Design of the Denil-type ladder at Dryden Dam was patterned after 

 the Herting installation and varied therefrom only to the extent that no 

 weirs were provided at the upper end for regulation of ladder flows with 

 accompanying forebay fluctuations. However, flow regulation c an be 

 effected to a small degree by the insertion of one or more stop-logs in 

 the guides provided at the upper end of the ladder for unwatering pur- 

 poses. The Dryden installation (see Figure 6) consists of a channel 1; 

 feet 3 inches in width, with 10 U-shaped wooden baffles spaced 2 feet 

 10 inches on centers along the floor of the channel and set at & h^- 

 degrse angle thereto. Clear ooening between the upright portions of 

 the individual baffles is 1 foot 9 inches, and the bottom slope of the 

 channel is 1 on 6, The ladder is d^ '. c^ned for a maximiun difference in 

 elevation betxreen forebay and tail. if approximately 5 feet 9 inches, 



Flow through the ladder was experimentally adjusted between 20 and 

 30 second-feet during the tests. According to the British Committee on 

 Fish Passes, minimum operating depth^ for, the Denil-type ladder with a 

 channel 3 feet in width was indicated to be 2 feet above the channel 

 floor. Observations made at Dryden Dam showed that fish could readily 

 negotiate the ladder at a lesser depth. 



The maximum operating depth was based on the assumption that the 

 maximum depth (3 feet) prescribed by the Committee on Fish Passes for 

 the channel 3 feet in width could be increased by U2 percent. The U2 

 percent represents the increase in linear dimensions of the Denil-type 

 ladder at Dryden Dam over that recommended by the Committee on Fish 

 Passes. From actual observations, the most suitable operating depth 

 appeared to be 3 feet. At this depth flow through the Dryden installa- 

 tion was computed from current-meter readings to be approximately 30 

 second-feet. 



GENERAL DESIGN FEATURES OF THE POOL- TYPE LADDER 

 AT DRYDEN DAM 



As previously mentioned, the width of the pool-type ladder was 

 reduced to about one-half of the original width (10 feet) as a result 

 of construction of the Denil-type ladder. The pool-type ladder con- 

 sisted of h pools each 5 feet wide and 6 feet long. This made 5 steps 

 of approximately 1 foot drop. Flows were regulated at from 9 to 12 

 second-feet. 



Tne pool-type ladder was damaged by high waber in the spring of 

 1950 when the lowest weir supports were vrashed out. This reduced the 

 number of ladder pools to three and created a short entrance channel 

 to the ladder from the tailwater area below the dam. This change in 

 the number of pools apparently did not affect fish passage. More fish 

 ascended the ladder in 19^1 than in 19ii9. 



