﻿300 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  The 
  tabulation 
  shows 
  that 
  during 
  the 
  rears 
  1892 
  to 
  1895, 
  

   inclusive, 
  the 
  mean 
  runoff 
  of 
  the 
  Upper 
  Mississippi 
  area 
  was 
  

   only 
  3 
  . 
  61 
  inches 
  on 
  the 
  total 
  catchment. 
  These 
  figures, 
  however, 
  

   are 
  subject 
  to 
  correction 
  because 
  the 
  state 
  of 
  the 
  reservoirs 
  at 
  

   the 
  beginning 
  and 
  ending 
  of 
  the 
  four-year 
  period 
  is 
  not 
  given 
  in 
  

   the 
  report 
  of 
  the 
  United 
  States 
  engineers, 
  from 
  which 
  these 
  data 
  

   are 
  taken. 
  This 
  correction, 
  however, 
  can 
  not 
  be 
  very 
  large, 
  

   because 
  the 
  reservoirs 
  are 
  so 
  operated 
  as 
  to 
  be 
  emptied, 
  generally 
  

   speaking, 
  each 
  year. 
  In 
  considering 
  the 
  runoff 
  of 
  these 
  Upper 
  

   Mississippi 
  reservoirs, 
  due 
  consideration 
  should 
  be 
  given 
  to 
  the 
  

   fact 
  that 
  the 
  water 
  area 
  of 
  the 
  reservoirs 
  is 
  585 
  square 
  miles, 
  or 
  

   nearly 
  18 
  per 
  cent 
  of 
  the 
  whole. 
  For 
  Lakes 
  Superior, 
  Michigan, 
  

   Huron, 
  St 
  Clair, 
  and 
  Erie 
  we 
  have 
  a 
  total 
  water 
  surface 
  of 
  

   87,895 
  square 
  miles, 
  with 
  a 
  total 
  catchment 
  area, 
  including 
  the 
  

   surface 
  of 
  the 
  lakes, 
  of 
  265,095 
  square 
  miles. 
  The 
  water 
  surface 
  

   of 
  these 
  several 
  lakes 
  is, 
  therefore, 
  about 
  33 
  per 
  cent 
  of 
  the 
  entire 
  

   area 
  of 
  the 
  basin, 
  or 
  nearly 
  double 
  the 
  relative 
  area 
  of 
  water 
  

   surface 
  and 
  catchment 
  area 
  for 
  the 
  Upper 
  Mississippi 
  reservoirs. 
  

   With 
  other 
  conditions 
  the 
  same, 
  this 
  fact 
  would 
  probably 
  lead 
  

   to 
  a 
  somewhat 
  greater 
  proportion 
  of 
  runoff 
  from 
  the 
  Great 
  Lakes. 
  

   The 
  Upper 
  Mississippi 
  reservoirs 
  are 
  in 
  a 
  forested 
  region, 
  and 
  it 
  

   is 
  interesting 
  to 
  consider 
  what 
  the 
  runoff 
  will 
  be 
  after 
  the 
  forests 
  

   are 
  removed. 
  Taking 
  into 
  account 
  results 
  in 
  other 
  places, 
  it 
  is 
  

   probable 
  that 
  the 
  runoff, 
  under 
  conditions 
  of 
  deforestation, 
  will 
  

   not 
  exceed 
  an 
  average 
  of 
  about 
  2 
  inches 
  per 
  year. 
  

  

  Runoff 
  of 
  Desplaines 
  river. 
  By 
  way 
  of 
  further 
  illustrating 
  the 
  

   yield 
  of 
  streams 
  in 
  the 
  vicinity 
  of 
  the 
  Great 
  Lakes 
  area, 
  we 
  will 
  

   refer 
  to 
  the 
  runoff 
  of 
  the 
  Desplaines 
  river, 
  as 
  given 
  in 
  table 
  No. 
  40. 
  

   This 
  stream 
  has 
  been 
  measured 
  by 
  the 
  Chicago 
  Drainage 
  Com- 
  

   mission, 
  with 
  certain 
  intermissions 
  as 
  shown 
  since 
  January, 
  1886, 
  

   the 
  catchment 
  area 
  above 
  the 
  point 
  of 
  measurement 
  being 
  633 
  

   square 
  miles. 
  The 
  catchment 
  comprises 
  a 
  long 
  and 
  narrow 
  flat 
  

   region 
  extending 
  from 
  near 
  Chicago 
  to 
  a 
  few 
  miles 
  north 
  of 
  

  

  