Small bodies of water with great significance
If no or very little rain falls over a longer period of time, the streams are mainly fed from the groundwater. This is referred to as "base flow". However, groundwater storage is also limited: Low rainfall and extensive sealing of surfaces reduce groundwater recharge. As a result, groundwater levels and the supply to watercourses continue to fall, which in turn increases the decline in water flow in watercourses. The years between 2018 and 2020 in particular were characterised by extremely low precipitation, very high temperatures and above-average sunshine, which had an impact on the water levels in streams and rivers, among other things.
Although the water level in watercourses rises rapidly during individual precipitation events, even in pronounced dry periods, it then quickly falls back to the low initial level. The reason for this is that the base flow only recovers when there is a stable rise in groundwater levels.
Protecting streams
These small watercourses in particular are of great importance for our city, for the microclimate, the water balance and the flora and fauna. Often hidden behind sturdy bank edgings, completely invisible in pipework, built over or distorted beyond recognition, they need our special protection.
One instrument for protecting streams are riparian strips. These are defined protection areas that are ten metres wide on both sides from the top of the embankment and five metres wide within built-up areas. According to the Water Resources Act and the Saxon Water Act, nothing may be built within these strips and the depositing of objects that could obstruct the flow of water or be washed away is also prohibited. During regular water inspections, it is very often found that the banks are built up using construction waste, rubble or similar. This type of bank construction creates sections of watercourse that are far removed from nature, with the risk of riverbed erosion and undermining of bank structures. In the event of flooding, this rubbish can block culverts and bridges and lead to flooding and massive damage.
A natural, meandering stream with sufficient margins can better withstand floods, keep water in the landscape for longer, improve the local climate and provide habitats for numerous species. It is therefore important to protect our watercourses and - where possible - restore them to a more natural state.
Streams are habitats
A stream is a small ecosystem in its own right. Fish, amphibians, insects and many plant species live in and around the water. Of particular importance is the so-called macrozoobenthos - that is the entirety of small invertebrates such as insect larvae, snails or freshwater shrimps that live at the bottom of the water.
On Whit Saturday last year, pupils from the Fortis Academy in Chemnitz took part in the Germany-wide Flow project, accompanied by the environmental agency. They took a closer look at the water structure of the Wiesenbach stream, determined and analysed macrozoobenthos as indicators of water quality in agricultural catchment areas and investigated the water chemistry. This showed that streams, regardless of their appearance, are rarely in a good ecological condition. Inputs of fertilisers (nitrate, phosphate), pesticides or anthropogenic changes to the streambed are not always immediately recognisable.
The water quality based on aquatic invertebrates is determined in the flow project using the SPEAR index. This requires an extensive database, which is collected by volunteer citizens. At the same time, ecological relationships can be taught as learning content.
The protection and preservation of our streams is a very important community task. Everyone can contribute by keeping the soil and water clean. In addition, all riparian owners are called upon to respect the riparian strips and to develop them in a near-natural way or to allow self-dynamic developments in close coordination with the transport and civil engineering office responsible for maintaining the watercourses. In addition, all possibilities should be exhausted to limit the sealing of new surfaces and to remove existing sealing in order to minimise the obstruction of groundwater recharge and thus not to reduce the base flow to the watercourse.