Citation:

Gudino-Elizondo, N., T. Biggs, R. Bingner, E. Langendoen, T. Kretzschmar, E. Taguas, K. Taniguchi, D. Liden, AND Y. Yuan. Modelling Runoff and Sediment Loads in a Developing Coastal Watershed of the US-Mexico Border. WATER. MDPI, Basel, Switzerland, 11(5):1024, (2019). https://doi.org/10.3390/w11051024

Impact/Purpose:

Excessive flooding and sedimentation threaten both ecosystems and human populations on the US-Mexico border due to urbanization. In the Tijuana-San Diego region, the Tijuana Estuary in the United States suffers from “excessive sedimentation”, and determining the source of the sediment and mitigating its production is a primary management goal of the US EPA and other cross-border agencies. In this study, we quantified the sediment budget of the Los Laureles Canyon watershed (LLCW), a mixed rural-urbanizing catchment in Northwestern Mexico, using the AnnAGNPS model and field measurements of channel geometry to help undertand sources of sediment production so that proper managment practices can be planned and implemented.

Description:

Urbanization can increase sheet, rill, gully, and channel erosion. We quantified the sediment budget of the Los Laureles Canyon watershed (LLCW), which is a mixed rural-urbanizing catchment in Northwestern Mexico, using the AnnAGNPS model and field measurements of channel geometry. The model was calibrated with five years of observed runoff and sediment loads and used to evaluate sediment reduction under a mitigation scenario involving paving roads in hotspots of erosion. Calibrated runoff and sediment load had a mean-percent-bias of 28.4 and − 8.1, and root-mean-square errors of 85% and 41% of the mean, respectively. Suspended sediment concentration (SSC) collected at different locations during one storm-event correlated with modeled SSC at those locations, which suggests that the model represented spatial variation in sediment production. Simulated gully erosion represents 16%–37% of hillslope sediment production, and 50% of the hillslope sediment load is produced by only 23% of the watershed area. The model identifies priority locations for sediment control measures, and can be used to identify tradeoffs between sediment control and runoff production. Paving roads in priority areas would reduce total sediment yield by 30%, but may increase peak discharge moderately (1.6%–21%) at the outlet.

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