GSS 



NEW YORK STATE MUSEUM 



Upoii the low ridges lying between the several streams cross- 

 ing Hempstead plain the inclination of the ground water varies 

 with the width of the ridge, and is steeper in these parts than on 

 the main slope toward the sea, the resistance of the retaining 

 material there being proportionately less. So long as the slope 

 of the ground water is left undisturbed by pumping, as from a 

 series of wells, the permanent slope of the ground water is deter- 

 mined by the resistance of the material through which it Hows. 

 As regards the minimum flow of the streams receiving these under- 

 ground waters, the longer the time occupied by that portion of 

 the rainfall which sinks into the ground in reaching the outlets 

 the greater will be the minimum flow of the stream as compared 

 with its total flow; on the other hand, the shorter the time the 

 smaller the minimum flow. In the case of Long Island streams 

 the maximum flows are not very large, a fact which indicates 

 that the permanent regimen of these streams is probably main- 

 tained by the accession of the absorbed rainfalls of several years. 

 It follows that so long as the basins are not drawn upon very 

 greatly in excess of their flowage capacity the permanency of 

 Long Island ground-water supplies is only moderately affected 

 by variations in the yearly rainfall. 1 



In his Report on the Future Extension of the Water Supply of 

 Brooklyn, Mr De Varona gives the total monthly and average 

 daily quantities of water pumped into the Ridgewood reservoir 

 for the years L860 to L896, inclusive. 



'Fable No. 88 has been condensed from this report, giving in 

 calendar years the total rainfall upon the catchment and the per 

 cent of this utilized by pumping at Ridgewood. The average 

 yield utilized is also expressed in cubic feet per second per square 

 mile of catchment. This was originally 49.9 square miles, but 

 w as increased in 1ST:!, being in subsequent years 52.3 square miles 

 until L883, when it was increased to 64.6 square miles, and in 

 L885 to ()o.4 square miles. Considerable additions were made in 

 L891, and from that lime on the area is given as 154.1 square 

 miles. In 1866 Hie rainfall was 37.65 inches, and the total amount 



^he foregoing Statements relating to the water-yielding properties of the 

 Long Island sands arc mostly derived from Kirkwood's History of the 

 Brooklyn Water Works and Sown-s. published in 1867. For a more recent 

 as well as more extended, discussion of the same subject see De Varona's 



History and Description of the Brooklyn Waterworks. 



