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Rain Garden Can Be an Efficient Solution for Drought and Overheated Cities

11.09.2018

High temperatures and extreme droughts during the summer season have negative impact on the quality of life of city inhabitants. Concrete buildings and their asphalted surroundings accumulate very much heat, resulting in so-called heat islands. We addressed this topic recently in the article about green roofs. Preventing the drought and overheating of cities should be achieved by using, besides green roofs and facades, also specifically designed gardens for retaining rain water from the surface (so-called rain gardens). Two experimental rain gardens can be found on the premises of CTU UCEEB. These are used, besides its natural function, also for research.

A cosmopolis, when seen from above, looks like an artificial island where heat gets accumulated due to concrete and asphalt surfaces. These heat islands are significantly warmer than the suburb environment. Rain water in cities flows directly to sewers as quickly as possible, and this prevents the natural evaporation of water into the air. As a result, the hydrological cycle which influences the climatic conditions is disrupted. This can be prevented by proper management of rain water and by incorporating rain gardens, green roofs and greenery into city infrastructure.

The purpose of rain gardens is to retain all precipitation before the water flows into sewers. This way, overloading of the sewer system is prevented and the risk of floods as well as the pollution of surface streams is decreased. By soaking in, the supplies of ground water are renewed and by evaporating from surface, the natural hydrological cycle is reinforced which has a positive impact on climate stabilization. Under the term “rain garden”, we can imagine a terrain depression, lower place in the garden or a bed with special plants which can capture and retain water in the root system before it either soaks in and gets filtered through soil layers into ground water, or evaporates.

Two identical experimental rain gardens established in December of 2017 can be found at CTU UCEEB. Water from the roof of the Crawl Space experimental house is brought to one of the gardens. The other rain garden draws water from the supply tank. CTU UCEEB experts monitor the humidity and soil potential, filtering layers, water level in the rain garden and also, for the purpose of evaluating the water regime, the amount of inflow and outflow water. The aim of both experiments is to check the quality of water in the long-term perspective and to observe changes in each soil layer of the garden from the point of view of permeability, retention of water, clogging up small holes with fine particles and capturing heavy metals. In future, periodical soil sampling for final evaluation of the development of functions of the filtering layer in long-term horizon is planned. As early as before starting to build these two experimental rain gardens, pilot surfaces of rain gardens were established here and the first evaluation related to changes of soil structure took place. The evaluation was carried out using soil samples taken from pilot surfaces of rain gardens after two months of growing plants on which infiltration experiments with exploring the soaking capability of soil were performed. The course of the experiment has been recorded using neutron and X-ray photography. The research is carried out under the project No. 17-21011S of the Grant Agency of the Czech Republic.

Dešťové zahrady na ČVUT UCEEB Dešťové zahrady na ČVUT UCEEB