Rainwater Harvesting and Reuse and Rainwater Runoff in Barcelona Thanks to The WSUDs (Water Sensitive Urban Design Systems)

Abstract

Water sensitive urban design (WSUD) is an approach to planning and designing urban areas to make use of this valuable resource and reduce the harm it causes to our rivers and creeks” WSUDs (Water Sensitive Urban Design Systems) try to integrate the urban water cycle in the urban design to improve the environmental behavior in the urbanization of the cities. When we urbanize we transform pervious surfaces into impervious surfaces. With WSUDs pervious surfaces are implemented.

Water presence should allow rainwater harvesting, decrease water runoff and improve surfaces thermal behavior. The two first hypothesis will be shown in this research. Thus the main question is: could it be possible to reduce water consumption and rainwater runoff thanks to WSUDs in the city of Barcelona? This paper shows a study case trying to answer this question in a flood area. The last question, about surfaces thermal behavior was explained last year in the CTV’2018. This two articles are a part of the current thesis taken by the author of which Dr.Josep Roca and Dr.Dolors Martínez are tutoring. This part of the research uses a calculation methodology (while the CTV2018 Congress showed an experimental methodology).

As climate change preview more intense rains in our territory the last IDF curves registered by the Fabra Observatory will be used instead of the IDF curves calculated with the MaxPluWin previously by the author due to the fact that the Fabra ones are more precise. Some considerations will be taking when using the “project rain” in order to approach it to the real pluviometry. Thus, reserve period of the water depos will have to be modified in the future and floods in the streets might be increased.

Trying to improve flood effects, water scarcity and the heat island effect, the WSUDs with better thermal effect could be used in some cases harvesting rainwater and reducing the rainwater runoff. This better thermal effect means that WSUDs surface temperature, in some cases, is lower in summer than the environmental temperature2.

This WSUDs implementation can be used as an urbanistic micro-acupuncture practice. Rainwater runoff also gets to the depuration central station much more polluted after urbanizing if WSUDs are not considered. Therefore, WSUDs allow to improve water quality when it arrives to the water treatment plant as well and reduce energy in its transportation to the sewage treatment plants.

Another question is in which area is better to harvest water if we need a good water quality. It will be possible to treat it, always or with hypochlorite or with ozone but the numbers of molecules required if we need to clean rainwater mixed up with oil or gasolines or without them reduce are much less. Also studies of water quality in blue roofs or green-blue roofs show that the best construction system is a green-blue roof. It’s been studied previously although it won’t be explained in this paper for not being the main goal.

The research is focused to work on the most flooded areas in Barcelona by changing impervious surfaces into pervious ones getting rainwater to be reused and removed from the streets. In the studied area results show a not negligible water quantity which could supply some domestic uses of the dwellings in the flood area, in this study case.

Although reducing rainwater with WSUDs is not new for the Barcelona Municipality, using their constructions as a complementary system to reduce water consumption in the city using systems which, at the same time, reduce surface temperatures, are added values studied in this paper. Currently Barcelona has some WSUDs in some areas just to minimize rainwater runoff but reduces water consumption thanks to phreatic waters. The study case shows an alternative, another way to reduce rainwater runoff and water consumption while improving surface temperatures of the city.

Brief, this preliminary communication tries show how we could reduce water consumption, rainwater runoff and “heat island” effect thanks to the WSUDs construction systems.