﻿12 
  WATER-POWER 
  DEVELOPMENT 
  IN 
  THE 
  MISSISSIPPI. 
  

  

  The 
  dam 
  structure 
  is 
  composed 
  of 
  119 
  spans, 
  each 
  consisting 
  of 
  

   two 
  piers 
  supporting 
  an 
  arch, 
  which 
  upholds 
  a 
  causeway. 
  Between 
  

   the 
  piers 
  is 
  placed 
  in 
  each 
  span 
  a 
  section 
  of 
  spillway, 
  the 
  part 
  over 
  

   which 
  the 
  water 
  flows. 
  This 
  bridge-like 
  structure, 
  with 
  the 
  water 
  

   flo\\dng 
  over 
  the 
  spillway 
  sections, 
  extends 
  from 
  the 
  Illinois 
  bluff, 
  

   to 
  which 
  it 
  is 
  tied 
  by 
  an 
  abutment, 
  across 
  the 
  river 
  to 
  the 
  upper 
  

   outer 
  corner 
  of 
  the 
  power 
  house 
  on 
  the 
  Iowa 
  side, 
  to 
  which 
  it 
  is 
  

   tied 
  by 
  another 
  abutment. 
  

  

  The 
  piers 
  are 
  6 
  feet 
  thick, 
  and 
  the 
  distance 
  between 
  piers 
  — 
  that 
  is, 
  

   the 
  width 
  of 
  each 
  of 
  the 
  119 
  spillway 
  sections 
  — 
  ^is 
  30 
  feet. 
  The 
  

   height 
  of 
  spillways 
  is 
  32 
  feet. 
  The 
  upstream 
  face 
  of 
  each 
  spillway 
  

   section 
  is 
  vertical, 
  the 
  downstream 
  face 
  having 
  a 
  curve 
  designed 
  to 
  

   conform 
  to 
  the 
  under 
  surface 
  of 
  a 
  body 
  of 
  water 
  of 
  this 
  size 
  and 
  

   depth 
  running 
  over 
  a 
  vertical 
  obstruction 
  to 
  the 
  current; 
  the 
  spill- 
  

   way 
  face 
  is 
  made 
  to 
  fit 
  the 
  under 
  surface 
  of 
  the 
  water 
  to 
  avoid 
  fric- 
  

   tion 
  as 
  much 
  as 
  possible; 
  the 
  curve 
  of 
  the 
  downstream 
  face 
  dehvers 
  

   the 
  water 
  in 
  a 
  horizontal 
  direction 
  dowai 
  the 
  river. 
  (PL 
  n.) 
  

  

  The 
  stream 
  over 
  the 
  spillway 
  has 
  a 
  depth 
  betw^een 
  7 
  and 
  11 
  feet. 
  

   We 
  thus 
  have 
  at 
  each 
  spillway 
  in 
  use 
  an 
  unretarded 
  waterfall 
  of 
  

   considerable 
  volume 
  wdth 
  an 
  abrupt 
  drop 
  of 
  32 
  to 
  40 
  feet, 
  deflected 
  

   only 
  at 
  the 
  bottom, 
  where 
  it 
  shoots 
  out 
  among 
  the 
  rocks 
  with 
  im- 
  

   mense 
  force 
  in 
  the 
  form 
  of 
  a 
  raging, 
  foaming 
  torrent, 
  dashing 
  against 
  

   the 
  rocks 
  with 
  indescribable 
  commotion. 
  For 
  the 
  protection 
  of 
  the 
  

   base 
  of 
  the 
  dam 
  from 
  the 
  erosion 
  due 
  to 
  back 
  currents, 
  a 
  broad, 
  

   low 
  concrete 
  apron 
  is 
  now 
  being 
  laid 
  to 
  flank 
  the 
  dam 
  on 
  its 
  lower 
  

   side. 
  It 
  would 
  be 
  impossible 
  for 
  a 
  fish 
  to 
  ascend 
  such 
  a 
  fall 
  from 
  

   below, 
  or 
  even, 
  in 
  all 
  probabihty, 
  to 
  pass 
  downward 
  through 
  it 
  and 
  

   escape 
  alive. 
  This 
  is 
  inevitable 
  to 
  the 
  existence 
  of 
  such 
  a 
  dam, 
  so 
  

   that 
  the 
  opportunity 
  for 
  fish 
  passage 
  must 
  be 
  sought 
  elsew^here. 
  

  

  Between 
  the 
  top 
  of 
  each 
  spillway 
  and 
  the 
  lower 
  side 
  of 
  the 
  over- 
  

   hanging 
  causeway 
  is 
  an 
  arched 
  opening 
  about 
  19 
  by 
  30 
  feet 
  w^hich 
  

   will 
  permit 
  the 
  passage 
  of 
  ice 
  and 
  drift 
  with 
  the 
  w^ater. 
  These 
  open- 
  

   ings 
  are 
  partially 
  closed 
  by 
  steel 
  gates, 
  11 
  by 
  32 
  feet, 
  which 
  work 
  in 
  

   deep 
  slots 
  in 
  the 
  concrete 
  and 
  serve 
  to 
  control 
  the 
  head 
  within 
  cer- 
  

   tain 
  hmits, 
  as 
  well 
  as 
  to 
  regulate 
  the 
  flow 
  to 
  conform 
  with 
  the 
  mini- 
  

   mum 
  requirements 
  for 
  navigation 
  as 
  determined 
  by 
  the 
  Govern- 
  

   ment. 
  

  

  The 
  dam 
  proper 
  is 
  not 
  at 
  right 
  angles 
  to 
  the 
  course 
  of 
  the 
  river 
  

   below 
  but 
  has 
  a 
  shght 
  downstream 
  direction 
  from 
  east 
  to 
  west, 
  so 
  

   that 
  the 
  upstream 
  end 
  of 
  the 
  dam 
  structure, 
  as 
  of 
  the 
  entire 
  plant, 
  

   is 
  on 
  the 
  Illinois 
  side. 
  In 
  ordinary 
  times 
  only 
  a 
  few 
  of 
  the 
  spillways 
  

   are 
  in 
  use 
  simultaneously, 
  so 
  that 
  the 
  mahi 
  stream 
  of 
  the 
  river 
  so 
  

   far 
  as 
  it 
  is 
  determined 
  by 
  the 
  flowage 
  over 
  the 
  spillways 
  — 
  the 
  waste 
  

   water, 
  so 
  to 
  speak 
  — 
  may 
  be 
  changed 
  at 
  any 
  moment 
  from 
  one 
  side 
  

   of 
  the 
  river's 
  course 
  to 
  the 
  other 
  through 
  a 
  distance 
  of 
  nearly 
  a 
  

  

  