The multiple aims of river and lake regulation

Any project aiming at regulating the water level or flow of a river or lake must account for the different objectives for the use of the watercourse: hydropower production, flood protection, waterborne traffic, recreational use, nature conservation and fish stock management. This adds up to a complicated balancing act.

Most of the on-going lake or river regulation projects were prepared and initiated as far back as the 1950s to 1970s. In those days, the primary goals were hydropower generation or flood protection, which did not leave much room for pursuing other objectives.

Today’s values are different, and aquatic environments and the recreational use of waters have received more attention in project development. For example, regulation is used to stop water levels from dropping excessively during dry summers – even if this means that hydropower production takes a hit. The upstream migrations of fish past power plants are also facilitated. Nevertheless, the situation often calls for balancing different objectives.

The fact that regulation results in different consequences in various sections of a river basin adds to the challenges. If a flood is imminent in Lake Näsijärvi, for instance, the situation can be alleviated by running more water through Tammerkoski rapids in Tampere. On the other hand, flood peaks downstream from Tammerkoski can be moderated by reducing the runoff. River regulation should be optimised for the entire river basin, and the flow control should be attuned to the hydrological conditions in the different sections of the lake and river system.