Problem

The popular bathing lake Kahrteich in the center of Wien Neudorf in 1996 had some increasing problems with the visual depth according to bathing water directive. The 120,000 bather per season led to an increase in phospherus concentration of an increasing density of algae resulting in a reduced visual depth.

Lake Data

Surface: 3.4 ha
Lake volume: 380,000 m³
Hypnolimnion volume: 200,000 m³
Stratification: The lake has a thermocline layer at 7 m.
Maximum depth: 19,3 m

Resolution


In October 1999 a deep water aeration system (TIBEAN) was installed in the Kahrteich. In May 2015 an installation of a repair pump as well as an online measuring station took place. The lake has been examined since 1999 to date for a limnological accompanying program of the DWS Austria (www.dws-hydro-oekologie.at) and detailed results are available. Furthermore the plant operation and the control of the functionality of the deep water aeration system by DWS have been realized.

System performance

Volumetric flow: 300 m³ / h
Power consumption: 1.7 kW
Oxygen ingress: 1.8 kg 02 / h
Removal depth: 18 m
Insertion depth: 7 m

Result

The oxygen enrichment after commissioning caused a significant reduction of the nutrient inputs from the deep water after the full circulation in the same year. In the year 2000 further positive results of deep water aeration (increase of the depth of sight, further nutrient reduction, avoidance of settling processes from the sediment) were shown. Based on the measurement data from the same year, a working plan was created for the device. By repeated oxygen measurements in the vertical profile, the operating times and the operating time of the TIBEAN were determined such that the oxygen supply in the deep water was sufficient to prevent undesirable processes. The results of 2001 and 2002 confirmed the success of deep water aeration in all relevant areas. Oxidized ratios were observed throughout the year, so that no re-solubilization processes (nutrients) occurred. The trophic wheel (nutrient content) showed a downward tendency, the transparency of the water increased. In 2003 and 2004 the TIBEAN suceeded in securing an attractive water quality as well as a high visibility even during the above-average warm summer months. The attempts to resettle with submerged aquatic plants, begun in 2005, brought first successes in 2006 (joint initiative of the fishing and diving association as well as the municipality, supervised by the DWS Austria). Both the "Auerige Tausendblatt" (Myriophyllum spicatum) and the "Growing Laichkraut" (Potamogeton perfoliatus) began to develop in small areas outside the experimental areas

Depth of visibility

Before the deep water aeration, the depths were 1-3 m. After the use of the TIBAN the sight depths rose to 2-12 m. So there has been a significant improvement in the apparent water quality.

Phosphorus

The long term data show a clear decrease in the P concentrations (graph on the upper right corner) from 30-45 μg / l to 10-15 μg / l. A power measurement showed that the pump power has decreased. The pump was renewed in 2015. Since then, the P concentrations in the water drop again.

All values ​​and graphics come from DWS, DWS Hydro-Ökologie GmbH, Technical Bureau for Water Ecology and Landscape Planning.