Germany is phasing out coal. In some parts of the country, coal production has long since ceased. What will become of the former opencast mine? Tractebel Hydroprojekt accompanies the recultivation of the post-mining landscapes on the state border between Saxony and Brandenburg. The region on Lake Sedlitz is to become an attractive holiday and residential area. Since the end of 2019, the work on the weir structure has been completed. With the completion of the Sielbauwerk in January 2021, another important milestone has been reached.
The recultivation of the lignite opencast mining area in the Lusatian coalfield creates the Lusatian chain of lakes northeast of Senftenberg. Its catchment area covers around 200 square kilometres.
Tractebel Hydroprojekt has been supporting the project since 2014: On behalf of the Lusatian and Central German Mining Management Company (LMBV), the hydraulic engineering experts are planning a conductor system to connect the chain of lakes from the future Sedlitzer See to the Schwarze Elster. They also monitor the construction of the measure.
Demanding planning and construction task
The demanding construction project benefits from the expertise of the experienced planners of Tractebel. From the shut-off system, formerly part of the artificial channel with seven meters bottom width, a two-field weir structure, and a two-field siel structure are completed. Until the arrester system is put into operation, a trough structure, a wildbridge, the associated open-air facilities, and around 5.8 kilometres of farm roads in the surrounding area will be newly laid out.
Weir structure ensures sustainable management
The weir structure was completed about 13 months ago and the inlet of the conductor system of Lake Sedlitz ensures the sustainable management of the chain of lakes. Its level system determines the discharge quantities. At the same time, the water quality can be measured here. The weir consists of two fields with five meters width each and has double stroke shooters as closures. With them, the water discharge from the Sedlitzer See can be regulated. The static support system of the closures was designed as a folding unit and is made of structural steel with passive corrosion protection. Rising spindles with electric drive take over the adjustment movement. They are accessible from the service.
The fact that the system is also functional in winter is ensured by a sealing surface accompanying heating and an air bubble system. The upper water level in Lake Sedlitz is regulated by automatic control. A new transformer station secures the power supply of the weir system. In the case of revision, i.e. for the inspection or repair of the closures, aluminium dam beams are used, which can be placed in front of the closures with the help of a so-called pliers beam and ensure dry access to the components. Outside the revision times, these dam beams remain in the newly built dam beam warehouse.
Siel building protects Rainitza and Sedlitzer See from flooding of the Black Elster
The siel building secures the deductant system against backwaters during flooding in the Black Elster. It is designed as a so-called beam weir, in which the upper area of the weir fields is each closed by a concrete wall transverse to the flow direction. The underlying "windows" can be closed with underflowable contactors. This prevents a backwater of the Black Elster in the feedwater system during flooding.
Drive blocks with electric drive take over the adjustment movement. They are accessible from the operating bridge. Many technical details are similar to the design of the weir structure: the field widths are five metres each and the static support system of the closures is made of structural steel with passive corrosion protection as a folding unit. Also a sealing surface-accompanying heating and an air bubble system are part of the equipment. Because of the same field widths, the aluminium dam beams of the weir can also be used at the siel.
The completion of the weir and siel structures marks an important milestone for the project, as they are an essential part of the conductor system. Next, Tractebel's experts will focus on the further construction of the artificial canal and the expansion of the existing Rainitza river.