Structure of watercourses
In the past, many watercourses were straightened or obstructed, to allow the use of flood-prone land for settlements, infrastructure and agriculture, and for electricity generation. This prevents them fulfilling many of their natural functions and the habitats for plants and animals in and around the water become depleted. The landscape becomes more monotonous. Obstacles such as weirs, hydropower plants, dams and other transverse structures impede the movement of motile aquatic organisms between lower and upper reaches, significantly impacting on their reproduction, their range and the mixing of populations.
Long stretches of Swiss watercourses are impaired by man-made structures and intensive use. 24% of the total watercourse length is artificial, seriously impaired or covered over and many lakesides are also built up. Watercourses in intensively used lower lying areas are particularly severely impaired. Below elevations of 600 m, 46% of watercourses are inadequate in structural diversity, whereas above 2000 m this figure is less than 1%. Mainly average-sized watercourses between 600 and 1200 m are affected by artificial obstacles, which impede fish migration (see map).
To reverse this long-term negative trend, efforts have increasingly been made since the 1980s to achieve renaturation of surface waters, for example by expanding their area, removing man-made structures or making obstacles open to fish migration. Since 2011 the Water Protection Act requires rivers and lakes to be rehabilitated. The goal is to restore 4000 river km over the next 80 years. Therefore the trend is assumed to be moving in the right direction even though only one initial value currently exists.
The data are partially comparable. The Swiss method is based on a four-step classification system. Five steps are standard in many EU countries and even seven in some. The parameters which are surveyed and form the basis for the evaluation also differ slightly. An international comparison is difficult at present because equivalent data are still lacking in the other countries. Switzerland has taken a leading position in terms of ecomorphological databases. In neighbouring countries such nationwide surveys are not yet carried out in many places.
The ecomorphological conditions of the watercourses were surveyed by the cantons (with financial support from the BWG) within the modular-stepwise procedure “Ecomorphology Level I (regional survey)”. The process required nearly 30,000 km of watercourses in 24 cantons to be mapped between 1998 and 2006. To survey the ecomorphological conditions of the watercourses, their naturalness, canalised sections and obstacle features were recorded.