LWI Region 3 Modeling Overview

c. Calibration – Gage Selection Gages selected based on data quality, period of record, and spatial relevance: { Eudora, Girard, Crew Lake, Alto, Fort Necessity, and Oak Grove were used for calibration and rating curve development. { Big Creek (Sligo) was excluded due to poor data integrity. Gage analysis provided critical validation for model peak flow estimates and boundary condition design. GAGE ANALYSIS RESULT SUMMARY { Seven gages within the Boeuf Watershed were evaluated for stage and flow behavior, including suitability for Bulletin 17C and rating curve development. { Gages with long periods of record, such as Girard, Eudora, and Crew Lake, were critical for model calibration. { Gages with known data issues (e.g., Big Creek at Sligo) were excluded from frequency analysis. { The flow records at key locations were compared with simulated hydrographs to validate peak flows and timing. { The flow records at key locations were compared with simulated hydrographs to validate peak flows and timing, as summarized in Figure 4-10. LEARN MORE: (B_4.1.3)

Figure 4-9: Rating curve development example at Boeuf Alto, using Nov15, Dec14, Sep08, and Aug22 events.

Simulation vs. EMA Comparison

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Crew Lake, by Lafourche

Alto, by Lafourche

Girard, Boeuf River

Alto, Boeuf River

Oak Grove, Big Colewa By

AR/LA Stateline, Boeuf River

100yr, 72 Hour Duration Peak Flow from Simulation

Gage EMA Result

Figure 4-10: Evaluated gages compared to HEC-SSP result. The comparison is done for the 100-year, 72-hour event.

Figure 4-11: Left: Relationship between rainfall and interior flow at Crew Lake in the Boeuf Watershed, derived from HEC-HMS simulations. Right: 3D response surface showing the combined influence of rainfall and Ouachita River stage on interior flow, used to estimate downstream boundary conditions for compound flood modeling.

LEARN MORE: (B_4.1.4)

Coincidence Frequency Analysis { A marginal frequency analysis (10% joint probability) was used in HEC-SSP to estimate Ouachita River stages that coincide with Boeuf River design flows. { HEC-HMS was used to establish rainfall-to-flow relationships at Crew Lake, using Atlas 14 data to represent interior watershed response. { A 7-day lag was observed and corrected between peak flows at Crew Lake and Ouachita River stages (Stafford gage) to develop a statistical flow-stage relationship. { Rainfall-flow and stage-flow relationships were merged into a single equation to estimate flow at Crew Lake using dual inputs while minimizing error. { The resulting 3D response surface (see Figure 4-11 ) relates rainfall, flow, and Ouachita stage, enabling realistic downstream boundaries in HEC-RAS and improving simulation of compound flooding.

LEARN MORE: (B_4.5)

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Precipitation and Frequency Analysis and Consequence Modeling