2-D Adh Modeling At The Crossing of The Gulf Intercoastal Waterway (giww) and The Brazos River: Hydrodynamic Modeling In Support of Ship Simulation Efforts and Sediment Transport Modeling In Support of Assessing Proposed Project Impacts

The Gulf Intracoastal Waterway (GIWW), a portion of the U.S. Intracoastal Waterway located along the Gulf of Mexico, is a high-traffic inland channel which is crucial to the U.S. economy. The Brazos River is the largest river crossing the GIWW west of the Mississippi River. The crossing is about 7000 feet upstream from the gulf near Freeport, TX. Approximately 45 million tons of commercial cargo crosses the Brazos River annually, with an estimated product value of $4.5 billion.

Tidal and fluvial flows into the GIWW are controlled by sector gates on both sides of the Brazos River, constructed by USACE in 1943 as part of the Brazos River Floodgates project. The gates control sediment movement into the GIWW for low flows as well as flood flows. Contrary to what the name suggests, the gates do not serve to reduce the threat of flooding. The location of the gates (near the Brazos River crossing flows) and the high velocities at the gates (caused by tidal fluctuations and high river flows) result in navigation challenges. Approximately 65 vessel allisions occur annually. Those allisions and the associate navigation delays result in an annual economic loss of approximately $10.8 million. In 2019, a Final integrated Feasibility Report- Environmental Impact Statement (FIFR-EIS) was conducted to investigate navigational delays and safety. The report recommended that the west gates be removed, the east gates be widened and set back, and the GIWW channel be realigned to increase safety and long-term navigational efficiency.

The paper will first address the 2-D AdH hydrodynamic model validation effort (which involved getting the model to reproduce USGS stage and velocity data in the project area) and the associated ship simulation efforts conducted at the U.S. Army Engineer Research and Development Center (ERDC) Ship/Tow Simulator in Vicksburg, MS. Regarding model validation, the needed attention to geometry, specifically the connections to off-channel storage, will be highlighted. Regarding the ship simulation efforts, the paper will cover 1) the discussions resulting in the scopes of work, 2) the efforts needed to provide the hydraulic and other input, and 3) a summary of the in-person simulation efforts and results.

Secondly, the paper will address the 2-D AdH sediment transport validation efforts and the subsequent simulations involving with-project conditions. The sources of input data (including already-existing data documented in the FIFR-EIS and bed and settling velocity data collected by ERDC) will be discussed as well as the qualitative to semi-quantitative results of sensitivity testing completed within the constraints of the project budget and schedule. The paper will conclude with the results of the modeling effort and the proposed path forward.