SUSTAINABLE DRAINAGE, WATER RESOURCES AND WATER QUALITY
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Introduction
At the end of this year 2009, our Basin Organizations must face the challenge of presenting their Management Plans, according to the guidelines set by the European Water Framework Directive.
Everything seems to indicate that with a Directive designed for European rivers with generous flows, our modest rivers and other bodies of water have serious difficulties in complying with the long-awaited standards, both in terms of quantity and quality. For these reasons, it is one of the best times to stop looking at our navels and learn from the experiences of other countries where, with resources and rainfall similar to ours, they have been replacing their traditional drainage systems for years to adapt them to the new needs. Among these systems, due to their broad advantages over the others, those of drainage by storage and infiltration at source stand out, which are timidly beginning to be used in our Country under the proper name of “Sustainable Urban Drainage Systems” (SUDS).
In summary, this communication aims to put into question our current drainage systems, comparing them with the so-called Sustainable Drainage Systems.
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Advantage
The main advantages of these systems is that they do not discharge pollution to the receiving media, unlike ours, mostly of a unitary type. On the other hand, they drastically reduce runoff flows, thereby minimizing flood problems. Last but not least, they increase the volume of available water resources (both underground and surface), thus compensating for the unstoppable process of urbanization and waterproofing of the soil.
Thus, while our traditional drains discharge the water into the rivers as quickly as possible, causing floods and heavily polluted discharges, the SUDS retain the runoff water and filter it in the unsaturated area of the land, taking advantage of its great natural purification capacity. Already in the saturated zone, these waters become part of the underground resource or resurface and return to the rivers as an additional surface resource, of excellent quality to be used for human consumption and also capable of being turbined in hydroelectric power plants. down.
Therefore, these systems are based on the storage and / or infiltration of runoff flows in the place where they originate, either next to the downspout of a building, in the ditch of a road or under the surface of a street or parking, under a park, or even on the roof or inner courtyard of a home. The principle is very simple and known: Divide and conquer.
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Applications
Among the main applications in which these systems are beginning to be used, the so-called “anti-tip gutters” stand out. These ditches come to solve the problem of accidents due to leaving the road on our roads and highways. This problem appears as a result of the large unevenness produced by traditional ditches, which have previously been solved through the use of bionda-type barriers or even by reducing the depth of these ditches by expanding their width, with the corresponding increase in expropriation costs and damage to the road.
But the main objective of these ditches is none other than to keep the roads free of water during rainy episodes, solving in addition a series of problems that, like the issue of overturning due to road exit, mean collateral problems of our current drainage systems.
Thus, as in the case of gutters, the main applications of the so-called sustainable drainage systems have to do with the evacuation of rainwater in the different works designed and built by human action.
Few of these works are likely to be spared, since most of them involve waterproofing surfaces that were previously more or less permeable. Therefore, as in many other cases, man’s action tends to quickly and effectively solve a problem that he has generated himself: having to evacuate the water generated by an impermeable surface that was not previously impermeable. This is the case for all paved surfaces such as roads, streets, roofs and roofs of buildings, car parks, airports, etc.
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Implantation problems
Despite the obvious advantages of these systems, at this point we find the strong inertia of the civil engineering sector due to standardization. Thus, there are few references in our road regulations (Instruction 5.2.I.C) to seepage drainage systems. In this, as in many other cases, the sectoral regulations attempt to effectively solve the problems that concern them, without taking into account other factors that affect, in a way that is difficult to quantify, other administrations. This is the case of the quality of the waters that are discharged, the underground resources that are lost or the effects on the environment that can be caused by these and other factors.
It is entirely evident that a sectoral norm cannot be asked to oblige us to take into account, and therefore force to re-study these factors every time a road or street is designed, but it does provide tools to assess whether it is more convenient to use one or the other system depending on the location and characteristics of the problem to be solved.
On the contrary, in our regulations there is no clear methodology for calculating drainage systems, having to resort to multidisciplinary knowledge that requires mastering meteorological, hydrological and geological aspects that are rarely applied in current civil engineering. Therefore, despite the fact that in some cases the applicability of infiltration systems is beyond all doubt, the fact that our regulations recommend and specify the traditional design methodology for ditches and tubes in free sheet, makes us discard in many cases a much more effective or even cheaper system in the long term.
The second problem to take into account is the lack of knowledge of these systems in our country, despite the fact that the most advanced countries in these matters, such as the United States, France, Germany or Australia, already have long years of favorable experience in their use. . In the case of Germany, for example, its design is standardized by an ATV standard.
But this ignorance brings in addition the main obstacle with which these systems are, and is the conservative option of the engineer on foot, legal and irreproachable, who decides to avoid the risk of adopting a non-standard solution and not covered under a regulatory umbrella Clear. That is why a regulatory advance in this sense is urgently needed to accommodate these systems, accompanying the technological development of civil engineering, which can have such an impact on the development of the country itself.
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Influence on Water Resources
At a time when the problems of climate change are lurking, and we are very aware of the correct management of water resources, knowing how we manage rainwater has a special impact and, above all, if we could do it better. We are talking about a large-scale problem, a part of our country is desertifying, which implies that runoff increases and in turn increases the loss of soil and decreases infiltration. Result: underground resources decrease and we “dump” more water into the sea.
Meanwhile, we continue to design our drainage systems to compensate for the waterproofing of the surface by evacuating rainwater as quickly as possible to the nearest riverbed or to the sea. Well, if we want to maintain our water availability and therefore our level of wealth in the coming years, we have no choice but to manage rainwater in a different way: we have to change our drainage systems to compensate for waterproofing. RESTITUTING the flow of rainwater into the aquifers and even increasing this flow. Only in this way will we be able to change the negative trend in the availability of underground resources in recent years.
To get an idea of what the waterproofing process can mean in our country, although only 2.1% of the territory is urbanized, if we look at the most populated autonomous communities, the community of Madrid reaches 11.7%, followed by the Balearic Islands with 5.1%, Catalonia with 4.5% and the Valencian Community with 4.3%. This means that an important part of the underground water resources generated by the infiltration of rainfall has been irretrievably lost and mainly during the last century.
But the availability of underground water resources also has an impact on the availability and stability of surface resources, since aquifers largely regulate the flows circulating through our rivers. This fact, in turn, has a strong correlation with the hydroelectric power generation capacity, especially in the so-called “flowing power plants”, which are fed by circulating flows and that, unlike the dam-standing plants, cannot take advantage of the flows of avenues of the rivers.
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Influence on the quality of surface waters
One last point to comment, but not least, is the issue of surface water quality. Most of the drainage systems in our country are of the unitary type, that is, they use the same conduit to transport wastewater and rainwater. This type of system presents a specific problem in that the treatment plants cannot cope with the extraordinary influx of flows during a rain event.
For this reason, during most of the rain events there are polluting discharges to the receiving environments, that is, our rivers and coasts. These discharges are called DSU (Unitary System Downloads). To alleviate these problems, policies are being developed in Spain aimed at alleviating the problems of these systems, mainly promoting the construction of anti-DSU reservoirs whose mission is to retain water from unitary systems during the rain event. Subsequently, these volumes of water are usually treated in the treatment plants in the hours after the episode.
It is precisely the high cost of these anti-DSU systems that should make us rethink the situation to find other solutions that can solve the drainage function without having as a consequence the need for additional investment to reduce discharges to <receiving media and additional costs. debugging. Here, as in the matter of solid waste, it must be separated in order to better manage it.
Now, as soon as we talk about separating, we find ourselves with the dilemma of whether we can solve the problem through the well-known “separative networks”, as indicated by abundant regulations at the level of the Autonomous Communities or Hydrographic Confederations. These drainage networks, in addition to duplicating the hydraulic infrastructure, greatly increasing costs, still does not have enough empirical knowledge to be able to affirm that they have a more or less beneficial effect on the environment. So much so, that in some cases pollution levels similar to those of a unitary network can occur. In this sense, sustainable drainage systems, by infiltrating rainwater into the subsoil, are already a type of separative network, but without the drawbacks of tube networks that transport water and pollution to receiving environments.
On the contrary, these systems infiltrate the rainwater in the unsaturated area of the land, taking advantage of its purification capacity, a capacity that has lately been coined the name of GEODEPURACION.
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Conclusions
Today we are obliged to remember the creation of the Hydrographic Confederations in our country in 1926, which has allowed us to turn it into one of the first economies worldwide in just over 80 years, through a long journey in which He highlighted first the development of irrigation, then industrial development and finally the supply to large cities.
With 80 years of delay, the Water Framework Directive reminds us of what we already knew, and forces us to seek solutions to the problems that beset us today, those innovative, imaginative and technically sound solutions such as those that have allowed the development of our Country in recent years.
What will be the future of our drainage systems? Will it eventually reach a total capacity comparable to that of our largest dams? Will we be able to change the downward trend of our available resources, attributed to climate change?
Therefore, a revolution in our drainage systems is necessary in order to continue evolving in the correct management of our main resource for development: Water.