Conventional rainwater drainage
Until a few years, the drainage of sealed surfaces was almost exclusively carried out through drainage systems. Traditional stormwater management was mainly to drain high peak flows away and was restricted through the use combined and separate systems. The results are an extensive network that was built up over the decades. The total length of all drainage systems in Germany is expected to be in the order of 1 million km.
Without any doubt, the goal and purpose of this reliable urban drainage system was achieved however; runoff from such sealed surfaces has a high velocity and loaded with pollutants, which regularly adds up to the drainage systems.
The aims of draining urban runoff as quick as possible with channels and pipes, increases peak flows, hydraulics stress and costs of stormwater management. Thus this type of solution, in most cases, transfers flood problems from one section of the urban catchment to another one.
Not only these types of infrastructures may have difficulties in draining stormwaters, with increasing urbanization, but this approach is in the way of an Integrated Urban Water Management that puts back city stormwater in a sustainable natural cycle.
In addition to this, construction and operation of conventional storm drainage systems requires a non-negligible investment. In Germany, the total cost for a new system, along with the necessary maintenance, is in the order of 10 billion € per year.