MAJOR and PAULIK: ENCROACHMENT OF WANAPUM DAM RESERVOIR 



which, at high tailwater elevations, appeared to 

 impede the entry of fish into the ladder. The 

 wall also eliminated the surging action across 

 the ladder that occurred under certain combi- 

 nations of spill pattern and tailwater elevation. 



Even after these changes, fishery biologists 

 continued to voice concern over the effectiveness 

 of the right-bank ladder. Some held that hy- 

 draulic conditions at the entrance to the right- 

 bank ladder impeded fish passage over the ladder. 

 In 1958, in response to the continuing concern 

 about the fish-passage conditions at Rock Island 

 Dam, the owners of the dam — Puget Sound Pow- 

 er and Light Co. and Public Utility District No. 1 

 of Chelan County — financed a study to determine 

 if fish passage could be improved by manipulat- 

 ing the spill pattern. 



The study showed that fish could be guided to 

 either the right or center ladders by spilling 

 adjacent to the respective ladder. The experi- 

 ment also indicated, but not conclusively, that 

 when low tailwater elevations prevailed, spilling 

 from gates 35, 36, and 37 (immediately adjacent 

 to the right-bank ladder) confused the fish and 

 interfered with their entry into the ladder 

 (Leman and Paulik, 1966). 



The construction in 1960-64 of Wanapum 

 Dam, 61 km downstream, brought about a fur- 

 ther change in fish-passage conditions at Rock 

 Island Dam. The lower portions of the fish lad- 

 ders at Rock Island Dam were flooded by Wan- 

 apum Reservoir. This condition, in the judg- 

 ment of the Federal Power Commission, required 

 certain modifications of the left and center fish 

 ladders. The modifications were completed by 

 1963 — 1 year before Wanapum Reservoir was 

 filled. The Commission also directed the owners 

 of Rock Island Dam and of Wanapum Dam (Pub- 

 lic Utility District of Grant County) to develop, 

 in cooperation with representatives of the U.S. 

 Department of the Interior and the Washington 

 State Departments of Fisheries and Game, a 

 program for the study and evaluation of the 

 further effects of encroachment by Wanapum 

 Reservoir on fish passage at Rock Island Dam. 



It is important to note that the question at 

 hand was the effect of the encroachment of Wan- 

 apum Reservoir on fish passage at Rock Island 

 Dam and not the effects of Wanapum Dam on 



fish passage in the broader sense, i.e., passage 

 over Wanapum Dam itself and passage through 

 the newly formed forebay. 



Representatives of the participating agencies 

 formed the "Rock Island Study Group" and en- 

 gaged the junior author as a consultant to serve 

 as chairman of the group. A major segment of 

 the research program, initiated and supervised 

 by the study group, consisted of a series of tag- 

 ging experiments conducted under postencroach- 

 ment conditions. These experiments were so 

 designed that the results would be comparable 

 to results available from preencroachment tag- 

 ging in 1954-55 (French and Wahle, 1966).' 

 The field work was conducted by experienced 

 personnel of the National Marine Fisheries Ser- 

 vice (formerly the Bureau of Commercial Fish- 

 eries) under the supervision of the senior author. 



In this paper we describe tagging experiments 

 at Rock Island Dam in 1964-65 and compare the 

 results to those obtained in the earlier (1954-55) 

 study. The primary purpose is to estimate the 

 differences between the times required for sock- 

 eye and spring chinook salmon (0. tshawytscha) 

 to move from tagging sites below Rock Island 

 Dam to the counting stations in the three (left, 

 center, and right) fish ladders before encroach- 

 ment and after encroachment. 



EXPERIMENT RATIONALE 



The basic experimental measures obtained 

 from this type of tagging are (1) elapsed time 

 from the release of tagged fish below Rock Island 

 Dam to the sighting of tagged fish as they passed 

 through a counting station near the top exit of 

 the fish ladders and (2) the percentage of each 

 release group passing over the dam. The elapsed 

 times include (a) the time, if any, required for 

 tagged fish to recover from possible effects of 

 tagging, (b) the time required to locate and enter 

 the fish ladders, and (c) the time required to 

 ascend the ladders. A statistical analysis of the 

 preencroachment tagging was employed to de- 

 termine adequate sample sizes and release 



* French and Wahle also tagged in 1956, but because 

 the tagged fish were released in a different manner and 

 at different locations than in any other year, the 1956 

 experiments were excluded from our comparisons. 



127 



