Effective operating depth, as recommended by the Committee, varies 

 between the limits of 2 to 3 feet above the floor of the channel. At a 

 depth of 2 feet J approximately 10 second-feet (cubic feet per second) 

 of flow would be required for operation of the defined practical Denil- 

 type ladder^ and at a 3-foot depth, flow requirements would be increased 

 to about 21 second-feet. 



As described by Furuskog (19h5) , the Denil-type ladder at the Herting 

 power dam represents a modification of the design recommended by the Com- 

 mittee on Fish Passes, involving a linear enlargement of about lU2 percent 

 and a decrease in bottom slope of the channel to 1 on 6. The channel width 

 was increased to 1,30 meters (i; feet 3-I/I4 inches), with a clear opening 

 between the upright portions of the individual baffles of O.76 meters (2 

 feet 6 inches) . The slope of the baffles was maintained at hS degrees 

 with respect to the floor of the channel, and the spacing of baffles was 

 maintained at two-thirds the channel width. The greatest channel dis- 

 tance between successive resting pools in 9*02 meters (29 feet 7-1/8 

 inches'^ . 



Flow requirements of the Denil-type fish ladder at the Herting 

 power dam was reported by Furuskog to be normally l.k cubic meters per 

 second (li9 second-feet) , although the figure is not particularly sig- 

 nificant in that the operating depth within t he channel was not 

 specified. 



GENERAL DESIGN FEATURES OF THE DENIL-TYPE LADDER 

 AT DRYDEN DAM 



The apoarent success of the Herting fish-ladder installation 

 designed by Furuskog, encouraged the Fish and Wildlife Service to con- 

 struct a Denil-type ladder side by side with an overflow weir pool- 

 type ladder. In this way the efficiency of the two types could be 

 compared under similar operating conditions and with the same species 

 of fish. The site at Dryden Dam (see Figure 3j on the Wenatchee River 

 was selected, inasmuch as it was a relatively low dam where concentra- 

 tions of salmon could be assured. The location was oarticularly advan- 

 tageous, since, as the r esult of reconstruction work at Dryden Dam to 

 replace sections of the dam damaged by high water in the spring of 19li3, 

 a temporary earthfill cofferdam made it possible to construct the Denil 

 fish-ladder in the existing pool-type ladder while the latter was 

 unwateredo The work was thus facilitated and resulted in a more econom- 

 ical installation than otherwise could have been effected. 



Construction of the Denil-type ladder reduced the width of the pool- 

 type ladder to approximately one-half of its original width of 10 feet 

 as shown in Figures h and 5. The two ladders could then be compared to 

 determine inhich was preferred by the fish. Work on the Denil-type 

 installation was initiated during the fall of I9U8 and was completed in 

 the spring of I9U9. 



