Definitions from the North American Lake Management Society (NALMS):

Natural Flow - The rate or quantity of water moving past a specified point on a natural stream from a drainage area where there are no effects from stream diversion, storage, import, export, return flow, or change in consumptive use caused by man-controlled modification to land use. Natural flow rarely occurs in a developed county.

Regulation - (Hydrology) The artificial manipulation of the flow of a stream.

In many rivers, the flows we record and see at any given time may not be "natural". As we have developed, we have diverted water for irrigation and agriculture, used it in our cities and industries, and contained it in reservoirs for storage and power generation. These uses of water can affect when and how much water we measure in a river at any given time. In heavily developed areas of the province we refer to the water measurements as "regulated". Natural flows can still be recorded in rivers that are relatively unaffected by our development and infrastructure. In Alberta these rivers tend to be in the mountains or in the northern part of the province where there are fewer people and less intense development.

The Red Deer River is an example of regulated flows in Alberta. The construction of Dickson Dam in 1983 had a noticeable effect to the flows in the Red Deer River as this chart shows.

The dam operations have increased seasonal flows the winter and decreased flows in the late spring and early summer. The dam stores water during high flow periods in spring and summer and releases water in the fall and winter when it is needed for a variety of uses.

Historically the flows in the Red Deer River could drop to as low as three cubic metres per second in the fall and winter months. This was not enough water meet the agricultural, municipal and industrial demands for water. The competing demands could put considerable strain on the river and the life it supported. The result is a more beneficial and regulated flow regime.

Another more visible example of flow regulation is in the Peace River. In the mid-1960s, W.A.C. Bennett Dam was constructed by B.C. Hydro on the Peace River upstream of Hudson Hope, B.C. Bennett Dam is operated to generate hydroelectric power. The resulting changes to the flow regime of the Peace River is shown at the gauging site near the Town of Peace River.

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Again, the major impact to river flows is in the seasonal distribution of water. The high flows from April to July are captured and released in consistently over the remainder of the year. At Peace River, the net result is that summer flow rates and volumes after the construction of the dam are half of what they were before the dam began operations. Similarly the winter flows can be up to three times higher than before Bennett Dam began operations.

Other factors that can cause a rivers flows to become regulated include:

• water for irrigation, agriculture and industry;
• water for municipalities;
• water for other uses like fish farms and golf courses.

In southern Alberta, where water use is the most intense, the effects of the cumulative uses is a significant factor in the amount of regulation that a river experiences.

We can calculate the "natural" flows for the river by eliminating or reversing the effects of the reservoir and other uses on the system. This process is called "naturalization". In Alberta we carry out extensive naturalization of river flows, especially in the southern part of the province. The natural flows are required to make operational and environmental decisions on how best to use our water.