In the Pacific Northwest the problem of safeguarding the passage 

 of upstream migrating fish at hydroelectric and irrigation developments 

 is becoming increasingly importanto 



New types of fishways are being considered in the hope that more 

 efficient ones will be found, A design known as the Denil-type fishway, 

 used to some extent in Europe, has had favorable comment as an economical 

 yet efficient means of enabling fish to surmount barriers. New interest 

 was stimulated hy an article by Valter Furuskog (19U$) of Stockholm, 

 Sweden, concerning the design and construction of a "fish pass" for the 

 Herting power dam on the Atran fliver, near Falkenburg, Sweden. As a 

 result of this interest, an experiment was designed to compare the effective- 

 ness of the pool-type and Denil-type ladders as fish-passage devices. 



Observations were made in a side-by-side installation at Dryden Dam 

 on the Wenatchee River approximately 17 miles above the confluence of the 

 Wenatchee and Columbia Rivers. 



HISTORY OF THE DENIL-TYPE LADDER 



The Denil-type fish ladder, "counter-current" in principle, was 

 developed by G, Denil of Brussels, Belgium who devised a system of 

 baffles in a channel whxich by nature of their shape and position im- 

 part a secondary outward circulation of flow, producing a momentum 

 transfer from the central portion of the channel toward the walls. 

 In a publication concerning "fish-pass" installations at the Meuse and 

 Orthe Dams on the Rhine River, Denil (1909) presented his fish-ladder 

 design in its original form, explained the ideas xirhich served as the 

 basis of his design, and described in detail the first fish ladders con- 

 structed with his principles. Work initiated by Denil in 1907 was con- 

 tinued over a period of 30 years. In his endeavor to develop a rational 

 basis for fish-ladder design, Denil (1936-38) conducted numerous experi- 

 ments on the hydraulics of "counter- current" fish ladders, the nature 

 and magnitude of resistance encountered by fish in various types of 

 ladders, and the^ility of fish to overcome those resistances. 



Denil 's principles were further investigated by the Committee on 

 Fish Passes, British Institution of Civil Engineers, who during the 

 period 1936-38 carried out hydraulic experiments at the Imperial College 

 of Science and Technology to confirm Denil' s results and, by application 

 of his principles, to develop a simpler design of baffle than the some- 

 what complicated cup-shaped baffle utilized by Denil in his experiments. 

 The type of baffle selected ty the British investigators as the most 

 practical was a single-plane baffle (see Figure 1) which is more readily 

 constructed than the cup-shaped baffle used by Denil. 



