LWI Region 3 Modeling Overview

3.3.3 Terrain Modifications for Modeling { Multiple iterations were needed to improve terrain accuracy: • Integrated bathymetry for stream channels and lakes (Figure 3-10 and Figure 3-11). • Addressed abrupt elevation changes affecting flow conveyance. TERRAIN INCONSISTENCIES { Differences existed between observed channel widths and DEM representations. { Sudden width variations along rivers introduced modeling challenges. FINAL TERRAIN IS AN APPROXIMATION { Channel shapes and slopes between surveyed sections were interpolated. { Terrain remains suitable for 2D HEC-RAS simulations but may not fully reflect actual ground conditions.

Figure 3-8: Significant oscillation in channel elevations along Youngs Bayou requiring hydro-flattening.

Figure 3-9: Example of stark changes in channel topography within the Region.

Figure 3-11: Terrain modification necessary for better representation of oxbow lakes and meander scars storage in topography within Region 3.

Figure 3-10: Example of channel width in DEM ~3 times width in imagery within Region 3 due to collection of LiDAR during or after high-flow event.

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Hydrologic and Hydraulic Modeling Methodology