Yakima County, in collaboration with the Seattle District of the US Army Corps of Engineers, is implementing an extensive ecosystem restoration project along a four-mile segment of the Yakima River immediately adjacent to the City of Yakima. The reach has historically been confined by a series of federal and local levees and subject to widespread gravel mining. These conditions, in concert with the 1996 flood of record, have led to channel incision, armoring, and overall degradation of a once dynamic riparian corridor. Corps project elements focus on levee setbacks and stabilization of relic gravel mine pits, while County design measures are intended to restore geomorphic processes and improve riparian habitat through floodplain reactivation.

NHC was contracted to provide specialized geomorphic and hydraulic services to develop and evaluate design features that would meet project geomorphic and habitat objectives while also considering the interaction with adjacent Corps project elements and nearby infrastructure.

NHC utilized a combination of remote and field-based geomorphic observations, geomorphic tools such as the UBC Regime Model, and two-dimensional (2D) HEC-RAS hydraulic modeling to design and evaluate a suite of design measures including pilot channel excavations, berm removals, side-channel reconnections, and engineered log jams. NHC also provided facilitation and public outreach services to ensure the various stakeholders maintain active involvement in project development and implementation.