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  PROCEEDINGS 
  OF 
  THE 
  CALIFORNIA 
  

  

  Suppose 
  we 
  have 
  an 
  open 
  sluice 
  box 
  twenty 
  feet 
  in 
  length 
  by 
  ten 
  feet 
  wide 
  

   with 
  the 
  gate 
  in 
  the 
  center, 
  10x10 
  the 
  square 
  of 
  the 
  bottom 
  outside 
  of 
  the 
  

   gate 
  =; 
  100 
  square 
  feet 
  X 
  375 
  pounds 
  = 
  37,500 
  pounds 
  or 
  18^ 
  tons 
  ; 
  and 
  the 
  

   pressure 
  of 
  each 
  column, 
  1,312% 
  pounds, 
  X 
  10 
  feet 
  wide 
  = 
  13,125 
  pounds 
  or 
  

   6}4 
  tons 
  on 
  the 
  gate 
  ; 
  width 
  of 
  water 
  has 
  no 
  influence 
  on 
  side 
  pressure. 
  

  

  Now, 
  we 
  generally 
  find 
  that 
  these 
  sluice 
  boxes 
  stand 
  for 
  some 
  time 
  until 
  the 
  

   water 
  inside 
  is 
  reduced 
  to 
  the 
  level 
  of 
  low 
  tide, 
  when 
  there 
  being 
  no 
  resistance 
  

   on 
  the 
  inside 
  of 
  the 
  gate 
  to 
  counteract 
  the 
  enormous 
  pressure 
  outside, 
  it 
  gives 
  

   way 
  gradually 
  day 
  by 
  day, 
  until 
  at 
  last 
  it 
  is 
  not 
  surprising 
  that 
  it 
  sinks 
  outside 
  

   and 
  cants 
  up 
  inside; 
  particularly 
  when 
  there 
  is 
  is 
  no 
  sheet 
  piling, 
  only 
  some 
  inch 
  

   or 
  1% 
  inch 
  boards 
  G 
  or 
  7 
  feet 
  long 
  put 
  in 
  the 
  mud 
  and 
  lacked 
  oa 
  at 
  each 
  end. 
  

  

  The 
  same 
  case 
  occurs 
  with 
  the 
  dams 
  unless 
  made 
  sufficiently 
  strong 
  to 
  stand 
  

   the 
  pressure, 
  which 
  against 
  a 
  dam 
  one 
  hundred 
  feet 
  in 
  length 
  is 
  at 
  high 
  tide 
  

   about 
  6^)4 
  tons. 
  

  

  We 
  have 
  been 
  referring 
  to 
  quiescent 
  water 
  ; 
  but 
  in 
  considering 
  the 
  force 
  of 
  

   waves 
  driven 
  by 
  wind, 
  the 
  pressure 
  of 
  flood 
  tides, 
  or 
  the 
  strength 
  of 
  a 
  strong 
  

   current 
  against 
  the 
  embankment 
  or 
  flood-gates, 
  a 
  large 
  allowance 
  must 
  be 
  made 
  ; 
  

   it 
  is 
  scarcely 
  possible, 
  however, 
  to 
  reduce 
  them 
  to 
  calculation, 
  but 
  wc 
  may 
  safely 
  

   add 
  one-fourth 
  to 
  the 
  pressure. 
  

  

  Great 
  care 
  should 
  therefore 
  be 
  taken 
  in 
  selcciing 
  a 
  site 
  for 
  a 
  dam 
  or 
  flood- 
  

   gate, 
  to 
  avoid 
  those 
  spots 
  that 
  are 
  exposed 
  to 
  any 
  great 
  currents 
  or 
  rush 
  of 
  tidal 
  

   waters, 
  particularly 
  where 
  a 
  stream 
  suddenly 
  narrows, 
  as 
  there 
  the 
  tide 
  comes 
  

   up 
  very 
  strong; 
  and 
  also 
  to 
  its 
  exposure 
  with 
  respect 
  to 
  the 
  prevailing 
  winds.. 
  

  

  Where 
  fresh-water 
  swamp 
  lands 
  are 
  adjacent 
  to 
  high 
  land, 
  calchwater 
  

   drains 
  should 
  be 
  made 
  to 
  intercept 
  the 
  upland 
  or 
  external 
  waters 
  and 
  conduct 
  

   them 
  oti 
  to 
  a 
  separate 
  oul 
  lei. 
  

  

  The 
  small 
  sluices' 
  from 
  the 
  ditches 
  or 
  draias 
  inside 
  of 
  the 
  levee 
  should 
  be 
  

   placed, 
  if 
  possible, 
  sufficiently 
  above 
  the 
  ordinary 
  low 
  water 
  to 
  allow 
  it 
  to 
  have 
  

   fiveorsix 
  hours 
  run 
  between 
  tide 
  and 
  tide, 
  beginning 
  at 
  half 
  ebb 
  and 
  continu- 
  

   ing 
  to 
  half 
  flood 
  tide 
  ; 
  if 
  placed 
  at 
  low 
  water, 
  the 
  gate 
  would 
  be 
  shut 
  sooner 
  by 
  

   return 
  of 
  tide, 
  although 
  so 
  long 
  as 
  the 
  weight 
  of 
  the 
  water 
  inside 
  is 
  greater, 
  

   so 
  long 
  will 
  it 
  continue 
  to 
  run. 
  

  

  The 
  best 
  level, 
  therefore, 
  to 
  afford 
  the 
  longest 
  run, 
  i?; 
  probably 
  between 
  the 
  

   mid-tide 
  level 
  and 
  the 
  lowest 
  low 
  water, 
  or 
  in 
  fact 
  as 
  high 
  as 
  it 
  will 
  admit 
  to 
  

   drain 
  the 
  low 
  land 
  in 
  the 
  interior, 
  18 
  or 
  20 
  inches. 
  

  

  The 
  trunk 
  or 
  box 
  sluice 
  has 
  been 
  used 
  in 
  the 
  rice 
  fields 
  of 
  South 
  Carolina 
  

   upwards 
  of 
  a 
  hundred 
  years, 
  and 
  has 
  been 
  found 
  to 
  answer 
  better 
  than 
  any 
  

   other. 
  A 
  good 
  size 
  for 
  our 
  use 
  is 
  about 
  six 
  feet 
  wide 
  by 
  eighteen 
  inches 
  deep, 
  

   with 
  self-acting 
  tide 
  gates; 
  if 
  made 
  of 
  redwood, 
  and 
  put 
  in 
  properly, 
  they 
  

   would 
  last 
  a 
  long 
  time, 
  stand 
  firmer, 
  and 
  are 
  not 
  liable 
  to 
  be 
  thrown 
  out 
  of 
  

   level 
  by 
  the 
  pressure 
  of 
  water. 
  Tliey 
  should 
  be 
  put 
  down 
  while 
  you 
  are 
  making 
  

   the 
  embankment, 
  as 
  it 
  is 
  useful 
  in 
  keeping 
  the 
  land 
  drained, 
  and 
  so 
  facilitates 
  the 
  

   work. 
  

  

  It 
  is 
  now 
  more 
  than 
  twelve 
  years 
  since 
  I 
  furnished 
  these 
  plans 
  to 
  a 
  gentleman 
  

   on 
  the 
  San 
  Joaquin, 
  who 
  found 
  them 
  to 
  work 
  well 
  on 
  his 
  place. 
  

  

  