Res-2020-152 Task Order 2 - Laserfiche WebLink

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6. Hydraulic Modeling The Consultant shall review and update the existing SRH2D hydraulic model of the project reach which was created for the 2015 corridor plan. The consultant will: Update the model topographic mesh using the 2019 L|DAR and surveys from Task 3 and updated publicly-available topography data, if available. Recalibrate the model if recent flood highwater marks and peak flow data are available. lf the data are not available, WSE will use engineering judgement to set model parameters. Run the model to estimate hydraulic conditions for up to four flow events. Two events will represent floods that are known to initiate geomorphic change, one will represent a typical summer prolonged flip-flop flow, and one a habitat flow. Model geometry will be modified to test up to four different Hanson levee, private berm, and floodplain reconnection alternatives for the four aforementioned flow events. Model results will be: o Compared to the existing condition hydraulic model runs to identify hydraulic changes attributable to the proposed alternatives. o Used to evaluate hydraulic patterns and forces in order to predict future geomorphic change including channel avulsion and migration potential. Deliverables: . Model results in the form of GIS figures and tables. Assumptions: t lf 2019 L|DAR can be obtained, the Consultant shall use it to update the SRH2D model geometry in the vicinity of the project. o Deliverables will be included in the project report. 7. Geomorphic Assessment The consultant shall conduct a geomorphic assessment to: . ldentify and characterize the geomorphic processes that currently shape the project reach and how they are affected by the existing Hanson Pits levee and private berm. . ldentify past hydrologic events have been responsible for generating significant geomorphic change to discuss the relationship between flow and the historical geomorphic evolution of the reach o Determine whether a river avulsion into the Hanson Pits and/or downstream floodplain is likely if no actions are taken. lf an avulsion is likely, determine the likely river path, impact to public and private parcels, and road, rail, flood protection infrastructure. . Determine whether the channel is likely to migrate into the Hanson Pits or downstream floodplain if no actions are taken. lf significant channel migration is likely, determine the likely migration path and rate, impact to the public and private parcels, and road, rail and flood protection infrastructu re. a a a a