The Formation and Future of the Upper Texas Coast: A Geologist Answers Questions about Sand, Storms, and Living by the Sea

7. Combating Coastal Change

7 Combating Coastal Change What can be done to slow the landward advance of the shoreline? In reality, there is only one way to slow the rate of coastal retreat, and that is to place more sand on the beach. This is referred to as beach nourishment. Trying to engineer our way around the problem has had a detrimental impact, namely the loss of beaches. A number of my colleagues in coastal geology would argue that we should do nothing to slow the process of coastal retreat. I think that there are areas where this advice would be well taken. However, we have to accept the fact that the citizens of Galveston are not going to allow their Houses constructed too close to the shore, like sand castles, have a short life span. 120 C H A P T E R 7 city to be washed out to sea without a fight. What if a Category 5 hurricane were to strike the island and destroy the seawall? Would we rebuild a bigger and stronger seawall? A major storm would also move sand into back-barrier settings and offshore where that sand may be lost from the longshore transport system indefinitely. How much coastal real estate would we be willing to relinquish? I am enough of a realist to know that if the worst happens, there is likely to be a frantic search for sand. Had Hurricane Rita maintained its strength and course, Galveston Island would have suffered major damage, and we would be hard pressed to replace sand that would be lost from the island. That is not to say that we have not spent a lot of tax dollars looking for sand resources. We just have not gotten much for our investment. Searching for Sand Resources First we have to accept the fact that sand resources for beach nourishment are in short supply along the upper Texas coast. I have been asked many times, “So why not pump sand from offshore onto the beach? It works in Florida, so why not in Texas?” The difference is that the Florida shelf is covered by sand, and our shelf is covered by mud. We have the Mississippi River to thank for this. Along the upper Texas coast, beach quality sand is mostly confined to the shallow part of the upper shoreface, generally in less than 15 feet of water and within a half mile from shore (fig. 1.2). It makes little sense to dredge sand from the shoreface to nourish a beach because that removes sand from the longshore transport system, which nourishes the beach naturally. If we take sand from the longshore transport system and place it on the beach at one location, we are removing sand that would end up on the beach in another location. Thus the effect is the same as building jetties. Furthermore, removing sand from the shoreface only steepens its profile, and nature will work hard to reestablish that profile by reclaiming that sand. What about taking sand from the lower shoreface? Sand that occurs in the lower part of the shoreface is finer than beach sand. This very fine sand is carried in suspension by waves and currents more easily than the sand that forms our beaches. That is why the very fine sand resides farther offshore, where it is not constantly influenced by waves and wavegenerated currents. If we place very fine sand on the beach it will simply C O M B A T I N G C O A S T A L C H A N G E 121 be transported right back out to the lower shoreface, probably in the first tropical storm. Furthermore, the very fine sands of the lower shoreface are typically interbedded with mud (see chapter 1). So the quality of sediment that could be acquired from the lower shoreface is not likely to meet the standards of beach-quality sand. The beaches that now exist along the seawall have been artificially nourished by sand pumped from offshore. This is a costly exercise, but the biggest problem with sustaining our beaches by this means is a shortage of offshore sand resources. The photo at the top was taken shortly after the beach was nourished in 1995 with the pipeline still in place, and the one at the bottom was taken in 2005. 122 C H A P T E R 7 How much...