Implications of conceptual channel representation on SWAT streamflow and sediment modeling

Authors: HER, YOUNGGU - University Of Florida; JEONG, JAEHAK - Texas Agrilife Research; BIEGER, KATRIN - Texas Agrilife Research; RATHJENS, HENDRIK - Stone Environmental Consulting; Arnold, Jeffrey; SRINIVASAN, RAGHAVAN - Texas A&M University

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2017
Publication Date: 8/1/2017
Citation: Her, Y., Jeong, J., Bieger, K., Rathjens, H., Arnold, J.G., Srinivasan, R. 2017. Implications of conceptual channel representation on SWAT streamflow and sediment modeling. Journal of the American Water Resources Association. 53(4):725-747. https://doi.org/10.1111/1752-1688.12533.

Interpretive Summary: Hydrological models are commonly used to determine the impact of land management and climate on water supply and quality. A model is a simplified conceptualization of the landscape and flow paths that introduces uncertainty in model outputs. In this study, we investigated the uncertainty in stream width and depth to demonstrate the input of the conceptual representation of the watershed on stream flow and sediment transport. The SWAT (Soil and Water Assessment Tool) was utilized to simulate flow and sediment transport. Model results showed that model performance did not vary significantly with stream dimensions and that uncertainty is watershed dependent and not specific to models or regions. The results have implications to model developers when selecting complexity of model components and in determining model uncertainty.

Technical Abstract: Hydrologic modeling outputs are influenced by how a watershed system is represented. Channel routing is a typical example of the mathematical conceptualization of watershed landscape and processes in hydrologic modeling. We investigated the sensitivity of accuracy, equifinality, and uncertainty of SWAT modeling to channel dimensions to demonstrate how a conceptual representation of a watershed system affects streamflow and sediment modeling. Results showed that the amount of uncertainty and equifinality strongly responded to channel dimensions. On the other hand, the model performance did not significantly vary with the changes in the channel representation due to the degree of freedom allowed by the conceptual nature of hydrologic modeling in the parameter calibration. Such findings demonstrated that good modeling performance statistics do not necessarily mean small output uncertainty, and partial improvements in the watershed representation may neither increase modeling accuracy nor reduce uncertainty. We also showed that the equifinality and uncertainty of hydrologic modeling are case-dependent rather than specific to models or regions, suggesting great caution should be used when attempting to transfer uncertainty analysis results to other modeling studies, especially for ungauged watersheds.