The Möhne Dam and Reservoir

The Möhne Dam and Reservoir was put into operation in 1913. At the time, it was the largest dam and reservoir in Europe, and it still covers more than 25 per cent of total reservoir stor-age capacity in the Ruhr river basin, serving as an important tool for controlling the flow re-gime of the River Ruhr. Its gravity masonry dam is 650 metres long and up to 40 metres high, and the reservoir has a storage capacity of up to 134.5 million cubic metres of water.

The water discharged from the reservoir as a result of normal operation is used to generate electricity in a power station located below the dam (main power station). Water duty depends on water quantity management requirements along the Ruhr. While power generation is primarily a side benefit, it supports overall CO2-free energy production. From the main power station, the water flows into a compensating reservoir, from which a controlled amount of water is discharged daily into the lower Möhne river via a smaller, secondary power station. The power stations are operated by the company Lister- und Lennekraftwerke GmbH in Olpe, a 100 per cent subsidiary of the Ruhrverband.

If the main power station malfunctions or exceeds its capacity, water can be discharged via two bottom outlet units with two independent bottom outlets each. The outlets of each unit are equipped with an annular valve to enable direct regulation of water discharge, and a gate valve witha conical jet. All four bottom outlets lead to the compensating reservoir.

The crest of the dam contains 105 outlets with a total length of 262.5 metres as a flood spill-way. As these outlets are evenly distributed over approx. three fourths of the crest’s length, an overflow makes the dam appear almost entirely flooded. The downstream side of the dam has a rough surface with protruding rocks to effect partial energy dissipation of the overflow-ing water. The bulk of the energy dissipation takes place in the compensating reservoir, which serves as a stilling basin. Moreover, larger volumes of water can be discharged from the compensating reservoir via a fish belly flap gate at the secondary power station.

At the end of the tailback, i.e. where the River Möhne and the River Heve flow into the reser-voir, two preliminary reservoirs where constructed when the Möhne Dam was first built. The two fixed weir preliminary dams provide for a relatively constant water level, thus helping to avoid swamp formation in the reservoir’s shallow inflow area. Moroever, they create a water body separate from the main reservoir with its own specific hydrobiological conditions, thus serving an important function in terms of water quality management.