Modelling runoff and sediment loads in a developing coastal watershed of the US-Mexico border

Authors: GUDINO-ELIZONDO, NAPOLEON - Centro De Investigacion Cientifica Y De Educacion Superior De Ensenada; BIGGS, TRENT - San Diego State University; Bingner, Ronald - Ron; Langendoen, Eddy; KRETZSCHMAR, THOMAS - Centro De Investigacion Cientifica Y De Educacion Superior De Ensenada; TAGUAS, ENCAMACIO - University Of Cordoba; TANIGUCHI-QUAN, KRISTINE - Southern California Coastal Water Research Project; LIDEN, DOUGLAS - Environmental Protection Agency (EPA); YUAN, YONGPING - Us Environmental Protection Agency (EPA)

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2019
Publication Date: 5/16/2019
Citation: Gudino-Elizondo, N., Biggs, T., Bingner, R.L., Langendoen, E.J., Kretzschmar, T., Taguas, E.V., Taniguchi-Quan, K., Liden, D., Yuan, Y. 2019. Modelling runoff and sediment loads in a developing coastal watershed of the US-Mexico border. Water. 11, 1024.

Interpretive Summary: Both rural and urban development can lead to accelerated soil erosion, including sheet, rill, gully and channel erosion processes. Measuring and modelling erosional processes is challenging in ungauged watersheds, especially in developing countries, where rapid urbanization complicates parameter identification, model structure and where processes like gullies are important component of the sediment budget. A simulation model was used to quantify the sediment budget in the Los Laureles Canyon watershed, a rapidly urbanizing watershed in Tijuana, Mexico. Suspended sediment concentration (SSC) collected at 10 different locations during one storm event correlated with modelled SSC at those locations, suggesting the model represented spatial variation in sediment production. Simulated gully erosion was shown to represent about 40-55% of hillslope sediment production, and 50% of the total sediment yield and is produced by only 23% of the watershed area that is on steep highly erodible marine sediments. The model identifies priority locations for installation of sediment control measures and can be used to identify tradeoffs between sediment control and runoff production. Scenario analysis for those locations would reduce total sediment yield by 30%, but may increase peak discharge moderately (2-21%) at the watershed scale.

Technical Abstract: Residential expansion in rural-urbanizing areas can increase soil erosion, including sheet, rill, gully and channel erosion processes. We explored the capacity of the model (AnnAGNPS) to quantify the sediment budget in the Los Laureles Canyon watershed (LLCW), a mixed rural-urbanizing catchment in Northwestern Mexico. We calibrated runoff and sediment loads to evaluate sediment reduction under scenario analysis. The simulation results were evaluated with five years of rainfall-runoff data series and annual sediment load at the watershed outlet. 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, suggesting the model represented spatial variation in sediment production. Simulated gully erosion represents about 16-37% of hillslope sediment production, and 50% of the total sediment yield is produced by only 23% of the watershed area. The model identifies priority locations for installation of sediment control measures, and can be used to identify tradeoffs between sediment control and runoff production. Scenario analysis for those locations would reduce total sediment yield by 30%, but may increase peak discharge moderately (1.6-21%) at the LLCW scale.