Significance of Groundwater Flow Processes in Hydrologic Models: A Model Comparison Study in a Small Watershed

Groundwater, as the largest component of available freshwater on Earth, provides support to the global hydrologic cycle and helps maintain healthy aquatic ecosystems. While a wide spectrum of hydrologic models of varying complexities are available to simulate surface water/groundwater flow, users of such models may question what level of complexity needs to be considered within a model to achieve project objectives.

Five integrated hydrologic models with increasing levels of subsurface complexity are developed using HydroGeoSphere (HGS) to highlight the significance of groundwater flow processes on surface water flow within the Alder Creek Watershed (ACW), a small watershed in southwestern Ontario, Canada. High-resolution topographic information, land cover representation, temporal precipitation records, evapotranspiration and wellfield operation data are used to capture the temporal and spatial variability of watershed behavior. Estimated streamflow records at three gauging stations are compared with observed records, while the impact of municipal well operations is also examined for both streamflow and groundwater flow.

Overall, our research reveals that: 1) models with different subsurface representation yield dramatically different results and the model with the most detailed representation of the subsurface yielded the best results; 2) shallow subsurface characterization is critical for surface water-groundwater interaction and streamflow estimation; 3) municipal well operations can greatly affect both surface water and groundwater flows. Consequently, more attention is required to consider the impact of the municipal well operations in hydrologic model construction, as well as streamflow and groundwater flow monitoring for the improved management of watershed fluxes and municipal wellfield.