Unceasing circulation of matter is ensured through constant maintenance, redirection and return to its original form. Dravske Elektrarne Maribor is taking every effort to preserve water’s natural characteristics by maintenance of the Drava’s reservoirs and embankments, ensuring living space for vegetation, wildlife and people, through well-planned environmental projects. Not only is their implementation important, but so is the manner of planning works that must be designed so that new ecological burdens are not placed on the environment.
The Črneče Bay or Dravograd Lake is one of the rare disappearing secondary marsh ecosystems with a large variety of plant and animal species and there habitats. The diversity of plant and animal species as well as the variety of marsh biotopes make it one of the ecologically most important wetlands in Slovenia. The rare ecosystem is the habitat of endangered animal and plant species and is a part of the Natura 2000 area. With restoration measures i.e. silt removal in the Črneče Bay we maintain a favourable conservation status of the bay and prevent that some areas of the bay would stay without water in times of low water levels of the river Drava.
Bay Tilkova mlaka
Within the framework of the ecological restoration of DEM reservoirs the cleaning of sediments was also foreseen for Tilkova mlaka in the reservoir of the HPP Vuhred. The area of Tilkova mlaka was heavily affected by silt and gravel deposits, created by the left tributary Suhi potok carrying enormous amounts of gravel to the bay Tilkova mlaka during heavy precipitations. The silting up also resulted from the transport of floating particles i.e. silt from the river Drava that deposited at the widened area. During operation of HPP Vuhred the water level oscillates by ca. 1 m. Before the cleaning, when the water level was low, the eastern part of Tilkova mlaka was absolutely dry, only the western part was covered with water. The dry eastern part of the bay showed no signs of overgrowing yet and emitted an unpleasant odour during longer periods of low water levels. The western part of the bay is rich in underwater macrophytes and according to the Fishing Family Radlje ob Dravi serves as spawning ground for many fish species. With the cleaning of the dry part of the bay we also prevented the risk of fish kill due to sudden changes in the water level when the fish could stay out of water.
Bay Vaški zaliv in the reservoir of HPP Vuhred
The ecological restoration of the Bay Vaški zaliv includes measures which, in addition to silt removal from the bay and its disposal (the stream Vaški potok flows directly into the bay), will contribute to the reduction of silt deposition in this area in the future. The broader area, including the Bay Vaški zaliv, is protected as a highly important habitat for many protected and endangered species by the Regulation on special protection areas Natura 2000.
The aim of restoration is to improve the functionality of the power plant by applying ecologically acceptable arrangements. The measures foreseen should at least preserve the existing status of the area's fauna and flora. In case of appropriate use the envisaged interventions will contribute to the conservation of nature.
Silt removal in front of the HPP Vuhred dam structure
Before the HPP Vuhred dam structure on the left bank, directly at the side wall of the dam structure, we had to remove the silt which, in times of increased flow rates, deposited directly at the left side before the dam structure and resulted in silting up of the gates of the first spillway and presented a risk to normal operation of the power plant.
Maribor Lake (Reservoir)
The Maribor Lake is an attractive recreational area. In the last decade, Dravske Elektrarne Maribor has successfully improved a number of tourist-recreational points on the lake. These include deeper moorings and the deepening of the lake floor for the boathouse and tourist facilities, the repair of tributary outlet, the creation of artificial islands, and the maintenance and expansion of tourism possibilities on the lake. During the maintenance work both here and at Ptuj Lake, the possibilities for water-related tourism and recreational use were taken into account.
Ptuj Lake (Reservoir)
The Ptuj Lake is an important refuge for migrating, rare and endangered species of birds, which have found a replacement habitat here. The lake also offers interesting recreational opportunities. Dravske Elektrarne Maribor has, through the thoughtful maintenance of valuable natural assets, set up a pilot project for the renaturation of the banks of Ptuj Lake.
Common tern nesting islands
At Lake Ptuj Dravske Elektrarne Maribor, in cooperation with BirdLife Slovenia, already in 2004 implemented an important ecological project, an artificial nesting island for the common tern. In 2014 the good cooperation between DEM and BirdLife Slovenia resulted in the creation of two more artificial islands, covered with gravel, serving as nesting grounds for the common tern. The islands contribute to the conservation of the common tern, a migrating shorebird that nests only on unplanted open surfaces, especially on gravel river islands. The common tern once nested on natural gravel beds on the Drava River, but the change in river dynamics influencing its overgrowth led to the moving of the birds to other regions. In 2004, only two colonies of the common tern still nested in Slovenia, and the critical shortage of nesting grounds could, in the future, cause the complete disappearance of local populations of this species. With the new artificial islands, with conditions similar to natural gravel beds, the bird can return to its natural habitat.
Removal of floating debris from ther river Drava
The current of the Drava River carries with it various types of floating debris, which can, during periods of high water, cause the blockage of turbine trash-racks and cause a decrease or even standstill in the generation of electric power, also influencing the ecological status of the waters downstream. In accordance with the concession agreement for the exploitation of the river Drava as well as our social and environmental responsibility DEM provides for regular removal of floating debris at all our HPPs.
All HPPs are, as part of their infrastructure, also equipped with temporary floating debris disposal sites for the temporary deposit (until further transportation) of floating debris removed from the river by our own maintenance personnel. Thus we ensure the optimal exploitation of the water potential for the generation of electric power and favourably influence the unhindered flow of the river Drava
Depending on the hydrological conditions we remove ca. 1000 tons of floating debris annually (in 2012, when the flow rates nearly reached 1000-years flow rates, we removed up to ca. 5000 tons). After the removal the floating debris has to be sorted and disposed of in line with the requirements of appropriate waste disposal legislation. Organic debris is treated like raw materials for additional processing – the ground up debris is used as humus.
From the operational point of view as well as in terms of safety (flow regulation, reduction of flooding risk, waste disposal) the removal of floating debris represents a very important activity of DEM.