Most recently the Texas Water Development Board (TWDB) has completed the bathymetry study of the West Fork of the San Jacinto River for the City of Houston. Data from this study has been given to the Army Corps of Engineers (ACOE) to determine the amount of sediment that resulted from Hurricane Harvey. This information is useful because this study identifies underwater topography allowing the City to understand where the additional sediment brought in by Hurricane Harvey has been deposited in the river and lake as well as changes in depth.

 

The TWDB continues to survey the entire lake for the Coastal Water Authority (CWA), the agency that contracts with the City for management of the Lake Houston Spillway Dam. The schedule for the TWDB to complete their survey of Lake Houston is Summer 2019. In addition to conducting a bathymetric study the City of Houston is currently reviewing data collected by the ACOE during a recent Light Detection and Ranging (LIDAR) study which uses light in the form of pulsing lasers to measure the distance from the water's surface to the bottom of the river and lake . Capacity losses due to sedimentation in the lake as well as East and West Forks of the San Jacinto River will be determined using the LIDAR data along with the completed bathymetric study once the TWDB has completed their survey and report.

 

The LIDAR study allows the City to map changes in shoreline as well as make digital elevation models. It is this data that is assisting the City and ACOE in determining the amount of sediment that needs to be removed from locations along the West Fork of the San Jacinto River like the "mouthbar" that is located just south of the Deerwood Country Club. The LIDAR Study results will also be used by the Harris County Flood Control District (HCFCD) for the creation of new flood insurance rate maps because of the changing rainfall patterns published by the National Oceanic and Atmospheric Administration. The flood insurance map study will utilize updated LIDAR surveys of the entire county and will take several years to complete, however HCFCD is already hiring consultants to assist with this work.

 

On October 11, 2018, Council Member Martin met with Governor Abbott's Executive Staff, TDEM, FEMA, and ACOE in Austin where a lengthy discussion was had about the amount of sediment deposit that will still remain in the San Jacinto River after the current emergency dredging project is completed. The current emergency dredging contract is not scheduled to be complete until the end of April 2019. At this meeting the City's consultant estimated that after the completion of the existing dredging project that there will be approximately 500,000 cubic yards of additional sediment that needs to be removed from the river known in the community as the "mouthbar".

 

This estimate however was based on a comparison between the LIDAR study completed by the ACOE this year and a bathymetric study completed by the TWDB in 2011. The important takeaway from this meeting in October is that FEMA agreed that the additional sediment qualifies as Harvey debris however, the estimate of 500,000 cubic yards was not a true amount directly associated with Hurricane Harvey. The City does not have survey data that is immediately pre and post-Harvey which would provide us a true amount of residual sediment that is a direct result of Hurricane Harvey. The City is currently waiting on the ACOE to complete its analysis of the City's data.

 

At the meeting in Austin the ACOE indicated that an additional disposal site would be needed in order to remove the additional material. As a result the City of Houston has been proactive in identifying a site, thanks to the assistance of a local landowner that has property on the south side of the West Fork of the San Jacinto. The land owner has retained an environmental consultant to determine any possible wetland issues that may prevent use of the property for disposal. As of right now it appears the property is a viable site and a formal permit was filed with the ACOE this week.

 

In summary, the process to have the "mouthbar" removed from the West Fork of the San Jacinto River has been an arduous one. All parties from local, state, and federal agencies have been working together to accurately define the area needed for additional removal so that capacity can be restored to the river and reduce the effects of future flooding. The removal of the "mouthbar" cannot begin until the existing emergency dredging along the West Fork of the San Jacinto River is completed. Since this is a reality the City is doing all that it can to be proactive in securing land as well as permits for the "mouthbar's" removal once the existing project is completed by the ACOE in April. This will allow the ACOE to keep equipment and crews in place without the need for demobilization and remobilization, saving roughly $18 million.