River flows can be highly variable, and are affected by natural changes in climate and seasonal weather patterns, as well as by human use and management of water, including dams and other infrastructure (such as weirs and canals).
River flow regimes are examined by Alberta Environment on a two-season basis:
An annual assessment is also reported, along with a ten-year average, which is an indication of potential long-term or cumulative stresses.River Flow Quantity Index (RFQI)
The River Flow Quantity Index (RFQI) is based on the assumption that a natural average flow regime can be expected to occur about 90 per cent of the time; this is indicated by a blue color on the index. During the other 10 per cent of the time, the river regime will be naturally at an “above average” or “below average” (green or yellow) state; however, these are still considered natural fluctuations and are expected from time to time.
However, there will also be some periods of time where the actual recorded flow of the river will be “outside of its normal natural range” and experience significantly higher or lower levels of flow. At this point we could expect to see ecological impacts to the existing aquatic ecosystem becoming more permanent, particularly if conditions are persistant and are not single-year or infrequent occurrences.
The condition of the River Flow Quantity Index is based on the seasonal and annual RFQI values (as reported by Alberta Environment):
This indicator is not designed to reflect real time flow data, and cannot specifically reveal the health of the ecosystem based solely on flow or quantity patterns.
Many aquatic communities depend on fluctuations that result from a variety of high and low flow periods. Ecological science generally recognizes that the maintenance and health of existing ecosystems and populations requires maintaining aspects of the natural flow regime, including fluctuations. An altered flow regime may not be “unhealthy” in the strictest definition, because it could still support a relatively productive river ecosystem.
Determining water quantity is also an important first step towards understanding other water-related issues, including fisheries and fish habitat, vegetation in both aquatic and riparian areas, biology and aquatic species, erosion and deposition, and river channel shape. And, significant and cumulative changes causing more frequent or sustained high or low flows may cause the river to evolve into a different ecological state with potentially different aquatic populations and riparian communities.
The longer term trend across the South Saskatchewan River Basin during the summer shows an increasing trend towards “stressed” or “reduced outside of natural”. For example, the Bow and Oldman Rivers are affected by flow regulation and water withdrawals in May to September (summer season) to support irrigation. The occurrence of long-term “stressed” rankings also indicates a cumulative human impact.
The following maps present different versions of the Alberta RFQI index.
Read more… about River Flows and Levels for the South Saskatchewan River Sub-Basin, as monitored by Alberta Environment.