Geography of Lake Krähen- and Mühlenteich

The Krähenteich and Mühlenteich are at the southerly edge of Lübeck’s town centre.

These two lakes are dams and connected to each other. The main outlet of the Wakenitz river is through these bodies of water. A culvert which runs under the Trave canal for 120 metres and flows into the Krähenteich serves as the supply. The Mühlenteich’s outlet is via a weir which is used to produce electricity.

On the north bank of the Krähenteich is a bathing area which is popular with swimmers in the summer months. The other banks of the lake are used extensively by Lübeckers and tourists for leisure and recreational activities.

View over the Krähenteich

	Expanse	Surface	Average depth
Krähenteich	390 m x 98 m	29,000 m²	2.40 m
Mühlenteich	300 m x 195 m	36,000 m²	2.25 m

Deepest point	5 m
Water retention time	1 day per lake (annual mean value)
Catchment area	170 km²

(The size of the catchment area is a result of the Krähenteich being the natural outlet of the Wakenitz river and, in turn, the Wakenitz drains the Ratzeburger See (lake)).

Sampling locations
Three sampling locations are established in the Krähenteich and Mühlenteich:

Culvert outlet
Bathing area
Mühlenteich outlet

These points were selected to assess the inflow of the culvert and to see the extent to which the composition of the water changes when running through these bodies of water. The bathing area is under particular observation in order to determine the causes of the variable quality of the bathing water (bacteriology) over recent years.

A few historic details about the origins of the Krahenteich and Mühlenteich
The town of Lübeck was planned to be laid out between the courses of two rivers, the Trave and the Wakenitz which flows out of the Ratzeburger See.

The Krähenteich and Mühlenteich are man-made reservoirs fed by the Wakenitz. The Wakenitz was dammed as early as 1180 to form the Krähenteich, partly to defend the settlement and partly to be used as water power and drinking water. In 1290, very foresighted senators of the Hansastadt Lübeck bought this increasingly important river for the inhabitants of the town.
In about the year 1200, work was begun to erect mills on the dammed up Wakenitz, on the east of the town. So-called water towers moved water from the Wakenitz in pipes made of hollowed out tree trunks into the city centre. The population was supplied with drinking water from the Wakenitz until 1972 but industrial plants had been supplied with underground water from a depth of approximately 80 metres since 1905.

The conditions in the lower course of the Wakenitz along the town changed over the centuries, defences were built and redesigned, but the levels of the reservoir remained constant.

With the building of the Elbe-Lübeck canal between 1895-1900, wide-reaching changes were made. Part of the route of the canal lay in the old bed of the Wakenitz. The canal was dammed by the Falkendamm against the Wakenitz which was higher. In order to ensure that the Wakenitz drains in accordance with the Level Agreements with Ratzeburg, the waters of the Wakenitz were directed under the canal through a culvert.

The fishing and reservoir rights are still held by the town of Lübeck.

Source:
Dr Manfred Diehl
Report by the ”Natur und Heimat” association and the Natural History Museum of Lübeck
”Wakenitz zweite Lebensader Lübecks”
no. 17/18 Lübeck 1982

Hydraulic tests in the Krähenteich and Mühlenteich
The test area of the Lübeck municipal lakes of Krähenteich and Mühlenteich comprises an area of approximately 6.5 hectares. Both parts of this body of water are connected to each other by a narrowing under a road bridge.

The water is no deeper than a maximum of 5.2 metres. The influx of water is regulated by a manually adjustable weir and continues through a culvert with a defined profile. The outlet is also regulated via a weir. In addition, some of the water flows through a hydro-station into the Trave canal. In controlling the water inflow for the Krähenteich/Mühlenteich, the levels in the upper reaches of the Wakenitz can be observed.

A numeric flow model was set up for the Krähenteich and Mühlenteich in order to take qualitative high-quality readings regarding the current situation and expected changes in the test area and to process scientifically-based prognoses in any interventions planned. These modern model systems make it possible to “depict nature on the computer”.

The present situation in the Krähenteich/Mühlenteich has now been ascertained. The results have created the basis for further tests. As a result, it has been possible to simulate the effectiveness of measures which direct the flow into the lakes and these measures are intended to improve the water quality in the bathing area.

The basis of these tests form the available data and mapping materials on the one hand, and on the other, a measurement campaign which is made up of the following components: bathymetric survey of the municipal lakes and flow measurements at some characteristic places in the area of the inflow (culvert) and in the area of the narrow connection (road bridge) between the Mühlenteich and the Krähenteich. These data are the driving data for the numeric model system and serve the verification of the model.

The measurements and flow simulation were carried out by the consultancy firm, HYDROMOD. All further information, the exact results and the flow simulation can be found here: www.hydromod.de/en/index.html

Restauration
It is not part of this project to make a restauration of the Krähenteich and Mühlenteich.