Groundwater modeling including climate change scenarios for an ecohydrological study in Covey Hill, Québec

Jana Levison, Marie Larocque, Marie-Audray Ouellet, Lisa van Waterschoot

Dans les comptes rendus d’articles de la conférence: GeoMontréal 2013: 66th Canadian Geotechnical Conference; 11th joint with IAH-CNC

Session: Groundwater-Surface Water Interactions II

ABSTRACT: Groundwater is an important resource for human use in Canada for industry, agriculture and potable water supply, but it is also critical to sustain various ecosystems. For example, sensitive flora and fauna can inhabit and depend on groundwater discharge areas including springs. It is important that groundwater-surface water interactions are characterized for various climate scenarios to protect sensitive groundwater-dependent ecosystems and to anticipate any climate change related impacts. Groundwater modeling is an important part of ecohydrological studies because it can be used to simulate past, current and future conditions. The aim of this research is to explore the effects of climate change on a groundwater-surface water interacting system that supports a fragile ecosystem to ultimately inform ecological conservation measures. The research site is the 175 km2 Covey Hill Natural Laboratory which is located on the Québec-New York State border in the Châteauguay River watershed. At various locations within the Natural Laboratory there is continuous monitoring of groundwater levels and river flows. Covey Hill is an important recharge zone for the sandstone aquifer. Endangered stream salamanders reside in groundwater discharge zones on the face of the hill. Two hydrogeological models were constructed to represent flow at the site. First, a transient, three-dimensional, finite difference model was developed using MODFLOW software to simulate site-wide groundwater flow. Second, a smaller-scale, surface to subsurface model was developed using HydroGeoSphere software to represent detailed flow from mid-slope bedrock springs. This paper will focus on the larger-scale (MODFLOW) model which was used to: 1) observe groundwater flow under current climate conditions; 2) quantify water dynamics in response to climate change using 10 scenarios from the Canadian Regional Climate Model (for 1971-2000 and 2041-2070 time periods); and 3) simulate past hydrogeological conditions (100 years). Results show that future predicted changes on groundwater recharge will impact flow to groundwater springs and seeps inhabited by the endangered salamanders. For example, some springs are expected to flow more days per year in the future, but the periods of flow are shifted which could be critical for the salamander populations. Using these results and ecological modeling that was conducted simultaneously by collaborators, measures to mitigate the impacts of climate change on the ecohydrology of Covey Hill and other similar locations were made to local water managers and conservationists. This study highlights the challenges related to and importance of conducting ecohydrological climate change-based studies at various scales and using numerous scenarios to help capture uncertainty of future flows.

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