Modeling ephemeral gully erosion from unpaved roads: Equifinality and implications for scenario analysis

Authors: GUDINO-ELIZONDO, NAPOLEON - Centro De Investigacion Cientifica Y De Educacion Superior De Ensenada; BIGGS, TRENT - San Diego State University; Bingner, Ronald; YUAN, YONGPING - Us Environmental Protection Agency (EPA); Langendoen, Eddy; TANIGUCHI, KRISTINE - San Diego State University; KRETZSCHMAR, THOMAS - Centro De Investigacion Cientifica Y De Educacion Superior De Ensenada; TAGUAS, ENCARNACION - Universidad De Cordoba; LIDEN, DOUGLAS - Us Environmental Protection Agency (EPA)

Submitted to: Geosciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/13/2018
Publication Date: 4/17/2018
Publication URL: https://handle.nal.usda.gov/10113/6473331
Citation: Gudino-Elizondo, N., Biggs, T., Bingner, R.L., Yuan, Y., Langendoen, E.J., Taniguchi, K., Kretzschmar, T., Taguas, E.V., Liden, D. 2018. Modeling ephemeral gully erosion from unpaved roads: Equifinality and implications for scenario analysis. Geosciences. 8(4)137. https://doi.org/10.3390/geosciences8040137.
DOI: https://doi.org/10.3390/geosciences8040137

Interpretive Summary: Severe gully erosion on unpaved roads in the Los Laureles Canyon Watershed in Northern Mexico is adversely impacting the Tijuana River Estuary by significantly contributing to the total sediment production. Evaluating gully erosion with models in urban areas is challenging due to difficulties with equifinality and parameter identification, which complicates quantification of management impacts on runoff and sediment production. Utilization of watershed models containing gully erosion components produced results that were similar to the observed values. The SCS curve number, erodible soil depth, and critical shear stress were the most sensitive parameters in gully erosion modeling. The 21 behavioral models used were consistent in their estimates of total sediment reduction when paving all roads (decrease of 90-94%). Conversely, total runoff of the behavioral models increased from approximately 1.5 to 2.3 times under the paved condition compared to the current condition. The results suggest urgency in implementing management practices such as pavement or other stabilization measures of unpaved roads to mitigate soil erosion, but that paving may increase peak discharge significantly (1.8-5.7 times) at the neighborhood scale.

Technical Abstract: Modeling gully erosion in urban areas is challenging due to difficulties with equifinality and parameter identification, which complicates quantification of management impacts on runoff and sediment production. We calibrated a model (AnnAGNPS) of an ephemeral gully network that formed on unpaved roads following a storm event in an urban watershed (0.2 km2) in Tijuana, Mexico. Latin hypercube sampling was used to create 500 parameter ensembles. Modelled sediment load was most sensitive to the SCS curve number, tillage depth (TD), and critical shear stress (tc). Twenty-one parameter ensembles gave acceptable error (behavioral models), though changes in parameters governing runoff generation (SCS curve number, Manning’s n) were compensated by changes in parameters describing soil properties (TD, tc), resulting in uncertainty in the optimal parameter values. The behavioral models were used to evaluate uncertainty under management scenarios. Paving the roads increased runoff by 146-227%, increased peak discharge by 178-575%, and decreased sediment load by 90-94% depending on the ensemble. Additional field data on the infiltration rates of unpaved roads will be critical to reduce uncertainty in management impacts on runoff. The method can be used in other watersheds to simulate runoff and gully erosion, to quantify the uncertainty of model-estimated impacts of management activities on runoff and erosion, and to suggest critical field measurements to reduce uncertainties in complex urban environments.