Description of the project area
The Enns has its source in the Pongau on the northern side of the Radstädter Tauern at an altitude of about 1.750 m above sea level in the municipality of Flachau. In Flachauwinkl the river flows into the Pleißlingbach as a left tributary, which at this point has the much larger catchment area and forms the main valley. From here, however, the watercourse is called “Enns”. It first runs north through Flachau and then east through Altenmarkt and Radstadt. In Mandling, a village within the municipality of Radstadt, the Enns leaves Salzburg in the direction of Styria. After about 250 km, the Enns then flows into the Danube north of the town Enns (Upper Austria).
The main tributaries of the river Enns in the province of Salzburg are the valley streams Litzling, Kleine and Große Loh, Hauptgraben III, Lohbach and Pfandling, as well as bedload-carrying tributaries such as Grießbach, Alte and Neue Zauchen, Taurach and Mandling.
The LIFE IRIS project area starts at the confluence of the Grießbach and Enns in Flachau and extends to the national province border in Mandling. In addition to the Enns, the downstream section of the Taurach is also within the project area. The investigated river sections in Salzburg have a total length of about 23 km.
In Radstadt, downstream of the Taurach estuary, the Enns has a catchment area of approx. 320 km². In this river section, discharges of 200 m³/s are to be expected during a 100-year flood event. Due to the alpine catchment area, the mean water discharge of the Enns has its maximum in the months of May and June. Extreme floods occur in particular in the summer half-year. The last severe flood events on the Salzburg Enns occurred in 1965 and 1966. These were classified as 30-year flood events.
The river regulation measures implemented in the 1980’s have severely changed the characteristics of the Salzburg Enns. The Enns, at that time still mostly in its natural state, was straightened and forced into a trapezoidal discharge profile. The goal of improving agricultural productivity by improved flood protection was achieved. What remained, however, was a river with little natural structures and steep banks made of stone pitching. The character of a near-natural river was lost.
Hot Spots & Highlights
The Salzburger Ennstal valley is mainly characterized by tourism. In the river Enns itself, recreational activities are very limited due to the narrow and straightened riverbed. Between 2012 and 2015, flood protection projects on the Enns were implemented in the municipalities Altenmarkt and Flachau, which resulted in beautiful restoration measures with widened river stretches, that can be used for recreation.
The so-called Mandlinger Moor on the border to Styria represents the most interesting part of the landscape of the Salzburg Enns. It is the remains of the formerly extensive valley moor landscape in Salzburg’s Enns Valley. The peat layers that built up after the Ice Age are silent witnesses of the landscape development of the Enns Valley. In order to preserve this important protected area for posterity, measures for balancing the backwater were implemented in 2014.
Need for action
As a result of the river regulation measures in the 1980’s mentioned above, the Salzburger Enns became a largely monotonous river with little natural structures and an ecological status of mostly moderate or worse. The ecological problems mainly result from hydromorphological deficits.
Over the past 20 years, numerous flood protection measures were implemented in the three municipalities of the Salzburg Enns Valley, which have resulted in an almost continuous flood protection of the settlement areas against a 100-year flood event. The need for action on the Salzburger Enns now lies above all in the improvement of the ecological status of the river.
Based on the River Development and Risk Management Concept (GE-RM), the planning and activities on the Salzburger Enns are coordinated in an interdisciplinary process.
The planned pilot measure within the IRIS project intends to restore a meander in the area of the Mandlinger Moor close the provincial border to Styria. Basis for the measure is the reference condition of the Enns before the regulation of the river.
The restoration of the meander according to the historical reference will significantly improve the ecological and morphological conditions of the Enns river basin in comparison to the actual state. In conjunction with the adjacent Mandlinger Moor, which will be taken into account in the detailed planning, the overall character of the Enns will be developed in the direction of its state before regulation. This will also have a positive impact on recreational value, leisure use and tourism.
Outlook and time plan
In the years 2019 to 2021 the GE-RM Enns-Taurach will be elaborated. Detailed planning for the pilot measure Mandlinger Moor, which will be implemented in 2022 and 2023, will follow this. The planning process and also the construction project will be accompanied by effective publicity measures. Monitoring, which examines the effects of the pilot measure, will run until 2027.