
 transportation seaward of previously deposited materials. 
 
 Broadly stated, the conclusion may be accepted that even in 
 estuaries in which appreciable diminution of tidal flow may be 
 caused by reduction of tidal capacity in certain positions, the 
 diminution may be compensated for by increased concentration of 
 flow and of consequent increase in the scouring power of the tidal 
 column and in the energetic efficiency of the land floods. 
 
 The questions relating to the possibility, or otherwise, of 
 improving the channels either in estuaries or in non-tidal streams 
 by means of the concentration of flow, or by " the attraction of 
 the waters," has not received as much attention in this country 
 as in other lands, mainly because less scope for such operations 
 can be found in the British Isles than abroad, owing to the 
 comparatively small sizes of British rivers. 
 
 Professor V. E. de Timonoff of St. Petersburg, an eminent 
 hydraulic engineer with large experience of great Eussian rivers 
 such as the Volga and the Dneiper, presented a useful report on 
 this subject to the Eighth International Congress on Navigation, 
 held in Paris in 1890. In that report Professor Timonoff described 
 the system of " training by dredging and attraction of the waters," 
 in which after the excavation of a channel suitable for the required 
 navigation by means of specially powerful dredgers, and the 
 determination of the most stable direction in the channel by posi- 
 tive experience, the channel is fixed by "plain and economical 
 works." The deep thus provided and fixed offers a line of least 
 resistance to flow, so that both velocity and volume of flow are 
 
ESTUARIAL WORKS 41 
 
 increased and waters are attracted towards the deep from neigh- 
 bouring parts of the river. Professor Timonoff instanced the 
 French river Garonne as exemplifying the results which may be 
 achieved by this method of " attraction of waters/' which he 
 proposed should be applied to certain of the larger rivers in 
 Kussia. 
 
 Mr. Timonoff stated that in his study of the question he had 
 been " inspired by the theoretical researches of French learned men 
 and the experiments of American Engineers," in which connection 
 allusion should be made in passing, to the excellent results which 
 have been secured by American engineers by the application of 
 the principle of concentration to the mouths of shoal-encumbered 
 rivers, and to which more detailed reference will be made in a 
 later chapter 
 
CHAPTEE VIII 
 
 SOME EUROPEAN EXAMPLES 
 
 The river Seine affords an example of training-wall construction, 
 which was effective for the purpose for which the works were pro- 
 jected, but which led to an amount of silting behind the walls 
 which was as unnecessary as it was unexpected ; the case is there- 
 fore valuable {a) as an instance of systematic and useful work 
 accomplished after years of effort; (h) as a warning against the 
 employment of prophetic language as to the effect of operations 
 in an estuary ; (c) as a testimony to the necessity for prudence in 
 the determination of the height of training walls ; and {d) as a 
 typical example of the differences of opinion which so frequently 
 arise between the seaboard interests (represented on the Seine by 
 the port of Havre) and those who dwell farther inland, who natu- 
 rally desire to have direct communication with the sea, and who 
 are in the present case represented by the manufacturing and 
 commercial community at Eouen, also situated on the Seine, but 
 at a distance of 78 miles from the sea. 
 
 Many schemes had been put forward for the improvement of 
 the Seine, but none commanded pubHc confidence until the pro- 
 posal of M. Bouniceau, a Parisian engineer, appeared in 1845. 
 M. Bouniceau's project consisted in the main in the construction 
 of what he termed " longitudinal embankments," that is to say, 
 training-walls on each side of the river, through which the low 
 water channel could be regulated and fixed between Eouen and 
 Havre. The project was received with favour both of a scientific 
 and of a popular sort, was accepted by the Government of the 
 day, and was begun in 1848, when training- wall construction was 
 commenced at La Mailleray, some 37 miles below Eouen. In two 
 years the work was carried forward to Quillebceuf, a distance of 18 
 miles from the starting-point, while in 1869 the two walls were 
 carried down to Berville; after the experiment had been made 
 
SOME EUROPEAN EXAMPLES 43 
 
 and failed, under which one wall only, that on the southerly side 
 of the channel, had been formed. At Berville the work was 
 stopped owing to an outcry from the Havre people, who thought 
 that their prosperity was threatened, and who feared that accre- 
 tion due to the construction of the walls would imperil the access 
 to their port. 
 
 The lines of training were laid out in a workmanlike manner. 
 The divergence between the two walls was at the rate of 1 in 
 200, or say 26 feet in a mile, which, as already hinted, proved 
 to be too small and which hindered the tidal flow. The height 
 of the walls on the contrary, was too great, particularly in the 
 first instance ; as on the right bank down to Tancarville and on 
 the left bank to La Eoque, the walls were carried to a level 
 equal to that of high water of an average tide, that is to say, of 
 a tide halfway between high water of neaps and high water of 
 springs. Below these points the heights were reduced, the level 
 being that of the mean height of a neap tide, or half the height 
 between the levels of low water and high water of a neap tide. 
 
 The effect of the works upon the condition of the channel 
 between the embankments was altogether satisfactory. The level 
 of low water spring tides was lowered to the extent of 2 ft. 3 J ins., 
 that of low water neap tides was lowered 2 ft. 9^ ins. It was 
 said that the height of high water was not affected, a statement 
 which should be received with caution. The navigable depth in 
 the channel to Eouen was increased to 18 feet, with the result 
 that seaborne traffic developed to such an extent that Eouen, 
 which had had an absolutely insignificant riverine traffic carried 
 in small boats and barges, and no seaborne traffic at all, became 
 the fifth port in France. 
 
 The works brought about a result of another kind, which gave 
 colour to the fears of the people in Havre, and point to their some- 
 what clamant expression of those fears, and which had a prejudicial 
 effect upon M. Bouniceau's reputation as a prophet; but which 
 had as experience has shown no further prejudicial effect. M. 
 Bouniceau had fully recognized that in the quiet waters in the 
 spaces behind his high longitudinal embankments, silting would 
 be inevitable, and thought that the accretion due to the deposit of 
 material from the uplands would probably be increased by the 
 transfer of material from the lower estuary, but concluded that 
 the joint result would progress in so deliberate a manner that 
 21,000 years would elapse before any effect at the mouth of the 
 
44 RIVERS AND ESTUARIES 
 
 estuary would be perceived, and therefore considered that it was 
 not necessary to attach practical importance to so remote a 
 development. 
 
 As the construction of the longitudinal embankments proceeded 
 it became apparent that there was something hopelessly wrong 
 ■with the prophecy as to the 21,000 years. The protests of Havre 
 became too much for the Government, so that the works were 
 stopped, and a survey was made in 1875. This survey showed 
 that the rate of accretion had been such that not in 21,000 years, 
 but in less than a century from the time of the commencement of 
 the operations, the silting up of the spaces behind the walls would 
 be accomplished ; the fact being that M. Bouniceau had in his 
 estimate left out of account wave action in the sea at periods of 
 heavy winds and storms when, under the combined movements of 
 waves and tides, masses of terrigenous material are torn from the 
 resting-place which they had found in the ocean bed, and are 
 deposited in any space which they may find in embayment, indent, 
 or estuary. 
 
 It is not possible to follow here the details of the more 
 recent developments on the Seine, suffice it to say that eventually 
 the training- walls were prolonged to the meridian of St. Sauveur 
 on the north side, and to Honfleur on the south, with the result 
 that the navigation to Eouen has been so greatly improved that 
 steamers drawing from 21 feet to 25 feet (according to the tides) 
 now reach that port regularly, while the depth in the outer 
 estuary, so far from being impaired, has been improved ; with the 
 further result that the increase of the trade to and from Eouen may 
 be measured by the fact that in the ten years ending 1902 no less a 
 sum than £1,212,000 was spent in extending the capacity and in 
 improving the facilities of the port ; since which time the develop- 
 ment has been continual, so that a scheme for the further extension 
 of the training-walls in a seaward direction is now being considered 
 by the French Government and by their engineers with a view to a 
 further increase of the depth to Eouen (Fig. 7). It is interesting 
 to note that while some of these experienced engineers are strong 
 advocates of the extension of the training-walls, others look 
 dubiously upon the proposal and would prefer the deepening of 
 the channel by dredging only, relying upon the effect of the 
 concentration which would follow upon the dredging for the 
 maintenance of the channel. 
 
 But what about Havre ? The Havre folk in the long contest 
 
SOME EUROPEAN EXAMPLES 
 
 45 
 
46 RIVERS AND ESTUARIES 
 
 demonstrated their virility, and proved their powers as combatants ; 
 but events have shown that their fears were unfounded. It was 
 admitted in the year 1880 that the accesses and entrances to Havre 
 had suffered no injury. That was over thirty years ago. It 
 should be noted that in the ten years already referred to a sum 
 of £1,160,000 (nearly equal to that expended at Eouen during the 
 same period) was spent in increasing and improving the dock 
 accommodation in Havre, that in 1904 they had in Havre a depth 
 of over 35 feet at high water of spring tides on the sills of dock 
 entrances which are nearly 100 feet in width, and that the accesses 
 to these entrances are from J metre to 1 metre deeper than 
 they ever were before, so that most of the vessels afloat can 
 be docked there at any time. Since 1904 Havre has again greatly 
 extended its accommodation and increased its commerce (the traffic 
 of the port in 1911 was 10,038,650 tons) ; and one moral to be 
 drawn from the story of the Seine is that dwellers on the seaboard 
 are apt to exaggerate the perils, both physical and commercial, 
 which they think they discern in the distance when the inland 
 people seek for themselves " a place in the sun," which in this 
 case, means a way of direct communication with the ocean. 
 
 A further scheme is now being elaborated by the French 
 Government engineers for continuing, though on a smaller scale, 
 the improvement of the Seine from Kouen to Paris, a distance of 
 145 miles ; the disastrous floods from which Paris and the 
 surrounding districts suffered in 1910 and 1911, having given 
 impetus to a project which for some time past has been slowly 
 taking shape and form. The proposal is for an improved system 
 of river canalization, after the manner of the Manchester Ship 
 Canal, which will at once serve the commercial and shipping 
 interests of the city and will provide an efficient outlet for 
 land floods. Thus improvement leads to improvement, and 
 development to development, and thus too, not merely are cities 
 rescued from decay and provinces from declension, but great 
 states and powerful nations are fortified and equipped for the 
 struggle for existence, which in these times means more than any- 
 thing else, a struggle for trade and commerce. 
 
 The river Clyde, around which so great an industrial population 
 has gathered, is in some respects a parallel case to that of the 
 Seine, while in others the Scottish waterway and the French 
 present features of well-marked contrast. 
 
 The object was the same in each case, to place Eouen and 
 
SOME EUROPEAN EXAMPLES 47 
 
 Glasgow respectively in direct communication with the sea for 
 commercial purposes ; and the means adopted were similar : in 
 each river the channel was regulated and fixed by means of 
 training-walls, the bed was deepened, the levels of low water were 
 lowered, and thus flow was concentrated and velocity and volume 
 were increased. 
 
 But there the resemblance ends. The Seine has a great water- 
 shed behind it, the catchwater area of the Clyde is comparatively 
 small, so that while the natural scour of the combined land and 
 tidal waters regulated and concentrated in the manner described, 
 was sufficient for the deepening and maintenance of the channel 
 in the Seine, the work on the Clyde has been almost entirely due 
 to the dredging operations which have been carried on so effectively 
 for so long a time. 
 
 Smeaton made his first survey of the river Clyde in 1755. He 
 then found that spring tides at Glasgow only rose 1 foot 9 inches, 
 while the rise at neaps was barely sensible. 
 
 Between that time and June 1910, over 80 millions of cubic 
 yards of material of various sorts, ranging from hard rock to soft 
 mud, have been removed from the channel between Newark 
 Castle (IJ miles above Greenock) and Glasgow with the result 
 that the low water line has been lowered over 10 feet, the rise 
 of spring tides increased to 12 feet 2 inches, and large steamers 
 enabled to lie and discharge and load cargo where Scotch boys 
 once waded across the river. 
 
 In the case of the Clyde, as in that of almost every other river 
 which has been improved by engineering operations, opinions 
 differ as to whether any rise in the level of high water has been 
 effected by the improvements. When dignitaries differ and 
 authorities disagree it behoves students, who are a modest class, to 
 hold their peace, to fall back on the operation of natural law (in 
 this case the law of the conservation of energy) and to ask one 
 another, not the dignitaries and the authorities in question, what 
 can have become of the energy stored up in the tidal column 
 which was at one time expended in overcoming resistances which 
 are now non-existent ? or how can that energy be expended under 
 the changed conditions except in the raising of the level of that 
 column against gravity, or in other words, in the raising of the 
 level of high water at the inner end of the improved channel ? 
 
CHAPTEE IX 
 
 SOME AMERICAN EXAMPLES 
 
 Another example (1) of bold engineering adventure, which like 
 the Seine, has become classical (although the works were not 
 the pioneers in their class), and (2) of marked effect produced 
 by concentration of flow, is presented by the regulation of the 
 South Pass of the Mississippi river, the " father of waters," which 
 finds a place of discharge in the Gulf of Mexico. 
 
 The story of the deepening of the South Pass stands amongst 
 the romances of public works as almost, if not altogether, the 
 most romantic of them all. The completeness of the success 
 achieved, the triumphant vindication of principle displayed, the 
 indomitable resolution and courage required for the achievement, 
 the persistence and resources of the powerful opposition arrayed 
 against the scheme ; all combine to render the narrative memorable 
 in the annals of engineering ; while the bright light of the ultimate 
 triumph is brought out upon the screen by the darkness of a long 
 history of failure in the background. 
 
 Efforts at improvement of the outlets of the great river date 
 from 1726 ; of these efforts it is sufficient to say that they were 
 varied in character, diversified in degree, and similar in effect. 
 They all failed, and failed utterly, the fatal defect throughout 
 being that no attempt was made to provide transporting power for 
 material in suspension; and transporting power was just what 
 was required in the diffused and obstructed passes through which 
 the waters flowed into the Gulf. 
 
 The effort which furnishes such strong contrast to those which 
 preceded it dates from 1874, when James B. Eads first publicly 
 propounded his scheme for the rectification and deepening of the 
 South-west Pass. The proposal furnished an admirable example 
 of conditions under which successful engineering projects are 
 conceived and designed, are advocated, and are executed; as it 
 
SOME AMERICAN EXAMPLES 49 
 
 was based upon accurate knowledge, of the sort which can be 
 obtained by personal effort only, of hydraulic principles, and of 
 the phenomena of the river in question ; such knowledge as has 
 in the foregoing chapters been insisted upon as essential before 
 operations in rivers and estuaries can be undertaken with 
 satisfaction and success. 
 
 In order that the character and extent of the operations may 
 be understood, a few leading figures should be supplied here, 
 through which the facts of the case may be grasped. 
 
 At "high water" — that is to say, when in flood — the Mis- 
 sissippi discharges into the Gulf of Mexico some 1\ millions of 
 cubic feet of water per second. 
 
 Like the Khine, the Danube, and the Nile, the Mississippi 
 discharges its waters through a self-formed delta. This delta is 
 intersected by three main passes, which were supplemented by 
 various gaps and crevasses, one of which (known as the Great 
 Bayou) carried as much water as the smallest of the passes. 
 
 The main channels through the delta are known as the South- 
 west Pass, the South Pass, and the East Pass; the latter, with 
 the curious persistency of place-names, being more generally 
 known by the old French cognomen, the Tasse a V Outre. 
 
 The disastrous effect of the diffusion may be measured by the 
 fact that whereas at New Orleans, 107 miles from the mouth of 
 the river, the stream with a width of half-a-mile had a depth of 
 150 feet ; the respective depth in the passes were in the South-west 
 18 feet, the South 8 feet, and in the East (or Fasse a VOiUre) 
 11 feet, the sectional areas in the same order being 60,000, 24,000, 
 and 69,000 square feet respectively. 
 
 Eads* proposal was that the principles of diversion, con- 
 centration, and regulation of flow, should be applied to one of 
 these passes so as to render it suitable for navigation by ocean- 
 going steamers of large size ; the concentration and regulation of 
 flow being affected by means of parallel jetties at and about the 
 shoal length in the pass, and the diversion by the construction 
 of dams across certain of the gaps and crevasses through which so 
 serious a loss of flow took place. For reasons which he advanced 
 he selected and strongly advocated the South-west Pass for the 
 great experiment, and so confident was he of the success of the 
 operation which he proposed to carry out that he expressed his 
 readiness to carry out the works at his own cost and that of his 
 friends and supporters, on the principle of "no cure, no pay." 
 
 £ 
 
so RIVERS AND ESTUARIES 
 
 Surely no bolder offer was ever submitted to responsible authority 
 in respect of a great engineering work. 
 
 The proposal was met with a storm of opposition on the one 
 hand, and was supported by a large measure of public approval on 
 the other, with the result that, as is so frequently the case, the 
 promoters of the scheme were only partly successful ; as although 
 an Act of Congress was obtained in 1874, it provided for the 
 improvement of the small South Pass, instead of the much more 
 suitable South-west Pass. 
 
 The success, partial as it was, was largely due to Eads' own 
 efforts ; Eads who advocated the scheme in season, out of season ; 
 who to a great extent, wore down the opposition ; who found friends 
 and money for the work ; and who carried it out in the face of almost 
 overwhelming difficulties on his '* no cure, no pay " principle, 
 receiving no payment from the American Government until he 
 secured first a permanent depth of 20 feet, then of 22 feet, then 
 of 24 feet, and finally of 26 feet in the channel between the 
 jetties. 
 
 The works were actually commenced in June 1875. The 
 alignment of the jetties was worked out on an accurate survey of 
 the South Pass which had just been finished ; very complete data 
 pertaining to the great river were in the possession of Eads and 
 his colleagues ; the unvarying and invariable principles of hydraulic 
 engineering were closely adhered to ; and the result was a triumph 
 for the promoters, and a distinct gain, not only for the population 
 interested in the Mississippi valley, but for the part of the human 
 race which wear cotton clothing of one sort or another; for by 
 August 1876, a depth of 20 feet had been secured ; by February 
 1878, a depth of 22 feet ; by July of the same year 24 feet, and by 
 October of that year 30 feet. 
 
 The improvement has been permanent and complete, the depth 
 has not only been maintained but has been increased, and so far 
 from experience having proved that constant prolongation of the 
 jetties has been required (as was predicted by opponents) Mr. 
 E. L. Corthell, who was the resident engineer on the work, found 
 in 1904 that the end of the eastern or windward jetty was actually 
 200 feet to the landward of the point where he laid it in 1875, 
 twenty-nine years before. 
 
 No more cogent proof can be advanced of the entire success of 
 the jetties than the fact that works on similar lines to those at 
 the South Pass are now in progress at the larger South-west Pass, 
 
SOME AMERICAN EXAMPLES 51 
 
 where Mr. Eads himself desired to make his experiment, but was 
 overruled by Congress. 
 
 The success of the works of the South Pass emboldened other 
 authorities to undertake operations of like character for the im- 
 provement of the mouths of other rivers which flow into the 
 Gulf of Mexico. Tampico is a case in point. Tampico is on the 
 river Panuco, which discharges into the Gulf on the east coast of 
 Mexico, some 300 miles to the southward of the Eio Grande, 
 the boundary between the United States and Mexico (Fig. 6). 
 The work of jetty construction was begun by Mr. Corthell at the 
 mouth of the river Panuco in 1890, and completed in 1892. The 
 results were again most gratifying. The river differed greatly 
 from the Mississippi in size, the total discharge being about 
 15,000 cubic feet per second at high flood, and in character, as the 
 discharge was effected through a single mouth instead of being 
 spread over a fan-shaped system of channels. The ruling depth in 
 the entrance channel was but little over 8 feet in May 1890, 
 it had increased to 19 feet 6 inches in October 1892, and to 
 24 feet in January 1895, while the effect upon the trade of 
 Tampico was correspondingly great, as from an obscure and 
 unimportant creek the port grew until its traffic returns ranked 
 second amongst those of Mexican harbours. 
 
 Mr. Eads' method of working has been followed in each case. 
 Subsidiary streams and crevasses have been stopped and thus con- 
 centration of flow has been secured ; the flow has been regulated 
 by means of parallel jetties, while hard knots and obstacles in the 
 channel have been removed by dredging so that resistance to flow 
 has been reduced. By these means increases in velocity and in 
 volume have been secured; in velocity, through which further 
 power for erosion was brought to bear upon the bed of the Pass ; 
 and in volume, by which the additional transporting power re- 
 quired to bear the eroded material out into the Gulf was supplied. 
 
 The methods are simple, direct, and efficacious, and were in 
 the first instance derived from the application of hydraulic 
 principles and from the example presented by the works carried 
 out by Sir Charles Hartley at the Sulina mouth of the Danube 
 with such great success. 
 
CHAPTER X 
 
 THE MERSEY 
 
 The estuarial length of the Mersey was once described by the late 
 Mr. Thomas Hawksley as a " raging wild beast " — a terse and 
 rememberable expression, by which Mr. Hawksley, who was not 
 given to paying unmerited compliments either to men or to things, 
 meant that he regarded the Mersey as a difficult river to deal with. 
 
 All estuaries are difficult to deal with if public benefit is to be 
 secured, but there is no gainsaying the proposition that in the 
 Mersey the difficulties are acute and are always present, being due 
 in fact to a combination of peculiar conditions at the entrance to 
 and in the form of the estuary, as well as in the economic and 
 commercial interests which have developed not only upon the 
 banks of the river but in the hinterland. 
 
 The entrance is situated in one of the most stormy corners of 
 the Irish Sea ; it is in an embayment in which the tidal currents 
 which have swept into that sea, northward through St. George's 
 Channel and southward through the N'orth Channel, meet and 
 turbulently argue in their own way, questions of priority and pre- 
 cedence : one resultant condition of a secondary sort, being the 
 great tidal range which is experienced in the Mersey during spring 
 tides and from the effects of which Mr. Hawksley's epithet 
 " raging " was derived. At high spring tides the range from low 
 water to high water is 31 feet, while at neap tides the range falls 
 to 10 feet, the tidal capacity of the inner estuary between the 
 respective planes of low and high water, being at springs, about 
 710 million cubic yards, and at neaps about 280 million cubic 
 yards. 
 
 The form of the estuary is singular, and may for convenience 
 sake be divided into three portions, (a) the outer estuary, (c) the 
 inner estuary and (6) the neck or conduit by which {a) and (c) are 
 linked together. (Fig. 8.) 
 
THE MERSEY 
 
 53 
 
54 RIVERS AND ESTUARIES 
 
 The outer estuary does not lend itself to lucid description. It 
 is almost triangular in shape, the boundaries of the triangle being 
 the coast lines of Lancashire and Cheshire (which at the junction 
 of {a) and (b) form a re-entrant angle of approximately 90°) and 
 the outer edge of an irregular mass of sandbanks which are partly 
 exposed at low water of spring tides, which cover nearly 25,000 
 acres, and which have had their origin in the destruction of the 
 marginal cliffs and banks of the upper estuary as well as of the 
 coasts of North Wales. 
 
 Through these sandbanks a natural and fairly stable main 
 channel serves for the inflow of the tidal waters and for the reflow 
 of those waters combined with the run-off from the watershed. 
 The seaward (and shorter) portion of the main channel is known 
 as the Queen's Channel, the inward portion is termed Crosby 
 Channel. There are subsidiary channels which need not be 
 referred to in detail, they lead to diffusion of flow and of scour, 
 that is, to the very opposite of concentration. 
 
 The outer end of the Queen's Channel was formerly encum- 
 bered by a bar which limited the capacity of the port of Liverpool 
 and of all the other ports of the Mersey, and which lay as a sullen 
 obstacle across the channel at a distance of some 11 miles below 
 the Eock Lighthouse, which marks the line of the Cheshire coast 
 and the junction between {a) and (5). This bar has been removed 
 entirely by the heroic dredging operations to which further 
 reference will be made. 
 
 The neck or conduit by which this outer estuary is connected 
 with the inner estuary is about 6 miles in length and has some 
 semblance in form to that of the vena contracta, the high water 
 width at New Brighton (at the seaward end) being 1,760 yards, 
 which diminishes to 1,000 yards at Seacombe, and expands again 
 to 1,530 yards at Tranmere, where at present the " neck of the 
 bottle " terminates and the upper estuary begins. 
 
 The upper estuary of the Mersey looked at on plan, has a 
 curious similarity in shape to a side view of the skins of the water 
 carriers which are yet familiar objects in some parts of the East. 
 From Tranmere the banks begin to diverge and the width of the 
 estuary to increase until at EUesmere Port (about 12 J miles above 
 the Eock Light) the width is over three miles ; from thence the 
 width diminishes in a somewhat irregular way until at Euncorn 
 Gap (18 miles from the Light) the natural width was under a 
 quarter of a mile, above the Gap a second expansion occurs to a 
 
THE MERSEY 55 
 
 width ot 1,230 yards, after which the waterway presents the 
 features of an ordinary tidal river of small and diminishing size, 
 the width near Warrington Bridge (28 miles from Eock Light) 
 being only 50 yards. 
 
 As a consequence of this combination of peculiar conditions, 
 the Mersey furnishes for the consideration of the student, an 
 almost unique example of the effect of the conversion of tidal 
 momentum into current velocity in the neck or conduit, and again 
 of the operation of momentum in the heaping up against gravity of 
 the waters in a tidal stream in the upper part of the estuary. 
 
 At spring tides the velocity of the flow through the contracted 
 vein, attains the remarkable limit of 7 miles per hour, while a 
 tide "uninfluenced by the wind" which rises to a height of 
 21 feet above the level of Old Dock Sill ^ at Liverpool will rise 
 to a height of 25 feet above the same datum at Warrington 
 Bridge. 
 
 The contrast between the conditions which obtain in the main 
 channel in the lower estuary, and those in the main channel in 
 the upper estuary, will also be rife with instruction as well as 
 with interest to students. For the greater part of its length the 
 channel in the outer estuary is stable in course and direction, and 
 where movement has taken place, i.e. where Crosby Channel 
 bends towards the line of Queen's Channel, the movement has 
 been due entirely to the sharpness of the bend, in which erosion 
 has occurred on the concave side, and accretion on the convex, 
 thus tending to make the sharp curve still sharper, precisely 
 as in the case of a bend in the course of an upland stream 
 flowing through an alluvial plain. For many miles in the upper 
 estuary, below the length at which the Mersey becomes little 
 more than a tidal creek, the main channel has during the last 
 century meandered about the bed of the estuary to such a degree 
 that there is no part of that bed in which the channel has not at 
 one time or another found a temporary resting place ; the mutations 
 having been at some times slow, steady, and ruthlessly continuous ; 
 at other times sudden and violent, and affected by causes which 
 appeared to be altogether incommensurate with the results which 
 followed them. 
 
 Some of the recollections of an experience now extending over 
 
 * The "level of Old Dock Sill" is the datum to which all tidal heights are 
 referred on the Mersey. It represents a level of 4-66 feet below Ordnance Datum, 
 and is an unhappy relic of a dead past. 
 
56 RIVERS AND ESTUARIES 
 
 forty years may be recorded as illustrative of the mutations of 
 these unstable channels. 
 
 What was once known as " the great fret of 1873," began by 
 a very ordinary movement of the channel at Hale Head from the 
 Lancashire side towards the Cheshire side of the estuary. No 
 attention was paid to this, the channel was always moving; 
 " fretting," Le. undercutting of the banks of silt and sand on the 
 concave sides of the bends, was normal in the Mersey ; the way of 
 the river being to swing the upper channel over to one side for a 
 while and then reversing the process, to swing it back to the 
 other. But on this occasion the progress from north to south was 
 continued for years, until the channel fretted for itself a course 
 into the bight which then lay to the eastward of Stanlow Point 
 and the river Gowy, where, being stopped by a rocky reef, it 
 swung back into the estuary, then fretted a way into the next 
 embayment, that at Ellesmere Port (the Mersey terminus of the 
 Shropshire Union Canal), where it wrecked the whole frontage of 
 the port, cut the foundations from the feet of the walls, and left 
 the walls nearly flat on their backs. This was in 1873-4, after 
 which the channel, apparently satisfied with the results of its 
 excursion to the Cheshire side of the estuary, reverted to the 
 Lancashire shore, and remained there more or less for several 
 years. 
 
 This "great fret" originated in and was maintained by natural 
 causes, but estuarial changes of considerable extent, and followed 
 by consequences of serious import, are sometimes caused by 
 accidents of small degree, as to which little concern is felt in the 
 first instance. 
 
 In the year 1874 a little coasting schooner went ashore on 
 a sandbank in the Mersey between Hale Head and Euncorn 
 Bridge, and there disappeared from sight, swallowed up by the 
 sands as a rabbit by a boa- constrictor. In the process of deglutition 
 that small and insignificant derelict caused so great a change in 
 the upper Mersey, that the port of Euncorn was for the time 
 being almost entirely blocked owing to the diversion of the deep 
 from the entrances to the Bridgewater Docks. 
 
 Again, the fact that even changes due to natural events in 
 estuaries are sometimes violent and very sudden, is instanced by 
 the occurrence of such a change in the Mersey in the year 1880, 
 when on one stormy summer's day (it was in the month of June) 
 of strong gales and floods, the low water channel at Hale Head 
 
THE MERSEY 57 
 
 changed its position laterally for more than a mile in less than 
 twenty-four hours. 
 
 Finally, as small causes sometimes lead to great estuarial 
 changes, so at other times apparently inconsiderable causes stop 
 the progress of dangerous channel movements. About the year 
 1900 it began to be noticed that the low water channel in the 
 upper estuary had begun a migration from north to south, which 
 led to misgivings on the part of the few survivors who remembered 
 the "great fret" and the havoc which it wrought at Ellesmere 
 Port. The migration was directed towards Ince Bay, across which 
 one of the embankments which separates the Manchester Ship 
 Canal from the estuary had been formed ; a circumstance which 
 added point to the misgivings, and which led to a close watch 
 being kept upon the movement of the channel. The movement 
 proceeded steadily until 1906, when the works which had been 
 undertaken preparatory to the raising of the water level in the 
 canal had been completed, and a small brook which drains the 
 Frodsham marshes and which had up to that time been permitted 
 to flow into the waterway, was syphoned under the canal into the 
 estuary. The waters of the brook cut a way for themselves through 
 the -expanse of mud-banks until they joined the low water of the 
 channel, the dangerous movement of which they first checked, 
 then arrested, and finally turned northward again until the channel 
 resumed a position on the Lancashire side of the estuary, and the 
 situation was saved for the time being. 
 
 The comparative stability of the channel in the lower estuary, 
 emphasized as it is by the mobility of the deep in the upper 
 estuary, is due, first, to the increased inertia derived from the 
 increased volume of flow in the lower channel; secondly, to the 
 more direct course of that channel and to the greater concentration 
 therein ; and thirdly, to the much smaller proportion which upland 
 waters and land floods bear to the tidal flow in the lower channel 
 through which the disturbing influences of storms and floods are 
 materially reduced therein. 
 
 Disturbing influences are not absent in the main channel in 
 the lower estuary. The situation is an exposed one, and wind 
 and wave affect the line of the deep, as witnesses the sharp bend 
 in Crosby Channel, a difficulty which has called for remedial 
 measures during late years, but a difficulty which is small, almost 
 insignificant compared with that which was once presented by 
 the bar, that formidable and permanent obstruction to the main 
 
58 RIVERS AND ESTUARIES 
 
 channel of the lower estuary, and to the traffic of the 
 Mersey. 
 
 From time to time in the past, many schemes were propounded 
 for the improvement of the access to the port of Liverpool, but up 
 to the year 1890 practically nothing was attempted, although the 
 increasing size of the steamers engaged in the Korth Atlantic 
 trade rendered the obstructed condition of the channel more and 
 more serious. At that time the depth on the bar varied from 
 10 feet at low water of springs, and 19 feet at low water of neaps ; 
 to 30 feet at high water of neaps, and 41 feet at high water of 
 springs ; which depths were about as good as those which were 
 then available in the harbours on the east coast of ISTorth America, 
 and were sufficient to enable practically all of the steamers then 
 working the trade to leave and to enter at high water. But 
 complaints were constant as to delays to large passenger steamers 
 which had to lie outside the bar, sometimes for hours, waiting 
 for the tide ; not only that, but shipowners clamoured for vessels 
 of larger size, and shipbuilders shewed themselves to be eagerly 
 ready to respond to their requirements, so that the authorities 
 which controlled the ports in which the American trade was 
 handled were obliged to accept the responsibility of providing 
 facilities for the leviathans which began to come into sight, and 
 therefore to carry out operations for the improvement of their 
 harbours and of the accesses thereto. 
 
 In the port of Liverpool the problems connected with bar im- 
 provement works were so complex, the expenditure which would 
 be entailed seemed likely to be so great, and the results seemed 
 likely to be so uncertain, that the responsible authorities were 
 reluctant to attempt to carry out any works ; and while desirous 
 of meeting the requirements of the trade, felt compelled to main- 
 tain the position which they had occupied so long with regard to 
 improvement works. 
 
 The alternative lay in an attempt to provide and to maintain 
 the increased depth by means of dredging, and the result has been 
 a series of dredging operations so bold, so impressive, and so success- 
 ful, that no study of Eivers and Estuaries which left them without 
 notice could be considered as complete. 
 
 The material of which the Mersey bar was formed, was 
 mainly derived from the sea and was principally composed of 
 sand; in this differing from the bars at the mouths of the 
 Mississippi and other like rivers, which were composed of sludge 
 
THE MERSEY 59 
 
 and fine silt brought down from the uplands; it was there- 
 fore suitable for suction dredging, which in suitable material has 
 great advantages over bucket dredging. Mr. A. G. Lyster, the 
 present engineer-in-chief to the Mersey Docks and Harbour 
 Board, who (under the late Mr. G. F. Lyster) organized the plant 
 and conducted the operations from the first, began in an experi- 
 mental way, by fitting two steam hoppers with sand-pumps and 
 suction-pipes. The hoppers had a carrying capacity of 500 tons 
 each, and the experiment proved so successful that dredger after 
 dredger was built until the series culminated in a suction-dredger 
 of which the hopper capacity is 10,000 tons and the pumping 
 plant is competent to lift and load this quantity in 55 minutes. 
 
 From the first modest essay to the close of 1910 this plant 
 dredged the amazing quantity of 161,000,000 cubic yards — 
 45,000,000 cubic yards from the bar, 56,000,000 cubic yards from 
 Queen's Channel, and 60,000,000 cubic yards from Crosby 
 Channel — the result being that a channel has been made and 
 maintained through the bar and its approaches with a depth of 
 from 27 to 32 feet at low water of spring tides (instead of 10 feet 
 as formerly) and of 61 feet at high water of the same tides. 
 
 But improvement leads to improvement, the observation has 
 already been offered in this study, and is repeated here because 
 experience in the Mersey as well as experience elsewhere has 
 shewn how well-founded the assertion is. 
 
 Keference has already been made to the sharp bend in the 
 main channel of the lower estuary. That channel takes a course 
 to the northward for about five miles, and then turns abruptly 
 to the north-westward through sandbanks which are known 
 locally as Taylor's Bank and Askew Spit ; Taylor's Bank being on 
 the outward or concave side of the bend and Askew Spit on the 
 inner or convex side. The low water channel undoubtedly owes 
 this peculiarity of form to the strong wind and wave action to 
 which it is subject, and it is obvious that on the principles laid 
 down by Professor James Thomson, the concavity in Taylor's 
 Bank would increase and the convexity in Askew Spit would 
 grow, so that in the course of nature the sharp bend would slowly 
 but surely become sharper. The dredging of a straight and deep 
 channel through the bar and approaches accelerated the natural rate 
 of erosion on the concave side of the bend, owing in part to the in- 
 crease in volume of the flow, but owing in even greater measure to the 
 increased concentration which followed upon the improvement of 
 
6o RIVERS AND ESTUARIES 
 
 the dmind.: md tihe awytoatiim becMiie so aerioos that it loctod 
 a8if(l)tiieboidwoii]d1ieoaniea pezil to nsw^ilun and (2) tibe 
 riTer would f(^m for itadf a wihwdiafy channel to tiie aea^ and 
 ao deatioy llie poaition. of advanta^ wMch baa been von Hmwigjb 
 the die^i^ cipealiana vbkii bad been undertaken and bad been 
 ponned fiv ao manj yean. 
 
 A eaae fiir tiie adoption of remedial measmes bad tfaevetoe 
 been made oat, and Mi: A. G. L jster (nov Yiee-F^reaident of liie 
 Insdtnlion of Civil Engineen) leeonnnended tiiafc tbe eoneaTifcy 
 inXiKflof^aBankabonldbepnitoetodvitb jfrneatonp nbblefora 
 ^esag^ of about 2| nuks, in aodi manner aa to pot a stop to the 
 ^osion there. 
 
 After TBiy eaiefiil camridiTition tbe Menejr Do^a and 
 Harbour Board aee^ted tbe leeommendatian and antboriaed tbe 
 formation of die ** tiainii^walL'' or " revetment," as tiie ^c^iosed 
 wodc was termed. Bolb tenv were aecmatB^ aa bodi in^lied 
 tibat tiie slope ol tbe c u nc a f itj r , lAoA was fiormed <rf mafmal 
 wbidk Ae c ment s aa tbef imposed i^on tbe bank were capable 
 <tf nanyvin^ waa to be prnteeted bj matmal idddi tbese currents 
 were ineorapetent to dialodge or to afieet^ 
 
 Tbe work ao anthnriaed waa doty earned ont^ tbe Kmestmie 
 rabble being c un f e y ed to tbe rite in bopper bsa^gei^ dna^ed lym 
 tbe line o£ tbe npper part of tbe leretBent, and left to adjnst 
 tbe aetion of tbe tidea to tiie akipe ol Ae bank. The 
 wbidi waa acbieved waa sneb tbat aimibnr operations bare 
 leeentlf for tbe icgnktion of tbe tidal stieama 
 at and aboot l^m^ Point between tbe aootbesfy tomination of 
 die Hcrcalaneun Bocks and Canton. 
 
 Tins fiwt does not stand abme. fbe revetment in tbe b^^ of 
 Tv^kr^s Bank was onlj enaqitetBd in 1911, jet aheadf fiormal 
 and official Botiee baa been given of tbe intentinn of tibelfers^ 
 Bocks and Haxbon- Board to extend Oat revetment and to 
 tainii^walls on botb sides of tbe darnnel of Ae 
 Hstneen Tkjifla's Bank and die Bock L^ik 
 
 It is onlf neeessaij to state tbe lengdis of die proposed 
 in order to enable tfaeatndcnt to gn^ tbe 
 of tbe propoaal and die aerkms natore of tbe 
 
 OntbeeasteityorMt-bandbank of die cdmnnel tbe ks^di 
 oftbetcuaiBg-wall will be ow2^ mibsB, wbife on die westofy 
 bank tbe les^ win be over 5 ndle^ wbile Ae 
 of tbe levetBMBt at Tajlor's Bank will bave a kngdi 
 
THE MERSEY 6i 
 
 of I of a mile ; so that it is now proposed to extend an existing 
 length of 2i miles of regulative works to a total length of about 
 11 miles. Without venturing to assume the mantle of the 
 prophet (a course which has already been deprecated in this 
 study), it is but reasonable to suggest that finality will not be 
 reached even if and when the works now proposed are carried into 
 execution, as further lengths amounting in all to some 12 or 
 13 miles will remain untrained and unprotected, which the force 
 of circumstances will almost beyond doubt, compel the Mersey 
 Authorities to deal with, whether by way of dock extension or 
 of training wall construction. 
 
 These protective and regulative works in the Mersey are of 
 more than ordinary interest to students. The revetment at 
 Taylor's Bank is probably the first work, to the design of which 
 the principles enunciated by Prof. James Thomson were applied 
 in actual engineering practice ; moreover, for the purposes of the 
 design Mr. Lyster and Lieut. Mace, R.N.R. (the Marine Surveyor 
 to the Dock Board) carried out a series of float observations, by 
 means of which not only were the lines and velocities of the 
 currents in the bend of Crosby Channel determined both for flood 
 and ebb tides, but the results obtained by Prof. Thomson in his 
 model experiments and represented by him in his diagrams were 
 verified and established by actual observations on a great scale. 
 
 The works have a further interest, as showing how the con- 
 ditions of modem life, increasing as they are in complexity and in 
 national interdependence as the population of the earth multiplies 
 and develops, and as the trade of the globe grows and expands, 
 impel and compel even the most cautious and conservative of 
 authorities to take measures, to sanction projects, and to carry out 
 operations, which neither their predecessors nor themselves would 
 have been willing to consider a comparatively few years ago. 
 
CHAPTER XI 
 
 ESTUARIAL MODELS 
 
 In the year 1885, when the Bill to authorize the construction of 
 the Manchester Ship Canal was before Parliament for the third 
 year in succession, and when engineering opinion was sharply 
 divided as to the results which might be expected to follow upon 
 the construction of the works proposed to be carried out in the 
 valley and estuary of the Mersey, Prof. Osborne Reynolds, F.R.S., 
 suggested a method by which he thought that the results likely 
 to be produced by such works in rivers and estuaries could be 
 indicated with a fair degree of accuracy. 
 
 Dr. Reynolds's view was that a systematic study of the con- 
 ditions of a river falls naturally into three divisions : 
 
 (1) Observations of the general phenomena relating to the 
 regime of the deep, i.e, the low water channel. 
 
 (2) The movement of sand corresponding therewith. 
 
 (3) The action of the water which produces these movements. 
 He therefore constructed two models of the estuary of the 
 
 Mersey from the bar to Runcorn Gap, a distance of 35 miles. 
 The first model had a horizontal scale of ^s^-qo ^^^ ^ vertical 
 scale of c,^f), with a tidal period of about 40 seconds, or 90 tides 
 per hour. The respective scales of the second model were yoJeir 
 and 3^-g, the tidal period being 80 seconds. Tidal flow and ebb 
 were simulated in each model by the addition of a hinged tray at 
 the seaward end, which was filled with water up to the level of 
 low water, and raised and lowered mechanically. 
 
 The tidal period on which the velocity of flow depended was 
 in each case based on the theory of the propagation of waves. 
 Velocities vary as the square roots of heights ; velocities in a 
 model ought therefore to be to velocities in the river in the pro- 
 portions of the vertical scales, and the times should be in proportion 
 to the horizontal scales divided by the proportion of the velocities. 
 
ESTUARIAL MODELS 63 
 
 Wheu the water was put into motion important changes took 
 place in the distribution of the fine sand which was spread over 
 the bed of each model ; the reasons for the changes could be 
 plainly seen, and after about 2000 tides in the small model and 
 6000 tides in the larger, banks and channels were clearly defined, 
 and, particularly in the large model, presented despite the dis- 
 tortion, as nearly as possible a reproduction of actual conditions 
 in the part of the estuary which had been modelled. 
 
 Professor Osborne Reynolds exhibited his models and described 
 the results which he had achieved at the third International 
 Congress on Inland Navigation held in Frankfort in 1888, and 
 again at the fourth Congress held in Manchester in 1889. At the 
 latter Congress the description excited much interest amongst 
 continental engineers, and Mr. Mengin, then engineer-in-chief to 
 the works in progress for the improvement of the estuary of the 
 Seine, was so impressed by the importance of this experimental 
 method, that he induced the Commission of Engineers, under 
 whose auspices the Seine works were being carried out, to 
 recommend the French Government to suspend further progress 
 with the training- walls until the effects of these walls as 
 then proposed had been tested on a properly constructed model. 
 
 Subsequently the attention of the British Association for the 
 Advancement of Science was drawn to the possibilities which lay 
 in so simple and practical a method of investigating a subject so 
 complicated and difficult, and the Association appointed a strong 
 committee to act with Dr. Reynolds in the matter, and made an 
 annual grant for three years in succession in order to assist him in 
 the conduct of his experiments. 
 
 Reports drawn by Reynolds and endorsed by his committee 
 were presented to the Association in 1889-90-91. Somewhat 
 regrettably the committee avoided the "very difficult task of 
 modelling any existing estuary " and constructed instead a model 
 of an ideal estuary with which they experimented. 
 
 (A) In a " natural " condition. 
 
 (B) With regulating works of various sorts. 
 
 (C) With tidal waters supplemented by upland waters flowing 
 
 in at the head of the estuary. 
 
 As might be expected, the experiments demonstrated the 
 marked effect which the discharge of the land waters had upon 
 the channel in the upper part of the estuary. 
 
 Professor Osborne Reynolds summed up the results of the 
 
64 RIVERS AND ESTUARIES 
 
 experience in one sentence of his own, for he said that ''the 
 models showed that in any trained channel the depth could be 
 maintained by scour, if that scour were supplemented by dredging,*' 
 and the committee finally reported that 
 
 (1) The model system had been tested over a great portion of 
 
 the ground which it is likely to cover. 
 
 (2) The difficulties which were likely to occur had been met. 
 
 (3) The precautions which were required to overcome these 
 
 difficulties had been discovered. 
 
 (4) The system may, if these precautions are carefully 
 
 observed, be applied with confidence to the solution 
 of practical problems. 
 
 The conclusions of the committee were, as is the way with 
 committees, expressed in terms of the most cautious and con- 
 servative sort, to which no exception can be taken, but for 
 which allowance should be made ; so that the conclusion of the 
 whole matter may be said to be when (1) the course of obser- 
 vation of conditions and the study of data already recommended, 
 have been perfected, and (2) works have been designed and a 
 project for improvement has been completed, the course and the 
 study should be supplemented by the construction of a model 
 of the estuary in question, through which the effect of tlie 
 proposed works may be tested experimentally, it always being 
 remembered that to the indications supplied by the model the 
 observer must add for himself the effect of wind action and of 
 wave stroke. 
 
 The modelling of an estuary on a sufficient scale and with 
 reasonable accuracy, for the purposes of experimental research 
 and of the testing of the effects of proposed works, is a trouble- 
 some business which takes time and involves expense. For this 
 reason, perhaps, it has never become popular, and is in danger of 
 being allowed by the present generation to drop out of sight and 
 memory. Unless this danger can be averted, a method whereby 
 works proposed in an estuary may be proved by trial to be 
 right or wrong will go through the process of euthanasia, and 
 will sink into a place amongst the graves of the forgotten. 
 
 If this happens, a useful adjunct to the equipment of the 
 student will be lost; a valuable aid to the arguments by which 
 the engineer (whose duty it must become in increasing measure 
 to recommend works for estuarial improvements) can support 
 the advice which he has given will be discarded, and a means of 
 
ESTUARIAL MODELS 65 
 
 demonstrating the value of the works recommended to boards 
 and authorities, which are composed of men who desire to do 
 their duty but who are hampered by tradition, and burdened by 
 fears of failure — having some knowledge of mistakes in the past — 
 will be recklesly thrown away. 
 
 Having regard at one and the same time to the formidable 
 difficulties which beset all questions relating to estuarial works 
 and to the irresistible forces which are compelling public 
 authorities to consider and to undertake such works, this note of 
 warning against the abandonment of an admittedly useful aid to 
 the investigation of the subject is sounded ; while, for the purpose 
 of deepening the note and in the hope of rendering the sound 
 more effective, an old-time narrative of destruction and of disaster 
 upon a great scale, which followed upon incompetent efforts for 
 the improvement of a sea channel, is added ; as it may be that 
 in this way the warning will be emphasized by a picturesque 
 illustration, and so this elementary study may be brought to a 
 practical conclusion. 
 
 The story is that of the Gulf of Ephesus ; which 3,000 years 
 ago was a well-marked indent on the western coast of the 
 peninsula which forms a bridge between Europe and Asia, which 
 British map-makers call Asia Minor, but which was then known, 
 in the speech of the Greeks, as Anatolia, the " place of the sun- 
 rising." That western coast looked out upon the ^gean, which 
 separated it from Greece, and the indent (which had deep waters and 
 an area of about fifteen square miles) was sheltered from all winds 
 except those from the west. At the head of the Gulf where the 
 waters washed the feet of the mountains of Anatolia, emigrant 
 Greeks laid the foundations of the city of Ephesus, which in pro- 
 cess of time became a leading emporium, first of the traffic between 
 the two sides of the ^gean and of the intervening Archipelago, 
 and subsequently of the immense trade which was exchanged 
 between the East and the West in the ancient world. On account 
 of the position which it occupied, and because of the maritime 
 advantages which it possessed, Ephesus grew to be one of the most 
 populous, wealthy, and important centres of that great prototype 
 of modem trade. 
 
 To-day the site of the Gulf of Ephesus has been silted up 
 until it has become land, partly fertile and useful land, but partly 
 land in the form of useless and unwholesome marshes through 
 which the river Kayster pursues a tortuous way to the sea, while 
 
 F 
 
66 RIVERS AND ESTUARIES 
 
 the name of the great city Ephesus has disappeared from the 
 map. 
 
 Strabo the geographer, himself a native of Anatolia, took an 
 intelligent interest in the Gulf and in the history of its fortunes 
 and misfortunes and has left the record for us. It appears that 
 the history began about 1000 B.C., that the coastline, after seven 
 centuries of disintegration on the hills and of transportation to the 
 Gulf, had advanced seaward for about a mile, and that it proceeded 
 to advance until somewhere about 150 B.C., when a King of 
 Pergamum, Attains Philadelphus by name, recognizing that the 
 matter had become serious for Ephesus, called in an eminent 
 engineer of the day, who carried out works in, and built a break- 
 water across the mouth of the Gulf, with the result that the 
 chaunel through the Gulf was irreparably injured. 
 
 At the death of King Attains, under the terms of his will, 
 Anatolia became part of the Eoman Empire and so came under 
 the capable government of the proconsuls. Various governors 
 made efforts at great cost, to maintain the access to Ephesus 
 (a canal is said to have been formed across the growing deposits 
 in the embayment), but these efforts were hopeless from the 
 beginning and were relaxed as the Imperial power was weakened, 
 and so the Gulf silted and so Ephesus sank into decay and death, 
 until the name of the city alone is left " to point a moral " if not 
 " to adorn a tale." 
 
 The " ill-advised engineering scheme " (as Sir William M. 
 Kamsay has called it), which was intended to frustrate Nature's 
 obviously destructive operations in the Gulf of Ephesus, can be 
 seen, at this great distance of time, to have accentuated and 
 hastened the course of destruction to no small extent ; the name 
 of the engineer who devised the scheme and carried out the works 
 has sunk into a merciful oblivion, no doubt he did his best 
 (as students are apt to say when they have tried and failed), but 
 the best that can be said about him is that considering the state 
 of knowledge in his day there was an excuse for him, which cannot 
 be held to be valid in the case of any successor of his in this 
 twentieth century a.d. 
 
INDEX 
 
 Abbot, Humphreys and, 14 
 Abstraction, tidal, 39, 40 
 Action, tidal, 8 
 
 , , in Southern Ocean, 7 
 
 , wave, 8 
 
 American coast, eastern, 9, 58 
 
 examples, 48 
 
 Anderson's Bay, 9 
 Area of globe, 5 
 
 , transitional or critical, 8 
 
 Areas and velocities in inverse! ratio, 
 
 31 
 Askew Spit, 63 
 Attraction of waters, 40 
 Average dry weather discharge, 12 
 
 Bailey, Sir W. H., 15 
 Baker, Sir Benjamin, 16 
 Bank, Taylor's Mersey, 59 
 
 , revetment, 59 
 
 Bar, Danube, 51 
 
 , Mersey, improvement of, 59 
 
 , Mississippi, 48 
 
 Bars, formation of, 25 
 Bass Strait, 9, 26 
 Bay, Anderson's, 9 
 
 of Pundy, 8 
 
 of Limon, 8 
 
 of Panama, 8 
 
 Bends, flow round, 18 
 Bonney, Professor T. G., 22 
 
 Oalver, Captain R.N., 16, 24 
 Canal, Manchester Ship, sluices, 32 
 Canals and Inland Navigations, 30 
 
 ,_^ Royal Commission 
 
 on, 38 
 Carving tools, nature's, 6 
 Challenger Expedition, 8 
 Changes, Mersey estuary, 56 
 
 Channel, Crosby, Mersey, 65, 67 
 
 , Mersey Lower, 54 
 
 , Upper, 55 
 
 , Queen's, Mersey, 54 
 
 Channels, estuarial, instability of, 37 
 
 , regulation of, 31, 37 
 
 Chili, coast of, 5 
 Classification of data, 12 
 Clyde, river, 24, 47 
 Concentration of flow, 48, 51 
 Controllable weirs, 31 
 Corthell, E. L., D.Sc, 23, 50 
 Coulson and Forbes, 2 
 Critical area, 8 
 
 Cross sections of rivers when regulated, 
 31 
 
 Danube bar, 61 
 
 Darwin, Dr., 5 
 
 Datum, ordnance, 16 
 
 Dee, estuary, 29 
 
 DifiBiculties of subject of estuaries, 1 
 
 , physical, 5 
 
 , special (in Mersey), 52 
 
 Discharge of floods, 30 
 Disintegration, 6 
 Displacement, tidal, 40 
 Drainage Boards, 32 
 Dredging, 34, 39 
 
 of detritus from uplands, 34, 35 
 
 , suction, 59 
 
 Drift, movement of, 27 
 Dykes, 38 
 
 E 
 
 Eads, James B., Captain, 23, 48 
 Eastern coast of America, 9, 68 
 Effects of gravitation, 5, 7 
 
 radiation, 5 
 
 Ephesus, Gulf of, 65 
 Erosion, Norfolk coast, 9 
 Estuarial models, 62 
 
 works, 37 
 
 Estuaries, forces by which formed, 1 
 
68 
 
 INDEX 
 
 Estuary of Dee, 29 
 
 of Mersey, 52 
 
 of Seine, 26, 42 
 
 of Severu, 26, 30 
 
 of Tamar, 26 
 
 of Thames, 26 
 
 , silt conveyed into, 28 
 
 -, right-hand bank of, 4 
 
 , what is it ? 2 
 
 Examples, American, 48 
 
 , European, 42 
 
 Experiments on models— results, 
 
 F 
 Fishery Acts, 2 
 Flood intensity grows with population, 
 
 36 
 
 prevention, 30, 32 
 
 sluices, calculations for area, 35 
 
 , Manchester Ship Canal, 32 
 
 , Weaver, 31 
 
 Flow, concentration of, 48, 51 
 
 round bends, 18 
 
 Forces to which rivers and estuaries 
 
 are due, 1 
 Formation of bars, 25 
 Fret in Mersey, 1873, 56 
 Fundy, Bay of, 8 
 
 G 
 
 Galveston harbour, 26 
 Gauges, 13 
 Globe, area of, 5 
 Gravitation, effects of, 5, 7 
 Great fret in Mersey, 56 
 Greenock Channel, 24, 47 
 Groynes, 38 
 Gulf of Ephesus, 65 
 
 H 
 
 Humphrey and Abbot, 14 
 Harbour, Galveston, 26 
 . Pensacola, 26 
 
 Ideal estuary, model of, 68 
 Improvement works, river, 30 
 Information, pursuit of, 11 
 Inland Navigations, Keport on Canals, 
 
 etc., 33 
 Instability of channels, 37 
 Intensity of floods increased, 36 
 
 Land and sea, proportionate areas, 5 
 Lea, F. C, 22 
 
 Limon Bay, 8 
 Liverpool, Port of, 58 
 Lower estuary of Mersey, 54 
 Lyster, A. G., 59, 60 
 , G. F.. 59 
 
 M 
 
 Mace, E.N.E., Lieut., 61 
 Manchester Ship Canal dredging, 35 
 
 flood sluices, 32 
 
 models, 62 
 
 Mersey, 52 
 
 Askew's Spit, 59 
 
 bar improvement works, 69 
 
 Crosby Channel, 55, 57 
 
 " ^eat fret " of 1873, 56 
 
 neck of the bottle, 54 
 
 outer or lower estuary, 54 
 
 Port of Liverpool, 58 
 
 Queen's Channel, 54, 65 
 
 Kock Light, 54 
 
 special difficulties, 52 
 
 suction dredging, 59 
 
 Taylor's Bank and revetment, 59 
 
 tidal conditions, 52 
 
 upper estuary, 54 
 Minimum dry-weather run-ofi, 12 
 Mississippi bar, 48 
 
 river, 14, 22, 48 
 
 Model, experiments on, 63 
 
 of ideal estuary, 63 
 
 of Mersey estuary, 62 
 
 Mouth of Bhone, 29 
 
 of river, 25 
 
 Movement of drift, 27 
 
 N 
 
 Nature, forces of, 5 
 Nature's carving tools, 6 
 Navigations, Inland, report on, 33 
 Neck of bottle, Mersey, 54 
 Norfolk coast, erosion of, 9 
 Northern Tasmanian coast, 26 
 
 O 
 
 55 
 
 Old Dock SiU datum. 
 Ordnance datum, 15 
 Osborne Reynolds, F.R.S., 62 
 Oscillation, waves of, 8 
 Outer estuary of Mersey, 54 
 
 Panama, bay of, 8 
 j Panuco, river, 51 
 ' Pensacola harbour, 26 
 
INDE. 
 
 69 
 
 Physical difficulties, 5 
 Port of Liverpool, 58 
 Prevention of floods, 32 
 Protection of slopes, 35 
 Pursuit of information, 11 
 
 Queen's Channel, Mersey, 64, 55 
 
 R 
 
 Radiation, effects of, 5 
 Regime of a river, 11 
 Regulation of channels, 31, 37 
 Results of model experiments, 63 
 Reynolds, Professor Osborne, F.R.S., 
 
 62 
 Rhone, mouth of, 29 
 Right-hand bank of estuary, 4 
 
 of river, 4 
 
 Riparian rights, 2 
 
 River improvement works, 30 
 
 , mouth of, 25 
 
 , what it is, 2 
 
 Rivers, classification of data, 12 
 
 , forces by which they were formed, 
 
 1 
 Robison, Professor, 2 
 Royal Commission on Canals, etc., 33 
 
 Salmon Fishery Acts, 2 
 
 Sea and land, proportions of, 5 
 
 Seine, river, 26, 42 
 
 Severn, river, 26, 30 
 
 Sewage discharge, 16 
 
 Silt borne into estuaries from sea, 28 
 
 Slopes protection, 36 
 
 Sluices, calculation of area, 35 
 
 , Manchester Ship Canal, 32 
 
 Sluices, Weaver, 31 
 
 Southern ocean, tidal action in, 7 
 
 Stevenson, David, 12 
 
 Strait, Bass, 9, 26 
 
 Suction dredging, 59 
 
 Tamar, estuary, 26 
 
 Tampico, 51 
 
 Tasmanian coast, northern, 26 
 
 Thames, estuary, 26 
 
 Thomson, Professor James, F.R.S., 18 
 
 Tidal abstraction and displacement, 40 
 
 action, 8 
 
 ■ in southern ocean, 7 
 
 Timouoff, Professor V. E. de, 40 
 ; Training-walls, 38, 42 
 
 Transitional (or critical) area, 8 
 
 Translation, waves of, 8 
 
 Transportation of material, 6 
 
 U 
 
 Unwin, Professor W. C, F.R.S., 22 
 
 Velocities and areas in inverse ratio, 31 
 
 W 
 
 Walls, training, 38, 42 
 Washburn, Emory, 2 
 Waters, attraction of, 40 
 Wave action, 8 
 Waves of oscillation, 8 
 
 of translation, 8 
 
 Weaver sluices, 31 
 Weirs, controllable, 32 
 Wheeler, W. H., 7 
 
 THE END 
 
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