﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  335 
  

  

  When 
  the 
  measurements 
  were 
  first 
  begun, 
  it 
  was 
  considered 
  

   that 
  the 
  formula 
  Q=1142 
  H 
  1 
  was 
  best 
  suited 
  to 
  the 
  form 
  of 
  the 
  

   dam, 
  but 
  after 
  more 
  careful 
  consideration 
  it 
  was 
  apparent 
  that 
  

   the 
  results 
  given 
  by 
  this 
  formula 
  were 
  somewhat 
  in 
  excess 
  of 
  

   the 
  actual 
  discharge, 
  specially 
  for 
  the 
  low-water 
  flows. 
  The 
  

   computed 
  discharges, 
  as 
  shown 
  by 
  columns 
  (3) 
  and 
  (4) 
  of 
  the 
  pre- 
  

   ceding 
  tabulation, 
  are 
  somewhat 
  irregular. 
  This 
  result 
  is 
  due 
  to 
  

   the 
  disturbing 
  effect 
  of 
  the 
  irregular 
  sections 
  of 
  the 
  crest, 
  the 
  

   highest 
  point 
  of 
  which 
  was 
  2 
  feet 
  above 
  the 
  lowest. 
  

  

  Column 
  (5) 
  shows 
  the 
  percentage 
  variations 
  between 
  the 
  dis- 
  

   charges 
  as 
  determined 
  by 
  a 
  sharp-crested 
  weir, 
  up 
  to 
  5200 
  cubic 
  

   feet 
  per 
  second, 
  and 
  the 
  discharges 
  computed 
  by 
  the 
  formula. 
  

   For 
  discharges 
  beyond 
  5000 
  cubic 
  feet 
  per 
  second 
  the 
  original 
  

   determination 
  has 
  been 
  used. 
  An 
  extension 
  of 
  the 
  plotted 
  curves 
  

   shows 
  that 
  some 
  little 
  distance 
  above 
  5000 
  cubic 
  feet 
  per 
  second 
  

   discharge, 
  the 
  results 
  of 
  the 
  two 
  methods 
  are 
  substantially 
  the 
  

   same. 
  The 
  two 
  curves 
  crossed 
  at 
  the 
  point 
  of 
  about 
  6000 
  cubic 
  

   feet 
  per 
  second 
  discharge. 
  For 
  discharges 
  above 
  10,000 
  or 
  

   15,000 
  cubic 
  feet 
  per 
  second 
  there 
  is 
  probably 
  an 
  error 
  in 
  the 
  

   results 
  of 
  from 
  5 
  to 
  10 
  per 
  cent. 
  Below 
  5000 
  cubic 
  feet 
  per 
  

   second 
  it 
  is 
  believed 
  that 
  the 
  results 
  are 
  now 
  accurate 
  within 
  a 
  

   few 
  per 
  cent. 
  Francis's 
  formula, 
  Q=3.33 
  L 
  H*, 
  has 
  been 
  used 
  

   for 
  the 
  weir 
  computations. 
  

  

  The 
  measurements 
  taken 
  previously 
  to 
  the 
  construction 
  of 
  the 
  

   weir 
  and 
  the 
  rating 
  of 
  the 
  dam, 
  have 
  all 
  been 
  corrected 
  to 
  con- 
  

   form 
  to 
  the 
  new 
  determinations; 
  hence 
  all 
  the 
  data 
  of 
  the 
  

   Genesee 
  measurements 
  of 
  this 
  table 
  may 
  be 
  considered 
  as 
  

   accurate 
  within 
  the 
  limits 
  stated. 
  

  

  The 
  original 
  Genesee 
  river 
  data 
  show 
  for 
  a 
  portion 
  of 
  the 
  

   range 
  more 
  error 
  than 
  is 
  consistent 
  with 
  good 
  work, 
  and 
  which 
  

   remained 
  inexplicable 
  until 
  the 
  experiments 
  at 
  Cornell 
  Univer- 
  

   sity 
  were 
  carried 
  out. 
  These 
  experiments 
  showed 
  that 
  for 
  high 
  

   heads 
  the 
  tendency 
  was 
  to 
  neutralize 
  the 
  differences 
  at 
  lower 
  

   heads. 
  The 
  flow 
  of 
  all 
  the 
  weirs, 
  in 
  short, 
  became 
  sensibly 
  uni- 
  

   form 
  at 
  from 
  5 
  to 
  6 
  feet 
  depth 
  and 
  at 
  10 
  feet 
  depth, 
  there 
  will 
  

   be 
  very 
  little 
  difference. 
  1 
  

  

  iTen 
  feet 
  depth 
  on 
  the 
  crest 
  is 
  not 
  unusual 
  in 
  flood 
  flows. 
  In 
  order 
  to 
  

   measure 
  such 
  flows, 
  a 
  weir 
  formula 
  should 
  be 
  worked 
  out 
  to 
  at 
  least 
  10 
  feet 
  

   depth 
  on 
  the 
  crest. 
  Such 
  a 
  formula 
  will 
  apply 
  without 
  more 
  than 
  15 
  per 
  

   cent 
  to 
  20 
  per 
  cent 
  error 
  to 
  almost 
  any 
  form 
  of 
  crest. 
  

  

  