LWI Region 3 Modeling Overview

Lake Chicot and Lake Macon Modeling The Bayou Macon Arkansas HEC-HMS model incorporates two lakes, Lake Chicot and Macon Lake, that operate based on a rule system defined by water level and outlet control structures. HEC-HMS version 4.11 incorporates the use of rule-based reservoir operations. These rules allow for the modeler to set target maximum and minimum flow values to achieve target storage patterns for the lake. Calibration For the calibration process in Bayou Macon Arkansas, events were selected based on historical data and community accounts. Calibration was done through adjusting model parameters and the lake system. More details about the calibration process can be found in the Macon report.

LEARN MORE: M, APPENDIX 1, 1.2.1 +

EVENTS The events chosen for calibration were the same events used in the calibration process for the Boeuf Arkansas Watershed Section 3.6.1.

PARAMETERS

MODEL PARAMETERS

• Subbasin Time of Concentration • Storage Coefficient

• Antecedent moisture conditions for loss calculations • Routing parameters, such as Manning’s Coefficient

LAKE SYSTEM (SEE FIGURE 3-29) { Using the Water Control Manual for the Chicot Pumping Plant, it was determined that the pumping plant at Rowdy Bend diverts flow from Macon Lake to the Mississippi River depending on water levels. { Water exits Macon Lake via: • The Rowdy pump system into the Mississippi River • Following the Connerly Bayou Dam Spillway to the gravity gates and ogee spillway at Connerly Weir to exit downstream to Lake Chicot • Combination of these methods

Figure 3-29: Lake system represented in the model.

Recurrence Interval Modeling { Atlas 14-derived rainfall was used to derive key storms for recurrence interval modeling. See Storm Generation (Section 4.11) for additional information.

{ Results were validated by applying subbasin ARF to Atlas 14 subbasin average precipitation depth durations and applied through HMS hyetographs, ensuring the model results were reasonable when compared to the recorded gage data.

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Hydrologic and Hydraulic Modeling Methodology