Fc ... ^ns GEOLOGICAL SURVEY AND MUSEUM. Jbrmyn Stebbt, London, S.W. NOTES ON SOURCES OF TEMPORARY WATER SUPPLY IN THE SOUTH OF ENGLAND AND NEIGHBOUKING PARTS OF THE CONTINENT. SOLD ONLY AT THE MUBEUM. 1914. Price Twopence, These notes were written primarily for the use of tlie Royal Army Medical Corps, 1st London Division, Territorial Force. They are designed to illustrate the possibilities of obtaining drinking-water at short notice by temporary works, and do not profess to deal with the construction of large or permanent water- works. They are based on personal experience of the varied sources of water existing in the South of England, and on the assumption that the conditions prevailing in the Tertiary and Chalk areas of the neighbouring parts of the Continent will be much the same as those in the English counties which are under- lain by those formations, due regard being paid to the changes in character undergone by the strata. A. Strahan, Director. Geological Survey Office, Jermyn Street, London, S.W 24th December, 1914. INTRODUCTORY. All running streams are highly dangerous as drinking-water in a seat of war or in a populated area. Wells are not open to the same wholesale condemnation, but, especially when shallow, are subject to suspicion. It is necessary therefore to take into account not only the capability of a Nsite for yielding water, but its freedom from pollution. For the special purpose of obtaining water with the least possible delay it is necessary to consider the sands, gravels and clays which form the soil or subsoil over much of the country (Superficial Deposits), as well as the earlier formations which underlie the Superficial Deposits or which, in their absence, themselves form the surface of the ground. The formations therefore come up for consideration which are arranged in order in the following column, commencing with the most recent : — 1. Blown Sand. \ 2. Alluvial deposits (Alluvium). o n - ^ -n -j. on 1 rr -11 > buperticial Deposits. o. (jrravei Terraces m valleys. 1 4. Gravel on the tops and sides of hills ) 5. Sands with pebble-beds, clays and limestones (Lower Tertiary or Eocene Strata). 6. Chalk. 7. Highly inclined strata of the Ardennes, &c. (Carboni- ferous, Devonian, &c.). The following diagram, Fig. 1, illustrates the relative positions of these deposits in the Chalk and Tertiary areas. (3599—10.) Wt. 37019—71. 1000. 1/1.5. D & S. G, 3, 313864 o ^^ 1 C) f-s> ?S ■ a o I .2 1—1 c? C3 OQ pj f-" "^ o |_2 o g ^ Is ^^^ o 'S Superficial Deposits. All water got irotn Superficial Deposits is open to the gravest suspicion and requires careful testing before use. 1. Blown Sand has been carried by the wind along the coast and has in places drifted inland for some miles. Generally it has been piled up by the wind into ridges (dnnes), which are separated by hollows or large fiat expanses. Though usually confined to the low coastal region, it has sometimes been carried by the wind far up the hill sides. The dunes may be as much as 100 feet high and are devoid of water, but the intervening hollows are often waterlogged. Fresh water may be got in the hollows or on the flats, even near the shore, by sinking shallow holes or driving down tubes. The yield of a well may often be increased by digging converging trenches and placing in them a layer of broken shells or small pebbles through which water can pass. The trenches must be covered and most carefully protected from pollution. They should not be so placed as to draw water from ground which is or has been occupied by troops or by dwellings. 2. Alluvium is the name given to the muds, sands and gravels which are being spread abroad in the bottoms of the valleys by the action of running streams, or which have accumulated in areas of obstructed drainage, such for example as low lying tracts hemmed in between dunes and hills, or any tracts where the gradient of the natural drainage is small. These materials form an almost dead-level surface (alluvial flat) below the level of floods, but slightly above the normal level of the streams. They are charged with water up to the level of the s'treams and often yield it abundantly. The quality of the water varies according to the nature of the alluvium. IN^ot infrequently the alluvium contains rotten wood or is so highly charged with decaying vegetable matter as to yield water which is obviously offensive. Alluvial flats, moreover, are particularly liable to artificial pollution, either by the dis- posal of sewage, the burying of carcases and other refuse or by the soakage into them of water from a polluted stream. They are also subject to floods. Great care therefore must be exercised in using water from alluvium. It may be taken as a general rule that the flow of the underground water will be in the direction of such slope as the ground may possess (if any) and towards any open channel by which drainage is effected. The most hopeful place to make a trial-well, therefore, would be up stream from any suspected source of pollution and further away from the nearest water-channel. Gravel often occurs at a few feet depth under an alluvial flat, and in such cases is likely to yield a better water than the siirface layers. 3. Gravel Terraces are frequently found in the larger valleys. They form gently undulating land, at a level slightly above that 6 of the alluvial flat, the difference of level ranging from two or three feet in the lowest terrace to as much as 50 or 100 feet in the higher terraces. These gravels are generally well charged with water at a small depth, and contain a natural water of better quality than that of the alluvium. In choosing a spot, however, for a well, care should be taken to avoid the neighbourhood of obvious sources of pollution, such as farm-yards, grave-yards, sewage-works, &c. These terraces, moreover, form some of the best land for cultiva- tion, and not infrequently manuring of the soil has rendered the water contained in them unfit for use. Here also a .site for a well should be chosen preferably higher up the valley than any obvious source of pollution. The water should not be used for drinking until it has been tested, and the tests should be repeated at frequent intervals. For in such porous material as river-gravel continued pumping sets up a: circulation in the und"erground water, and may draw in impure water from a distance. 4. Gravel on the tops or high up on the sides of the hills. — The chalk-country may be described as a plateau intersected by numerous valleys. The hills which form parts of the plateau are for the most part overspread on their tops with gravel, sand and stony clay. On their sides also there are patches of gravel, but more especially there is a soil composed of gravel washed down from above, which may be very extensive, but is generally of no great thickness and of little importance as a source of water. It is, however, apt to disguise the true character of the subsoil. The larger patches of gravel on the hill-tops contain local and limited supplies of water, and their situation, at a height which may amount to some hundreds of feet above the valley-bottoms, may be of much importance. The character of the gravel is apt to vary from yard to yard, and is subject to no rule. Trial-holes are likely to reveal the existence of clayey material through w^hich water can pass but slowly in one place, or of porous sands or gravels in another, If the gravel rests on Chalk, the well must not be sunk so deep as to touch the Chalk, for a reason which will appear later. A well sunk in one of these high-level patches of gravel should be placed more or less centrally on the patch in order that it may draw water from all directions, but the w^ater is a surface-water, and, as such, is subject to the usual causes of pollution. Clusters of dwellings, farm-yards, grave-yards, &c., must be avoided, and careful testing for organic impurity is essential. When a source of good water has been found in Superficial Deposits, an increased supply can be obtained, and time saved, by sinking several wells simultaneously,- spacing them out at distances of 30 yards or so. The gravels generally rest upon an uneven surface. The largest stores of water are found along the hollows in that surface, but can only be located by probing. Local enquiry on the possibilities of obtaining water in shallow e i >< a ^ a u « S e3 ^ f*^ fH . % Or^ ^ - -^ f-** -< •^ f< 55 S ? ^ ^ 1 t-> to . s o s ^ 1 - 1° ^ s ^ J^l oVA E? M 8 wells is likely to be of great service, but it must not be assumed that strangers can drink water which the natives drink with impunity, and it must be remembered that water is not neces- sarily pure because it is clear. Clear sparkling water may be highly contaminated. The neighbourhood of wells must be effectively protected from pollution. Geological Formations underlying the Superficial Deposits. 5. Lower Tertiury or Eocejie Strata. — In the London district, in Hampshire, in Central France and in Belgium there rests upon the Chalk a great series of strata comprising pebble-beds, sands, clays and limestones. On the Continent these strata occupy two main tracts. The one, in which Paris is situated, extends to the north and east as far as Beauvais, Compiegne, La Fere, Laon and Eeims. Along this line the Chalk emerges at the surface and, rising gradually, forms a typical Chalk-country. In the direction of the Belgian frontier it descends again aj:id disappears from view along a line drawn through Calais, St. Omer, Bethune, Lille, Douai and Tournay under the second of the tracts referred to. Even in the Chalk-country the tops of the hills are occupied by outlying remnants of the pebble-gravels, sands and clays, though the valleys cut down deeply into the Chalk. On the other hand in the Paris and Belgian basins the Chalk is far below the bottom of the deepest valley. In the following table the characters and names of the Low^er and Middle Tertiary strata in England and on the Continent are compared : — England. Paris Basin. Belgium. ^ Sands with a bed of Limestone (Calcaire Sands and sand- clay (Bagshot Grossier or Lu- stones of Brussels. Beds). tetian) Dense clay (London Sands of Cuise. Sand of Mt. Panisel Tertiary Clay). Limestone. (near Mons) and Beds Clay of Flanders (Middle and (Ypresian). Sand and clay Lignite of the Sois- Marls and sands Lower (Woolwich and sonnais and plas- (Heersian and Eocene). Reading Beds) tic clay (Sparna- Landenian). with shingle beds cian). (Oldhaven Beds) Sands of Bracheux. and sands (Thanet ^ Sands). Chalk. Chalk. Chalk. It is to be noticed that the dense London Clay of England becomes a sandy formation in the Paris Basin, but partly pre- serves its argilla(!eous character as the Clay of Flanders. Thick limestones appear in tlie Paris Basin which are not represented as such in England or Belgium. The following vsection drawn in an easterly direction from Compiegne towards Soissons illus- trates the emergence of the Chalk from beneath the Tertiary Beds, and the tendency of the limestone (Calcaire Grossier) to form the crests of the hills. m I 5^ eg ^ J 1 *§ ■« H*« ^ ^ 5* rH •«« "« +3 ^ M •^ c8 •g P O 1 1 it X 5>^ fl PQ '1^ ^ S S o O *. 1 ^ 1 1 CO 6 M Ph V s -J P^OQO -O) S o O o P 0.2 9 "^ 9 O o o CO no GQ ^ (/) 10 In the tracts of sand and clay recourse may be had to shallow wells if a low situation is chosen and an outcrop of clay avoided. The water is open to suspicion both of local contamination and of natural impurity due to the organic remains embedded as fossils in the strata. Water containing- a sufficient quantity of iron in solution to form a yellow scum of iron oxide after exposure to the air is not uncommon. The outlying remnants of these sands and clays on the tops of the chalk-hills may be regarded from the point of view of water-supply in much the same light as the gravels (4). They may, however, attain a greater thick- ness, occupy a larger area and contain larger reserves of water than the gravels. Wells in them cannot be carried into the Chalk without risk of losing water {see after). The finding of water on tracts of limestone such as are shown in Fig. 3 is a different problem. The rock is usually fissured, and the fissures, having been enlarged by the solvent action of water, act as traps for the rainfall. Consequently an absence of running water or shallow springs is noticeable in many elevated limestone-tracts. On the other hand the water thus trapped is thrown out at the base of the limestone, or by any impervious bed in the limestone. Not infrequently it issues in such volume as to form a small river. These issues from limestone differ from springs from other formations, for they may consist merely of polluted surface-water which has temporarily pursued an under- ground course in caves and fissures. It must not be assumed that an issue of water from limestone, even though it may be clear and cold, is safe from pollution. 6. TJie Chalk is usually a source of hard but organically pure water. It is saturated with water up to a certain plane, which undulates in accordance with the undulations of the ground, but in a modified degree. Thus the level of the plane is determined by the depth of the deepest valleys, but under the chalk-hills it rises slightly. A valley which is deep enough to touch the plane of saturation is occupied by a perennial stream. Many valleys are not sufficiently deep and then form that familiar feature of a chalk-country, dry chalk-valleys. (Fig. 4.) It follows that a well sunk in the bottom of a chalk-valley which is occupied by running water will reach the plane of saturation at a small depth, while a well sunk in a dry chalk-valley must be deeper in proportion to the shallowness of the valley. A well sunk on a chalk-hill may have to be carried to a depth nearly corresponding to the whole height of the hill above the neigh- bouring streams, in order to reach the plane of saturation. The chalk above the plane of saturation absorbs water in place of yielding it, and it is for this reason that a well sunk in sand or gravel on the top of a hill is likely to lose its water if it is carried deep enough to touch the chalk. Chalk varies much in its capability of yielding water. Much of the Lower Chalk is of a soft marly character and yields little or none, but more massive chalk, if it happens to be fissured, may yield a practically inexhaustible supply. 11 ^ ccO&WO •§ l«0 :^ V. ^ s ^ R- %) 'S^ Si, e 6 12 A running stream in a chalk-valley usually has its visible source in a spring or cluster of springs. Above that source the water is pursuing an underground course but may be within easy reach by wells. The depth to the water becomes greater as the valley ascends. See also under the heading, S'prings. T. Highly inclined strata of the Arderuies, ^-c. — A tract of ground lying east of Valenciennes presents wholly different I;!-;: I •^ g « 05 "e <^ ^ ^ 5S tib § 3 "tS "a ^ cc C "Ki f^ r< vS «a^ r< 1: • « ^ §) s pj c < 'C sc ^ > S f* 1^ < 'S^ 5ri « s ^ OS ^) <4j "to %. •+0 ec S !>«» '^nJ •c* ^C Si 1 1^ •0 6 M ^ o pq problems. It is roughly bounded on the north by a line drawn through Mauberge, Namur and Liege, and on the south by a line drawn through Avesnes and Mezieres. It consists of highly 13 : • • ' inclined or vertical strata. In tlie northern part of it there are many beds of limestone. In this tract it is likely that recourse may be had to springs. Springs. — True springs are colder than the air in summer and warmer than the air in winter. They are not turbid in rainy weather, and do not increase in volume quickly after rainy weather sets in. They should be permanent, and the character and vegetation of the channel by which the water flows away is usually a guide to their permanence. Frequently on a hill composed of strata of sand and clay, a line of small springs will be found at the top of a clay-bed. The water may be collected by a trench cut along this line. If the line descends in any direction the supply is likely to become greater at the lower elevation. On the sides of chalk-hills it is seldom of use to look for springs, but in the bottom of a chalk- valley occupied by running water there are usually vsprings issuing at the foot of the valley-side. The springs may be chiefly con- fined to one side of the valley. In limestones of the Ardennes {e.g., under 7) streams are often found issuing from caverns or visible channels in the rock. These streams are not necessarily springs, but may be polluted surface waters which have fallen down open fissures and after flowing underground are coming out again. On the other hand some can be trusted, but none should be used without testing. In the other strata of the Ardennes small springs are common and many of them are to be trusted. UNIVERSITi Or CAi_l^^^'K^. \ : '? R \R\