Development of a tool for the estimation of spatially distributed recharge – Application to the Bécancour watershed (Centre-du-Québec)

Guillaume Meyzonnat, Marie Larocque, Sylvain Gagné

In the proceedings of: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Regional Aquifer Characterization III

ABSTRACT: Often associated with large uncertainties, recharge evaluation is nevertheless a crucial information in hydrogeology. If the estimation of the mean annual recharge rate at the watershed scale is relatively accessible with a water balance method, the estimate of spatially distributed recharge requires much more data and computational efforts. Spatially distributed recharge can greatly increase the quality of hydrogeological investigations such as numerical modeling or vulnerability mapping. The objective of this work was to develop a simple tool to estimate spatially distributed recharge that only requires data that are usually available. This tool is applied to the lower part of the Bécancour integrated water management area (2 924 km2). The model estimates surface infiltration by calculating a spatial water balance with a 500 m x 500 m grid resolution. In this water balance, the daily available water from rain or snowmelt comes from vertical inflows generated by the Centre d'expertise hydrique du Québec (CEHQ) for the Bécancour area. Potential evapotranspiration is calculated from mean daily temperature and solar radiation. The temporal evolution of runoff is calculated according to the Runoff Curve Number (RCN) method adapted for southern Quebec. Most parameters required in this tool are dictated by the RCN method. Slope, land use and soil type data come from a database available for the area. A limited number of parameters (soil freezing and moisture conditions, percentage of water that effectively infiltrates daily into the soil) require calibration. The tool was developed in Visual Basic and allows daily water balance calculation over a duration of 20 years and for 4 000 cells. The model was calibrated on a sub-basin of the Bécancour area (2 300 km2) to minimize the error between calculated runoff, evapotranspiration and the seasonal evolution of the infiltration, with: 1) simulated results of the MOHYSE hydrological model and 2) river gauging station data. The calibrated parameters were then used throughout the study area. The model estimates the average potential recharge to be 177 mm/yr. Potential recharge, evapotranspiration and runoff respectively represent 20%, 30% and 50% of the vertical inflows. Estimation of the spatially distributed recharge were used to build DRASTIC vulnerability map for the bedrock aquifer. Distributed recharge is also used in a numerical groundwater flow model for the Bécancour area.

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