Surface-subsurface flow analysis of the Raquette River watershed (Vaudreuil-Soulanges, Quebec, Canada)

English Abstract:

Located 50 km west of Montreal (Quebec, Canada), the Raquette River watershed covers an area of 133 km² and its main river is 34 km long. Groundwater resources are under pressure in this region, notably due to an important population increase in the past decades. These changes are expected to impact the hydrology of the entire watershed. The main objective of this research was to evaluate the relative contribution of surface and subsurface flow to the Raquette River using field data and the fully-coupled MikeSHE model. Upstream, the river flows through an agricultural zone on a thick clay deposit, where drained soils cover a sandy aquifer in a major bedrock depression. Towards its center, the river flows over the bedrock between Mount Rigaud and the Sainte-Marthe Hill (in the Sainte-Marthe channel). The river flows downstream over clay deposits and then over fluvioglacial sandy deposits towards the Ottawa River. Groundwater recharge is limited to Mount Rigaud and the Sainte-Marthe Hill. Low-flow measurements have shown that the main groundwater contribution to the river takes place on a 3 km long segment located in the Sainte-Marthe channel, where the river gains 35% of the flow measured at the outlet. The fully-coupled model is built with 10 layers and 165 870 cells (100 m x 100 m) and is run with a daily time step over two hydrological years. The spatial distribution of geological units in the surface layer was used to represent the spatial heterogeneity of parameters, such as the Manning roughness coefficients and the infiltration fractions. The calibrated model simulates adequately the measured heads, as well as the spatially variable flow rates and river-aquifer exchanges. The model shows that the stratigraphy and hydrogeological parameters in the Sainte-Marthe channel, as well as recharge rates over the Sainte-Marthe Hill control groundwater inflows to the river. Results from this study are also used to estimate the impacts of land use changes on the watershed hydrology.