LWI Region 3 Modeling Overview

BOEUF

MACON TENSAS

COCODRIE

4.2.4 Cocodrie INTRODUCTION AND DATA COLLECTION LEARN MORE: (C_7.1)

GAGE SELECTION Of five USACE gages in the Cocodrie Watershed, only Deer Park and Wild Cow Upper were used. Deer Park, upstream and unaffected by operations, has reliable data from 1990–2023. Wild Cow Upper, near the pump station, was used only under Open Gate (No Pumping) conditions, the only scenario with 10+ years of valid

This assessment analyzed flood risks in the Bayou Cocodrie Watershed using a calibrated 2D flood model detailed previously . Open Gates, No Pumping: { All outlets were set to normal depth conditions. { The Tensas-Cocodrie Pump Station was not operated. { Starting water levels were based on the September 2020 event, when both gravity drain structures were open. { The model showed that changing the slope for normal depth had minimal impact on water levels due to the levee structures and internal drainage systems. Closed Gates, Pumping Only { Boundary conditions forced all levee outlets (flap gates) to remain closed. { A steady stage hydrograph and closed gate settings were used to simulate high river levels. { Initial water levels came from the March 2016 event, when gates were shut, and pumps were active. For both scenarios, the model assumed 50% soil saturation to reflect average ground conditions before a storm. Although soil moisture was standardized, using actual past events for starting water levels helped ensure realistic gate and pump operations during peak storm conditions.

data (See Figure 4-20). LEARN MORE: (C_7.3)

RATING CURVE DEVELOPMENT Rating curves were developed using the calibrated 2D HEC-RAS model. Deer Park had one rating curve (Open and Closed Gate Combined); Wild Cow Upper also had one rating curve (Open Gate) (Figure 4-21 and Figure 4-22 ). Events with backwater effects were excluded. Rising limb data was smoothed with Python, and a fourth-order polynomial provided the best fit. Modeled curves matched model flow well.

LEARN MORE: (C_APPENDIX_A-5)

Figure 4-20: Gravity drainage Structures and USACE gage.

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LWI REGION 3 TRAINING

LOUISIANA WATERSHED INITIATIVE