﻿120 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  

  therefore, 
  very 
  largely 
  on 
  whether 
  or 
  not 
  the 
  rainfall 
  of 
  the 
  stor- 
  

   age 
  period 
  — 
  December 
  to 
  May, 
  inclusive 
  — 
  is 
  large 
  or 
  small. 
  If 
  

   the 
  winter 
  rainfall 
  is 
  relatively 
  large, 
  the 
  runoff 
  will 
  also 
  be 
  rela- 
  

   tively 
  large, 
  even 
  though 
  the 
  total 
  rainfall 
  for 
  the 
  year 
  is 
  small. 
  

   This 
  fact 
  must 
  be 
  taken 
  into 
  account 
  in 
  estimating 
  the 
  value 
  of 
  

   streams. 
  Whether 
  any 
  given 
  stream 
  is 
  low 
  during 
  the 
  summer 
  

   months 
  or 
  has 
  then 
  a 
  well-sustained 
  flow 
  will 
  depend 
  very 
  largely 
  

   on 
  the 
  rainfall 
  of 
  the 
  month 
  of 
  May. 
  When 
  the 
  May 
  rainfall 
  

   is 
  heavy 
  enough 
  to 
  produce 
  full 
  ground 
  water, 
  the 
  flow 
  is 
  likely 
  

   to 
  be 
  well 
  sustained, 
  even 
  though 
  the 
  rainfall 
  is 
  comparatively 
  

   low 
  during 
  the 
  summer 
  months 
  following. 
  If, 
  on 
  the 
  contrary, 
  

   the 
  May 
  rainfall 
  is 
  so 
  low 
  as 
  to 
  leave 
  a 
  deficiency 
  in 
  ground 
  water 
  

   for 
  that 
  month, 
  the 
  flow 
  will 
  be 
  low 
  during 
  the 
  summer, 
  even 
  

   though 
  the 
  rainfall 
  is 
  large. 
  

  

  The 
  foregoing 
  explains 
  why 
  for 
  certain 
  years 
  the 
  runoff 
  of 
  

   a 
  stream 
  may 
  be 
  relatively 
  small, 
  even 
  with 
  rainfall 
  considerably 
  

   above 
  the 
  average. 
  

  

  To 
  more 
  particularly 
  illustrate 
  this, 
  assume 
  a 
  stream 
  with, 
  say, 
  

   6 
  inches 
  of 
  ground-water 
  flow 
  and 
  further 
  assume 
  that 
  on 
  any 
  

   convenient 
  date 
  the 
  ground 
  water 
  is 
  practically 
  depleted. 
  Under 
  

   these 
  circumstances, 
  the 
  6 
  inches 
  of 
  ground 
  water 
  must 
  fill 
  up 
  

   before 
  any 
  very 
  large 
  flow 
  can 
  occur. 
  On 
  the 
  other 
  hand, 
  we 
  may 
  

   consider 
  the 
  sequence 
  of 
  the 
  rainfall 
  such 
  as 
  to 
  leave 
  full 
  ground 
  

   water, 
  whence 
  it 
  results 
  that 
  there 
  will 
  be 
  a 
  much 
  larger 
  runoff, 
  

   even 
  though 
  rainfall 
  and 
  other 
  conditions 
  are 
  the 
  same. 
  

  

  What 
  is 
  wanted 
  in 
  a 
  stream, 
  therefore, 
  is 
  as 
  large 
  a 
  ground 
  flow 
  

   as 
  possible, 
  with 
  small 
  evaporation. 
  That 
  there 
  are 
  very 
  great 
  

   differences 
  in 
  streams 
  in 
  this 
  respect 
  may 
  be 
  easily 
  seen 
  by 
  exam- 
  

   ining 
  a 
  series 
  of 
  tables 
  of 
  stream 
  flow. 
  It 
  may 
  be 
  remarked 
  that 
  

   these 
  two 
  conditions 
  are 
  obtained 
  only 
  on 
  a 
  forested 
  area, 
  for 
  

   proof 
  of 
  which 
  see 
  Bulletin 
  No. 
  7, 
  Department 
  of 
  Agriculture, 
  

   Forest 
  Influences. 
  

  

  Effect 
  of 
  low 
  ground 
  water. 
  Moreover, 
  when. 
  rainfall 
  is 
  below 
  

   the 
  mean 
  for 
  several 
  months, 
  the 
  ground 
  water 
  may 
  be 
  expected 
  

   to 
  become 
  continuously 
  lower. 
  This 
  is 
  a 
  subject 
  about 
  which 
  

   comparatively 
  little 
  is 
  known, 
  although 
  the 
  data 
  are 
  vefy 
  import- 
  

  

  