The Valhi Drainage Improvements Project is designed to protect several industrial and residential developments not only from rainfall but also from highwater associated with backwater flooding from a high Mississippi River event. The project consists of approximately 2 miles of levee and three water control structures that will function as a gravity drainage system with a pump assist depending on the water level on the flood side of the system.
A HEC-RAS model was built that encompassed not only the drainage basin but the adjacent forced drainage system as well as the discharge basin. The reasoning for the model size and the interaction between all the different systems was to make sure that the systems could work together to minimize water levels within the systems and not cause any adverse impacts to any of the downstream communities.
In order to accurately depict the systems, a combination of LIDAR data with field survey information was used. The survey data was used to ground truth the LIDAR data and adjust it to match the elevational data for the area. Cross-sections and culvert crossings were input into the model to increase the accuracy of the model. A combination of 1-D channelized and 2-D storage areas were used to model the different drainage systems. The channels were modeled as 1-D while the developed areas as well as the discharge basin was modeled as 2-D systems connected to the channels to show how these areas were used as reservoirs during the rainfall event.
Ultimately, the model showed that the area could be protected from not only rainfall events but also from backwater flooding from a high Mississippi River event and not have any adverse impacts to the proposed project area or any of the downstream communities.
Terrebonne Parish Consolidated Government
Terrebonne Parish, Louisiana
Engineering
2019
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