URBANIZATION AND THE GROUNDWATER SYSTEM SUPPLYING THE WAGNER NATURAL AREA (EDMONTON, ALBERTA)

The Wagner Natural Area (WNA) is a 230 hectare conservation area on the outskirts of the City of Edmonton, Alberta. It is renowned for its mineral-rich fen(s) made up of wet meadows, marl ponds, black spruce, and tamarack forest. For such a small area the overall biodiversity in the WNA is unusual, and the WNA owes its diverse array of flora and fauna to groundwater-fed calcareous springs that flow year-round and precipitate marl. Long-term stability of the natural groundwater flow regime in the vicinity of the WNA is crucial for the protection of this unique ecosystem.

Unfortunately the groundwater flow system around the WNA is under increasing pressure due to urbanization. It is fed by a near-surface (<100 m deep) aquifer made up of mixed Quaternary-aged materials. The WNA faces a dual threat: development in the recharge area that reduces infiltration could alter water levels in the WNA, and any contamination introduced into the flow system there could impact water quality in the natural area. Secondly, any development in the discharge area that lowers water levels (pumping, ditching, drainage, etc) could have a similar negative impact.

To better understand the groundwater flow system supplying the WNA and in particular, to identify the exact location of its recharge area, a three-dimensional numerical model of the groundwater flow system around the WNA was constructed. The model was calibrated using available water well data (levels, and hydraulic properties) from the study area. Particle tracking analysis was used to delineate the recharge area, and to study different development scenarios. Results showed that reducing infiltration in the recharge area has significant impacts on the flow system and water levels in the WNA. Additionally, preliminary modelling suggests that nearby alterations to the surface drainage in the discharge area could affect groundwater levels in the WNA.

These results are being incorporated into land use planning to protect the long-term integrity of the WNA groundwater flow-system.