C – Concrete conservation actions
Action C.1: Restoration of Istragov marsh
Responsible beneficiary: VVB
Istragov, a large marsh complex with an area of 77 ha, was formed of reeds, open shallow waters and many kinds of wetlands. After construction of the Gabčíkovo dam, wetland ecosystems in Istragov were drained and disappeared. The main objective of this activity is to restore the water flow in the marsh as a place of feeding, nesting and resting for target bird species.
In the field we started with the marsh restoration in 2012. Culverts enabling water inflow from the seepage channel were repaired and opened, the channels to Veľký háj and Dedinský ostrov were cleaned and also missing parts of the channels were dug so that water from the seepage channel can flow up to Istragov. In the lower part of the Istragov side-arm a small weir was constructed, which can retain the water that it will not flow out to the old riverbed of the Danube. The effect of the inflowing water was seen in the site Veľký háj immediately; however, it was a bit smaller effect within the Istragov marsh, where the amounts of water are limited, especially during dry periods. Afterwards other supportive measures were implemented. Water level in the seepage channel was increased which caused higher water inflow into the system. The gravel bottom of the channel between Veľký háj and Dedinský ostrov oxbows was sealed with clay, which helped to reduce loss of water through seepage into the ground. Since 2014, at least during major part of the vegetation season, the Istragov side-arm is fi lled with water and during some short periods even the Istragov marsh is being flooded. Some species of aquatic plants and animals appeared in the site again – for example, several species of amphibians started to reproduce here. Some water birds with less niche requirements are living again in the side-arm – Wild Ducks, Grey Herons, Great White Egrets, Kingfi shers and also the rare Black Stork sometimes appears here.
Action C.2: Restoration of Dunajské kriviny river branch system
Responsible beneficiary: VVB
Large river branch system, Dunajske kriviny, cannot fulfil its ecological functions anymore due to lack of water or low water levels. Adaptation of water supply for oxbows in Dunajské kriviny was finished in summer 2013. Former dried oxbows got flooded in the length of approximately 1200 m. Some common fish species got to the side-arm basically immediately and since 2014 we can see gradual restoration of bank and aquatic vegetation and colonization by water animals. Already in 2014, we recorded breeding of Common toad and Agile frog, in 2015 we recorded eight species of water beetles. Kingfisher, one of the project target species, occurs here regularly as it found suitable feeding habitats. Improving water subsidies is also important for the surrounding floodplain forest. In the past, they have been reclassified from the category of commercial forests to protective forests because of lowering of the ground water and related problems with reforestation.
At the present time: Restoration works ended in July of 2013. photos
Action C.3: Construction of the fishway on two strategic points in river branch system
Responsible beneficiary: VVB
River weirs in the branch system are causing barriers for fish migration and spawning. The activity include the construction of two fisways in areas Bačianske ramená (47°53´24´´S, 17°29´58´´N) and Veľkolélske rameno (47°45´13´´S, 17°55´43´´V).
In 2014, a few kilometres long of biocorridor was built. New channels interconnecting separate river side-arms were dug at three places. Another channel was deepened and enlarged. At four sites, pairs of frame culverts with a size of 2x2 meters were placed where channels are crossing the forest roads. Immediately after completion of the biocorridor, fish started to use it and the water flowing through improved water supply in the small side-arms and marshes. In addition to fish, birds also responded to restored habitats – up to four pairs of Kingfisher started to nest here and other species like Black Stork, Grey Heron and Little Egret appeared at the sites.
Action C.4: Restoration of selected dried and isolated river branches
Responsible beneficiary: VVB
In the past, inner Danube delta was formed as a complex river network. In the present this network is fragmented and fails to accomplish its ecological functions with a significant negative impact on the habitats and its species. Removal of barriers in the river branch system will improve water regime and integrate river branches. Raising water level will renew dried shallow wetlands, small river branches and natural channels. Feed sources (fish, amphibians) for target species as Common Kingfisher, Black Stork, White-tailed Eagle, Black Kite will be provided after restoration.
Activities include integrate 2,5km or river branches what assumes to renew least 18 ha of wetlands and release river paths for aquatic organisms migration what assumes growth of fish and amphibians in former fragmented branches.
Action is finished. The location we restored is Dolný Rusovský ostrov: All artificial barriers were gradually removed in the years 2013-2014. The nature reserve now has a much improved natural look, now that the side-arms and wetlands are not crossed by concrete and stone weirs or roads. Immediately after completion of the work, during floods, the side-arm was scoured and large quantities of the debris were carried away. Former ordinary illegal entrances of vehicles to the inner part of the reserve have completely disappeared. The movement of people in remote parts of the reserve became less frequent, thus a zone without human disturbance appeared where many sensitive bird species found a refuge. We expect that the nesting sites of some of them will gradually reappear.
And the another location was White-tailed Eagle island: the main problem of the site is lack of water and absence of floods. Therefore any kind of restoration has to start with improvement of the water regime. Because a complex restoration of the river branch system is a technically and fi nancially diffi cult process, which is also time-consuming, we decided to stabilize the area of the island through improvement of the water regime, which the situation allowed. The water level in river branch upstream of the island is quite high that it is able to fl ood the dry lakes in the central part of the island and also the lowered parts of the fl oodplain forests. Digging of a channel connecting the branch and the dry wetlands in the central part of the island was designed. A simple sluice gate in the infl ow part allows to regulate the quantity of infl owing water. The aim is to get some amount of water to the site all year long and a bigger quantity of water during some periods, especially in spring and summer, which allows the temporary fl ooding of depressions on the island.
In 2013 the described solution was constructed and set into operation after agreement of the foresters. After more than 20 years, the water came back to the White-tailed Eagle island. Several of the depressions were permanently or temporarily fi lled with water. Although the restoration of natural vegetation requires more time, the locality already was re-occupied by aquatic birds – the Black Stork is regularly feeding here, the Kingfi sher is nesting, and the Grey Herons and Mallards are coming here. Several species of amphibians started to spawn on the island again.
See the photo gallery - Rusovský ostrov island, photo gallery - White-tailed Eagle island
Action C.5: Restoration of Medvedovske rameno river branch system
Responsible beneficiary: BROZ
River branch system Medvedovske rameno (47°47´60´´S, 17°38´55´´ N) was flowing freely until the end of 80's when regulation works on Danube caused disconnection from the main stream on the upper part of Medvedovske rameno. This action changed water regime, water dynamics and the composition of bird and vegetation species. Some of the species had lost completely their habitats and some of them had decreased their feed sources.
In the beginning, the excavated inflow part of the river branch had a shape of straight channel with equal banks. In the end of 2012, immediately after termination of the restoration works, higher flows entered the branch and started fast lateral erosion. The result of this erosion process, which continued also in the first half of 2013, was the enlargement of the river branch to the originally designed 30 meters and also the change of shape of the channel – from straight to slightly meandering. One of unintended consequences was the sedimentation of washed away bank material, which increased its bottom further down in wider parts of the channel and caused restricted flow capacity at low and medium water levels. Subsequently, this material was excavated. Erosion and spontaneous „naturalization“ of river bed occurred only in the area of former river branch without threatening the surrounding land. Continuous erosion in the area of the inflow from the main channel was preventively stopped by the installation of a buried quarry stone dumping. It is worth noting, that the Danube flow 10 200 m3 s-1 in Medveďov in June 2013, which is more than the hundred year flood, had no bigger influence on the shape of the river branch. During following years – 2014 and 2015, the river bed was not changing anymore and was stabilized.
The restored water flow had an immediate influence on animals and plants. Right after the river branch restoration, Kingfishers started to nest here. They used two concave banks for nesting, which were restored. Furthermore, the river branch provides them excellent opportunities for hunting – the flowing water creates depressions, which are filled by clear water during periods with low water levels. The Black Stork, which is in extinction in the area of the Danube floodplains, also started to visit the site for feeding. Of course, rheophilous fish species from the Danube main channel immediately occupied the flowing branch, where they can find good conditions for life and reproduction during some periods. Other phenomenon, which was restored in the area thanks to the fl owing water is the natural regeneration of the softwood willow-poplar floodplain forest on gravel and sand sediments along the river branch.
Please, see the photo gallery.
Action C.6: Restoration of Velkolelske rameno river branch system
Responsible beneficiary: BROZ
River branch system Veľkolélske rameno (47°44´60´´S, 17°55´47´´V), flowing around Veľkolélsky island, was in the end of 80's disconneted from the main stream by blocking all inflows during the regulation works on Danube. An artificial runway on a dike from concrete was set up through isolated river branch. River branch system was damaged by these interventions. After every flood, the deposition of sediments rises and disable life in water.
Our main objectives are to interrupt the concrete dike and open the river branch on its upper and lower part, so water can flows through the river branch. We expect sediment loss, fish migration for spawning, renewed nesting and feeding for target bird species. There will be built a new bridge over an interrupted concrete dike, so the access to the island will remain.
Within 2013 – 2015, the water inflows to the river branch by 100 meter wide inflow channel. One part of the crossing dam was substituted by a new bridge, which allows the water flow, and also allows the visitors and land managers to access to the island. The water now flows through three 15 m wide fields and more than 4 m high, instead of two former culverts, just 2x2 m wide. On both outflows the dam was removed and the river branch is now freely connected with the main Danube channel. Between the outflows, a small island called Golden island is located. This small island is inaccessible by feet now. In 2015 the water flow in the river branch was restored after decades. Positive results and fast returning of wildlife to river branch are confirmed not only by scientists, but also by local fishermen.
Action C.7: Restoration of lowland meadows as feeding and nesting bird habitats
Responsible beneficiary: BROZ
The largest area of alluvial meadows on the Slovak side of the Danube has been preserved on the Veľkolélsky Island. However, these meadows were used only minimally after 2000 and they started to become overgrown, therefore our attention was focused right here. We purchased a herd of 70 cattle, 100 sheep, 20 goats and 8 Hucul breed horses and we have introduced a grazing system. Grazing is regulated through mobile electric fences. Cattle are clearly the best for restoration of abandoned and derelict areas. Sheep and horses are again appropriate to maintain low vegetation on already restored grasslands and pastures. Already during the fi rst grazing season in 2009 we saw excellent results. Areas overgrown by two meters tall thicket of weed were managed by cattle in a short time and turned into the low grassy vegetation. The cattle are “mowing down” vegetation even in rough or flooded terrain and under scattered trees. It is impossible to do this work with any kind of machine. During several years of grazing animals reduced continuous stands of invasive plants, especially Goldenrod. On regularly managed meadows and pastures there has been a visibly better expansion of the rare and protected plant species such as Clematis integrifolia or summer snowflake. The grazing was later supplemented with milling of the rest of the invasive tree species and mulching of the sprout shoots of removed plants. Grassing of arable land with seed mixtures of native herb species was used on an area of 20 ha near the villages of Veľké Kosihy and Číčov. In cooperation with local farmers in the villages of Iža and Dunaszeg, we have improved pasture conditions by the Danube by removing non-native invasive trees and by supporting the pasture infrastructure. Overall, during the project we have restored fl oodplain grasslands and pastures on an area of nearly 200 hectares. With the support of water managers in the Hungarian part of the area, we began the grazing of cattle on the fl ood-protection dyke and their buff er zones (out of project activities). Grazing improves the quality and structure of grassland and also saves operating costs for mowing and mulching of the dykes.
Action C.8: Planting of native tree species - restoration of natural birds refugia and nesting areas
Responsible beneficiary: BROZ
The original floodplain forest along the Danube was largely replaced by plantations of the fast growing non-native Euroamerican poplars. These monocultures are usually harvested after 30 years. For many species of birds and other animals that need old trees for living, these do not provide sufficient nesting and feeding opportunities. A number of typical tree species of varied floodplain forests had become rare under intensive forest management. To support species diversity within the forest and create a mosaic of possible breeding sites for birds in the future, we planted over 45,000 trees of several native species during the project. We planted mostly native poplars – Black and Grey Poplars, then White willow and Common alder at the moist softwood floodplain forest habitats. On the drier and higher situated sites of hardwood fl oodplain forest Pedunculate oak, Narrow-leaved ash and to a lesser extent also maples, elms and wild pears were used. Reforestation was carried out by planting of native trees in groups to gaps in nonnative poplar plantations as well as planting whole forest stands of domestic species at places without trees. Trees were planted on land purchased from private owners or on land used by others after agreement.
Action C.9: Restoration of steep river banks as nesting bird habitats
Responsible beneficiary: BROZ
Due to river regulation, vertical river banks almost vanished in the project area after this type of banks had been reinforced by large stones to minimalise side-erosion of the river bed. Such banks are the only habitats suitable for the nests for sand martin. This bird nests on suitable places in big colonies – by choosing suitable localities, a favourable increase and stabilisation of it´s nest population in our country will be ensured. Within this action, we restored vertical banks on Veľkolélsky ostrov island in the lenght of 50 m (rkm 1782) in May 2010 and 200 m long and 3 m high bank section at the inflow of river Ipeľ and Danube (rkm 1709). We know that in the past, colonies of sand martin lived in this locality. By restoring vertical banks we are creating favourable conditions for their return in the area. In 2012 almost 1000 pairs of this bird successfully nested on restored vertical bank near Chľaba, which was the largest colony of this species in the whole section of Danube. You can see the process of bank restoration and the colony in a photogallery.
Action C.10: : Restoration of Szárazerdei river branch
Responsible beneficiary: EDUVIZIG
- Szárazerdei river side-arm restoration was ended in November 2011, when the water returned to the 1.5 km long part of the river bed. The return of lifegiving water received a quick response. Native inhabitants started to return to the river-bed – many fish and water invertebrates found their homes here again. Several species of amphibians, the Grass snake and some aquatic bird species came to live here again. Floodplain forests in surroundings also get more humidity.
Action C.11: Restoration of wetlands in the Ásványi river branch system
Responsible beneficiary: EDUVIZIG
Planned restoration work was carried out at four locations in 2011. Because of the good results and project savings, the second phase was designed and implemented in 2013, where four other wetlands were recovered in a similar way. By the restoration of wetlands we managed to bring back water to the places that would otherwise gradually lose its specifi c nature and species richness. Overall, we improved the water regime of eight sites where we restored temporarily fl ooded wetlands on an area of 56 ha and permanent shallow lakes on an area of over 11 ha. Besides the lakes and marshes themselves, the water supply in the surrounding softwood fl oodplain forest was improved as well.
