﻿68S 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Upon 
  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 
  flows. 
  

   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 
  A^arona 
  gives 
  the 
  total 
  monthly 
  and 
  average 
  

   daily 
  quantities 
  of 
  water 
  pumped 
  into 
  the 
  Ridgewood 
  reservoir 
  

   for 
  the 
  years 
  18G0 
  to 
  1896, 
  inclusive. 
  

  

  Table 
  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 
  

   was 
  increased 
  in 
  1872, 
  being 
  in 
  subsequent 
  years 
  52.3 
  square 
  miles 
  

   until 
  1883, 
  when 
  it 
  was 
  increased 
  to 
  64.6 
  square 
  miles, 
  and 
  in 
  

   1885 
  to 
  65.4 
  square 
  miles. 
  Considerable 
  additions 
  were 
  made 
  in 
  

   1891, 
  and 
  from 
  that 
  time 
  on 
  the 
  area 
  is 
  given 
  as 
  154.1 
  square 
  

   miles. 
  In 
  1860 
  the 
  rainfall 
  was 
  37.65 
  inches, 
  and 
  the 
  total 
  amount 
  

  

  x 
  The 
  foregoing 
  statements 
  relating 
  to 
  the 
  water-yielding 
  properties 
  of 
  the 
  

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

   Brooklyn 
  Water 
  Works 
  and 
  Sewers, 
  published 
  in 
  1867. 
  For 
  a 
  more 
  recent, 
  

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

   History 
  and 
  Description 
  of 
  the 
  Brooklyn 
  Waterworks. 
  

  

  