Study Description
The Sedimentation Study will identify which sub-watersheds in the Upper San Jacinto River Basin produce the most sediment and which store the most sediment. With this information, sub-watersheds and individual locations can be prioritized for conceptual solutions, potentially including structural solutions and non-construction best management practices. The ultimate goal is to develop an implementation plan to reduce sediment inputs and, if needed, enhance sediment storage to mitigate the loss of floodway conveyance.
Efforts will include development of cost estimates, preliminary exhibits, and preliminary permitting requirement evaluation, where applicable. All identified projects, efforts, and practices will be ranked and included in an implementation plan, and ultimately all information developed as part of the Sedimentation Study will be compiled into a regional sediment management plan which can guide sedimentation mitigation efforts in the future.
For construction solutions, these efforts will include development of cost estimates, preliminary exhibits, and preliminary permitting requirement evaluation. All identified projects, efforts, and practices will be ranked and included in an implementation plan, and ultimately all information developed as part of the Sedimentation Study will be compiled into a regional sediment management plan which can guide sedimentation mitigation efforts in the future.
The cost of the project is estimated at $750,000. City of Houston, City of Humble, and HCFCD (the Partners) have each agreed to fund a portion of the fifty percent local match ($375,000) required by the Texas Water Development Board (TWDB) Flood Infrastructure Fund (FIF) grant. SJRA will perform in-kind services in an effort to reduce the local match amount to be funded by the Partners. The remaining fifty percent ($375,000) of the project cost will be funded by TWDB FIF grant funds.
Study Purpose and Goal
The purpose of the Sedimentation Study is to understand the characteristics of sedimentation in the Upper San Jacinto River Basin, including sediment sources, transport, and storage locations, and to ultimately develop feasible and cost-effective conceptual solutions, best management practices, and an overall implementation strategy that can help better manage sediment in the Basin. The findings and recommendations of the study will be summarized in a Regional Sediment Management Plan (Sedimentation Plan).
Study Area
The Sedimentation Study Area includes the Upper San Jacinto River basin and extends from Huntsville in the north to Lake Houston in the south. The subwatersheds within the study area are represented by the various colors shown in the map below.
Calibration and Categorization of Subwatersheds
As part of the Sedimentation Study, the project team will acquire and organize relevant prior studies, models, and data (e.g., soils, land use, impervious cover, topography, and regional geology) related to completing the study. This includes preliminary data analysis to locate highly erodible soils and areas of sediment erosion and accumulation.
Subwatersheds will be grouped into categories based on shared characteristics, and ultimately narrowed down to three subwatersheds to be used as calibration for detailed analysis. These calibration subwatersheds will form the basis for estimating the sediment characteristics of other subwatersheds with similar characteristics.
Sediment Budget
In addition to characterizing and calibrating the subwatersheds, an annual sediment budget will be determined for the Study area. Sediment budget refers to the balance between sediment added to and removed from the river basin; in this respect the river basin sediment budget is like a bank account. When more material is added than is removed, there is a surplus of sediment and the streambank builds.
To determine the sediment budget, detailed assessments of sediment supply and storage volumes will be conducted on the three subwatersheds used for calibration. This will include determination of the types of sediment sources found in the subwatersheds (e.g., sediment originating within stream channels or from overland flow and erosion). Sedimentation in Lake Houston will also be analyzed, including comparison of historic volumetric surveys and water storage estimates.
Using modeling, additional information will be gathered regarding sediment transportation in the basin. The project team will perform sediment sampling to quantify and characterize sediment that is transported along the streambed during storm events. These results will be used in modeling efforts to estimate the total sediment yield along the sampled streams.
Hotspot Subwatersheds
The data obtained from the above tasks will be extrapolated and applied to all other subwatersheds in the Upper San Jacinto River Basin. This will provide a total sediment budget and sediment yield for the basin. Subwatersheds will be ranked based on their relative contribution of sediment. Hotspot subwatersheds will be identified for further evaluation. “Hotspot subwatershed” refers to locations of significant, individual sediment contributions. Examples of potential hotspots include stretches of extreme eroding streambank and streambed and land uses or operations that produce excess sediment runoff.
The findings of this evaluation will inform identification of conceptual sediment mitigation solutions and confirm which sites are the highest priorities for implementation of those solutions.
Conceptual Solution Development and Implementation Strategy
Finally, conceptual solutions will be identified and vetted. These solutions may include structural projects (e.g., stream restoration, sand traps) and/or non-structural best management practices like riparian buffer requirements. Conceptual solutions will be developed for the top ten ranked sediment sites, and each will include a conceptual schematic, preliminary estimates of expected sediment reduction, capital and/or operations and maintenance cost estimates, evaluation of cost-benefit (e.g., cost/tons of sediment removed), landowner agreement requirements, and environmental permitting requirements. Impacts and/or benefits to any local drainage infrastructure will also be discussed. The next steps for each recommended solution, potentially to include additional analysis, modeling, ground-truthing, etc., will be determined.
As part of this effort, the project team will identify potential partners and/or sponsors who could assist with the future implementation of the recommended solutions. The task will also include identification of permitting agencies and regulatory requirements that need to be coordinated with and met for the recommended solutions to be implemented.
The final Sedimentation Plan will include next steps and potential future phases to implement the recommended sediment management solutions. A one-page handout summarizing the Sedimentation Plan’s goals, findings, and recommendations will also be developed for public review.
Study Schedule
The Sedimentation Study project was kicked off in May 2022 and is anticipated to be completed by September 2024.
