IMAGE EVALUATION TEST TARGET (MT-3) t^ i. /j /.. 1.0 I.I I 45 150 ■ 3.6 1-25 lllllu M M 1.8 1.6 150mm e /, ^} m 07^ % (?/^ /. /4PPLIED_^ IIVMGE . Inc .= 1653 East Main Street ,^=-- Rochester, NY 14609 USA .^S"^ Phone: 716/482-0300 -= Fax: 716/288-5989 © 1993. Applied Image, Inc., All Rights Reserved ^ W A ^\ '.N % \ ."^ /.A ^ /^ CIHM Microfiche Series (l\1onographs) ICIMH Collection de microfiches (monographles) Canadian li-sstitute for Historical l\Aicroreproductiont / institut Canadian de microreproductions liistoriques I ^^U Technical and Bibliographic Notes / Notes techniques et bibliographiques The Institute has attempted to obtain the best original copy available for filming. Features of this copy which may be bibliographically unique, which may alter any of the images in the reproduction or which may significantly change the usual method of filming, are checked below. Coloured covers.' 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Les cartes, planches, tableaux, etc., peuvent dtre fllmis d des taux de rMuctlon diffdrents. Lorsque le document est trop grand pour dtre reproduit en un seul clichi, 11 est filmi d partir de I'angle supirieur gauche, de gauche d droite, et de haut en bas, en prenant le nombre d'images nicessaire. Les diagrammes sulvants illustrent la mdthode. 1 2 3 4 5 6 Currents and Shore Processes in Lake Ontario ALFRED W G. WILSON MONTREAL, QUE. {Read before the Engineers' Club, To,onto) THE CANADIAN ENGINEER PRESS TORONTO. ONT. PRICE 25 CENTS boo- 51 '*',!.•■ 1^ '\ ^: (*' i i ^ .„'>lf^}'SfA C'l •-. ■ ,"i.. ^.•i •*, ' ,''>' ,1 y '^■^ .1" ^ ' K • -). ',-- , , 1 isJ ' ^";»^-V: cM^^ 'i-y~\^ ^Sah"^ ^^s'ST^'V" ,3^.p_ ^iV^ i4 "<-S'*?',.^ f Currents and Shore Processes in Lake Ontario By Alfred W. C. Wilson, Montreal. Introduction i — Within the last twenty-five or thirty years there has gradually grown up, as an offshoot from the Science of Geology, a science whose specific object is the systematic study of land forms, their characteristics, origin and history — the Science of Physiography. Under the impetus of new methods of investigation there have been marked advances made in our knowledge of the history of land forms and their processes of growth and disintegration. The results of these investigations have a very direct bearing on all engineering operations which attempt to guide or control those natural processes which produce or modify topographic forms. Shoreline processes and shoreline forms have been in- vestigated by many observers, and many important papers have ,been published. It is only about ten years ago, how- ever, that the subject was systematized by the recognition that there are progressive stages in the development of shore- lines and shoreline topography ; that initial forms, character- istic of newly formed lake basins or of sea coasts recently elevated, are followed by a sequential series of forms char- acteristic of later stages of the life history of shorelines, until extreme old age is reached.* The life history of shores, the processes which are involved in the formation of shore zones and the later development of any given shoreline have all a very direct bearing on the construction and maintenance of docks and harbors on all our large water bodies, whether lake or ocean, on the preservation of coast lines, and to a certain extent on water supply and sewage disposal. The problems presented by Toronto Harbor, Toronto water supply and sewage disposal form no exception to the generalization, and it is because of their bearing on these problems that the data given in this paper are here presented. Only a summary of the results of a study of the shore- lines, and shoreline processes on lake Ontario can be given here, but, I wish especially to emphasize the fact that the •Gulliver, Shoreline Topography Proceedings of Am- erican Academy of Arts and Science, vol. 34, iSog. &' processes described are world-wiHo i„ .i.«- that t,e , , , :jztJo: iirz:TZ\::^ Lake* are forms characteristic of a certain stage of shore de velopment wherever shorelines occur. Ceologfo Prooetsas on th« Shores. cess::rrrr-:::— ^---^p^ movements of the water itself. The movement of "he wate :L :av^e"" '*'" ^" °^ ^^"^ •^^"-'<^^' --K current: While the existence of periodic movements of the water of the Great Lakes corresponding to the tides is known the amphtude of this u:ovement is very small and in the pres n d scuss:on ,t does not need to be considered. On all S o water exposed to the action of winds three d^^tin t^ype lTTh?lu"%'"''°'"^-^''= ^^^^^«' the current an X or InHi J M l °^^^«™^«' ^^y also be developed directly or indirect y by gravity. All shore processes-degradaTon TcZTT' ^^f ^^^^-" -d sedimentatio^^on a ^^s^: a ficantly large scale at least, must be through he operation oi rco^z^r ''-'' ''—'- '^''- -in;sera:s siderlbLrerioroTr ""' '''--^ continuously for a con- s. to force lee shore. whole is ody as a Ilation is nee in a propagra- ■e of the , and of nsporta- Actingr through Me very vesterly epth of le lake. ly quite ■ee feet Curr«ntti-In 1892 and 1893 the United States Weather Bureau carried out a series of investigations on the distribu- tion of the surface currents of the Great Lakes— bottle floats being employed. In his report on the results of the inves- tigations M. H. Harrington groups the currents of the Great Lakes under four heads :-The body current, a surface current due to the prevailing winds, the return currents and surf motion.* The body currents and the return currents may be re- garded as constant. With these may also be associated the locally constant currents found at points of inflow and outflow of the main streams of the lake-the Niagara and St Lawrence Kivers. At these points there is a small but con- stant current, really a portion of the body current of the main lake. Usually these local currents are too weak to be active transporting agents except in the immediate vicinity of the outlets or inlets. At the mouth of the Niagara River the discoloration of the lake water shows that a small amount of fine waste is carried out into Lake Ontario. Two miles off the mouth of the river the coloration has disappeared and the current has been merged with the general drift of the surface waters of the lake. The outer portion of the Niagara River current in Lake Ontario has been found to shift its position with the winds. The waters of the St. Lawrence where it leaves the lake are clear and practically free from sediment. In Lake Ontario there is a slow general set of the mass of the water towards the outlet, while there is a pronounced vortical movement of the mass of water at the west end of the lake forming a backset eddy. Where, by the action of the wind, surface currents have driven more water to the east- ward of the lake than can well pass through the discharge there must be more or less of a return current. In this lake no return current, so well marked as in the other great lakes of the system, has been found. The probability seems to be that in part it breaks up into smaller whirls along the great pockets of the coast on either side of the general current and that a considerable body of water is returned as an under- current. The rate of the general east flowing drift is very slight, probably never exceeding twelve miles per day, more fre- quently being much less than this. The currents of the general ci rculation and the return currents are too feeble to ♦Currents of the Great Lakes, Bulletin B., United State, Weather Bureau iB^* ►1«'-/ SI ;< A ' "■-( /•J i "^ i/^:j 1^' ^ I k . 4^' ? ?« ' ,'^'- .f, 1 ^tl if^ transport even the finest sand which occurs along the beaches. They must, however, assist in the distribution of the finest silts and clays over the bottom of the lake The currents of streams tributary to the lake only effect the waters a very short distance from their mouths. After discharge,, except for the first few yards of their course the J^ticctior. that the river water takes in flowing through the lake .3 determmed wholly by the direction in which the lake waters at the point of discharge happen to be flowing at the ttme. Except in the immediate vicinity of the mouths of the streams .n question these currents have no effect in modify- ing the lake shores. With regard to the surface currents produced by the pre- vailmg winds, their general direction is the same as that of the wmd with which they are associated. A study of the pre- vailing winds for the lake stations, made by the officials of the United States Weather Bureau, and covering .a period of seventeen years, shows that there were on the average 66 per cent, of westerly winds for the whole year. For the months from May to September s6 per cent, were from a westerly direction. For the same period of time a study of the re- su tant w,nd directions shows that in ,83 out of 204 monthly valuei and in all the annual values the resultant is westerly Out on the open lake the transitory movement of the water before the wind takes the form of a drift, and because of the prevalence of westerly winds this drift is most fre- quently Identified with the easterly flowing body currents of the lake. The drift currents vary their direction with the wind that causes them, usually starting a short interval after the wind has commenced to blow and continuing for some time, often several hours and occasionally several days, after the winds that caused them have ceased. Where this drifting surface water impinges on a shore a longshore current is de- veloped, the direction of the current being dependent on the angle at which the drift impinges on the shore. These cur- rents, which for convenience may be designated wind cur- rents, are seen during wind-storms, and reach their maximum velocity at times cf the strongest storms. They are so in- timately connected with wave and surf movements that both must be considered together. It is when they act in conjunc- tion that active erosion, transportation, and deposition take place. During a period of heavy storm a longshore current may require a velocity as great as four miles an hour The occurrence of undercurrents, movin«f in a direction contrary to that of the surface current or of the prevailing wind IS a common feature. They will be caused wherever in any part of the lake the water is piled up above the mean level, since the head of water thus raised forces a portion ot the water back as an undercurrent. They are ilso frequently formed when there is a change in wind direction following the development of a strong longshore current. The mo- mentum acquired by the water will often maintain a strong undercurrent a little way off shore, for a long period after the direction of the longshore currents on the surface has changed. WtVM.— The same wind that generates a surface drift which becomes a longshore current where it impinges on the shore also develops waves. At a few points the water of a wave may roll up on the beach at the shoreline and run directly back again, but only at those points where the shore- line is parallel to the wive front. On the shores of the Grea» Lakes, where the shorelines sweep in great open curves wi'.h chords often from 4 to 8 miles \n length, the wave front very frequently advances at such an angle to the shoreline that the waves roll up the beach obliquely. Where this hap- pens the water never returns by the same path that it came, but runs off obliquely ; so that material on the beach when moved by the waves tends to travel along the shore by a zig- zag path, the angle at which the wave strikes the shore de- termining the angle between any two limbs of this path of travel. Intei^raiatlons, wavts and Currtntt 1— Along a stretch of lake shore where the waves are impinging obliquely and where a number are always breaking sk once, the tendency will be for the waves themselves to generate a longshore cur- rent flowing in the direction in which the ■ '"ertor of the acute angle between the wave front and the u ^reline points. This wave-generated current is always accordant with the longshore drift current caused by the same wind, and as they operate together in shore transportation they may be referred to simply as the longshore current. After the wind which has started the waves and currents has ceased to blow, the swells still continue for some time, and even after the swells have ceased to be perceptible the longshore wind current remains quite strong, the momentum which the water acquired during the period of storm not be- ing expended for some time after the storm has ceased. It not infrequently happens that a new wind from a different quarter may spring up and start to generate a current in an opposite direction. This affects the surface water first, while the lower water still retains the motion in the original direc- tion, also thft water immediately along the shore is affeeted to I'M' i#.i- the bottom some time before the deeper water off ,hore hai changed ™°'"''"'"" destroyed and its direction of flow TranspertatlOfi During Storm, by W«w«.O.n«r.U(l Loii«.h.r« Ourrtntt. •ff J" ''*' ''**^''"*' °' materials along the shore, the only effective agents of transportation are ^he wave-generated . longshore current, and the waves associated wifh thm Transportat.on of all but the finest material, cease a, s^n as the swell, d.sappear, and is at its maximum at th i^ Zl Z^n "' "^"'- ""'^ '°"*^''°''= ^""«"'« -f ^hemse v« are usually not strong enough to hold even fine sand, in suspe ^on for any length of time-a, may readily be a ce" tamed by experiment, or a, i, shown by the rapidity with «a,e. Clay ,n suspension is carried for .ome time by long. la^l^ ""T' ?^ '^^^ '^ '*■* *=""*"'^ «^ 'he general circu. ation; sand, and all coarser material, along the shores cease" to move a, soon a, the agitation caused by the swells stons hey are transported both by waves and current. The ^e^ s; bTSe ta-;:;'''" ^-^ ^"'^^"— '^^-^ *•»- of th??al!T''f" *'••»• '-B«''°<=k exposures on the shore clays and silts" \ T '"' ''^^^"'^^ '° '''''™ «<= «"» clays and s.lts sand and gravels, cobbles and boulder, The clay, and s.lt, in large part are derived from similar ma tcnal, in situ and are brought to the shore, by varTou, pro cesses, in small part they are produced at the sho"e by the o glacial origin. The gravels and cobbles come from beds of till in large part; along those portions of the shore whtre fro™ r 'T"'" "' ^"^^""^ ''"^^'' «" °f them are derteS mg mixed with the rest. The boulder, and large blocks are bio" s'of th ":;' °""'";''°"^' '"' ^-' thereone mt note ^om u^U;.:.^^^^^"^ '^^-^ ^'^i^-d only a short distance DUtrlbutlon Of the Watte on th. 8hore.,_The wasie ,un Phed to the shoies from the different sources is spread It fn a nearly even sheet parallel to the shoreline much of the finer material is earned out rapidly to the deeie^water, and S'alot'^r'^l: "'"^ '^' "°'^ ^""^ coarser deTri,rshm ed along the shore within the limit, of the wave swept ^oae. '■tad Lonffthort Most of the active transportation takes place during greater storms ; during a period of light winds only sands and fine gravels arc moved. Probably the greatest amount of trans- portation takes place durin,r the period of autumn storms though a very considerable movement takes place in the •pnng. During the summer months, except when there occurs an unusually heavy storm, transportation is ve«y slight. Dunng the winter months when the shores become lined with ice, transportation of all materials except sands and silt >s at a minimum. In the shifting of waste along the shore it is being moved locally now in one direction, now in the other, according to the wind direction. It is found, however, that a single great storm will undo the work of many previous gentler winds. A study of the transportatioa conditions along the shores of the lake shows that two distinct resultant shifting move- ments may be recognized. On the north shore it has been found that in the vicinity of Whitby there is a division point west of which the resultant shifting movement is west, and east of which the resultant movement is east. The corres- ponding nodal point on the south shore lies somewhat west of Charlotte. The general eastward and westward shifting of the shore waste is also shown by the direction of transporta- tion of certain well-known and easily recognized materials, such as fossils from known horizons, and also by the manner in which waste accumtlates around docks and other obstruc- tions, whether natural or artificial. It is also well shown by the forms of the various constructional features of the shore- line. 8 W,.. :^ This systematic resultant movement of the .waste towards the east and west ends of the lake respectively from distinct nodal zones near the middle of the length of the lake, is seen to be directly associated with the size of the storm waves. In Lake Ontario storms from the southwest will roll waves of maximum size on the northeast shores, the wind and waves having a free sweep toward this section of the shor^ over the longest part of the lake. Similarly storms from the southeast and east wUl roll maximum waves toward the north'- west shore of the lake. It is these storm waves with the strong longshore currents associated with them that perform the maximum amount of transportation, and are the cause of the resultant shifting movements in the directions indi- cated. Not only from actual observation may the waves be seen to be greater at the eastern and western ends of the lake than towards the middle zone at times when storms are blowing toward one end or the other of the Iake,but the greater power of these waves is well shown in the height and character of the storm beaches along the shores. Near the middle of the lake on both shores the storm beaches of coarse debris lie about six feet above water level. At the eastern and western er ds they lie about fifteen feet above the same level, being a little higher at the east than at the west end. Also at or near the middle of the north and south shores below the storm beaches there is a large accumulation of finer pebbles, gravel, and sand. At the ends of the lake the entire beach is at times made up of very coarse materials, the finer having been rolled out below the calm water level. Wave-base will also lie deeper below the mean level of the lake at the east and west ends than near the middle of the north and south shores. ! r ClMraottr of the thorallfM i— In its initial stages the shoreline of the basin now occupied by the present lake must have been very diverse in character. All later shore processes have tended to smoothen out these initial irregularities pro- ducing the long sweeping curves and beaches of graded waste tha» are its most characteristic feature. In the process of straightening and grading headlands were" truncated, lines of sea-cliffs were formed, and bars and barrier beaches were built across many of the originally deep bays. >f the .waste towards ctively from distinct of the lake, is seen if the storm waves. wst will roll waves res, the wind and lection of the shor^ rly storms from the es toward the north' irm waves with the 1 them that perform and are the cause the directions indi- r the waves be seen n ends of the lake when storms are >f the lake,but the n in the height and ; shores. Near the storm beaches of Iter level. At the fteen feet above the ist than at the west th and south shores ccumulation of finer ; the lake the entire materials, the finer er level. Wave-base of the lake at the the north and south initial stages the i present lake must iter shore processes I irregularities pro- les of graded waste In the process of re" truncated, lines irrier beaches were )ays. The barrier beaches which have formed the broad lagoons at the east end of the lake and also at Burlington bay are the most notable of these. Among other shore forms which are characteristic of the present stage of development of the shores of all the lakes is Toronto island, a form tec^inically known as a flying spit. Toronto Island I — Lake Ontario stood at its present level long enough prior to the formation of Toronto island to cut IH a sea-cliff along the shore that now forms the mainland ad- jacent to the harbor. The old beach line can be traced for some distance east of the Don, but opposite the eastern end of Ashbridge's bay. if the old abandoned beach exists, it is not readily distinguishable There is enough of the earlier beach discernible to show that lake Ontario waves e once actively cutting at the Don mouth, from which it is .nferred that at that time the Don delta was not encroaching on the lake shore. The formation of Toronto island has been, geologically speaking, recent. Its present location, form and growth are the result oi action of several processes whose mode of operation is well understood. As might easily be inferred^ and as has been shown by actual observation in numerous instances, abrupt changes in the trend of the shoreline may frequently cause well, defined longshore cbrrents to be carried past the salient and out into deep water, where of necessity they will gradually lose their velocity and discharge the greater portion of their load Raby Head, near Port Darlington, is just such a locality On a number of occasions when strong storms were blowing from the southwest the writer has observed the waters of the ' longshore current moving eastward along the coast and dis- charging into the clear waters of the lake off Raby Head. The discolored water, which marked the course of the cur- rent, could readily be seen for as much as three miles east of the head, lying probably about two miles off-shore, with clear blue water between it and the mainland. Coming west from Scarboro along the lake shore, one readily notes that there is a rather obtuse angle between the shoreline in front of the bluffs and that of the old beach back of Ashbridge's bay and Toronto harbor. At Scarboro and Toronto the strongest waves and associated longshore cur- rent would come from the east and southwest in former times It lO M i I ! ! I ■ ! ■ I as now. Because of the marked change in the trend of the coastline, the longshore westbound current ' would tend to discharge out into the lake at the point where the relatively abrupt change in the direction of the shoreline took place. The chfTs at Scarboro would supply an exceptional amount of oose debris, much more than is found anywhere else along the north shore. The result would be the construction of a flying spit from Scarboro waste reaching out into the lake from the point of discharge of the shore current. This spit would gradually increase in length and also tend to broaden. In time it would protect the land adjacent to the mouth of the Don from eastern storms. Such storms as come from the west would not only be weaker agents of shore processes, but would tend to force the debris which the Don was dis- charging back into the bay, between the flying spit and the shore. In the early history of the lakes and of the bar it seems probable that the greater portion of the debris from the Don„like that from all the other streams up to the present t>me, was distributed along the shores by the shore processes, and that no distinctive delta was built up. In later times the protection afforded by the young Scarboro spit guarded the mouth of the Don from master storms, and forthwith it began to build up a delta, and, during the course of delta formation, to aid in filling of what is now called Ashbridge's bay The westward progress of the spit was, however, far more rapid than the Don filling, so that in time the portion that now forms Toronto harbor was built west of the Don mouth. At first the flying spit would be narrow and ridge-like but as the apex advanced into deeper water its progress westward would be slower, giving time and opportunity for storms from other than the dominant direction to variously modify its apex. The general history of all such spits seems to be that when they reach deeper water the outer end shall be turned shoreward by waves and currents from deeper water offshore. The combined action of forward building and shoreward spreading lead. ■;. this as in other cases, to the broadening and hooking of the free end of the spit, and incidentally to the inclosing of a number of lagoons between minor bars built at successive intervals, according as the longshore or transverse processes were more active. Conolutlonsi-Toronto island as it stands to-day owes Its existence to the inter-relations which have existed between snort Prooasua of Transportation and the Supply of Wast*. Interference with either of these will immediately be followed by other changes and modifications on all parts of the island. It is DOSsihlfi tn rptarri »Vi * • d' . '^ & t"*i' .'■•• ■im n -. r M-^ > ''< J* All' ■ " " _j^ / V ' , I • ' J .9' J^l ^^■■E* P./"i^" 1 ^K^ '"-s ip\' --^-tM 1 bhi Hfevt v^^l 1 ^^^1 Ke' '*-'" Lil H i^^l , ?■)**