13 



their lorg-term corarelation shcms that in 1890 or about that year the imter 

 table Tfiras at its highest stage since 1850# A secoisdaa^y high was reached in 1905# 

 On the basis of precipitatioB data it is estimated that in Nassau and western 

 Suffolk Counties the water tatie should have averaged about four or five feet 

 lower in 1943 than in 1905# The profiles of plate 2 show approsdjaataLy that 

 imioh difference in the stage of the water table at the beginning and end of this 

 40-year period* 



Another significant difference between Hie paresent contour map and earlier 

 maps is in the shape smd extent of the water-table depression in Brooklyn and 

 western Queens* The probable original shape of the water table in Brooklyn is 

 indicated on section A-A* on plate 2, irtiich is based on Wiggings extension of 

 the 1905 contours (8)# The dec£Line that has occurred there is the result of puicp- 

 tng for industrial purposes and for public water supplies (17) • In the early 

 years of the ground-water development in Brooklyn the decline was gradual^ In 

 recaib years it has been accelerated and the water-table depression has e3cpanded« 

 A caB5)arison of the 19S3 and 1936 contour maps shows that the water table in 

 parts of Brooklyn and Queens declined rather sharply during that three-year 

 period. Since 1956 there has been only a soiall net decLixiBj althoijgh the depres- 

 sion has continued to expands In general^ low water levels were reached about 

 1941. Since then there has been a sli^t a?ecovery of water levels in the area 

 of most concentrated pramijDg# 



Referring to section B-B* on plate 2, it is seen that in 1943 the water table 

 was lower everywhere along that section than it was in 1905# Part of that dif*- 

 ference in levels is due to the difference in average rates of precipitation 

 before 1905 and before 1943, ishich was discassed above» However, the major part 

 of the difference in water levels theare is due to the puag)ing distribated over the 

 area adjacent to that section ( (17), Hgm 6)# 



In view of the relative nearness of the center of hea^ punping in Brooklyn 



