How did the Texas Gulf Coast Wetlands form?
About 60 to 1000 million years ago the edge of the continent was about where Dallas, Austin, and San Antonio are now. The region that would become the Texas coastal plain was at that time at the bottom of the newly forming Gulf of Mexico. Since then, The Gulf has been continuously filling in with sediment carried by rivers. Layers of gravel, sand, silt and clay extended the edge of the continent some 250 miles into the Gulf. The process of sediment deposition continues today as Texas rivers add their sediment loads to area bays or directly into the Gulf of Mexico. The Texas mainland sore, coastal plain, beaches, barrier islands and peninsulas, river deltas, and bays and estuaries are all products of the processes of erosion and deposition of sediments.
The development of the Texas Coastal Plain is the result of sedimentary deposition over the last two million years. The younger the sediments are, the easier it is to see the remains of the depositional processes. Many of the freshwater wetlands on the Texas Gulf Coast today have formed in old sediment-filled channels that once formed the deltas and floodplains of ancient rivers.
During the peak of the last ice age, about 18,000 years ago, sea level was 300 to 400 feet lower than it is today and the shoreline was at least 50 miles farther out in the Gulf of Mexico. During this time the coastal rivers cut deep valleys into the coastal plain sediments, which flooded and filled with sediment once the climate warmed and sea level rose as a result of melting glaciers. Most of our fringing salt marsh wetlands have formed in the bays and estuaries that resulted from the flooding and filling of these river valleys.
The rise in sea level resulted in the formation of large sand bars along the coastline that developed into barrier islands. Galveston Island and Padre Island are among the most well known. As these islands built seaward over time, a series of swales have been left behind the building sand ridges. These depressional swales are the location of freshwater wetlands on these islands. Tidal fringe wetlands occur on the back or bay side of the islands.
If you are interested in learning more information about Bayou City W.A.T.E.R. wetland monitoring sites, check out these links.
 | Addicks and Barker Reservoirs: Prairie pothole and marsh, potholes and old rice fields. |
| Katy Prairie: Prairie pothole and marsh -potholes, ricefields. Riparian forested-bottomland hardwood corridor. |
| White Oak Bayou - Riverine forested-bottomland hardwoods and swamp. |
Excerpt from Texas Coastal Wetlands Guidebook, by Daniel W. Moulton and John S. Jacob, Texas Sea Grant Publication TAMU-SG-00-605, p.3-4.
