﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  115 
  

  

  The 
  data 
  required 
  for 
  ordinary 
  computations 
  may 
  be 
  frequently 
  

   limited 
  to 
  the 
  totals 
  of 
  the 
  storage, 
  growing, 
  and 
  replenishing 
  

   periods, 
  although 
  when 
  ground 
  water 
  is 
  to 
  be 
  taken 
  into 
  account 
  

   the 
  monthly 
  data 
  should 
  be 
  given. 
  

  

  Formulas 
  for 
  runoff. 
  At 
  the 
  risk 
  of 
  being 
  considered 
  some- 
  

   what 
  elementary 
  the 
  writer 
  will 
  give 
  the 
  more 
  important 
  of 
  the 
  

   formulas 
  for 
  runoff, 
  expressed 
  in 
  terms 
  of 
  inches 
  on 
  the 
  catch- 
  

   ment 
  area: 
  

  

  ^XQX864Q0X12 
  

   Im 
  ~~ 
  Ax 
  640x43560 
  W 
  

  

  Whence 
  we 
  deduce, 
  

  

  Also, 
  

  

  and 
  

  

  . 
  ^xQxCx 
  

  

  I 
  m= 
  X 
  W 
  

  

  Cj 
  X 
  Q 
  2 
  /n\ 
  

  

  h— 
  A 
  V 
  I 
  

  

  D=§ 
  (8) 
  

  

  Also 
  

  

  To 
  change 
  gallons 
  per 
  day 
  into 
  inches 
  per 
  month 
  we 
  have: 
  

  

  J 
  m 
  = 
  nxGcXC 
  3 
  (9) 
  

  

  G 
  =^ 
  (10) 
  

  

  In 
  the 
  reports 
  of 
  the 
  United 
  'States 
  Geological 
  Survey 
  the 
  dis- 
  

   charge 
  of 
  streams 
  is 
  sometimes 
  given 
  in 
  acre-feet 
  per 
  month. 
  To 
  

   reduce 
  such 
  to 
  inches 
  per 
  month, 
  we 
  have, 
  when 
  total 
  acre-feet 
  

   are 
  given 
  : 
  

  

  i 
  m 
  =^ 
  (id 
  

  

  In 
  these 
  formulas, 
  

  

  A=area 
  of 
  catchment 
  in 
  square 
  miles. 
  

  

  B=total 
  acre-feet 
  per 
  month. 
  

  

  D=ioiiibic 
  feet 
  per 
  second 
  per 
  square 
  mile. 
  

  

  O=gallons 
  per 
  day. 
  

  

  I 
  m 
  =inches 
  in 
  depth 
  per 
  month 
  on 
  the 
  catchment 
  area. 
  

  

  I 
  y 
  =inches 
  in 
  depth 
  per 
  year 
  on 
  the 
  catchment 
  area. 
  

  

  ti=number 
  of 
  days 
  per 
  month. 
  

  

  