Laserfiche WebLink
Attachment 1 to Amendment 2 — Scope of Work <br />Reecer Creek Floodplain Mapping and Levee Certification Support <br />Services Design and Certification Services <br />Scope of Work <br />Aspect Consulting LLC <br />Prepared January 4111; 2029 <br />Background <br />Aspect Consulting, LLC (Aspect) has developed this Amendment 2 Scope of Work to provide <br />additional consulting services to the City of Ellensburg for the Reecer Creek Floodplain <br />Mapping and Levee Certipcation Support Services Project (Project). <br />Pursuing certification of the Reecer Creek levee system (with a reduced freeboard of 2 ft in <br />some areas) will require additional analyses and technical reports not developed during prior <br />work: <br />a. Hydraulic assessment report to support the certification and reduced freeboard <br />request. An engineering analyses to show adequate protection with reduced freeboard <br />must submitted to support a levee freeboard reduction request. The analysis must <br />evaluate uncertainty in base flood elevation and include, but not necessarily be limited to <br />an assessment of statistical confidence limits of the 100 -year discharge; changes in <br />stage -discharge relationships; and the sources, potential, and magnitude of debris, <br />sediment, and ice accumulation. It must be also shown that the levee will remain <br />structurally stable during the base flood when additional loading considerations are <br />imposed. Aspect assumes that the County's modeling consultant (WSE) would use their <br />model for the overtopping analysis and to provide scour velocities for the high flow <br />condition. Aspect's engineers would complete the stability assessment and produce the <br />hydraulic report. <br />Embankment protection. Documentation is required to show that no significant erosion <br />of levee embankments will occur during the base flood (also for the "worst case <br />scenario" in areas where we want the reduced levee freeboard). This includes assessing <br />erosion risk due to water velocities, debris, ice, etc., and needs to account for the <br />duration of the erosive conditions as well as the embankment materials and <br />susceptibility of different areas of the levee to erosion (for instance at bends, or areas of <br />deepest/fastest flowing water). Aspect engineers will complete this assessment, focusing <br />on several key risk areas. Scour was considered during the prior design work but will be <br />reassessed given the higher flows that need to be reviewed. <br />Embankment and foundation stability. An engineering evaluation of seepage issues <br />is required to document that the levee embankment and foundation is designed/built to <br />be stable. Aspect engineers will complete this assessment using information and data <br />from prior geotechnical reports, which is not expected to be a significant effort. <br />Reecer Creek Floodplain Mapping and Levee Certification Support Services Project 11 Page <br />