LWI Region 3 Modeling Overview

BOEUF

MACON TENSAS

COCODRIE

b. Hydraulic Model Setup (HEC-RAS 2D) Model Overview and 2D Mesh Design The hydraulic model of the Boeuf River Watershed was developed using a fully integrated HEC-RAS 2D ROM approach, replacing the previously segmented 1D/2D hybrid model architecture. This decision was based on calibration findings that showed improved hydraulic behavior and interaction when using a seamless 2D setup. As shown in Figure 3-20 , the model domain includes an additional 170 sq. mi. added upstream in Arkansas. The modeled domain covers approximately 2,000 sq. mi. in Louisiana, with added refinement in Arkansas during calibration. The base mesh resolution in rural areas was kept coarse to optimize runtime but refined to 50–100 ft in urban and channelized areas, such as the City of Monroe, and along narrow bayous. These refinements allowed the model to capture localized flood behavior and flow through control structures with greater precision. Breaklines were used extensively along levees, roads, channels, and high ground to ensure the mesh honored important hydraulic features and gradient changes, preventing computational shortcuts across bends and preserving realistic flow paths. The Arkansas portion of the watershed was modeled with coarser mesh and necessary refinement along the Boeuf River to simulate continuous flow across the state line and eliminate artificial boundaries. This portion was later merged into the Louisiana ROM model during calibration.

Figure 3-20: Additional Arkansas portion added to 2D ROM model domain.

Hydraulic Structures and Control Features A total of 657 major hydraulic structures were included, covering:

Structures were modeled using Storage Area/2D connections with surveyed data, including deck elevations, culvert diameters, and spillway profiles where available. Lateral structures and flap gates were added at strategic locations along levees and embankments. Key structures, such as Gunby Dam, were transitioned from static outflow boundaries to dynamic weirs within the ROM system to improve calibration of flow splits. The Monroe urban drainage system was captured through detailed modeling of its 11 pump stations.

{ 280 bridges { 258 culverts { 8 dams/spillways { 52 weirs/diversions { 48 gated levee outlets { 11 stormwater pump stations in Monroe

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LWI REGION 3 TRAINING

LOUISIANA WATERSHED INITIATIVE