Rainwater Needs Space
As a result of climate change, the rainfall patterns are expected to change significantly. According to estimates by scientists, climate change can lead to an increase in heavy rainfall events. Moreover, there has been a recent trend to seal off surfaces in Hamburg. The consequences of this are increased runoff, which can lead to an overloading of the drainage systems, additional flooding and water pollution. The city's growth combined with the expected consequences of climate change present the city of Hamburg with new challenges on how to deal with stormwater. Pioneering concepts and solutions for protecting against high water levels and flooding, as well as water conservation measures, require additional space in order to implement decentralized management methods.
Characteristics of Rainwater
Rainwater is a part of the natural water cycle, and in its natural form, rainwater is generally clean and uncontaminated. However, once the precipitation flows over urban surfaces, impurities and contaminants are introduced into the water. The contamination level present is largely dependent on how contaminated the surface is on which the water falls. The runoff from lawns and rural areas is generally less polluted and cleaner. In cities however, the condition of water is much worse due to the city traffic. Polluted city conditions, in places such as Hamburg, lead to a more polluted runoff, in addition to an increase in the material inflow and the hydraulic load.
Rainwater in the HAMBURG WATER Cycle®
In many parts of Germany rainwater is separated from blackwater and greywater and it is discharged separately (separate sewers). In Hamburg, there are still areas where the rain is discharged together with wastewater from households and industry, in so-called combined sewers. This means that during heavy rainfall the capacity of the sewer may be exceeded, leading to an overflow, and a discharge of the combined sewage and the thus the pollutants contained within. The aim of the HWC is to divide the individual wastewater streams and to manage the stormwater in a manner which is on-site and as natural as possible. Thus, the rainwater may be used for local purposes, such as watering lawns, for example. Alternatively, the water can be managed using decentralized methods such as retention ponds, where water is able to either evaporate or join nearby waters. The actions of decentralized rainwater management improve both the so-called micro-climate in addition to the recharge of groundwater. Another advantage is the decreased load on the sewer and water-way systems. The separation of the rainwater from wastewater streams has notable benefits such as: a strengthening of the natural water cycle, a reduction of the risk of flooding and high-waters, as well as increased drainage capacity for the future.