The existing safety features, specifically, walkways and the trash rake mechanism do not meet current industry standards. The trash rake is particularly problematic, as wood and large debris in the Yakima River is often trapped in the headworks forebay where it can become lodged in the headgates.
The BIA is challenged, at times, to maintain adequate water diversions at peak irrigation demand during the summer. In addition, WIP crews cannot safely dewater the Main Canal headworks forebay to perform maintenance on the deteriorating headworks facility.
The current fish passage facilities are operated and maintained according to Federal criteria for adult and juvenile salmon and steelhead. Fish ladders at diversion dams in the Yakima Basin were not originally designed to pass Pacific lamprey efficiently, and lamprey passage modifications recently tested at other diversion dams will need to be retrofitted at the Wapato Diversion. 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 serious. This project provides an opportunity to modify the headworks and bypass system at the Diversion to minimize its contribution to this problem.
The current structure provides very limited ability to pass transported river sediments downriver. Sediment accumulates upstream of the Diversion and contributes to the operational challenges of the facility. Dredging has historically been performed in the west channel upstream of the Diversion to clear sediment and debris; however, the environmental impact of this practice makes dredging undesirable.
In 1996 a severe flood event on the Yakima River resulted in undermining (erosion caused by the water current) below the East Diversion. This was addressed in 2004; however, additional undermining may have occurred during subsequent flood events.
The 1996 flood event reportedly came close to overtopping the railroad tracks on the west bank of the Yakima River. In addition to infrastructure risk, an overtopping event could result in an uncontrolled release of water into the WIP Main Canal, with catastrophic results.
Traditional fish harvest sites are present south of the Diversion; a goal of the project is to avoid or minimize impacts to these traditional uses.