Acoustic Camera Evaluation of Juvenile Salmonid Approach and Fate at Surface Flow Outlets of Two Hydropower Dams
The objective of this study was to estimate and compare fate probabilities for juvenile salmon approaching two surface flow outlets (SFOs) to identify effective design characteristics. The SFOs differed principally in forebay location, depth, discharge, and water velocity over a sharp-crested weir. Both outlets were about 20 ft wide. The 22-ft deep Bonneville Powerhouse 2 Corner Collector (B2CC) was located in the southwest corner of the forebay and passed 5,000 ft3/s of water at normal-pool elevation. In contrast, The Dalles Dam ice and trash sluiceway outlet above Main Unit 1-3 (TDITC) was not located in a forebay corner, was only 7-ft deep, and discharged about 933 ft3/s at normal-pool elevation. The linear velocity of water over the weir was about 15 ft/s at the B2CC and 5 ft/s at the TDITC. We used a Dual-Frequency Identification Sonar (DIDSON) to record movements of fish within about 65 ft of the B2CC and within 35 ft of the TDITC. We actively tracked fish by manually adjusting pan and tilt rotator angles to keep targets in view. Contrary to expectations, active tracking did not provide a predominance of long tracks that clearly indicated fish fate because most tracks were incomplete. Active tracking did increase error in fish-position estimation, which complicated data processing, so we plan to sample multiple fixed zones in the future. The probability of fish entering each SFO was estimated by a Markov chain analysis, which did not require complete fish tracks. At the B2CC, we tracked 7,943 juvenile salmonids and most of them entered the B2CC. Fish moving south 40 to 60 ft upstream of the dam face were more likely to enter the eddy at the south end of the powerhouse than to enter the B2CC. At the TDITC, we tracked 2,821 smolts. Fish movement was complex with active swimming toward and away from the entrance. The high entrance probability zone (EPZ), where over 90% of tracked fish entered the SFO, extended 32 ft out at the B2CC and only 8 ft out at the TDITC. Greater discharge at the B2CC pushed the entrainment zone (EZ - where flow exceeded 7 ft/s) upstream from the entrance so that fish were entrained before they began to struggle against the flow. The high EPZ also was extended by flow along the powerhouse face at both sites, but more at the B2CC (about 450 ft) than at the TDITC (about 50 ft). Fish entering the large south eddy that circulated past the B2CC entrance were provided multiple opportunities to discover and enter. In contrast, fish moving past the sampled TDITC entrance either entered adjacent sluiceway openings or moved west to the spillway because there was no eddy to provide additional opportunities. Information from our study should be useful to fisheries managers and engineers seeking to transfer SFO technologies from one site to another. There are two important components to designing SFOs, the location within the forebay to take advantage of forebay circulation and specific entrance characteristics such as discharge and depth which affect the size and shape of the EZ and the high EPZ. Providing SFOs with an EZ extending upstream of structure could reduce entrance rejection, decrease forebay residence time and risk of predation, and increase passage of schools of smolts.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 897384
- Report Number(s):
- PNNL-SA-48572; 400403209; TRN: US200704%%795
- Resource Relation:
- Conference: HydroVision 2006, 13 pages
- Country of Publication:
- United States
- Language:
- English
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