Northwest Fisheries Science Center

Display All Information

Document Type: Contract Report
Center: NWFSC
Document ID: 6550
Title: Relative survival of juvenile salmon passing through the spillway and the ice and trash sluiceway of The Dalles Dam, 1998
Author/Editor: Earl M. Dawley, Lyle G. Gilbreath, R. F. Absolon, Benjamin P. Sandford, John W. Ferguson
Publication Year: 2000
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: E96970020, W66QKZ82167243, W66QKZ83437725
Pages: 97
Date: 08/01/2000

In 1997, we initiated a study at The Dalles Dam to evaluate survival of juvenile Pacific salmon Oncorhynchus spp. passed through the spillway when 64% of the river flow was spilled.  Results suggested mortality rates of about 13% for coho salmon O. kisutch and 8% for subyearling Chinook salmon O. tshawytscha passing at 64% spill.  In 1998, we expanded the research to include assessment of passage survival through the spillway at high spill (64% of river flow) and moderate spill (30% of river flow) and through the ice and trash sluiceway during daytime periods at moderate spill (30% of river flow).

Test fish were collected from the juvenile bypass system at the Bonneville Dam Second Powerhouse, tagged with passive integrated transponder (PIT) tags, and transported to The Dalles Dam for release.  We tagged approximately 64,000 yearling coho salmon in April and May, and 80,000 subyearling Chinook salmon in June and July.  Nearly equal portions (20% each) of these fish were released through the spillway at 64% spill, the spillway at 30% spill, and the sluiceway at 30% spill; about 40% were released in the tailrace as survival reference groups.

Relative survival for passage at 64% spill was 89% for coho salmon (CI 82-96%) and 75% for subyearling Chinook salmon (68-83%).  These survival rates were substantially lower than survival at 30% spill, where coho survived at 97% (88-107%) and subyearling Chinook at 89% (80-99%).  The difference between passage survival at 64% and passage survival at 30% was insignificant for coho and significant for subyearling Chinook.  Relative survival for sluiceway passage was 96% for coho (87-105%) and 89% for subyearling Chinook (81-98%), and these rates did not differ appreciably from those of spillway passage at 30% spill.  Spillway passage survival of coho and subyearling Chinook salmon appeared to decline through the period of testing.

From the 2 years of study, results that appear important to operations at The Dalles Dam are as follows: 

  1. Detection rates of fish passing through the spillway at 64% spill were significantly less than those of fish released downstream from the dam.
  2. Estimated spillway passage survival for juvenile salmon at 64% spill was lower than at other dams and similar to or lower than survival expected for turbine passage at The Dalles Dam (spring flows ranged 5,099-14,929 m3/second (180,000-527,000 ft3/second) and summer flows ranged 4,447-14,986 m3/second (157,000-529,000 ft3/second).
  3. Estimated relative survival rates for fish passing at 30% spill were substantially higher than for fish passing at 64% spill.
  4. Relative survival for daytime fish passage through the sluiceway at 30% spill was similar to that of daytime fish passage through the spillway at 30% spill (one year of testing).
  5. Spillway passage of subyearling chinook salmon during daytime hours with adult spill patterns produced substantially lower survival than passage during nighttime hours with juvenile spill patterns.
  6. Evaluation of survival in relation to tailwater elevation, spill volume, river flow, and water temperature indicated poor correlations for both spring and summer tests.

We recommend continued testing of 30 vs. 64% spill rates during spring and summer fish migrations, followed by testing of a constant rate of spill (less than 64%) with a 24-h/d juvenile fish pattern comparing spillway vs. sluiceway releases.  Additionally, recovery and evaluation of PIT tags deposited in estuarine bird rookeries should be continued so as to provide increased detection numbers, and comparisons of survival rate differences among detection sites should also be continued.  To maintain sufficient detections at Bonneville Dam Second Powerhouse, we also recommend minimal use of the sluice chute.