Stripping Reservoir Lands.
As there has been some controversy lately as to whether or not it is an advantage to “strip land” for reservoir purposes, the writer thought that possibly his own personal experiences, with rather notable examples of each class, might be of some interest and, better, bring out some discussion on this important question. The first experience was with a “stripped” reservoir, at Elmira, N. Y. This reservoir was built in 1871 and 1872, and was filled in the fall of 1872. 1 he drainage-area is 4J2 sq. miles, all hilly and sparsely inhabited farm land. A small portion only is under cultivation, most of the land being pasture or woodland. The soil is clay or heavy clay loam, the rock formation, a shaley slate. The land is all hilly and contains numerous ravines with steep sides. The reservoir is formed by an earth dam across a narrow ravine, in which a small creek flows, or rather used tor flow, as the wholesale cutting of the timber on the watershed has made it a flooded creek in the rainy season, and a dry creekbed in dry seasons. The dam was designed by A. Feltey and is of earth, with a clay-puddle core-wall. The outer slope is ij4 to T, sodded inner slope 2 to 1, riprapped with rough “field stone,” gathered mostly from the reservoir site during the construction. The dam is 700 ft. long on top and 36 ft. high at centre, or over the old streambed; the overflow is 33 ft. above the bed of the stream, and is constructed in the hill at the end of the dam. There is a stormwater canal the entire length of the reservoir, and the inlet is controled by suitable head-gates. The flood-water or first wash of the drainagearea during heavy rains and floods is carried round in this canal. The reservoir covers 38 acres and holds 113,000,000 gal. All of the top soil of the area to be flooded was stripped off rapped, except on the face of the dam. The much of the material for the dam was taken from this area, so that most of the reservoir site was excavated to a considerable depth. 1 he land was then thoroughly grubbed; all roots of trees and underbrush being carefully removed. This left a clean, new soil, free from all vegetable growth. This bottom soil is a heavy clay or hard-pan mostly, the shale rock being exposed over a small portion. The sides were not riprapped, except on the face of the dam. The outlet-pipe * or supply to the city is 16 in. in diameter, the inner end fitted with a swiveljoint and the standpipe controled by floats, so that water is drawn at any desired depth. There is also a 20-in, waste-pipe under the dam. This reservoir yields about .300,000 gal. per day and was the only supply for the city at that time. As stated above, this reservoir was first filled in the fail of 1872. During the winter of 1875 and 1876, an extremely cold winter, when the reservoir was covered with ice nearly 2 ft. thick, a pronounced odor and taste were noticed in the water. This was variously described as musty, fishy and cucumber. The trouble was not serious and soon passed away. At that time little was known about the growths that imparted these disagreeable odors and tastes to water. It is doubtful if even the general name of algae had been applied to them; certainly, we could not then pick out and name the particular organism that gave the various odors and tastes. It was even some years after this—in 1811—when this association appointed a committee, headed by the late Alfred Leeds and having as its other mem hers, Colonel 1. 11. Gardner, New Orleans, and L. J. LeConte. Oakland, Cal., to investigate vegetable and animal growths affecting water supplies. The trouble of 1875-6 was attributed to the wood pipes, of which the distribution system then consisted, a considerable amount of new pipe having been laid in the summer of 1875. After the trouble of the winter of 1875-6, no furthei trouble was experienced for several years, when in the summer of 1883 or 1884. it returned in a very much worse form—so bad, indeed, that it was necessary temporarily to abandon this gravity supply, though the reservoir was nearly full, a pumping plant having been erected on the Cheming river—a stream with a large drainagearea and a minimum flow of about uo,ooo,ooo gal. per 24 hours. This trouble also disappeared in time, but reoccurred with more or less intensity every year thereafter, apparently gradually growing worse and the trouble periods longer. In 1896 a Jewell high-type, gravity filter was installed; but this would not entirely remove the odors and tastes. At times the water from this reservoir Vas so bad that it could not be filtered. It would clog the filterbeds in a few minutes and left a sticky, disagreeable, gelatinous coating on the sides of the tanks. The odor when the filters were washed at times was very disagreeable, indeed, almost unbearable. It lias been so bad in the reservoir that it was disagreeable, if not even nauseating, to stand on the banks with the wind blowing towards one over the water. This, of course, made it necessary to abandon the supply until the trouble passed, that is, until the water had purged itself, and the dead algae had settled to the bottom. Every known expedient was tried; the mains were thoroughly and frequently flushed, but without success. Water was drawn from the surface, the outlet screen-head being at times lifted partly out of the water, so that considerable air was drawn into the supply pipe with the water; we did not know that analxetia was the cause of the trouble and that it stayed near’ the surface—various depths, to the very bottom of the reservoir were tried, but with no good results. And, here, a word more about aeration. Before the introduction of the filters the water from this reservoir flowed to a distributing reservoir, the surface of which was 110 ft. below the base of the dam. It entered this reservoir through a fountain having a 4-in. centre-jet and I32j4-in. sidejets, the pipe between the reservoir was 12-in. diameter, cement-lined, wrought iron. In still weather the centre-jet threw a stream over 70 ft. high, which, in falling, pounded the surface of the water into a foam, undoubtedly adding large quantities of oxygen to the water. The sidejets threw streams at an angle of about 25°, which fell near the edges of the reservoir, so that the entire surface was constantly agitated. During one of the outbreaks of algae, the writer made a tj4-in. tap in the top of the outlet from the distributing reservoir, a few feet from the outlet-chamber, and ran an open pipe to a height of a few inches above the surface of the water in the reservoir, which was quite constant, the inlet being controled by float-valves, hoping that the outflow current would suck air into the supply main to the city. Some air was drawn in, how much is doubtful, anyhow it was not enough to do any good. In 1904, vvhen algae was very bad in the storage-reservoir, it was’ treated under the direction of Mr. James M. Caird, with copper sulphate, and the treatment was entirely successful. The treated water was, filtered without difficulty and supplied to the city in good condition, free from all odor and taste. This treatment lasted about two years, when it was necessary to retreat the water. Asterionella and anaboena were the principal organisms that caused the trouble. The second experience is at Charleston, S. C-, where the conditions are an exact opposite. The reservoir at Charleston was built in 1904-5, and was first filled in the spring of 1906. The drainage-area is 49!^ sq. miles, all flat land and much of it swamp. The population on the drainage area is small, there being no towns. The soil that is not swamp is either sand or red clay, containing considerable iron, and black muck. A part of the flooded part was salt marsh, subject to tidal overflows. The reservoir was formed by a low earth dam across the creek and about half mile of salt marsh. The land is flat, no elevation on the entire watershed being more than 40 ft. above mean low-tide, and the water is backed up for about 8 miles. The reservoir covers about 2,300 acres, when full; the land was salt marsh, swamp, old rice fields and high ground, mostly grown up to second-growth, loblollcy pine. The capacity of the reservoir is 3.127,820,000 gal. The spillway is o‘/2 ft. above mean-tide and the dam was built as much to dam out the tide-water as for storage. As will be seen from the above description, the reservoir is mostly very shallow. The original stream, which was narrow and winding, had a considerable depth; but the flooded ground is covered to an average depth of less than 4 ft. The contour lines are very irregular, many small swampy places, side gulches being overflowed. No attempt was made to clear, clean or “strip” this land before flooding, except burning the grasses in part; and even this was not done over all the surface, and for the most part they had time to grow up again before the land was covered with water. Even the standing timber was left and, except cypress, was, of course, killed. This timber, much of it large pines and undergrowth, which was dense in places, has died out and fallen into the water. The fresh water killed all the grasses on the salt marsh, and fresh water grasses took their place. When first flooded, there was little clean space free from timber, underbrush or coarse grasses, except where the stream originally flowed, and some old rice fields, which were flooded to a sufficient depth to hide the grasses. But, the water-surface has gradually cleared up; the grasses and underbrush have disappeared entirely, and the trees are little more than the bare trunks, where they are standing, stripped of their bark, with the exception of cypress which flourishes in water. The higher marshes that were covered with grasses or rushes have broken away from the shores and floated down to the dam, where they have been cut up and thrown over. Large sections of old rice fields have come to the surface, forming floating islands, some of them several acres in extent, and stable enough to walk on. These are bare when they come to the surface; but a rank growth of sedge-grass soon covers them. They are composed of a mass of the roots of these coarse grasses, and alluvial black mud or decayed vegetable matter. Thev are from 18 to 36 in. thick. They are cut up into blocks of a convenient size with saws, very much as ice is cut, and skidded over the dam, to which they are carried by the current and the prevailing winds. When dry, they burn quite freely; they also make an excellent fertiliser. There is in the more shallow places a luxuriant growth of water verbena; lemna also, covers ‘a good deal of the water in summer. Shortly after the reservoir was filled, during the first season, algae appeared in troublesome quantities; crenothrix appearing first and giving the most trouble. The water contained 3.5 parts per 1,000,000 of iron. Anaboena, oscilliaria and some others of the taste and order, importing algae, were present in large quantities. An aerating plant was put in to get rid of the crenothrix, and copper sulphate was used freely, about six tons being used this first year, the consumption being 3,500,000 gal. per day. By these means the situation was satisfactorily handled and the water kept good. The second year the trouble was much less, it disappeared entirely during the winter, though there was always some crenothrix present in the raw water. About 2yi tons of copper sulphate was used the second season, and less than 1 y2 the third, indicating that the growths of algae are gradually lessening. The summers are long—about nine months; but there are some sharp frosts during January and February— the conditions not being tropical. The conditions, however, are ideal for algae growths; but they are gradually improving, and it is hoped that in a few years this water will be no more subject to these growths than any other impounded water. This hope is based on data obtained from numerous smaller but similar reservoirs in the vicinity. Many were built years ago as rice reserves, to store water for flooding rice fields. These were originally flooded exactly as the Charleston waterworks reservoir was, but are now clear ponds, the water having very little color, much less than in the waterworks reservoir. The vegetable growths about the edges of these ponds are entirely different from the original growth, and the water is good to look at and is palatable. The Elmira reservoir was as thoroughly stripped as possible: great care was taken to keep out the first washing from the drainage-area and the muddy floodwaters. There was little or no marsh land on the drainage-area, the catchmcnt-area being seemingly ideal. The reservoir was clean and clear; on the sides the slopes were abrupt; and there was very little shallow water. At Charleston, the drainage-area was largely swamp, and there was much decayed vegetable matter on all of the area drained, the water being decidedly peaty. The reservoir covered a large surface, was shallow, and absolutely unstripped or even cleared. Much of the land flooded was composed of black muck or decayed vegetable matter. In the first, the conditions were at the first satisfactory and the water good for several years. But trouble from algae growth came in time and has steadily grown worse, in spite of strenuous efforts to remedythe condition. The second was troublesome and unsatisfactory from the first, but has somewhat improved and promises to continue to improve. The writer’s experience and information cover over thirty years—in the case of the Elmira plant. The Charleston plant has been in use only about three years, so that the future has much to develop.
•Paper rend at the twenty-eighth annual convention of the American Water Works association; Washington, D. C., May, 1908.