﻿372 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Experience 
  in 
  flows 
  over 
  dams 
  of 
  this 
  length 
  and 
  with 
  depths 
  

   as 
  great 
  as 
  from 
  7 
  to 
  8 
  feet 
  is 
  as 
  yet 
  rather 
  limited 
  in 
  this 
  coun- 
  

   try, 
  and 
  the 
  question 
  was 
  raised 
  as 
  to 
  the 
  best 
  method 
  of 
  comput- 
  

   ing 
  the 
  discharge 
  for 
  a 
  case 
  like 
  the 
  one 
  under 
  discussion. 
  The 
  

   engineers 
  of 
  the 
  British 
  government 
  in 
  India 
  have 
  had, 
  in 
  con- 
  

   nection 
  with 
  their 
  large 
  irrigation 
  works, 
  perhaps 
  more 
  experi- 
  

   ence 
  in 
  this 
  class 
  of 
  measurement 
  than 
  all 
  others 
  combined, 
  and 
  

   the 
  formulas 
  used 
  by 
  them 
  appear 
  more 
  rational 
  in 
  form 
  than 
  

   those 
  commonly 
  used 
  in 
  the 
  United 
  States 
  for 
  such 
  computa- 
  

   tions, 
  and 
  after 
  some 
  study 
  it 
  was 
  decided 
  to 
  use 
  these. 
  As 
  

   many 
  American 
  engineers 
  may 
  not 
  be 
  familiar 
  with 
  these 
  

   formulas 
  they 
  are 
  here 
  reproduced. 
  They 
  take 
  the 
  following 
  

   form 
  — 
  

  

  Q=f 
  L 
  C 
  \ 
  "2^3*; 
  (3?) 
  

  

  in 
  which 
  — 
  

  

  Q=^the 
  discharge 
  over 
  a 
  thin-edged 
  clear 
  overfall, 
  in 
  cubic 
  

  

  feet 
  per 
  second, 
  

   L 
  = 
  the 
  length 
  of 
  the 
  dam 
  in 
  linear 
  feet, 
  

   C 
  = 
  coefficient 
  depending 
  for 
  its 
  value 
  on 
  d, 
  

   g 
  = 
  acceleration 
  of 
  gravity 
  = 
  32.2, 
  

   d 
  = 
  depth 
  on 
  crest, 
  in 
  linear 
  feet. 
  

   Equation 
  (37) 
  may 
  also 
  take 
  the 
  form 
  — 
  ■ 
  

  

  Q 
  = 
  5.35 
  L 
  C 
  V 
  J\ 
  (38) 
  

  

  To 
  find 
  C 
  for 
  different 
  values 
  of 
  d, 
  we 
  have 
  — 
  

  

  = 
  1- 
  (° 
  04 
  (34 
  4 
  6 
  + 
  "J. 
  (39) 
  

  

  This 
  gives 
  a 
  series 
  of 
  values 
  of 
  corresponding 
  to 
  d. 
  For 
  

   instance, 
  for 
  d 
  — 
  0.25 
  foot, 
  C 
  = 
  0.651; 
  for 
  tf=^0.50 
  foot, 
  

   C 
  = 
  0.649, 
  and 
  so 
  on. 
  

  

  For 
  a 
  wide-crested 
  dam 
  the 
  coefficient 
  is 
  further 
  modified 
  to 
  

   suit 
  the 
  actual 
  width 
  of 
  the 
  crest. 
  For 
  this 
  we 
  have 
  given 
  the 
  

   expression 
  — 
  

  

  „, 
  ^ 
  /0.025 
  C 
  (B 
  + 
  1)V 
  

  

  c=c 
  -( 
  i+Y 
  > 
  (w 
  > 
  

  

  1 
  Equation 
  (39) 
  may 
  be 
  written 
  in 
  a 
  simpler 
  form, 
  C^l 
  — 
  0.0l(34.6+d). 
  

  

  