clear so that individual fish could be seen entering the ladders and 

 later crossing the counting board. The short time required for a 

 salmon to pass upstream through the Denil-type never failed to startle 

 the observers, and was especially in contrast to the slow progress 

 through the pool-type ladder. 



During short periods of observation, fish passed through the 

 Denil-type at an average of 2U second intervals. (On August 18^ 1951, 

 in 100 minutes of observation, 2^7 fish passed through) „ On numerous 

 occasions several bluebacks passed through the ladder simultaneously, 

 or in rapid succession. However, it would be desirable tu make an 

 additional study at a location where there is a greater concentration of 

 fish and other species of salmon present. The apparently more attractive 

 entrance flow of the Denil-type could be a deciding factor in preventing 

 delay or acc^;lmulation of salmon such as now occurs below pool-type ladders. 



From the standpoint of flow and number of fish concerned,, the Denil- 

 tj'pe ladder conveyed more fish per second-foot of flow than the pool-type 

 ladder. That is, 89 percent of the fish used the Denil-type ladder, al- 

 though it carried only 1|0 percent more flow, 



A saving in space can be an important factor where there is limited 

 room for construction. Fishery engineers in Sweden are convinced that 

 the Denil-type ladder, with a width of approximately that of the Dryden 

 Dam installation ( h feet 3-l/U inches), will replace the pool-type 

 ladder with a width of 10 feet, commonly used in Sweden. In addition, 

 the steep gradient of the Denil-type ladder would result in a somewhat 

 shorter over-all length than for a pool-type ladder with pools of normal 

 length, thereby conserving space. 



Some difficulty was experienced in keeping the Dool-type ladder con- 

 tinually adjusted to produce optimum flow conditions for upstream passage 

 of fish. The removal or addition of stop-logs or for that matter, even 

 minor changes in water level, will alter the hydraulic conditions within 

 the pool to influence to some de gree the response of fish to the fishway. 

 A distinct advantage in the Denil-type structure is the automatic adjust- 

 ment for changes in water level obtained from use of the vertical baffles. 

 Although the optimum conditions for salmon have never been adequately 

 determined, the accepted operational procedure for pool=type ladders was 

 followed to even a greater degree than would be done in normal operational 

 practice. 



Although it might at first appear that there would be considerable 

 savings affected — due to the smaller size of the Denil-type ladder, size 

 alone does not necessarily control cost. The Denil-type ladder requires 

 higher walls, and numerous specially constructed baffles which increase the 

 cost. Therefore, it is the opinion of the authors that the Denil-type 

 ladder would not represent any savings in construction cost over the 

 pool-type ladder, 



lU 



