﻿HYDROLOGY 
  OF 
  NEW 
  YORK 
  429 
  

  

  suitable 
  distances 
  apart 
  will 
  be 
  necessary 
  to 
  confine 
  such 
  floods, 
  

   and 
  enable 
  them 
  to 
  flow 
  off 
  gradually 
  without 
  causing 
  damage. 
  

   From 
  forty-eight 
  years' 
  observation 
  and 
  experience 
  of 
  exten- 
  

   sive 
  works 
  undertaken 
  for 
  (the 
  improvement 
  of 
  rivers, 
  the 
  author 
  

   can 
  confidently 
  affirm 
  that 
  by 
  careful 
  attention 
  to 
  the 
  points 
  

   above 
  recommended, 
  even 
  the 
  most 
  tortuous 
  rivers 
  and 
  the 
  

   swampiest 
  valleys 
  have, 
  generally 
  within 
  a 
  few 
  years, 
  but 
  in 
  

   some 
  cases 
  only 
  after 
  many 
  years, 
  yielded 
  the 
  most 
  satisfactory 
  

   results, 
  as 
  for 
  instance 
  — 
  

  

  a) 
  The 
  increase 
  of 
  fall 
  due 
  to 
  the 
  more 
  uniform 
  section 
  and 
  

   more 
  direct 
  course, 
  and 
  the 
  concentration 
  and 
  confinement 
  of 
  the 
  

   •stream 
  within 
  a 
  single 
  channel 
  provided 
  with 
  firm 
  banks, 
  con- 
  

   siderably 
  increases 
  the 
  force 
  and 
  velocity 
  of 
  the 
  current, 
  which 
  

   tend 
  to 
  deepen 
  the 
  channel, 
  and 
  to 
  carry 
  away 
  the 
  material 
  thus 
  

   scoured 
  out 
  as 
  well 
  as 
  that 
  brought 
  down 
  from 
  above. 
  

  

  b) 
  By 
  lowering 
  the 
  bed 
  of 
  the 
  river, 
  in 
  some 
  cases 
  to 
  the 
  

   extent 
  of 
  from 
  3 
  to 
  6 
  feet, 
  the 
  general 
  water 
  level, 
  both 
  of 
  the 
  

   river 
  and 
  of 
  the 
  ground 
  springs 
  in 
  the 
  neighborhood, 
  is 
  propor- 
  

   tionately 
  lowered, 
  so 
  that 
  the 
  adjoining 
  country 
  is 
  less 
  liable 
  

   to 
  inundation, 
  and 
  the 
  swamps 
  are 
  more; 
  easily 
  drained 
  and 
  

   brought 
  under 
  cultivation. 
  

  

  c) 
  The 
  velocity 
  being 
  accelerated 
  in 
  the 
  new 
  channel, 
  as 
  

   shown 
  by 
  (a), 
  floods 
  pass 
  off 
  more 
  rapidly 
  and 
  do 
  not 
  rise 
  so 
  

   high, 
  consequently 
  the 
  low 
  country 
  1 
  is 
  seldom 
  or 
  never 
  under 
  

   water, 
  or 
  at 
  any 
  rate 
  not 
  to 
  the 
  same 
  extent 
  as 
  before.' 
  If, 
  how- 
  

   ever, 
  these 
  lesser 
  and 
  lower 
  floods 
  are 
  to 
  be 
  entirely 
  prevented, 
  

   dikes 
  parallel 
  to 
  the 
  course 
  of 
  the 
  river 
  must 
  be 
  added. 
  

  

  d) 
  In 
  rivers 
  exposed 
  to 
  the 
  action 
  of 
  frost, 
  floating 
  ice 
  is 
  

   apt 
  to 
  accumulate 
  in 
  the 
  unregulated 
  portions 
  of 
  its 
  course, 
  

   especially 
  at 
  sharp 
  bends, 
  and 
  on 
  shallows 
  and 
  sandbanks, 
  occa- 
  

   sionally 
  to 
  such 
  an 
  extent 
  as 
  entirely 
  to 
  obstruct 
  the 
  flow 
  of 
  

   the 
  stream, 
  and 
  to 
  raise 
  the 
  water 
  in 
  the 
  river 
  to 
  such 
  a 
  hight 
  

   that 
  it 
  overflowis 
  the 
  banks, 
  inundates 
  the 
  neighboring 
  country, 
  

   and 
  spreads 
  ruin 
  far 
  and 
  wide. 
  

  

  When 
  once 
  a 
  river 
  has 
  been 
  regulated 
  this 
  can 
  not 
  take 
  place, 
  

   as 
  there 
  would 
  then 
  be 
  nothing 
  to 
  hinder 
  the 
  free 
  passage 
  of 
  

   floating 
  ice, 
  and 
  should 
  a 
  temporary 
  stoppage 
  occur, 
  the 
  concen- 
  

   trated 
  force 
  of 
  the 
  current 
  would 
  soon 
  overcome 
  every 
  obstacle, 
  

   by 
  raising 
  the 
  blocks, 
  and 
  bearing 
  them 
  away 
  without 
  causing 
  

   any 
  flood. 
  

  

  e) 
  It 
  is 
  a 
  matter 
  of 
  general 
  experience 
  that 
  even 
  in 
  a 
  deep 
  

   river 
  following 
  a 
  winding 
  course 
  and 
  dividing 
  into 
  numerous 
  

   branches 
  navigation 
  is 
  often 
  obstructed 
  to 
  such 
  an 
  extent 
  that 
  

   the 
  river 
  becomes 
  all 
  but 
  impassable, 
  yet 
  when 
  the 
  same 
  river 
  

   has 
  been 
  regulated, 
  a 
  direct 
  channel 
  is 
  provided, 
  facilitating 
  

  

  