﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  

  

  687 
  

  

  Area 
  of 
  

  

  surface 
  

  

  Pond 
  (acres) 
  

  

  Jamaica 
  40 
  . 
  00 
  

  

  Brookfield 
  8.75 
  

  

  Clear 
  stream 
  , 
  . 
  1 
  . 
  07 
  

  

  Valley 
  stream 
  17.78 
  

  

  Rockville 
  8.00 
  

  

  Hempstead 
  32.52 
  

  

  Minimum 
  

  

  flow 
  (cubic 
  

  

  feet 
  in 
  24 
  

  

  hours) 
  

  

  Elevation 
  

  

  of 
  overflow 
  

  

  above 
  tide 
  

  

  (feet) 
  

  

  419,315 
  

  

  7.90 
  

  

  265,098 
  

  

  15.40 
  

  

  100,448 
  

  

  11.50 
  

  

  325,291 
  

  

  12.80 
  

  

  353,388 
  

  

  12.60 
  

  

  1,054,713 
  

  

  10.60 
  

  

  The 
  same 
  streams 
  were 
  measured 
  in 
  October 
  and 
  November, 
  

   1851, 
  and 
  the 
  aggregate 
  result 
  then 
  was 
  3,137,500 
  cubic 
  feet. 
  With 
  

   the 
  exception 
  of 
  Clear 
  stream, 
  they 
  were 
  again 
  measured 
  in 
  

   October, 
  1852, 
  the 
  result 
  then 
  being 
  2,606,300 
  cubic 
  feet 
  in 
  24 
  

   hours. 
  

  

  According 
  to 
  a 
  survey 
  made 
  by 
  Theodore 
  Weston 
  in 
  the 
  fall 
  

   and 
  winter 
  of 
  1859, 
  the 
  catchment 
  area 
  of 
  the 
  stream® 
  originally 
  

   taken 
  for 
  the 
  municipal 
  supply 
  of 
  Brooklyn 
  was 
  found 
  to 
  measure 
  

   46.8 
  square 
  miles, 
  but 
  -subsequent 
  measurements 
  have 
  placed 
  it 
  at 
  

   49.9, 
  which 
  is 
  the 
  figure 
  now 
  used. 
  1 
  

  

  The 
  drainage 
  grounds 
  lie 
  mainly 
  on 
  the 
  Hempstead 
  plains, 
  

   although 
  a 
  small 
  portion 
  may 
  be 
  considered' 
  as 
  lying 
  on 
  the 
  

   southern 
  slope 
  of 
  the 
  central 
  ridge. 
  The 
  ridge 
  slopes 
  are 
  com- 
  

   posed 
  of 
  clay 
  and 
  alluvial 
  earth, 
  with 
  little 
  power 
  of 
  retaining 
  

   water. 
  Hempstead 
  plain, 
  on 
  the 
  other 
  hand, 
  consists 
  of 
  a 
  very 
  

   uniform 
  deposit 
  of 
  sand 
  and 
  gravel 
  with 
  occasional 
  thin 
  veins 
  

   of 
  clay 
  ; 
  hence 
  Hempstead 
  plain 
  is 
  largely 
  receptive 
  and 
  retentive 
  

   of 
  water. 
  The 
  sand 
  and 
  gravel 
  on 
  this 
  plain 
  serves 
  two 
  purposes 
  

   as 
  regards 
  the 
  rainfall 
  sinking 
  into 
  it: 
  (1) 
  It 
  retains 
  the 
  water, 
  

   only 
  gradually 
  delivering 
  it 
  to 
  the 
  surface 
  in 
  the 
  valleys 
  of 
  the 
  

   brooks 
  or 
  on 
  or 
  near 
  the 
  seashore 
  in 
  the 
  form 
  of 
  springs; 
  (2) 
  it 
  

   filters 
  and 
  purifies 
  it, 
  the 
  gravel 
  and 
  sand 
  performing 
  the 
  func- 
  

   tion 
  of 
  a 
  natural 
  filter 
  bed. 
  It 
  is 
  considered 
  that 
  but 
  a 
  small 
  

   portion 
  of 
  the 
  ground 
  water 
  of 
  this 
  gravel 
  plain 
  has 
  been 
  derived 
  

   from 
  the 
  rainfall 
  of 
  any 
  single 
  year. 
  The 
  greater 
  portion 
  of 
  it 
  

   is 
  considered 
  to 
  have 
  collected 
  during 
  a 
  series 
  of 
  years. 
  Borings 
  

   and 
  open 
  wells 
  show 
  that 
  this 
  ground 
  water 
  has 
  a 
  nearly 
  uniform 
  

   inclination 
  toward 
  the 
  south 
  shore 
  of 
  about 
  12 
  feet 
  per 
  mile. 
  

  

  *As 
  to 
  the 
  difficulty 
  of 
  determining 
  just 
  what 
  the 
  catchment 
  area 
  of 
  any 
  

   one 
  of 
  these 
  streams 
  actually 
  is, 
  see 
  De 
  Varona's 
  History 
  and 
  Description 
  

   of 
  the 
  Brooklyn 
  Water 
  Works, 
  1896. 
  

  

  