﻿80 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Division 
  of 
  the 
  year 
  into 
  storage, 
  growing 
  and 
  replenishing 
  

   periods. 
  In 
  reference 
  to 
  taking 
  as 
  a 
  water 
  year, 
  the 
  period 
  

   extending 
  from 
  December-November, 
  inclusive, 
  instead 
  of 
  from 
  

   January-December, 
  inclusive, 
  it 
  may 
  be 
  stated 
  that 
  such 
  or 
  a 
  

   similar 
  division 
  has 
  been 
  customary 
  with 
  advanced 
  hydrologists 
  

   for 
  many 
  years, 
  although 
  in 
  the 
  United 
  States 
  the 
  advantages 
  

   of 
  this 
  division 
  have 
  not 
  thus 
  far 
  generally 
  appeared 
  obvious 
  

   to 
  writers 
  on 
  this 
  subject. 
  In 
  England 
  a 
  water 
  year 
  beginning 
  

   with 
  September 
  and 
  ending 
  with 
  August 
  is 
  quite 
  common. 
  The 
  

   same 
  thing 
  has 
  been 
  done 
  by 
  the 
  Philadelphia 
  Water 
  Department 
  

   in 
  tabulating 
  the 
  data 
  of 
  Neshaminy, 
  Perkiomen, 
  Tohichon 
  and 
  

   Wissahickon 
  creeks 
  and 
  Schuylkill 
  river. 
  However, 
  no 
  hard 
  and 
  

   fast 
  rule 
  can 
  be 
  laid 
  down 
  for 
  the 
  beginning 
  and 
  ending 
  of 
  these 
  

   periods. 
  In 
  some 
  years 
  the 
  storage 
  period 
  will 
  end 
  soon 
  after 
  

   May 
  1, 
  while 
  in 
  other 
  years 
  it 
  may 
  be 
  extended 
  into 
  the 
  first 
  or 
  

   second 
  week 
  in 
  June. 
  After 
  some 
  consideration 
  a 
  division 
  'of 
  

   the 
  storage 
  period 
  from 
  December-May, 
  inclusive, 
  has 
  been 
  taken 
  

   as, 
  on 
  the 
  whole, 
  best 
  representing 
  average 
  conditions. 
  

  

  The 
  storage 
  period 
  is 
  the 
  period 
  when 
  evaporation 
  is 
  lowest 
  

   and 
  the 
  largest 
  amount 
  'of 
  water 
  may 
  be 
  stored. 
  On 
  reference 
  

   to 
  table 
  No. 
  67, 
  runoff 
  data 
  of 
  Croton 
  river 
  for 
  the 
  water 
  years 
  

   1877-1899, 
  inclusive, 
  it 
  appears 
  that 
  the 
  mean 
  runoff 
  for 
  the 
  

   storage 
  period 
  is 
  16.83 
  inches; 
  the 
  mean 
  evaporation, 
  6.85 
  inches; 
  

   and 
  the 
  mean 
  rainfall, 
  23.68 
  inches. 
  The 
  mean 
  runoff, 
  therefore, 
  

   is 
  71 
  per 
  cent, 
  of 
  the 
  mean 
  rainfall. 
  In 
  the 
  growing 
  peri'od 
  on 
  

   Croton 
  river 
  the 
  mean 
  runoff 
  is 
  2.57 
  inches, 
  with 
  13.58 
  inches 
  

   mean 
  rainfall, 
  or 
  the 
  runoff 
  is 
  19 
  per 
  cent, 
  of 
  the 
  rainfall. 
  In 
  

   the 
  replenishing 
  period 
  the 
  mean 
  runoff 
  is 
  3.42 
  inches 
  and 
  the 
  

   mean 
  rainfall 
  12.08 
  inches, 
  or 
  the 
  runoff 
  is 
  27 
  per 
  cent, 
  of 
  the 
  

   rainfall. 
  It 
  is 
  obvious, 
  therefore, 
  that 
  it 
  is 
  only 
  during 
  the 
  

   months 
  'of 
  the 
  storage 
  period 
  that 
  any 
  large 
  amount 
  of 
  water 
  

   can 
  be 
  stored. 
  A 
  similar 
  condition 
  is 
  shown 
  by 
  tables 
  Nos. 
  43 
  

   and 
  61. 
  

  

  During 
  the 
  storage 
  period, 
  vegetation 
  is 
  inactive 
  and 
  evapora- 
  

   tion 
  takes 
  place 
  chiefly 
  through 
  wind 
  action. 
  It 
  seems 
  clear, 
  

  

  