AN ANSWER TO SPI BEACH NOURISHMENT IN SIGHT?

By Juan Montoya

In the late 60s into the mid-70s, the U.S. Corps of Engineers sent a couple of researchers to South Padre Island to see whether they could develop methods to stop the sand from blowing away from the beach through sand construction using native plants and fencing.

I was in high school then and was hired part time to assist them erecting nylon and and plastic fencing, digging for water, watering the plants and help the crews with miscellaneous errands.

Years later, the problem of beach depletion, a lack of a sand budget, and the constant blowing of sand away from the southern part of South Padre Island brought home the purpose of the Corps' projects.

This past summer my kids and I visited the part of the island where the work was done. The dunes that were built by a combination of fencing and plants are some of the largest in the area. To their credit, SPI officials, property owners, corporations and residents have undertaken similar projects to hold the sand. Some dunes are already forming.

Dunes are instrumental in protecting the island and mainland against storms.

From 1969 to 1974, an experimental project was conducted by B. E. Dahl and others (1974) to test the capability of various beach grasses to grow and stabilize fore-island dunes along two segments of Padre Island. These some of the same dunes that were built during my summer job.


Their research paper notes that the northern test segment was located along the National Seashore. Several plant species, including both exotic and indigenous (native) species, were tested to select the ideal plants and planting techniques for dune formation and stabilization.


Their research showed that sea oats and bitter panicum, both indigenous to the island — were selected as having the most ideal attributes of the species tested. Panicum was the more desirable of the two, according to their paper.

Dahl noted in his paper that "artificial process can create in just a few years what probably takes 10 to 20 or more years to occur naturally."

But the lack of a "sand budget" has remained a constant problem with nourishing the beach on the extreme southern section of the island because of another man-made feature, the Brazos-Santiago Pass and the jetties constructed years ago to facilitate the entry and fishing and freight ships.

Like in Port Mansfield, the jetties have caused localized changes in the Gulf shoreline by interrupting longshore sediment transport. Deposition of sediments has occurred on the upcurrent side of the jetties, and erosion has occurred on the downcurrent side.

If you stand on the southern side of the jetties on the Boca Chica side, the beach on northern side starts a quarter mile or more inland and is rapidly sand-poor. If you look at a satellite picture, the silt that's not deterred by the granite jetties can clearly be seen drifting around them, and being carried to the extreme northern part of the island.

That impact upon the shoreline by the jetties has been documented in a geological paper https://store.beg.utexas.edu/geologic-circulars/412-gc7502.html.

The abstract on the paper reads, in part: The apparent effect of Falcon Dam upon the discharge of water and suspended sediment of the Rio Grande is marked, and the entrapment of sediment by the south jetties at Brazos Santiago Pass and Mansfield Channel is obvious. Structures that retard or eliminate sediment transport add to the sediment deficit already present in the littoral drift system."

Some researchers have suggested that a constant desilting regimen combined with better designed jetties that don't stretch out so far into the Gulf can help keep the precious silt closer to the shoreline to prevent it from being carried out far from SPI beaches.

Those are the first hopeful suggestions that are being considered by newly elected District 37 state rep Alex Dominguez and Cameron County Parks System Director Joe Vega and they say they will try to bring a representative of the U.S. Geological Survey and the U.S. Corps of Engineers to see what can be done to address the beach depletion problems there.

"This is a problem that has bedeviled the folk at SPI for decades with only partial solutions being offered so far," Dominguez said. "I know Joe (Vega) is excited to try something and we are ready to look at any suggestions people may have."