Sediment Load Estimation of the Tijuana River Watershed under Existing and Future Scenarios for Best Management Practice Implementation
Watershed Physical Processes Research Unit
Project Number: 6408-13000-023-49
Interagency Reimbursable Agreement
Start Date: Dec 01, 2013
End Date: Nov 30, 2018
The long-term research objective of this project is to develop a model to estimate the sediment loadings from the watershed under existing conditions and evaluate the effects of planned and unplanned urban development in the Tijuana River watershed on hydrology and sediment loadings. Furthermore, the impact of sediment mitigation practices on hydrology, flood risk, erosion and sediment yield will also be evaluated. Due to funding constraints, the project will focus primarily on one sub-watershed (Goat Canyon/Los Laureles); this will include modeling and analysis of the sediment budget (i.e. determine the magnitudes of sheet and rill, gully, and channel erosion). However, the modeling results for the subwatershed will be used to determine an effective framework for estimating sediment loadings from the entire Tijuana River watershed, including defining the model parameters (e.g., hydrology, soil, etc.) for the entire watershed. This project will also evaluate and provide a detailed assessment of the reduction/prevention of sediment loads that could result from implementation of conservation easements, re-vegetation, sediment basins, road paving, and other Best Management Practices (BMP).
The objective of this interagency agreement is to perform work necessary to characterize hydrological processes, soil erosion and sediment transport from the Tijuana River watershed and to estimate the sediment loads being transported in the Tijuana watershed and the representative sub-watershed Goat Canyon/Los Laureles. Specifically, the following questions will be addressed:
• How to best estimate storm runoff and the sediment budget under existing conditions in the Goat Canyon watershed given limited hydrological and sediment data?
• How to best adapt what is learned in Goat Canyon to the entire Tijuana River Watershed?
• How to best estimate the soil erosion and sediment reduction due to future changes in the watershed, including road paving, continued urbanization, and implementation of conservation easements, re-vegetation, sediment basins, and other BMPs?
• How would storm peak discharge and runoff volume change due to future changes in road paving, urbanization, and the implementation of conservation measures and other BMPs?
• How could changes in peak discharge impact the channel stability and erosion?
• Will sediment control measures, like road paving and channel stabilization, potentially increase the frequency over overbank flooding in populated areas?
The overall approach combines fieldwork with modeling to construct a water and sediment budget of the Goat Canyon watershed in cooperation with the U.S. Environmental Protection Agency (USEPA), USDA Agricultural Research Service (ARS), and San Diego State University (SDSU).
• Collect and analyze existing data and relevant information regarding hydrological, erosion and sediment transport processes from the watershed and from the literature (USEPA and SDSU).
• Perform channel cross section survey and analyze soil properties (Identification of erosive substrates) (ARS and SDSU).
• Compile a database of watershed characteristics describing hydrologic, vegetative, soil, topographic and other features including erosion control structures and conservation measure locations (USEPA and SDSU)
• Monitor rainfall, and runoff and sediment load at the watershed outlet (SDSU).
• Establish permanent monitoring locations where channel changes would be monitored over time, measured once per year from repeat cross sections and/or using aerial photos from different periods (SDSU).
• Quantify gully dimensions using topographic surveys and high resolution Digital Elevation Models (DEMs). The DEMs will be created using either aerial or ground-level stereo pairs taken before and after major rainfall events (SDSU).
• Set up hydrological and erosion models to estimate the flow duration curve, frequency of over-bank flows, and annual total sediment loading by erosion process (sheetwash, rill, gully, channel) from the existing condition of the watershed and after implementation of conservation measures and BMPs (ARS, SDSU and USEPA).
• Compile and analyze information regarding sediment yield reduction from various implementation measures and BMPs (SDSU).