In naturally dry regions such as southern Alberta, rivers provide a critical supply of water. Ever increasing human demands on this precious resource have natural consequences and limits. It is urgent that we understand what flows are needed to keep rivers healthy and functioning. Instream Flow Needs (IFN) are streamflows required to be left flowing in the channel to preserve river function.

Our demand for river water is highest during the growing season for irrigation agriculture, but continues year-round to supply ever-increasing domestic and industrial uses. For more than 100 years we have engineered dams and diversion systems to utilize river flows in the South Saskatchewan River basin. We store spring flood water in reservoirs to supplement lower summer flows to use later downstream and to dilute waste effluent year-round. As a result, we have substantially altered natural flows and triggered a wave of downstream ecological effects on river health; involving everything from channel form and wildlife habitat to water chemistry.

Concerns about the effects of declining river flows on water quality and fish in southern Alberta led to assessment of instream flow needs beginning in the early 1970s. These IFN assessments initially identified a single minimum flow required to dilute pollution and achieve acceptable water quality, known as an Instream Objective (IO).  This spurred improvements to wastewater and runoff management by municipalities and industry. 

IFN assessment evolved through the 1980s to consider not only base flows that would ensure adequate temperature and oxygen levels for fish survival during low flow periods but also a pattern of flows that would maintain suitable habitat for individual fish species at various stages in their life cycle. These fish rule curves, developed using the Tennant or Tessman method, became a consideration in making decisions about new water licenses primarily in headwater rivers and streams.

Declining poplar forests along prairie rivers led to research in the 1980s and 1990s that linked dams with seedling failures. These trees time their seed release to have seedlings sprout on wetted river banks high enough to escape being washed away and low enough for their roots to keep contact with the gradual retreat of the water table. After high spring floods, the Oldman Dam (built in 1991) has been operated to gradually ramp flows down to encourage seedling survival.

The conservation value of natural stream flow variability became widely recognized in the late 1990s. An integrated IFN for fully protecting the aquatic environment was defined in the 2000s to inform water management planning within the South Saskatchewan River Basin. It integrates seasonal requirements for water quality, fish habitat, riparian vegetation and channel maintenance processes – all key attributes of river health.  The resulting flow regime would amount to about 80% of natural flows during times of moderate to high flow and natural flows during times of low flow.

Unfortunately, when these fully protective IFN are compared to what is actually allowed to flow in lower reaches of our basin, the conclusion is that our river health is in a state of long term decline due to over allocation. Extensive scientific assessments of aquatic and riparian condition confirm this.

The South Saskatchewan River Basin Water Management Plan (approved 2006) acknowledged this dire situation by closing the Bow, Oldman and South Saskatchewan River Sub basins to new water allocations and setting a Water Conservation Objective (WCO), defined under Alberta’s Water Act (2000) as the amount of water necessary for the minimum protection of a natural water body or its aquatic environment.  WCO for main stem reaches has been somewhat arbitrarily set at 45% of natural flow or the already defined minimum Instream Objective (IO) +10%.  This WCO, although woefully inadequate for protecting river health, is at least a recognition of a danger threshold. Unfortunately, we already fail to meet WCO during the growing season in dry years like 2021.

For our rivers to continue to support us and the whole ecosystem, we need to recognize our natural limits and stay in balance with ecosystem function. The signs are clear that we have already crossed the tipping point.  Our river is over allocated based on historic flows and climate change will only worsen the situation. We need to prioritize the value of at least conserving what is left of instream flows and recognize that we have reached the natural limit of our water supply and plan accordingly.

Resources:

Alberta Environment (June 2003). South Saskatchewan River Basin Water Management Plan Phase Two: Background Studies: finding the balance between water consumption and environmental protection in the SSRB. (here)

Lalonde K. et al. 2005. Southern Alberta’s Watersheds: An Overview. Prairie Conservation Forum Occasional Paper Number 5. (here)

Alberta Government (August 2006).  Approved water management plan for the South Saskatchewan River Basin (Alberta). (here)

Alberta Environment (June 2007). Aquatic and Riparian Condition Assessment of the South Saskatchewan River Basin. (here)

Bow River Basin Council (2010). Bow River State of the Watershed Report Summary (here)

Oldman Watershed Council (2010). Oldman River State of the Watershed Report Summary (2010) (here)

Alberta Government (2014). South Saskatchewan Region Surface Water Quality Management Framework: for the main stem Bow, Milk, Oldman and South Saskatchewan Rivers (Alberta). (here)

Basin Advisory Committees for the Bow River, Oldman River, Red Deer River and South Saskatchewan (sub-basin) River (2018). Review of the Implementation of the Approved Water Management Plan for the South Saskatchewan River Basin. Available (here.)

Harwood A.J, D. Tickner, B.D. Richter, A. Locke, S. Johnson and Xuezhong (May 2018). Critical factors for water policy to enable effective environmental flow implementation. Frontiers in Environmental Science 6, Article 37. 7 pp.

Alberta Environment and Parks.  (February 2019).  Surface Water Allocation Directive. (here)

Poff, N. L., Allan, J. D., Bain, M. B., Karr, J. R., Prestegaard, K. L., Richter, B. D., Sparks, R. E., & Stromberg, J. (1997). The natural flow regime: A paradigm for river conservation and restoration. BioScience, 47(11), 769-784. https://doi.org/10.2307/1313099