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Planning for sustainable resource use

At San Luis Pass on the Gulf of Mexico, Mott MacDonald helped identify the optimum location and dimensions for borrow areas that could be mined for beach quality sand.

San Luis Pass Inlet Management

Opportunity

In order to maintain the beaches along the Gulf coast, sources need to be identified in order to provide sand for beach nourishments. There are limited resources offshore and there are numerous placement areas that are being used beneficially, but don’t contain beach quality sand.

San Luis Pass is a natural tidal inlet at the border of Brazoria and Galveston Counties on the Gulf of Mexico. Used in the past as a “back entry” for pirates and smugglers entering Galveston Bay, the area includes a sensitive habitat and is popular with fishermen. The flood shoal of San Luis Pass contains more than 40 million cubic yards of beach-quality sand, and is growing at about 200,000 cubic yards per year. This represents a valuable resource for beach nourishment and marsh restoration.

Solution

In 2009, the Texas General Land Office retained Mott MacDonald to conduct a feasibility study that would identify the optimum location and dimensions for borrow areas that could be mined for beach quality sand and would act as “sediment traps” to capture sediment moving from the Gulf into the flood delta to create a renewable source of sand.

Mott MacDonald conducted numerical modeling to identify the migration corridor of sand, identify areas of deposition, and evaluate the hydraulic and sedimentation changes that might occur from dredging sediment traps or tidal channels.

We also consulted and coordinated with regulatory agencies to identify areas of environmental concern, and analyzed potential impacts:

  • Morphological modeling was used to assess changes to the habitat and tidal flats of San Luis Pass.
  • Salinity modeling was conducted to predict changes in salinity in Galveston Bay and adjacent sensitive habitat.
  • A sediment budget was developed to quantify sediment transport pathways.

Outcome

We are currently developing a permit package and design drawings to utilize San Luis Pass as a source of sand for a demonstration nearshore beach nourishment project on Follet’s Island. This project will be monitored to validate the modeling results and assist the General Land Office in securing a long-term renewable source of sand in the area.

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