LWI Region 3 Modeling Overview

Bayou Lafourche at Crew Lake and Girard at Boeuf River represented the western watershed, while Oak Grove covered the eastern side. Calibration of both regions was essential for accurate results at Fort Necessity, where flows from both converge before discharging into the Ouachita River. Calibration outputs for these areas are shown in Figure 3-25 (Crew Lake, August 2022), Figure 3-26 (Crew Lake, March 2016), and Figure 3-27 (Big Colewa Bayou, March 2016). ROOT MEAN SQUARE ERROR (RMSE) FOR STAGE: <5% in nearly all cases PERCENT BIAS (PBIAS): ±3%, with slight conservative bias (high estimates) CORRELATION COEFFICIENTS (r): 0.92–0.99 at key sites CREW LAKE: RMSE ~2.2%, PBIAS ~1.2%, r ≈ 0.989 Big Creek at Sligo presented poor correlation due to unreliable gage data and was excluded from overall performance metrics. Validation against 19 high water mark points in Monroe showed over 70% of modeled elevations within 1.0 ft of observed values, with several within ±0.2 ft. Spatial comparison of flood extents confirmed accurate ponding and inundation. Spatial comparison of flood extents confirmed accurate ponding and inundation.

Figure 3-26: Bayou Lafourche at Crew Lake calibrated to the March 2016 event (located western side of the Boeuf Watershed).

Figure 3-27: Big Colewa Bayou calibrated to the March 2016 event (On the eastern side of the Boeuf Watershed).

Boundary Condition Enhancements and Final Validation { Adjustments included adding weir-based lateral inflow from Bayou Bartholomew to simulate levee overtopping. { Boundary inputs from Ouachita River were extended temporally and aligned with observed hydrographs to capture backwater delays. { Refined pump and gate rules simulated operational shutdowns when external water levels (e.g., Ouachita) exceeded internal stage, preventing unrealistic reverse flows. { Final validation runs (e.g., May 2009 flood) showed strong alignment with observed hydrograph peaks and recession limbs, demonstrating model robustness.

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Hydrologic and Hydraulic Modeling Methodology