Wenas Creek Passage & Screening Prelim Des

The North Yakima Conservation District (NYCD) developed alternatives assessments and preliminary designs aimed at improving fish passage and providing protection from entrainment for Mid Columbia steelhead at two diversions on Wenas Creek, approximately 0.75 miles upstream of Sisk Road in Yakima County. The alternatives assessment also included a third diversion which requires additional analysis. The project used desktop and field investigations to produce conceptual design alternatives originally aimed at potential consolidation of the three diversions, to provide fish passage and screening for all life stages of steelhead and native fish at all periods of the hydrograph, and improve flow monitoring capabilities at the WID diversion. NYCD developed the preferred alternatives for first two barriers (listed below) into more detailed permit application-ready preliminary designs (per Manual 18 Appendix D-2). The three diversions consist of

1) A pumping station located on left bank, currently equipped with a non-compliant fish screen and regularly inundated with alluvial deposition which requires instream work to keep clear. The preferred alternative provides a compliant fish screen and updates infrastructure at the pumping station.

2) An unscreened right bank gravity check dam is a fish passage barrier. The preferred alternative provides fish passage and screening at the right bank gravity diversion.

3) The Wenas Irrigation District (WID) diversion dam diverts flow between the North and South Fork Wenas Creek for irrigation and creates a fish passage barrier. Due to the complexity of the WID site, NYCD was unable to get to preliminary design as it was not feasible to consolidation the three diversions. Design alternatives for the WID diversion needs further development and input to achieve the goals of fish passage and to require less maintenance to cost effectively and accurately measure flow.

The goal of this project is to prepare a conceptual design alternatives analysis and preliminary designs that when constructed will improve fish passage and provide protection from entrainment for Mid Columbia steelhead at three diversions on Wenas Creek. Specifically the designs will 1) Decrease irrigation-related juvenile steelhead mortality in Wenas Creek caused by water withdrawal; 2) Increase the quantity of accessible habitat for adult and juvenile steelhead in Wenas Creek below Wenas Dam; and 3) Increase the ability and accuracy to measure discharge at the Wenas Irrigation District Diversion.