﻿456 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  worked 
  out 
  for 
  Genesee 
  river, 
  the 
  following 
  is 
  herewith 
  included 
  

   to 
  illustrate 
  the 
  subject 
  : 
  

  

  The 
  most 
  unfavorable 
  case 
  that 
  can 
  be 
  assumed 
  is 
  that 
  of 
  the 
  

   occurrence 
  of 
  an 
  extreme 
  runoff 
  when 
  the 
  reservoir 
  is 
  full 
  to 
  the 
  

   flow 
  line. 
  Even 
  under 
  such 
  circumstances 
  the 
  reservoir 
  will 
  still 
  

   act 
  as 
  a 
  great 
  mitigator 
  of 
  an 
  extreme 
  flood-flow, 
  as 
  may 
  be 
  seen 
  

   by 
  inspecting 
  table 
  No. 
  80, 
  which 
  has 
  been 
  prepared 
  specially 
  to 
  

   illustrate 
  the 
  point 
  in 
  question. 
  The 
  following 
  discussion 
  will 
  

   indicate 
  the 
  principle 
  embodied 
  in 
  this 
  table. 
  

  

  The 
  efficiency 
  of 
  a 
  storage 
  reservoir 
  as 
  a 
  flood 
  moderator 
  will 
  

   depend 
  upon 
  the 
  storage 
  capacity 
  in 
  relation 
  to 
  the 
  quantity 
  of 
  

   water 
  flowing 
  in 
  from 
  the 
  catchment 
  area. 
  This 
  capacity 
  in- 
  

   cludes 
  all 
  storage 
  space, 
  whether 
  above 
  or 
  below 
  the 
  crest 
  of 
  

   the 
  overflow 
  weir, 
  which 
  may 
  be 
  available 
  at 
  any 
  time 
  of 
  heavy 
  

   storm. 
  Water 
  is 
  stored 
  in 
  the 
  space 
  above 
  the 
  crest 
  only 
  tem- 
  

   porarily, 
  but 
  this 
  space 
  may 
  still 
  play 
  an 
  important 
  part 
  in 
  

   reducing 
  the 
  maximum 
  discharge 
  below 
  the 
  reservoir, 
  by 
  extend- 
  

   ing 
  the 
  time 
  within 
  which 
  the 
  total 
  surplus 
  has 
  to 
  be 
  passed 
  down. 
  

  

  Inasmuch 
  as 
  extreme 
  flood-flows 
  are 
  of 
  short 
  duration, 
  we 
  may 
  

   neglect 
  the 
  effect 
  of 
  evaporation, 
  absorption 
  and 
  leakage, 
  whence 
  

   it 
  becomes 
  evident 
  that 
  the 
  discharge 
  by 
  the 
  overflow 
  weir 
  or 
  

   sluices 
  will 
  be 
  equal 
  to 
  the 
  quantity 
  received, 
  less 
  the 
  quantity 
  

   retained, 
  whether 
  temporarily 
  or 
  otherwise. 
  

  

  We 
  will 
  assume 
  that 
  the 
  water 
  stands 
  at 
  the 
  level 
  of 
  the 
  crest; 
  at 
  

   the 
  instant 
  when 
  the 
  inflow 
  becomes 
  equal 
  to 
  30,000 
  cubic 
  feet 
  per 
  

   second, 
  and 
  that 
  the 
  inflow 
  remains 
  constant 
  at 
  that 
  figure 
  for 
  24 
  

   hours, 
  after 
  which 
  it 
  gradually 
  decreases. 
  We 
  desire 
  to 
  deter- 
  

   mine 
  the 
  length 
  of 
  time 
  which 
  will 
  elapse 
  before 
  the 
  outflow 
  

   reaches 
  30,000 
  cubic 
  feet 
  per 
  second, 
  and 
  the 
  approximate 
  time 
  

   it 
  will 
  remain 
  at 
  about 
  that 
  figure. 
  With 
  the 
  following 
  notation 
  : 
  

  

  h=sany 
  given 
  hight 
  above 
  the 
  crest 
  in 
  linear 
  feet 
  and 
  h 
  1? 
  h 
  2 
  , 
  

  

  h 
  3 
  , 
  etc., 
  successive 
  equal 
  hights. 
  

   "0 
  = 
  storage 
  capacity 
  corresponding 
  to 
  h, 
  and 
  C 
  1? 
  C 
  2 
  , 
  C 
  3 
  , 
  etc., 
  

  

  successive 
  capacities. 
  

   Q 
  = 
  discharging 
  capacity 
  of 
  the 
  overflow 
  weir 
  in 
  cubic 
  feet 
  per 
  

  

  second, 
  as 
  determined 
  by 
  the 
  formula 
  Q 
  = 
  3.33 
  V 
  h 
  3 
  x 
  L 
  

  

  for 
  the 
  given 
  values 
  of 
  h, 
  h 
  1; 
  h 
  2 
  , 
  h 
  3 
  , 
  etc. 
  

  

  