Modeling coupled surface water - Groundwater processes in a small mountainous headwater catchment

- A coupled surface water-groundwater model is developed for a headwater catchment.
- Bedrock is considered permeable and recharge to bedrock is estimated.
- Outflow from the catchment through the bedrock is estimated at 2%.
- A range in bedrock outflow within 0-4% does not compromise model calibration.
- The study has implications for estimating cross-catchment groundwater flow.

SummaryHydrological models for headwater catchments have typically excluded deep groundwater flow based on the assumption that it is a negligible component of the water budget. This study tests this assumption using a coupled surface water-groundwater model to explore the potential contribution of deep groundwater recharge to the bedrock in a snowmelt-dominated headwater catchment (Upper Penticton Creek 241) in the Okanagan Basin, British Columbia. Recharge to the bedrock is estimated at ∼27% of the annual precipitation over the period 2005-2010, recognizing the uncertainty in this estimate due to data limitations, parameter uncertainty and calibration errors. A specified outward flux from the catchment boundary within the saturated zone, representing ∼2% of the annual water budget, was also included in the model. This outward flux contributes to cross-catchment flow and, ultimately, to groundwater inflow to lower elevation catchments in the mountain block. This modeling exercise is one of the first in catchment hydrologic modeling within steep mountainous terrain in which the bedrock is not treated as impermeable, and in which recharge to the bedrock and discharge to the surrounding mountain block were estimated.