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THE  .NORRIS  PETERS  CO.,  WASHINGTON.  C  C.
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Plate  XXV.  Completed  Foundations  of  first  250  feet  of  Navigable  Pass.
Plate  XXVII.  Navigable  Pass  adjoining  Pier  No.  1  during  Construction.
*


Plate  XXXI.  Bear-Trap  Gates  During  Erection.
Plate  XXXII.  Lower  Leaf  of  Bear  Trap  No.
17


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greater  stiffness  would  have  resulted,  and  the  piles  would  have  pene¬
trated  to  neater  depths.
BEAR-TRAP  WEIRS.
The  bear  traps  are  of  the  single  two-leaf  style,  known  as  the  ''old
bear  trap.”  This  type  has  been  in  use  in  the  Pittsburg  district  for
many  years,  the  first  bear-trap  weir  in  the  district  having  been  placed
in  operation  at  Davis  Island  Dam  in  1889.  Both  bear  traps  at  Dam
No.  4  are  identically  the  same  except  for  differences  in  the  founda¬
tions  rendered  necessary  by  the  different  sources  of  water  pressure,  as
explained  later.  The  bear-trap  sills  are  both  at  the  same  elevation  and
about  3  feet  above  the  sill  of  the  pass.
The  calculations  of  the  principal  dimensions  of  the  bear  traps  for
Dam  No.  4  were  made  by  means  of  the  formulae  devised  by  Capt.  H.
M.  Chittenden,  Corps  of  Engineers,  and  Mr.  A.  O.  Powell,  assistant
engineer.  These  formulae  can  be  found  in  the  Journal  of  the  Asso¬
ciation  of  Engineering  Societies  for  1896,  Vol.  XVI.  The  gates
were  designed  to  have  a  ratio  of  hydraulic  lifting  force  to  downward
pressure  of  making  of  the  formula  equal  to  .6.
