Study of Complex Flows in the Lower San Bernard River, Texas

The San Bernard River, TX, joins the Gulf of Mexico between the mouths of the Colorado River and the Brazos River. The Gulf Intracoastal Waterway GIWW intersects all three rivers. Two floodgates have been provided on the Brazos River and a navigation lock has been provided on the Colorado River for preventing sediment influx from rivers into the GIWW. The 6.5-km- 4-mile- long segment between the Brazos River and the San Bernard River is the focus of the study. The barge navigators have complained that they experience a strong west to east current through the Brazos west gate, which is related to tides and river discharge. Shallow lakes and marshlands connected to the rivers complicate the hydraulic conditions due to storage and release of floodwater. This report describes the field data collection and its analysis as well as the numerical model study. The main objectives of the study were to construct a verified, working numerical model of the relevant water bodies that are hydraulically connected and to examine the effect of a new San Bernard River outlet to the sea on improving flow conditions. The model reasonably reproduced prototype trends in water-surface elevation, velocities, and discharges. In general, providing a new outlet is favorable for navigation through the Brazos west floodgate during low flow conditions, but some adverse effects are shown during high flow events. Factors such as the frequency of high flow events, the operation of the floodgates, the drop of water surface elevation throughout the system, and the cost of keeping the new outlet open should be considered at the time of acceptance or rejection of the proposed plan.