Shift Change in Cottbus-Nord Opencast Mine
Over the next ten years a lake Cottbus Ostsee will be created at the gateway to Cottbus city. The water expanse of 19 square kilometres will be the largest lake in Brandenburg and Germany´s largest mine pit lake. The bed of the lake will be laid by the former Cottbus-Nord opencast mine. After more than 30 years lignite mining it closed in December 2015.
After the permitted reserves were mined from the mining field, according to the plan, a new phase of the Cottbuser Ostsee development will start. Lakes normally follow after opencast mines in Lusatia. Nothing is left to chance when designing the post mining landscape. Everything is planned in minute detail, and checked by the authorities and approved.
Preparation for Flooding
Before the water can take over, the lake bed and safe slopes have to be created. For this the south, west and northern slopes are flattened, so that the lapping lake waters do not erode the soil away. There will be earthworks to move soil within the future lake bed, so that at low water levels the minimum depth will still not be less than 2 metres.
We will build a flooding facility and prepare the connection of the lake to the water regime in the surrounding area.
Vibrators Compact the Eastern Shore
The lake's eastern shore, borders on the opencast mine's recultivated areas, these have been mostly afforested after coal mining. To stabilize this shoreline area which consists of dumped soil, so-called vibro displacement compactors are used.
Vibrating lances are inserted 30 to 50 meter into the ground. They produce fine vibrations and thus compact the loose dump sand.
New soil is constantly introduced, so that a resulting firm soil structure is produced. With the succession of such 'vibro columns' an underground dam wall or what is called a 'hidden dam'. It secures the soil in the shoreline areas.
Flooding with Spree River Water
As soon as the work on the lake bed and slopes are finished and the flooding facility is built, we can start with the flooding activities. It should all be completed by the end of 2018, meaning five to six years. The Spree plays an important role from its source near Bautzen it flows through the Lausitz and meanders on towards Berlin. The Spree River should provide 80 per cent of the waters for the lake. It will be diverted via the Hammergraben and flow through an underground pipe to the lake bed.
Water will only be diverted from the Spree River when the water level is high enough. This is predominantly in the winter months or when it floods in the middle of summer. Thus the ecological balance of the Spree does not suffer. We also consider the interests of the priority water users.
The Cottbuser Ostsee should have a volume of approx 126 million cubic meters water, as a portion will seep and drain away in the dry soils of the opencast mine dumps and slopes. For flooding purposes around 280 million cubic meters have been planned.
The Spree water will fill the lake significantly faster than the ground water that is rising again and with its neutral pH value has a positive influence on the water quality on the Cottbuser Ostsee.
Opportunities for Man and Nature
The Cottbuser Ostsee will provide opportunities for the region, especially for leisure activities and tourism. The southwestern to the northern shoreline zone is mainly planned for tourism.
The neighbouring municipalities can create beaches or build harbours and other recreational facilities. It can also be used for fishing.
Nature conservation is not forgotten: Islands with their diverse structures and shallow waters on the eastern shoreline have the potential to develop nature conservation relevant areas. In this area flora and fauna can flourish without major intervention from mankind.