A system dynamics based socio-hydrological model for agricultural wastewater reuse at the watershed scale

Abstract

The purpose of this study was to develop and verify a socio-hydrological model using system dynamics (SD), thereby combining a deterministic conceptual hydrological model and a social model incorporating population, land use, economics, technology, and policy dimensions. Applied to a central South Korean watershed where wastewater is reused for paddy irrigation, the present model was verified in terms of structure and behavior. Structural validity was confirmed when expected simulation sensitivity and consistency criteria were met during behavior sensitivity and extreme conditions tests. The model's behavioral validity in predicting hydrological processes including evapotranspiration, stream flow, and groundwater level, was also confirmed as the calibrated model performance during the validation period showed good agreement with those of the Soil and Water Assessment Tool (SWAT) model, validated for the study watershed, as well as observed groundwater levels. The values of Nash-Sutcliffe efficiency (ENS), percent bias (PBIAS), and R2 which compared model results with those of the SWAT model were 0.77, 3.0%, and 0.79, respectively, for the evapotranspiration, and 0.69, 1.4%, and 0.75, respectively, for the stream flow, while the generated and observed groundwater levels exhibited a linear relationship with an R2 value of 0.70. The validated model indicated that urbanization within the study watershed could lead to increased stream flow and greater wastewater reuse. Instream flow regulation led to a decrease in stream flow tied to a lower base flow, and a decrease in social benefits associated with a decline in wastewater reuse. An assessment was made of the SD-based socio-hydrological model's usefulness when acting as an element of an integrated framework in providing a better understanding of small-scale socio-hydrological systems' interactions and the underlying causes of general trends and problems. SD-based socio-hydrological modeling was deemed a suitable decision-support framework for designing water resource policies contributing to successful integrated water resources management practice.