﻿ACADEMY 
  OF 
  SCIENCES. 
  293 
  

  

  each 
  in 
  its 
  place 
  important 
  to 
  the 
  whole, 
  that 
  we 
  can 
  only 
  give 
  a 
  few 
  condensed 
  

   remarks, 
  in 
  the 
  hope 
  of 
  their 
  being 
  useful 
  to 
  those 
  who 
  are 
  reclaiming, 
  and 
  to 
  

   show 
  some 
  of 
  the 
  errors 
  in 
  the 
  present 
  manner 
  of 
  draining. 
  

  

  Drainage. 
  — 
  The 
  first 
  thing 
  to 
  be 
  examined 
  is 
  the 
  difiference 
  of 
  level 
  between 
  

   the 
  interior 
  of 
  the 
  land 
  to 
  be 
  leveed, 
  and 
  the 
  bank 
  of 
  the 
  river 
  or 
  slough 
  on 
  

   which 
  the 
  dike 
  is 
  to 
  be 
  constructed 
  ; 
  and 
  in 
  order 
  to 
  know 
  the 
  required 
  depth 
  

   of 
  the 
  ditch 
  to 
  enable 
  it 
  to 
  keep 
  the 
  waters 
  down 
  to 
  a 
  level 
  of 
  18 
  or 
  20 
  inches 
  

   below 
  the 
  surface 
  of 
  the 
  interior. 
  

  

  Frequently, 
  however, 
  one 
  or 
  more 
  small 
  sloughs 
  extend 
  into 
  the 
  interior, 
  

   which 
  are 
  of 
  great 
  advantage, 
  forming 
  a 
  natural 
  reservoir 
  and 
  drain 
  for 
  dis- 
  

   charging 
  the 
  surplus 
  water 
  at 
  every 
  low 
  tide. 
  

  

  The 
  difference 
  in 
  the 
  level 
  of 
  the 
  land 
  is 
  frequently 
  two 
  or 
  three 
  feet. 
  

  

  Tides. 
  — 
  The 
  next 
  thing 
  to 
  be 
  considered 
  is 
  the 
  tides. 
  In 
  each 
  lunar 
  day 
  of 
  

   24 
  h. 
  50 
  m., 
  there 
  are 
  generally 
  two 
  high 
  and 
  two 
  low 
  tides, 
  which 
  are 
  un- 
  

   equal 
  in 
  height 
  and 
  occur 
  at 
  unequal 
  intervals. 
  

  

  In 
  a 
  series 
  of 
  observations 
  on 
  the 
  tide, 
  taken 
  by 
  me 
  last 
  summer 
  on 
  the 
  coast 
  

   in 
  San 
  Mateo 
  County, 
  the 
  result 
  of 
  one 
  day 
  shows 
  thus 
  : 
  Commencing 
  at 
  low 
  

   water 
  large, 
  it 
  rose 
  4.1 
  feet 
  to 
  high 
  water 
  small, 
  then 
  fell 
  1.7 
  to 
  low 
  water 
  

   small, 
  then 
  rose 
  again 
  1.3 
  feet 
  to 
  high 
  water 
  large, 
  making 
  a 
  total 
  rise 
  6.7 
  feet, 
  

   then 
  fell 
  7.5 
  to 
  low 
  water 
  large. 
  

  

  Now, 
  for 
  some 
  distance 
  above 
  the 
  confluence 
  of 
  the 
  Sacramento 
  and 
  San 
  

   Joaquin 
  Rivers, 
  the 
  greatest 
  rise 
  and 
  fall 
  of 
  the 
  tide 
  is 
  about 
  6 
  feet 
  ; 
  high 
  water 
  

   small 
  would 
  average 
  perhaps 
  3)^ 
  feet 
  above 
  low 
  water 
  large 
  ; 
  and 
  low 
  water 
  

   small 
  about 
  two 
  feet 
  above. 
  A 
  fiood-gate 
  at 
  a 
  level 
  with 
  the 
  lowest 
  water 
  

   would 
  be 
  most 
  of 
  the 
  time 
  under 
  water, 
  and 
  therefore 
  afford 
  but 
  a 
  very 
  short 
  

   run 
  in 
  the 
  discharge 
  of 
  the 
  water. 
  

  

  Flood 
  Gates. 
  — 
  In 
  the 
  attempt 
  to 
  reclaim 
  our 
  tule 
  lands, 
  the 
  flood 
  gates 
  

   have 
  been 
  a 
  great 
  source 
  of 
  trouble 
  and 
  expense, 
  from 
  the 
  imperfect 
  manner 
  in 
  

   which 
  they 
  are 
  constructed 
  and 
  secured. 
  In 
  many 
  places, 
  no 
  calculation 
  having 
  

   been 
  made 
  for 
  the 
  amount 
  of 
  pressure 
  they 
  have 
  to 
  sustain, 
  they 
  frequently 
  give 
  

   way, 
  and 
  the 
  sluice 
  box 
  is 
  sometimes 
  canted 
  with 
  one 
  end 
  4 
  or 
  5 
  feet 
  lower 
  than 
  

   the 
  other. 
  The 
  reason 
  is 
  evident. 
  I 
  speak 
  now 
  more 
  particularly 
  of 
  the 
  large 
  

   sluices 
  at 
  the 
  mouth 
  of 
  sloughs 
  that 
  are 
  dammed 
  ; 
  they 
  have 
  generally 
  been 
  

   made 
  of 
  an 
  open 
  box 
  twenty 
  or 
  thirty 
  feet 
  in 
  length, 
  ten 
  or 
  twelve 
  feet 
  wide, 
  

   and 
  placed 
  at 
  the 
  level 
  of 
  low 
  tide 
  ; 
  the 
  levee 
  being 
  five 
  or 
  six 
  feet 
  high 
  gives 
  a 
  

   gate, 
  say 
  ten 
  feet 
  wide, 
  twelve 
  feet 
  deep, 
  and 
  three 
  or 
  four 
  inches 
  thick. 
  This 
  

   heavy 
  gate, 
  equal 
  to 
  about 
  one-half 
  a 
  ton, 
  is 
  placed 
  in 
  the 
  center 
  of 
  the 
  box. 
  

   Consider, 
  now, 
  what 
  a 
  loss 
  of 
  power 
  a 
  small 
  body 
  of 
  water, 
  perhaps 
  only 
  one 
  or 
  

   two 
  feet 
  in 
  depth, 
  has 
  to 
  raise 
  the 
  gate 
  in 
  discharging. 
  But 
  this 
  is 
  not 
  the 
  

   only 
  error 
  — 
  we 
  come 
  now 
  to 
  the 
  

  

  Pressure 
  of 
  Water. 
  — 
  The 
  weight 
  of 
  a 
  cubic 
  foot 
  of 
  fresh 
  water 
  is 
  62j4 
  

   pounds. 
  Water 
  standing 
  in 
  an 
  enclosure 
  presses 
  with 
  equal 
  force 
  on 
  the 
  bot- 
  

   tom 
  and 
  the 
  sides 
  at 
  the 
  junction, 
  but 
  the 
  force 
  on 
  the 
  sides 
  will 
  be 
  in 
  com- 
  

   pound 
  ratio 
  of 
  its 
  depth. 
  The 
  pressure 
  of 
  a 
  column 
  of 
  water 
  a 
  foot 
  square 
  

   and 
  six 
  feet 
  deep 
  = 
  375 
  pounds, 
  but 
  the 
  side 
  pressure 
  = 
  1,312)^ 
  pounds. 
  

  

  