What is the Elbow River Alluvial Aquifer?
Why should future development be limited or carefully managed on the Elbow River Alluvial Aquifer?
What are some of the negative impacts that have occurred already due to development on the Elbow River Alluvial Aquifer?
What is the Elbow River Alluvial Aquifer?
The Elbow River alluvial aquifer refers to the shallow, unconfined aquifer made of gravel and sand as outlined on the attached map. It represents just over 5% of the entire land area of the Elbow watershed, which is 1238 km2 in total area. 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 and the other surfaces are bounded by less permeable materials. The alluvial aquifer is characterized by significantly higher hydraulic conductivity then the adjacent uplands. These adjacent uplands form the lateral extent of the flood plain 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. There is considerable groundwater - surface water interaction along the Elbow River. The floodplain and riparian areas of the Elbow River fall on 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 2 km wide as it spreads across the prairie. Click here for a map of the alluvial aquifer within the Municipal District of Rocky View. For a map of the Elbow River alluvial aquifer within the Bragg Creek area, click here.
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Why should future development be limited or carefully managed on the Elbow River Alluvial Aquifer?
- Developments on the alluvial aquifer can be negatively impacted during periods of water flow in the Elbow River as the water table rises in the entire alluvial aquifer due to high hydraulic connectivity. Damage from flooding can be very costly for homeowners and governments.
- Any land use on the aquifer has the potential to negatively affect the groundwater and the Elbow River water quality, since they are hydraulically connected. For example road salt, septic effluent, soap, fertilizers, animal waste, oil and chemicals have the potential to flow into Elbow River once they are in the ground over the alluvial aquifer. If we want to protect the Elbow River's water quality, we should limit or carefully manage development on the alluvial aquifer. This would be of benefit to the aquatic environment and to downstream users of the water. The Elbow River supplies 45% of Calgary's drinking water and the cost to treat this water rises as water quality deteriorates.
- Protecting the alluvial aquifer also protects the floodplain and riparian areas of the Elbow River, which is important for both water quality and wildlife habitat.
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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 contaminated the adjacent groundwater and over 50% of resident's water wells with total 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 deteriorate river water quality.
- During 2005 and 1995 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 by rising water tables in the Elbow River alluvial aquifer. This can be expected to recur, but can be avoided with new development by not building on the alluvial aquifer.
Past and present research at the University of Calgary focuses on the groundwater-surface water dynamics in the alluvial aquifer and the Elbow River
because contamination of this shallow aquifer will directly affect river water quality. Therefore, land use in the flood plain is of more importance than land use in the uplands. For more information, visit our University of Calgary - Environmental Science Research page.
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© 2007 Elbow River Watershed Partnership
Elbow River photo courtesy of Jack Ng for The Weaselhead Glenmore Park Preservation Society
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