Following upstream, no particularly good sites are found until mile upstream from Webatuck, where the excellent site exists which was finally adopted as the basis of these estimates (and which I subsequently learn had also been noted as a favorable dam site by Mr. Birdsall). No site further upstream and below the confluence of the Swamp river and the Ten Mile was found that appeared nearly so economical as this for a high dam flowing the whole river back through Pawling into the Croton. The drainage here at Webatuck is 7 per cent. smaller than at the State line site, but the best data now at hand indicate that a dam at Webatuck will cost about one million dollars less than a dam at the State line site, because of the smaller volume of masonry required to close the gap. From such surveys as we found time to make it appears certain that the dam site mile above Webatuck is the best that the Ten Mile river affords. Taking it as the basis of our estimate of cost is certainly safe, because if a better site or series of sites is found, they will be judged as better because of a reduced cost. While a more detailed exploration by instrumental survey would naturally be made before becoming definitely committed to the Webatuck location, it now seems plain that this location presents sufficient adavantage over any possible series of small reservoirs and canal around Dover Plains to more than justify the expense of buying out these houses and changing the railroad location. ESTIMATES OF YIELD OF TEN MILE RIVER WATERSHED. With dam about 150 feet high located about three-quarters of a mile above Webatuck. Areas of watersheds and reservoirs taken by planimeter from maps of U. S. Geological Survey. Net land surface in watershed. Per cent. of water surface to land-average conditions ... Storage volume between elevation 450; proposed Storage volume per square mile of net land surface surface finally adopted as best adapted to Per square mile of gross area. Or per square mile of net land........... Safe yield per day from this entire watershed of 185 square miles net land corresponding to above figure of 810,000 gallons per square mile-185 x 810 == This 150 million gallons per day is the figure finally adopted by J. R. Freeman for the safe yield in the most severe drought, and cycle of years of smallest rainfall, of this Ten Mile River Watershed with dam three-quarters of a mile above Webatuck, and reservoir having area and available depth as given above. 200 In proportion to gross area of watershed this corresponds to a Probable greatest length of time in course of half The Sudbury records indicate three or four years-the Croton records for thirty-two years indicate two or three years as the longest period of depletion, with this rate of draft of 750,000 gallons per square mile gross area, and this per cent. of water surface. See Table No. 31, page 232, also Diagrams Nos. 46 and 47. 185.0 square miles. 8.1 per cent. 61 billion gallons. *330 million gallons. 750,000 gallons per day. 810,000 gallons per day. 150 million gallons. 3 years. *In these estimates of safe yield of the Ten Mile and Housatonic rivers I have closely followed the Croton estimate of safe yield of 275 million gallons per day from 360 square miles, but for confirmation have followed the method of estimate of F. P. Stearns, C. E., as formulated and explained in the Report of the Massachusetts State Board of Health, 1890, page 348 et seq. This Stearns method, by the aid of diagrams like Fig. 48 and Fig. 49, is very easily applied and is a much more logical method and more accurate than the old way of assuming a certain number of inches of rainfall as collectible, and available with the given storage capacity; and then distributing this through an assumed number of dry months. Maximum yield as confirmed by Diagram 48, from Croton record- Safe yield entire watershed, 920,000 x 200—. "as Safe yield entire watershed, 855,000 x 200 ... -according to the adjusted Croton records of Fig. 48. Period of depletion per Croton record "as occurred" ........ 305 million gallons. 184 million gallons per day. 171 million gallons per day. 6 years. From the above check-estimates it appears that with this very large volume of available storage, it would be safe to rely upon a daily draft of about 170 million gallons per day instead of the 150 million gallons per day which I have adopted as a conservative figure. The reasons in favor of the smaller figure are similar to those which lead me to call the safe Croton yield 275 instead of 300 or more million gallons per day; mainly the fear of impairment of quality of water by keeping a reservoir too long drawn below high-water mark. Whenever this objection is removed by filtration, then a larger figure may be adopted for the safe yield. PROBABLE COST OF A SUPPLY OF 150 GALLONS PER DAY FROM the Ten MILE RIVER, WITH DAM ABOUT THREE-QUARTERS OF A MILE ABOVE WEBATUCK (OR ONE AND ONE-HALF MILES UPSTREAM FROM BOUNDARY LINE BETWEEN NEW YORK AND CONNECTICUT). (The details of the following rough estimates are stated with more than ordinary fullness in order that whatever margin of uncertainty there is may be clearly apparent, and that it may be the easier to critically examine, check or modify them. It is to be kept in mind that they are based merely upon a careful reconnaissance in advance of detailed surveys.) Cost of Masonry Dam (See Fig. 75). Dimensions above present surface of ground are based on surveys and levels in October, 1899, by George A. Taber, C. E., under my supervision. The line of levels upon which these elevations and estimates are based were started from bench-marks kindly given us by the New York Water Supply Department, and were checked across country by Mr. Taber to the bench marks and levels of New York, New Haven and Hartford Railroad near Merwinsville. Form of dam proposed is similar to upper portion of Housatonic straight dam (Fig. 80). For cross-section of valley see Fig. 75. There is an excellent outcrop of hard limestone ledge on both sides of the Ten Mile river at this proposed dam site. No borings were made to ledge in bed of river, but excellent indications that it is not deep are found in the bare ledge bottom of the river half a mile above dam site, and again found three-quarters of a mile below this site, and in the level limestone formation. The probable excavation below the present surface was estimated at 20 feet near middle, according to judgment made while on the ground in company with an expert geologist, from the visible outcrops of ledge and from the apparent geological formation (see Appendix No. 16, p. 587). Probable total masonry in Webatuck dam..... The unit cost, $7.50 per cubic yard, adopted in this preliminary estimate for Webatuck Dam, complete, in view of the possible distance of a good granite quarry, is believed to be liberal. Estimated cost of dam located mile above Webatuck 214,000 cubic yards, at $7.50 per cubic yard of entire bulk... Titicus Dam, built by Croton Aqueduct Commissioners in 1890-4 contained 208,450 cubic yards, cost... Total cost per cubic yard of Titicus Dam, including earthwork, masonry, gate-house fittings and clearing up... New Croton Dam, if containing 614.000 cubic yards, as originally expected, at contract prices would have cost..... 214,000 cubic yards. $1,605,000. $933,065. $4.47 per cubic yard. LAND DAMAGES AND COST, TEN MILE DIVISION ONLY. Areas Required to be Taken for Reservoir Purposes with Dam on Ten Mile River Three-quarters of a Mile above Webatuck and Flow Line 450 Feet above Sea Level. Basis of estimate-cultivated land, $100 per acre, including legal and other expenses. Pasture land, $30 per acre, including legal and other expenses. This from various examples of actual sale appears 50 per cent. above fair market value of average. Some lots worth more, some less. The following amounts of land required include large marginal areas TEN MILE RIVER PROJECT. 349 to be taken for protection of the quality of the water, around the entire circumference of reservoir, estimated to 250 feet outside the flow line on steep hillsides, and to 500 feet outside the flow line on flat slopes, and including nearly all of the peninsulas. Values of buildings and dwellings were estimated by hasty external inspection of each by Morris Knowles, C. E., and adding 50 per cent. to the probable fair market value. (Many of these farm buildings are small, old and out of repair, and the fair value of these lessens the average cost.) Total for land and dwellings and accessory buildings, within and From such few of the buildings and such of the lands in the Ten Mile basin as I inspected personally with a view to valuation, I think it probable these prices are as high as those at which lands and buildings were acquired by the Massachusetts Metropolitan Water Board; but this item more than any other in the estimate is subject to errors of judgment and to being increased by unnecessary friction or extravagant methods in settlement, and should be reviewed by local experts. About 360 buildings, including dwellings and factories, were taken for the Massachusetts Metropolitan Works for the Wachusett Reservoir to supply III million gallons per day to Boston and vicinity. Out of all the dwellings and lands acquired by the Massachusetts Metropolitan Water Board, three-fourths were bought and paid for under an amicable agreement as to price-without recourse to litigation, eminent domain or referees, and with no noteworthy expense for experts outside the office force; whence it may be assumed that the prices paid were reasonably liberal. 1,216,000 $2,307,000 |