Residential areas
Foto: Vojta Herout
Protection against Torrential Water in Schwertberg
The town of Schwertberg is regularly affected by torrential rain, which unusually often leads to large floods. Strong storms and particularly bad weather on 23rd July 2016 became the impetus to ensure the protection of all problem zones of the municipality against storm water flowing from the surrounding slopes. EUR 4 million has been invested so far. In addition to building 10 retention tanks, sophisticated drainage channels and ditches, the municipality has also signed agreements with farmers so that more than 5 hectares of hillside fields can be turned into permanent green meadows and pastures. The retention areas have a greater ecological value now with lowering meadows for bees having been established and trees and bushes planted to protect against erosion.
The Adaptation Journey
The positive impact
With the scientific support of the University of Salzburg, the municipality of Schwertberg alerted the authorities at the regional and national level to its specific topographical and geological conditions. In Schwertberg, problems with water after torrential rain running off the slopes are mainly of natural origin and less the result of ill-advised settlement development.
In addition to many of the municipality's own initiatives (division of the sewage system into wastewater sewers and storm rainwater sewers, the construction of inflow manholes on steep sections of roads, construction measures of houses or culverts at the outlet to the Aist River, contracts about using green fallows with farmers and the establishment of smaller retention tanks) and with the support of experts and partly with the financial support of the country, the state and the EU, sophisticated complex retention measures were implemented.
The aim is to finally eradicate the danger of flooding water from the slopes for the municipality of Schwertberg. More than three quarters of the planned measures have already been implemented.
How does it work?
The Poneggenbach retention basin holds approximately 43,000 m³ of water, all 3 retention basins at Lesterl hold a total of about 4,000 m³, the Wingegg retention basin has a volume of 800 m³, the Broat´n basin 550 m³, the 3 existing retention basins at Sommerhaus approx. 900 m³, the Mühlenweg basin 3,620 m³ - a total of around 53,000 m³ can be retained in 10 retention basins.
About 20,000 m² of privately owned land was transformed into retention areas: with flowering meadows open to the public, about 30 trees and more than 100 shrubs were planted. Water constantly flows in the open ditches (valuable for the ecosystem and an artificial lake has been created in the Mühlenweg retention basin. The measures have had a positive effect on approximately 60 ha of partially densely populated territory.
Despite all the protection offered, residents must always expect a certain amount of small risk and bear responsibility for this. The municipality, therefore, also supports education and information campaigns and residents can learn about simple measures to protect themselves against floods.
Original state
Floods of such unusual intensity are no accident in the municipality of Schwertberg, they have their own clear causes. Schwertberg lies on the hilly spurs of Mühlviertel on the edge of Machland. From a topographical point of view, this area is characterized by many large-scale segments in the form of channels and basins. The so-called The Czech massif is now partly covered with very thin layers of humus, and in many places, granite is as high up as in the depth of 70 cm. Therefore, water cannot soak into the ground. In addition, the soil is often very clayey and almost impermeable to water when it is dry. During heavy rainfall, surface water flows into natural hollows and depressions. At the transition to Machland, there is almost no water outflow on the plain, as a result of this the rivers and streams Wingeggerbach and Aisthofener Bach as well as Poneggenbach overflow their banks.
Operation and maintenance
An essential part of the maintenance is mowing in the area of the retention basins, which represents a great challenge due to the slopes and high vegetation. Additional costs are calculated to be approximately 10,000 - 15,000 EUR per year, as it is necessary to use special machines to cut tall grass on steep surfaces. The finance for this budget comes from the regular municipal budget for communal maintenance.
Why was the measure chosen?
One possibility would be to implement only individual measures. But instead, the municipality decided to go for a complex concept of a sustainable solution to the issue of slope water, whilst taking into account the climatic conditions of the future. In addition, we consciously opted for partially open ditches for drainage, which are very valuable from an ecological point of view and offer even more protection than pipe systems. They are, unfortunately, very high-maintenance (mostly manual work). A limiting factor is the unwillingness of residents to cede their areas to public property for the purpose of protection against slope water or at least rent it out.
Obstacles and challenges
Without the financial support of the country, the state and the EU, we would not be able to implement protection against water running off the slopes in all dangerous places in the municipality. At the beginning, it was also difficult to clarify the different competences (between the water administration "Gewässerbezirk" and the organization Lawinen- und Wildbach Verbauung). The wishes and demands of owners and negotiations on land purchases, which in some cases dragged on for more than a year, and the positive outcome of negotiations was only possible with a high degree of citizen involvement, were also challenging.
Operation and maintenance
The community accepted the new areas very positively. For example, the Lesterl basin in the Poneggen part of the village has become a skating paradise for children from the area. Many people did not want to believe that retention measures would have such a positive effect on the overall image of the landscape and that they would be so beneficial to nature. In the meantime, even critics of slope water protection projects have reacted positively to the implemented measures.
How much did it cost?
So far, more than 4 million EUR has been invested - the municipality of Schwertberg, the state of Upper Austria, the state (Federal Ministry of Agriculture, Regions and Tourism), and the EU (European agricultural fund for rural development). Over the next 30 years, savings of up to €2,000,000 are expected with regard to water damage caused by slope water runoff.
Use of rainwater Flood control measures Floods and torrential rainfall Lack of water and drought Soil erosion Landscape greenery