Development of a tool for the estimation of spatially distributed recharge – Application to the
Bécancour watershed (Centre-du-Québec)
Guillaume Meyzonnat1, Marie Larocque1, Sylvain Gagné1
1
Département des sciences de la Terre et de l’atmosphère et Centre de recherche pour l’étude et la
simulation du climat à l’échelle régionale, Université du Québec à Montréal, C.P. 8888, Succursale CentreVille, Montréal (Québec), Canada, H3C 3P8
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 maps for both the granular and bedrock aquifers. Distributed
recharge is also used in a numerical groundwater flow model for the Bécancour area.