Status of Flow on the Bow

Current water management practices have imposed significant changes to the Bow River's natural flow regime, and have left their mark on the watershed. While some information has been gathered to understand these impacts, more research is needed.

According to the Organization for Economic Co-operation and Development (OECD), a watershed is considered to be "stressed" when greater than 40 percent of the available renewable water is used by humanity for industrial, agricultural, or other uses. On average, 46 percent of the average annual natural flows are extracted from the river.On the Bow River, we extract (on average) 46 percent of average annual natural flows. In the lower stretches of the Bow, the situation is more dire: In average years we extract 68 percent of the average annual flows, and in low flow years, the percentage of flows diverted reach 80 to 90 percent. The environmental repercussions are significant. The problem is compounded since demands on the river are greatest during the summer, once the spring runoff flows have subsided.

In a study conducted in 2003, the government identified the Instream Flow Needs (IFN) for the Bow River. Determining a river's Instream Flow Need applies the most up-to-date science to conserve river ecosystems. IFN determinations are founded on the "natural flow paradigm" that links the health of a riverine system to its natural range of flow variability to sustain the ecological processes and diversity within the system.

According to the Alberta government, alterations to the river's hydrological regime from hydropower dams and irrigation diversions are having a negative impact to the river's ecological health. In some places this has reduced the diversity of plants and riparian and wetland areas, and has hampered the regeneration of cottonwoods and other trees.

A 2004 study completed by the Alberta Government evaluated riparian health at 21 stations along the length of the Bow River. The report found that 29 percent of the sites were considered "healthy," 48 percent of the sights were considered "healthy but with problems" (meaning there was some impact to the riparian health), and the remaining quarter of sites were considered "unhealthy" (meaning that the riparian zone was non-functioning).

An Unhealthy Stretch of River

In the lowest stretches of the Bow, there are many factors causing the problems for the riparian zone. But for river reaches below Calgary, the two most significant impacts come from irrigation diversions and dam operations.

In most years, we do not meet the Instream Flow Needs of the lowest third of the river - most significantly in the lowest 175 kilometres below Bassano Dam. Here, the health of the aquatic environment is believed to be following a long-term declining trend.

This lowest reach of the Bow River (from Bassano Dam to Grand Forks) is characterized by higher than acceptable levels of nutrients (e.g. phosphorus, nitrogen) and is shallow due to upstream extractions. The South Saskatchewan River Basin (SSRB) State of the Basin report described this section as "degraded" and among the worst of all river reaches in the SSRB.