Sedimentation rates in Texas estuaries and lagoons

Detailed unpublished soundings of Texas bays made by the United States Coast and Geodetic Survey in the last century have been compared with recent surveys. The depth changes appear to show a reasonable relation to river mouths and to the silt-load measurements of these rivers when taken in connection with tide-gauge data which suggest coastal sinking. The fill has occurred primarily as general shoaling of the flat bay floors and secondarily as a direct encroachment of subaerial deltas onto the bays. So far as could be determined only two rivers, the trinity and the Colorado of Texas, have extended their deltas appreciably since the time of the old surveys. An estimated average rate of bay shoaling of 1.26 feet per century comes from the compilation of 20,518 points of comparison. However, the silt load of Texas streams, which probably is deposited largely in the bays, is too high for this rate and suggest that there has been submergence. By allowing for submergence the amount of 1.8 feet which is the average relative sea-level rise per century for four Gulf Coast tide stations, a total estimated rate of sedimentation in the bays becomes 3 feet per century. This material, however, has a high water content and would make only about half as much sedimentary rock, depending on the degree of compaction.