Water flow and flow regime in watercourses

In principle, Switzerland has a large water supply that depends on natural factors such as weather conditions or glaciation. However, the volume of water in watercourses is influenced by hydropower production in many areas (residual flow, hydropeaking). In the future, water availability will be limited regionally during dry periods as a result of climate change. The FOEN is monitoring the water flow and flow regime of Swiss bodies of water.

Seasonal variations

The water flow in bodies of water is influenced in the short and long term by weather conditions, while individual flows are subject to huge seasonal variations. The FOEN illustrates and evaluates the state of and changes in the water flow with indicators.

Evaluations of current situations and flood warnings

To monitor changes in the water levels and flows in Swiss rivers and lakes, the FOEN operates a large monitoring network. Cantonal measurements and current FOEN data provide the bases for evaluating the current state of Swiss rivers. The data are used for various planning activities, waterbody protection measures, water management, flood protection efforts and navigation.

The evaluations are incorporated in various forecasting products, such as flow forecasts, the hydrological news bulletin, weekly forecasts, flood warning maps and federal natural disaster bulletins.

In addition, the FOEN operates a network of hydrological study areas. The goal is to monitor long-term changes in the water regime in the most near-natural catchment areas possible in Switzerland's various climate regions. The FOEN provides an overview of the discharge, water levels and water quality for Swiss bodies of water in the Hydrological Yearbook of Switzerland.

The influence of hydropower use

Changes in water flow are not only caused by natural variations, but also human influences. The use of hydropower influences the water volume (residual flow, hydropeaking). In watercourses, discharges downstream from power plants can fluctuate daily. During hydropeaking, the water level, flow speed and breadth of the river change within a short period of time.

In addition, there are hardly any rivers with a natural flow regime in Switzerland as a result of regulated flows downstream from lakes or river power plants.

Residual flow map

The FOEN's residual flow map shows where water is withdrawn from rivers and streams in Switzerland, what it is used for, how much remains in the river at specific points, and where water withdrawals are causing ecological problems. It shows 1,488 withdrawals. Most of these withdrawals (1,406) are used for hydropower. Of these, 1,262 are presumed to be extremely relevant from an environmental perspective, since the various withdrawn quantities account for more than 50% of the average low flow volume of a watercourse. The map provides a preliminary survey of the application of residual water provisions.

Alpine rivers downstream from storage power plants are particularly affected by changing flow rates all the way up to their mouths in Pre-Alp lakes. In addition to electricity production, water is also withdrawn from bodies of water for irrigation or cooling.

Hydropeaking: Remediation required by 100 power plant installations

At the end of 2013, the cantons submitted their surveys of ecological damage in bodies of water to the federal government. Based on the FOEN's analysis of these interim reports and the planned mitigation efforts, around 100 power plant installations need to be remediated to eliminate the hydropeaking problem.

The FOEN had previously commissioned several baseline studies to illustrate the importance and impacts of hydropeaking. An overview of the hydropower plants causing hydropeaking revealed that around 1,000 km of watercourses are influenced by it. The most affected are the Rhone River up to Lake Geneva, the Rhine River up to Lake Constance, and the Ticino.

Consequences of climate change on the water regime

Climate change affects the entire water cycle. Surface and underground waters are equally exposed to changes in water quantity and quality. This has direct repercussions on hydropower, water supplies, urban drainage, navigation, agriculture, ecology and water-related natural hazards.

Further information

Last modification 24.04.2019

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