Matagorda Ship Channel, Texas: Jetty Stability Study

The entrance of the Matagorda Ship Channel, connecting the Gulf of Mexico to Matagorda Bay, Texas, has experienced a strong currents since its construction in 1963-1964. Strong currents had been predicted in physical model experiments performed during design to determine the optimal location of the new inlet cut through Matagorda Peninsula and entrance configurations. The current has produced a large area of scour on the bay side of the inlet adjacent to the west jetty, and vessels encountering a strong along-channel and cross-channel current at the entrance experience difficulty in navigation. This study was performed to understand the hydrodynamics of the existing condition and evaluate alternatives for stabilizing the jetties to reduce the current velocity, thereby reducing the scour and improving navigation reliability. The interaction between the entrance and Pass Cavallo, the natural inlet to Matagorda Bay located southwest of the Matagorda Ship Channel entrance, was also examined in a regional approach. The study proceeded by review of the engineering and scientific literature, analysis of regional and local trends in the shoreline change at the entrance and at Pass Cavallo, field measurements of the water level and current, bathymetry surveys, and hydrodynamic numerical modeling of tidal circulation, including wind forcing and river discharges to the bay. Alternative configurations of the jetties were investigated with the hydrodynamic model. A frequency-of-occurrence methodology based on the current velocity magnitude was introduced to evaluate the alternatives. Possible changes in salinity were also investigated.