LWI Region 3 Modeling Overview

Model Update/Change { The Tensas River Watershed model was refined from TO3 to TO4 to improve stability and reduce runtimes. { Model runtimes decreased from ~40 hours (TO3) to ~16 hours (TO4) for final design storm runs. { Optimizations included refining the 2D mesh, removing overly detailed cells, and eliminating hydraulically insignificant structures. Boundary Conditions { The downstream boundary is influenced by Ouachita River backwater; TO4 updated the boundary condition from a historical hydrograph to constant stage levels by event frequency. { Stage levels were derived using data from HaHa Pump Station and Jonesville and Stafford gages, with a relationship established between HaHa and Clayton gages. Model Results and Analysis { Seven storm events (20%, 10%, 4%, 2%, 1%, 0.5%, and 0.2%) and five rainfall critical durations (6-hour, 12-hour, 24-hour, 48-hour, and 72-hour). { The primary focus for design storm calibration was the 1%, 24-hour storm event for comparing gage and model results. { Tendal gage (2,747 cfs) and Southeast of Tendal gage (2,839 cfs) closely matched model outputs (2,773 cfs and 2,849 cfs, respectively), indicating strong calibration, Table 4-2. { Calibration was not possible for consistently backwater-affected areas (e.g., near Newlight).

Figure 4-17: HEC-SSP curve results.

Figure 4-18: Best fit rating curve for the Tendal Gage.

Table 4-2 Gage analysis results compared to simulated results.

Figure 4-19: Comparison of rating curve predicted flow and model flow hydrograph at Tendal Gage (Fall 2009 event).

1% EVENT HEC-SSP PEAK DISCHARGE (CFS)

1%-24-HOUR EVENT MODEL PEAK DISCHARGE (CFS)

GAGE

2,747 2,839

2,773 2,849

TENDAL

SOUTHEAST OF TENDAL

49

Precipitation and Frequency Analysis and Consequence Modeling