Update on District Study

Since Hurricane Harvey, the First Colony Levee Improvement District’s (FCLID) Board of Directors has cooperated with the other districts in the Steepbank Creek watershed in developing a comprehensive watershed model for use by all districts. Steepbank Creek is the receiving stream for the drainage systems within FCLID south of SH 6, certain parts of Riverstone (MUD 115, LID 19 and the eastern side of LID 15) and a small area in LID 2 (the powerline easement).

The new watershed model was developed through a cooperative effort by LIDs 15, 19, MUD 115 and FCLID. The districts engaged an independent engineering consultant, APTIM, to develop this model. The model was developed using a recently released hydraulic analysis computer program named HEC-RAS, available from the U.S Army Corps of Engineers. This program incorporates traditional channel computations and new advances in 2-Dimensional (2D) modeling. It allows the model to simulate both channel flow and surface flows in the areas outside of the channel through the use of a surface elevation grid in the overbank areas. Additionally, the model uses a rain-on-grid technique to simulate the rainfall over the entire studied area. This provides the ability to “see” the runoff traversing the grid and flowing along the channel.

Several rainfall events were simulated in the model, including Hurricane Harvey and several hypothetical rainfall patterns traditionally used to design and analyze drainage systems. One series of these hypothetical events uses the newly released Atlas 14 rainfall data from the National Oceanic and Atmospheric Administration (NOAA). The resulting 100-year design rainfall event in Atlas 14 is now 16.5 inches in 24-hours for traditional flood studies, an increase of almost 1/3 more rainfall.

Recently, APTIM presented their preliminary results to the boards in an on-line meeting. During the course of the model development, Costello, Inc., the District Engineer for all of the participating districts, reviewed and guided the model development to ensure that the results produced by the model would closely represent actual conditions within the watershed. The resulting models are now complete, with APTIM preparing their final report and exhibits for presentation to the boards.

The next steps in this process will be for the boards to evaluate the results, identify components of the system which may need improvement and develop a comprehensive plan for the future of this watershed.