Washington Phase II Fish Diversion Screen Evaluations in the Yakima River Basin, 1997 Annual Report.
- Pacific Northwest National Laboratory
The Pacific Northwest National Laboratory evaluated 19 Phase II screen sites in the Yakima River Basin at least three times each between April 30 and August 22, 1997. The sites were examined to determine if they were being effectively operated and maintained to provide fish a safe, efficient return to the river. Data were collected to determine if velocities in front of the screens and in the bypass met current NMFS criteria and promoted timely fish bypass, if fish were protected from injury due to impingement, entrainment, and predation, and whether bypass outfall conditions allowed fish to safely return to the river. A bi-directional flow meter and underwater video system were essential in completing the investigation. In general, water velocity conditions at the screen sites were acceptable by NMFS standards. High approach velocities and slow bypass flow were the most common problems noted. Although velocities often fluctuated from one sampling location to the next, average sweep and approach velocities were very good. In general, fish should not be impinged or experience delays in returning to the river under normal operating conditions. Most screens were properly sealed to prevent fish entrainment and injury, although potential problems were identified at several screen sites. Three sites had gap openings from the forebay to the aftbay, allowing fish to be entrained. Other sites had spaces larger than 3/32 inch where small fish could become trapped. Some drum screens had flat spots but these were not been confirmed as underwater gaps, primarily because of siltation. On rare occasions, seals were intact, but cracked or turned under. Submergence levels at the drum screen sites exceeded 85% for one third of our evaluations. Eight of 12 drum screen sites experienced high water levels during at least one evaluation. Only one operating site's submergence was measured at less than 65% submergence. Two flat plate screen sites were completely overtopped with water during one evaluation each. Although 1997 was an extreme high-water year, these overtopping events point out that some screens do not completely protect fish under the full range of potential operating conditions. Water depths at the outfall pipe were acceptable at all but four sites. Generally, water depths were low near the end of the irrigation season due to low river flows. Rock removal around the outfall pipe or pipe extension would improve the situation. We gauged the potential for predation by qualitatively measuring the types and amount of cover provided for predators in front of the screens and by recording random observations of fish large enough to be considered predators in the forebay. Predation was more likely to occur at drum screen sites than at flat plate screen sites. Drum sites provide more predator hiding places because greater amounts of woody debris accumulate under the drums and against the concrete walls that divide one screen bay from the next. Four sites had both woody debris and large fish present. These four sites were considered most likely to experience juvenile salmonid loss to predation. Periodic removal of woody debris from underneath the curvature of drum screens would decrease the likelihood of predation at these sites. Screens were generally well maintained. Automated cleaning brushes functioned properly, chains and other moving parts were well greased, and inoperative and algae-covered drum screens were eventually repaired and cleaned. However, removal of sediment build-up and accumulated woody debris are areas where improvement should be considered. Maintenance checks should include observation of bypass outfalls on a regular basis, as conditions at the end of the bypass pipe are likely to change seasonally, especially in streams with high gradients or unstable gravel. Post-season evaluations were conducted at 11 sites in November to try and confirm seal and drum screen defects, and locations of excessive sedimentation. This proved effective in several cases, but the winterization process eliminated some of the evidence. Several forebay areas had already been cleared of silt. It was difficult to evaluate screens and seals when the screens were in the storage position because the screens could not be rotated. Also, two sites remained in full operation while others were submerged, precluding detailed examination of parts still under water. Periodic, regular screen evaluations will increase the effectiveness of screen operation and maintenance practices by confirming the effectiveness (or ineffectiveness) of screen operating procedures at individual sites. Where procedures are being followed and problems still occur, evaluation results will suggest means to improve the procedures to better protect fish at screening facilities.
- Research Organization:
- Bonneville Power Administration (BPA), Portland, OR (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 962137
- Report Number(s):
- DOE/BP-00029-5; R&D Project: 1985-062-00; TRN: US200916%%200
- Country of Publication:
- United States
- Language:
- English
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