In March 19ii3j further investigations were made by Swedish fishery- 

 interests at Stockholm, of experimental fish ladders constructed in 

 accordance with the recommendations of the Committee on Fish Passes. 

 Based on the results of these experiments ^ a Denil-type ladder was de- 

 signed by Furuskog for the Herting power dam in Swedeno Furuskog's 

 design represented a modification of the design recommended by the 

 Committee on Fish Passes, involving an increase in linear dimensions 

 and a decrease in bottom slope of the channel. 



Further comparative experiments of models of the Herting fish 

 ladder were undertaken in May 19^3 "under the guidance of Professor 

 Hellstrom of the Royal Technical University of Stockholm. One of the 

 models was sawed down the middle, and one of the halves was placed 

 against the glass wall of a test flume, so that observations could be 

 made of currents inside the fish-ladder model„ By use of a wire with 

 thread banderoles attached, it was found that the currents near the 

 bottom of the channel were nearly vertically upward with the higher 

 velocities in a longitudinal direction occurring near the water surface 

 (see Figure 2) . The baffles being placed at an angle with the floor of 

 the channel catch the faster-flowing water near the water surface, forc- 

 ing the flow downward to the floor where it is directed upward in such a 

 manner that it slows down the current in a longitudinal direction. Ex- 

 periments utilizing small fish gave no indication of their being disturbed 

 by the vertical currents. 



The Herting fish ladder was completed in May, 19hS ^ and counting 

 observations were initiated in September of the same year. According 

 to Furuskog (19U5), Sh Atlantic salmon i^eighing up to 20 pounds and 6 

 sea-run trout negotiated the new fish ladder during one 3-hour period. 

 The success of the Denil-type ladder at the Herting power dam was con- 

 sidered proved, although the information furnished by Furuskog gives 

 no indication of the size of run involved. 



i DESICM DEVELOPMENTS OF THE DENIL-TYPE LADDER 



Based on experiments conducted by the British investigators during 

 the period 1936-38, a practical Denil-type fish ladder as defined by the 

 Committee on Fish Passes (19^2) would have a channel width of 3 feet, 

 with single-plane baffles spaced at a distance of two-thirds the c hannel 

 width and laid sloping upstream at a h5=-degree angle with the channel 

 floor. As further defined by the Committee, a practical Denil-type fish 

 ladder would have a clear opening between the upright portions of the 

 individual baffles of 1 foot 9 inches 5 the channel would have a bottom- 

 slope not exceeding 1 on U, and resting pools would be provided at verti- 

 cal intervals of 6 to 8 feet. A bottom slope of 1 on 5 was, however, 

 recommended where a channel length of 30 feet is provided between resting 

 pools. 



