Existing headworks safety features such as the walkways and trash rake mechanism do not meet current industry standards. The trash rake is particularly problematic, as wood and large debris in the Yakima River are often trapped in the headworks forebay and can become lodged in the headgates. In addition, WIP crews cannot safely dewater the Main Canal headworks forebay to perform maintenance on the headworks facility.
Due to bedload accumulation in the west channel upstream from the headworks, the BIA is often challenged to maintain adequate water diversions during peak irrigation demand. The only existing method available to manage sediment accumulation is mechanical dredging, requiring heavy equipment in the river channel and significant associated environmental considerations.
The current fish passage facilities are operated and maintained according to federal criteria for salmon and steelhead. Fish ladders at diversion dams in the Yakima Basin were not originally designed to pass Pacific lamprey, but some, including ladders at the Wapato Diversion, have been retrofitted to accommodate adult lamprey. Bypass systems at the Diversion and the numerous other diversions in the Yakima River were designed to screen juvenile salmon and steelhead out of irrigation canals and safely return them to the river, but recent studies have shown that their cumulative effect on juvenile migration timing and survival is significant. This project provides an opportunity to modify the Diversion to improve adult and juvenile fish passage and survival.
Sediment continuity is recognized as a healthy river system characteristic. The current structure restricts sediment transport resulting in the accumulation of sediment upstream of the Diversion.
The 1996 flood event reportedly came close to overtopping the railroad tracks on the west bank of the Yakima River. In addition to localized infrastructure risk, an overtopping event could result in an uncontrolled release of water into the WIP Main Canal, with catastrophic results.
Existing Diversion features were not designed to accommodate traditional fishers. Opportunity and access for traditional fishers will be considered in developing long-term design modifications to the Diversion.