PATRIMONIO, URBANISMO Y MEDIO AMBIENTE DEL AULA A LA RED

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Sustainable Urban Drainage Systems

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Pedro Ortega Montes

Faced with an exponential increase use of the water resources of our planet, in part associated with the population growth. What we know as Sustainable Urban Drainage Systems looks as a feasible solution to this problema.

Based on the data provided by UNIFEF, the water needs of our planet could be summarized in the following points:

  • 2/3 of the world’s population live in water-scarce areas for at least one month a year. This percentage of the world’s population is concentrated in China and India.
  • The ratio of water consumption to local renewable water resources is 2 to 1. Around 500 million people live in this situation.
  • Some areas where groundwater continues to decline depend on water transfers from other water-rich areas. Due to the massive development of urban areas there are run-off problems arising from the modification of land use.

Due to the massive development of urban areas there are run-off problems arising from the modification of land use.

Classic drainage systems have unquestionably contributed to the denaturation of urban environments. Cities today tend to develop by understanding rainwater as a problem to be disposed of as soon as possible.

Since the implementation of SUDS, the aim is to improve the treatment of run-off by modifying the design of cities so that we create large sources of rainwater collection.

SUDS are not only proposed as a solution for reducing water consumption, but also as a way to reduce pollution associated with urban drainage (Animal waste; garbage and waste; road traffic; erosion of pavements, etc.)

We could describe it as an approach to urban development through a sustainable design whose main purpose is to imitate, as far as possible, the natural behaviour of a basin (U.S.E.P.A, 2012). By focusing it in such a way that we can not only reduce the amount of rainfall runoff in terms of flow and volume. Through the use of these treatments we manage to improve the quality of the water circulating through the runoff; and it brings benefits to the environment in terms of environmental quality.

The techniques applied can be classified from different points of view, the classification to be dealt with in this article will be depending on whether they require a constructive project (Structural measures) for implementation or whether it can be corrected by reducing or improving runoff (Non-structural measures) through education policies, planning and awareness of the citizen without the need for any specific intervention.

  • STRUCTURAL OPERATIONS:

This section is dedicated to the systems used in the Good Practice example of this article, so that we improve your future understanding.

 – Green roof, are a multilayer system, composed of a substrate with vegetation which can be intensive (with large vegetation, even wooded) or on the other hand vegetation with plants type sedum or lawn. Depending on the needs of the area of implantation, so if we want to reduce run-off drastically we will choose for extensive vegetation, while if what we are looking for is a re-afforestation from the area will be chosen the solution offered by the intensive vegetation.

The benefits of this system will therefore be:

– Decrease mainly the volume of runoff.

– Reduce the impermeable area

– Large amounts of precipitating water are returned to the atmosphere both by evaporation and by the transpiration of plants, with the resulting elimination of contaminant.

– It offers a high ecological, aesthetic and recreational value.

– Water collection by installing a waterproof membrane under the draining layer formed by the vegetable substrate.

Filtering drains/draining pavements, are filtering ditches that, generally, has a perforated drain at the base. They can also consist of cells and reticular boxes wrapped in geotextiles and granular material. They receive runoff from the adjacent waterproof areas along the sides. This runoff is temporarily filtered and stored in the gravel or crates, while being transported downstream of the system through the drain.

Benefits:

  • Reduce run off pollution levels
  • Reduce peak flow
  • It is use as runoff transport
  • Can be created or designed by creatively way to build attractive edges

Figure 01; Model of the function of a drain filter. Source: LDS blog: http://sudsostenible.com/

  • Water reservoir, these are simple structures that allow to store rainwater use. It intercepts run-off from the green roof or drain system. The water Will be stored for use in uses that do not require a high quality level to be involve for example as drinking water, such as the use of irrigation for garden áreas or to feed the cisterns from the bathroom, after the minimal treatment.

Benefits:

  • Reduce the water Bill
  • Improve the operations of the municipal sewerage systemn, as it prevents relatively clean water from get inside the system.
  • It can be visually attractive and with a correct landscape.
  • This is a componen of green roof, which contributes to get certificate as sustainabilty infrastructure
  • NON STRUCTURAL OPERATIONS:

The actions included on this part will not be capable to be build but could be included by the public administration to promote the proper use of infrastructure relating to the improvement of public roads.

To sum up, I will explain the description of the works carried out in the urbanization “Las Tres Carabelas”, located in Velez-Malaga (Malaga). The urbanization covered by this article is a group of 50-year-old buildings which presented problems of flooding around their surroundings, in particular the landscaped areas. The following actions were proposed:

  • On the roofs of the buildings, 340 m 2 of green roof has been installed consisting of intensive vegetation on an impermeable membrane that incorporates a cubicle system in order to obtain a passive irrigation before normal floods and collection of excess water by a pile system that connects all buildings to the buried water reservoir located at an equidistant point. Collecting up to 170,000 liters/year.

– To this first system we will add the installation of filter drains along the perimeter of the urbanization and in areas with a potential risk of flooding. These drains were executed with special attention to the minimum slopes necessary to ensure the correct transport of rainwater to the buried water reservoir. This time 150 linear meters of filter drains were run in the areas described above, which were able to collect annually a total of 5,000 liters/year.

Following the implementation of both Urban Systems of Sustainable Drainage, it was possible to reduce run-off affecting urbanization and to create an autonomous system for watering the green areas of urbanization and feeding the cisterns of the bathroom pool (4 tanks).

Graphic material added to the article:

Figure 02; Infographic by own modelling, Which is a great comination of photovoltaic plates over the green roof. Location: Urbanization “Las Tres Carabelas”, Vélez-Málaga (Málaga).

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