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4.1.2 2D Area Computational Mesh and Geometry Development <br />The 21) area boundary was drawn to follow high ground at the edges of the Crystal Creek floodplain within <br />Cie Elum. The 21) computation cell mesh was generated using RAS Mapper, and refined by enforcing break <br />lines along roadways and flow control features to improve hydraulic computation accuracy around <br />complex terrain. Figure 2 shows the 2D area, cell boundaries, and breaklines. The 21) area domain was <br />extended to allow mapped results to tie into effective shallow 100 -year flood zones based on flooding <br />from the Yakima River. <br />- f <br />r <br />- I <br />Figure 3. Example of computational mesh layout at.rbad.and chirnel centerlines. <br />4.1.3 Model Calibration <br />WSE set Manning's 'n%"toughness',values •.biksed on land use classifications determined from satellite <br />imagery and site observations. A land)use layer was created in GIS, and Manning's n values corresponding <br />to each classification were applied p cording to the relationships shown in Table 1. The land use layer was <br />also imported into the 21) area t6define spatially varying Manning's n values. <br />,2- WATERSHED P 6 <br />`~w SCIENCE & ONGiNEERING <br />