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Easton Reach Yakima River Hazard Analysis and Mapping lnvestigation <br />Consultant Scope of Work <br />Kittitas County (County) is concerned that there are undefined flood and channel stability <br />hazards in the 1 1-mile Yakima River Easton Reach (RM 1 91 to 2Q2) which extends downstream <br />from Easton Dam. The reach contains four communities with large-scale developments with <br />urban densities that are routinely flooded by the Yakima River and are repetitive loss areas. <br />Despite their reputation as locations with flooding issues, flood hazards have not been <br />adequately assessed and specific strategies to address flood hazards are lacking. These risks <br />need to be defined to support County land use planning. <br />The County has requested that Watershed Science & Engineering (Consultant) develop a scope <br />of work to conduct a flood, avulsion, and channel migration hazard assessment to identify areas <br />that are most at risk along this reach of the Yakima River. The study will include new HEC-RAS <br />two dimensional (2D) hydraulic modeling of the reach developed in accordance with FEMA <br />guidelines for Flood Risk Analysis and Mapping (FEMA 2016). Results will be used to support <br />flood and geomorphic hazard assessment and to develop new inundation mapping to update <br />FEMA flood insurance rate maps. <br />The scope is described in the tasks below <br />TASKS <br />1 DATA COLLECTION AND FIELD RECONNAISSANCE <br />1.1 Background Data Collection and Review <br />The consultant shall collect and review existing data needed to complete the flood, avulsion, <br />and channel migration investigation. lnformation will include but not be limited to: <br />o L|DAR data (2005 ,2011, 2014, and more recent if available)o Etfective FEMA Flood lnsurance Study <br />. FEMA HEC-RAS 1D Hydraulic Model of the Yakima River (covers the lower 5.5 miles of <br />the Easton Reach). <br />o Existing Yakima River Channel Migration Zone Analysis <br />o Current and historical aerial photographs and maps <br />r Recent and historical highwater marks <br />o USGS National Land Cover Dataset Surficial soil data <br />o River discharge data <br />. River sediment grain size, supply, transport, and deposition data (if they exist). Design data for levees and revetments (if they exist) <br />Assumptions: <br />o The County will provide the Consultant with data they possess. <br />T WATERSHED1+SCIENCE & ENGINEERING