LWI Region 3 Modeling Overview

BOEUF

MACON TENSAS

COCODRIE

4.2.2 Macon The calibrated 2D ROM HEC-RAS model for the Bayou Macon Watershed was used to simulate design storm events. Multiple gages across the watershed were analyzed for events ranging from the 0.2% to 20% annual chance to support flood frequency analysis and model calibration. A 100% soil saturation assumption was applied to reflect conservative runoff conditions typical of extreme events in the Region. a. Model and Boundary Condition Update Model geometry was updated prior to the design storm assessments to reduce simulation runtime and structural instabilities. { Overbank Manning’s around some bridges were modified to eliminate high oscillations in their flow hydrographs. { Mesh Cell or faces that underwent a significant number of iterations were identified and modified to reduce errors. { To reflect realistic antecedent conditions for design storm simulations, water levels at the end of the 2-year, 24-hour event were used as initial conditions instead of IC Points. { A combined Macon-Tensas model was run for the 500-year event to update rating curves at Macon outlets. New rating curves were developed for JoesBy_BelowSwan_ out and ByMacon_TE_out using stage and flow data at their locations. To maintain one-way flow from Macon to Tensas, ByMacon_1_out and WardsBy_out were removed. LEARN MORE: (M_3.1)

Gage selection and assumptions.

NEAR DELHI: USGS flow records were excluded due to backwater effects; a rating curve from calibrated model outputs was used to estimate peak flows from stages. SOUTH DELHI: Excluded from analysis due to incomplete, inconsistent, and unverifiable data. COMO: With no historical flow records, peak flows were estimated using a rating curve developed from calibrated storm data and corrected stage records. LEARN MORE: (M_3.1.3)

Five gages (Eudora, Kilbourne, Near Delhi, South Delhi, and Como) were assessed for data availability, quality, and spatial relevance. Figure 4-12 displays gage locations. EUDORA: 78 years of reliable USGS peak flow data were verified through USGS consultation and used directly in the flow frequency analysis. KILBOURNE: Inconsistent historical flow records led to development of a rating curve from calibrated storm data to estimate peak flows from stage data.

Figure 4-12: USGS and USACE gage locations.

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LWI REGION 3 TRAINING

LOUISIANA WATERSHED INITIATIVE