Biological filter bed in the Alte Donau Water Park

Since summer 2016 low-nutrient water from the Neue Donau is fed into the Alte Donau via a biological filter bed in the Water Park.

People sitting on benches which are installed on the embankment enclosing the filter bed

This artificial water supply compensates for the low groundwater throughflow in the Alte Donau. This measure implemented by Municipal Department 45 - Water Management (MA 45) as part of the LIFE+ Alte Donau project will safeguard the outstanding water quality of the urban lake for the long term.

The water intake passes through a biological filter bed implemented in the Water Park. The surface has been landscaped with water plants to enhance the visual attractiveness of the installation.

The embankment enclosing the filter bed is topped by a promenade furnished with three contemporary seating elements and waste bins, creating a landscape design feature that serves as an "outdoor living room" for visitors to the Water Park.

Purpose and function

The man-made inflow from the Neue Donau is channelled into the Alte Donau via the body of the filter bed, which consists of layers of stones and gravel coated with biofilm. Since the water from the Neue Donau has a higher phosphorus content than that of the Alte Donau, levels of phosphorus and other nutrients in the water are reduced in the filter. This prevents additional nutrients being introduced into the water of the Alte Donau.

Stabilization of pH values

Recent summers have seen increasingly lengthy periods of hot weather with intense sunlight, which causes large quantities of carbon dioxide to be extracted from the Alte Donau. This subsequently leads to a shift in the chemical balance of the water, whereby calcium is precipitated. As a consequence, the pH value rises so significantly that fish and many other aquatic organisms are endangered.

And this is where the new filter bed comes in: before being fed into the Alte Donau, the water from the Neue Donau is enriched with calcium in the body of the filter. This helps to stabilise the pH value of the Alte Donau.

Key data

The filter bed is situated on the southern shore of the Water Park at the end of the upper section of the Alte Donau.

The filter bed has a total surface area of around 2,000 square metres, allowing it to process a water intake of up to 90 litres per second.

  • Start of construction works: March 2016
  • Operational start-up: August 2016
  • Contracting authority: Municipal Department 45 - Water Management (MA 45)
  • Contractor: DWS Hydro-Ökologie GmbH, in collaboration with GRUPPE WASSER ZT-Büro, POLYPLAN GmbH (plans and documentation for submission to water authorities) and Büro Dipl.-Ing. Schattovitz Ziviltechniker GmbH (detailed planning)
Logo of the LIFE+ Programme of the European Union: The word "Life" in yellow, surrounded by yellow stars

The LIFE+ Alte Donau project was funded under the LIFE+ Programme of the European Union as part of the "Environment Policy and Governance" strand.

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City of Vienna | Water Management
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