Groundwater and Our Alluvial Aquifer
Everyone is familiar with surface water in a watershed, since it is easily observed in rivers, streams, lakes and ponds. Our Elbow River, Bragg Creek, Elbow Lake and Springbank Creek – all are available to us to see, and enjoy. Just as important, however, is the water below the ground, which we cannot see. Groundwater, is found nearly everywhere under the land surface in the pores and fractures of all materials, clay, silt, sand, gravel, and rock. It is critically important as a source of drinking water and water for agriculture and other industry in many parts of the world, including our Elbow River watershed. Groundwater can flow through water-bearing formations called aquifers, which are geological units of permeable rock or loose material that can store and transmit water in significant quantities. In the Elbow River watershed, our alluvial aquifer is the porous bed of river-deposited sand and gravel that is adjacent to, and hydraulically connected with, the Elbow River. Because of this connection, water is continually exchanged between the aquifer and the river, resulting in water quality that is similar. The water quality of both can then be negatively impacted by land use and resulting runoff throughout the watershed; however, given the that the aquifer is a potential conduit for contaminants, protection of the aquifer is of critical importance to the health of the river and ecosystem. .
The Elbow River alluvial aquifer refers to the shallow, unconfined aquifer made of gravel and sand as outlined on the attached map. The surface of the mapped aquifer represents just over five percent of the 1238 square kilometre watershed (about the size of Yoho National Park). This aquifer was formed by alluvial deposition and is generally very permeable and highly hydraulically connected to the Elbow River. The upper surface of the unconfined aquifer is the water table, with the other surfaces bounded by typically less permeable materials. The alluvial aquifer is characterized by significantly higher hydraulic conductivity than the adjacent uplands. This means that water flows more readily through this area. These adjacent uplands form the lateral limits of the extent of the floodplain and are assumed to be the boundary of this unconfined aquifer. Groundwater from the alluvial aquifer flows into the river and river water flows into the aquifer alternately, depending on the height of the water table and the stage of the river . Thus, there is considerable groundwater-surface water interaction along the Elbow River. The floodplain and riparian areas of the Elbow River lie overtop of the alluvial aquifer.
Below is an aerial view of the lower Elbow River watershed (Bragg Creek to the city of Calgary), with the alluvial aquifer outlined in yellow. The alluvial aquifer is narrow in the upper watershed (above Bragg Creek), then becomes nearly two kilometres wide as it spreads across the prairie. Click here for a map of the alluvial aquifer within Rocky View County.
- Development on the alluvial aquifer can be impacted during periods of high water flows in the Elbow River such as during spring runoff or freshet, or during other flood events. This is due not just to flooding of the river itself, but to the fact that the water table rises in the entire alluvial aquifer due to recharge and the effective movement of water as described previously. Damage from high water in these flood prone areas can be very costly for homeowners, businesses and ultimately taxpayers.
- Land use, whether it be urban, rural residential, commercial or agricultural in nature, has the potential to negatively affect groundwater quantity and quality, and Elbow River water quality. For example, road salted-icing chemicals, effluent from on-site septic systems , detergents, fertilizers and other agricultural chemicals, animal waste, hydrocarbons and other pollutants have the potential to flow into the Elbow River once they enter critical aquifer recharge areas. To help protect water quality in the Elbow River watershed, development and other land use activities should be restricted in these aquifer zones. If permitted, they should be carefully managed and their impacts mitigated where practical. Proper planning and management will benefit not only the aquatic environment, but downstream water users as well. The Elbow River supplies 45% of Calgary's drinking water and the cost to treat this water rises as water quality degrades upstream.
- Protecting the alluvial aquifer also protects the floodplain and riparian areas of the Elbow River; this is important for both water quality and wildlife habitat.
Prepared by T. Grasby
What are some of the negative impacts that have occurred already due to development on the Elbow River alluvial aquifer?
- Septic systems on the alluvial aquifer in the Hamlet of Bragg Creek have in the past contaminated the adjacent groundwater and over 50% of resident's water wells with coliform bacteria (an indicator of pathogens), making the water unsafe to drink. Some of this contaminated groundwater eventually flows into the Elbow River and may lower river water quality.
- In 1995, 2005 and 2013, there was significant flood damage in both the Hamlet of Bragg Creek and Redwood Meadows, with the majority of basements experiencing some flooding. This was caused, in large part, by rising water tables in the Elbow River alluvial aquifer as the river rose during these high flow events.
- Flooding is a natural watershed process that provides benefits to riparian areas and ecosystems, and more floods can be expected in the future. Economic losses and infrastructure damage can be managed by making “room for the river” and avoiding development in the flood prone areas, or those areas consisting of channel migration zones, riparian areas within them, and the alluvial aquifer.
Past and present research at the University of Calgary focuses on groundwater/surface water dynamics in the alluvial aquifer and the Elbow River, since contamination of this shallow aquifer can directly affect river water quality. For information on recent U of C research in the Elbow River watershed, click here.