Table 1 shows the characteristics of the Swist river catchment. The Swist is a stream with a total length of 43.6 kilometers. The catchment area covers 289 sq. km. The source is located at 330 m above sea level in the northern part of the Eifel. The Swist flows in the upper reaches at an average gradient of 0.5 % and then runs with only 0.13 % gradient to the confluence with the Erft between Weilerswist and Bliesheim at 108 m above sea level.

The water level of the Swist is highly variable. As a result of flood events the natural water course has been modified. Over long stretches a trapezoidal profile has been built, which increases the flow rate significantly. In longer periods without rainfall many tributaries of the Swist are dry. Currently the aim is to make the Swist more natural and improve water quality.

In the upper reaches of the Swist the water body corresponds to the type loess-clay dominated lowland brook, in the lower reaches to gravel dominated lowland brook, although it is modified by strong anthropogenic influences. However, due to the preserved natural river bed and the lack of weirs, the longitudinal migration for riverine fauna is ensured. From its source to its mouth the Swist belongs to biological water quality class II (moderately polluted, betamesosaprobe).

A total of nearly 30 % of the catchment is forested (see Figure 1). The climatic situation and fertile loess soils in the catchment allow intensive agricultural use (44 % arable land). Widespread arable fields are cultivated with wheat and sugar beet. Orchards are characteristic in the Meckenheim area. About 95 % of farms are located at a distance of less than 500 meters from the waters; 10 % are less than 50 meters from the waters. Parts of the Swist basin are classified as drinking water protection zones.

The Swist watershed serves as a suitable study area within the M³-project for several reasons. The Swist is a receiving watercourse for discharges from wastewater treatment plants. Swist water is used for irrigation of field crops. The local population frequents the watercourse for recreation. Due to the size of the catchment a certain natural spatial uniformity is given. This makes it easier to compare results from different river segments of the water course.


In summary, the Swist has been selected as part of the M³-project for the following reasons as a case study for consideration of substance fluxes:

• Types of water and catchment structure ensure transferability to a wide range of comparable water courses.

• High effluent wastewater load in relation to the natural water flow is typical for the densely populated regions of Western Europe.

• Sewage treatment plants in the catchment employ different process techniques (nitrification, denitrification, biological and chemical phosphorus removal, flocculation filtration step).

• Combined sewage and separate sewage as urban drainage systems are in place.

• Water withdrawal is maintained for irrigation purposes.

• Pathogens and micro-pollutants are in the waters at significant level.

• Pesticide loads are given through intensive crop cultivation (wheat, sugar beets, apple orchard).

• High demands on water quality are imposed by agricultural / industrial users and the public.