﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  365 
  

  

  Geologically, 
  Lake 
  Champlain 
  lies 
  mostly 
  in 
  the 
  horizon 
  of 
  the 
  

   Trenton 
  limestone, 
  the 
  drainage 
  being 
  from 
  the 
  Laurentian 
  

   granites 
  and 
  Plutonic 
  norites. 
  

  

  Discharge 
  measurements 
  of 
  Hudson 
  river 
  at 
  Mechanicville. 
  

   Measurements 
  of 
  the 
  flow 
  of 
  the 
  Hudson 
  river 
  at 
  Mechanicville 
  

   have 
  been 
  made 
  over 
  the 
  dam 
  of 
  the 
  Duncan 
  Company. 
  In 
  1887 
  this 
  

   company 
  began 
  daily 
  measurement 
  of 
  the 
  amount 
  of 
  water 
  flow- 
  

   ing 
  in 
  the 
  Hudson 
  river 
  at 
  their 
  mill. 
  1 
  With 
  the 
  exception 
  of 
  one 
  

   or 
  two 
  days, 
  this 
  record 
  has 
  been 
  kept 
  for 
  every 
  working 
  day 
  

   since 
  October 
  1, 
  1887. 
  A 
  record 
  has 
  also 
  been 
  kept 
  of 
  the 
  num 
  r 
  

   ber, 
  size, 
  and 
  kind 
  of 
  turbine 
  water 
  wheels 
  in 
  use 
  for 
  the 
  same 
  

   period. 
  The 
  Duncan 
  Company 
  placed 
  all 
  this 
  material 
  at 
  the 
  

   disposal 
  of 
  the 
  survey 
  of 
  the 
  upper 
  Hudson 
  valley, 
  thus 
  enabling 
  

   one 
  to 
  compute 
  the 
  mean 
  daily 
  flow 
  of 
  the 
  river 
  for 
  each 
  working 
  

   day 
  from 
  October 
  1, 
  1887, 
  to 
  November, 
  1897. 
  The 
  flow 
  of 
  Sun- 
  

   days 
  and 
  holidays, 
  when 
  no 
  observations 
  were 
  taken, 
  has 
  been 
  

   assumed 
  as 
  a 
  mean 
  between 
  the 
  preceding 
  Saturday 
  and 
  the 
  fol- 
  

   lowing 
  Monday, 
  etc. 
  The 
  dam 
  is 
  a 
  substantial 
  structure 
  of 
  

   masonry 
  16 
  feet 
  high, 
  with 
  a 
  length 
  of 
  794 
  feet 
  between 
  the 
  abut- 
  

   ments. 
  The 
  crest 
  is 
  stated 
  to 
  be 
  perfectly 
  level, 
  and 
  from 
  all 
  

   that 
  can 
  be 
  learned 
  it 
  appears 
  that 
  the 
  daily 
  observations 
  have 
  

   been 
  taken 
  with 
  such 
  care 
  as 
  to 
  leave 
  no 
  reason 
  for 
  doubting 
  

   that 
  this 
  is 
  a 
  fairly 
  accurate 
  exhibit 
  of 
  the 
  daily 
  flow 
  of 
  the 
  

   stream 
  for 
  the 
  period 
  covered. 
  

  

  The 
  catchment 
  area 
  of 
  the 
  Hudson 
  river 
  above 
  the 
  Mechanicville 
  

   dam 
  is 
  taken 
  at 
  4500 
  square 
  miles, 
  although 
  a 
  recomputation 
  

   from 
  the 
  latest 
  maps 
  made 
  for 
  the 
  Board 
  of 
  Engineers 
  on 
  Deep 
  

   Waterways 
  gave 
  4507 
  square 
  miles. 
  This 
  is 
  only 
  0.15 
  of 
  one 
  per 
  

   cent 
  different 
  from 
  the 
  former 
  computation 
  of 
  4500 
  square 
  miles 
  

   and 
  is 
  not 
  enough 
  to 
  make 
  it 
  worth 
  while 
  to 
  recompute 
  the 
  

   runoff. 
  

  

  The 
  flow 
  of 
  the 
  Hudson 
  river 
  at 
  Mechanicville 
  prior 
  to 
  1899 
  has 
  

   been 
  computed 
  by 
  using 
  the 
  East 
  Iudian 
  engineers' 
  formula 
  for 
  

   flow 
  over 
  a 
  dam, 
  and 
  when 
  flashboards 
  are 
  on, 
  the 
  Francis 
  formula 
  

   for 
  a 
  sharp-crested 
  weir 
  has 
  been 
  used. 
  Since 
  that 
  time, 
  the 
  

   computations 
  have 
  been 
  made 
  by 
  R. 
  P. 
  Bloss, 
  Engineer 
  of 
  the 
  

  

  x 
  Ann. 
  Rept. 
  of 
  State 
  Engineer 
  and 
  Surveyor 
  of 
  New 
  York, 
  1895, 
  p. 
  104. 
  

  

  