﻿HYDROLOGY 
  OP 
  NEW 
  YORK 
  457 
  

  

  Q 
  p 
  = 
  the 
  mean 
  discharge 
  in 
  cubic 
  feet 
  per 
  second 
  for 
  any 
  given 
  

  

  Qhi 
  + 
  Qh 
  2 
  

  

  period, 
  as 
  for 
  instance, 
  Q 
  = 
  and 
  

  

  2 
  

  

  Qh 
  2 
  + 
  Qh3 
  

  

  Q 
  Pl 
  = 
  ? 
  etc 
  

  

  2 
  

   S 
  = 
  inflow 
  from 
  catchment 
  area, 
  taken 
  in 
  the 
  present 
  case 
  at 
  

  

  30,000 
  cubic 
  feet 
  per 
  second; 
  and 
  

   t 
  = 
  the 
  time 
  in 
  seconds 
  in 
  which 
  the 
  water 
  will 
  rise 
  to 
  any 
  given 
  

   value 
  of 
  h 
  above 
  crest. 
  

   Whence 
  we 
  have 
  the 
  formula, 
  

  

  

  

  t 
  = 
  (41) 
  

  

  S— 
  Q 
  p 
  

   by 
  which 
  table 
  No. 
  80 
  has 
  been 
  computed. 
  

  

  On 
  referring 
  to 
  table 
  No. 
  80 
  we 
  learn 
  : 
  

  

  1) 
  That, 
  with 
  water 
  surface 
  in 
  reservoir 
  at 
  level 
  of 
  crest 
  of 
  

   overflow 
  weir 
  and 
  a 
  constant 
  inflow 
  of 
  30,000 
  cubic 
  feet 
  per 
  second, 
  

   it 
  will 
  be 
  about 
  6.5 
  hours 
  before 
  the 
  outflow 
  will 
  reach 
  15,000 
  cubic 
  

   feet 
  per 
  second. 
  

  

  2) 
  That 
  under 
  the 
  same 
  conditions 
  it 
  will 
  be 
  about 
  24 
  hours 
  

   before 
  the 
  outflow 
  will 
  reach 
  approximately 
  30,000 
  cubic 
  feet 
  per 
  

   second. 
  

  

  3) 
  Inasmuch 
  as 
  the 
  original 
  assumption 
  was 
  that 
  the 
  inflow 
  

   should 
  only 
  be 
  at 
  the 
  rate 
  of 
  30,000 
  cubic 
  feet 
  per 
  second 
  for 
  24 
  

   hours 
  and 
  then 
  gradually 
  decrease, 
  we 
  may 
  therefore 
  say 
  that 
  the 
  

   flow 
  at 
  rate 
  of 
  about 
  30.000 
  cubic 
  feet 
  per 
  second 
  would 
  only 
  be 
  

   for 
  say 
  two 
  or 
  three 
  hours, 
  instead 
  of 
  at 
  least 
  24, 
  as 
  it 
  would 
  have 
  

   been 
  without 
  the 
  assistance 
  of 
  the 
  surface 
  storage 
  of 
  the 
  reservoir. 
  

  

  4) 
  The 
  total 
  inflow 
  in 
  22.5 
  hours 
  would 
  be 
  2,431,782,000 
  cubic 
  

   feet, 
  of 
  which 
  34 
  per 
  cent 
  of 
  the 
  whole 
  would 
  be 
  stored 
  during 
  

   that 
  time 
  temporarily 
  in 
  the 
  reservoir. 
  

  

  Other 
  deductions 
  can 
  be 
  made, 
  but 
  the 
  foregoing 
  are 
  enough 
  to 
  

   show 
  the 
  value 
  of 
  such 
  a 
  reservoir 
  as 
  a 
  moderator 
  of 
  floods 
  even 
  

   when 
  entirely 
  filled 
  at 
  the 
  beginning 
  of 
  the 
  maximum 
  flow. 
  

  

  In 
  the 
  same 
  way 
  if 
  Ave 
  assume 
  the 
  reservoir 
  full 
  and 
  an 
  inflow 
  

   at 
  the 
  rate 
  of 
  40,000 
  cubic 
  feet 
  per 
  second, 
  we 
  learn 
  on 
  making 
  

   the 
  numerical 
  computation 
  that 
  about 
  19 
  hours 
  would 
  elapse 
  

  

  