Portal de Cartagena
www.portaldecartagena.com
In order to clarify the possibility of dispensing with storm tanks in sensitive areas such as the Mar Menor, a debate that has arisen in the Region of Murcia in recent days, and based solely on technical approaches, the experts in Hydraulic Engineering and Sanitary of the Polytechnic University of Cartagena (UPCT) believe that it is necessary to explain the following: The anti-pollution storm tanks are intended to reduce the discharge of the flows transported by the sanitation networks during an episode of rain, do not serve to prevent flooding.
If that were the purpose of these infrastructures, their scale, location and design would be totally different.
Anti-pollution storm tanks are considered necessary tools in consolidated urban areas and this is included in the legislation of most countries of the European Union.
Several Spanish cities have protected their receiving media, ravines, rivers or the sea from discharges from sanitation networks through these infrastructures.
Multiple examples can be cited as those of cities such as Madrid, protecting the Manzanares, Alicante, its beaches, or Bilbao the Nervión, and of course in the big world cities, such as London or Tokyo.
It has been quantified and contrasted that up to 30% of the pollution transported by sanitation networks throughout the year can reach the receiving environment through discharges during the rain episodes.
Hence the need for these building elements, which are integrated into the sewerage system.
This is the reason why RD1290 / 2012 appears in our legislation, which obliges us to dispose elements of the anti-pollution tank type in sanitation systems and give us a deadline of 2019 in many cases.
Anti-pollution storm tanks retain a part of the pollution generated by street washing or sanitation networks in our cities when it rains, and the fact that they fill and overflow can not be deduced that they are not fulfilling their function , many of them work to retain only the first most polluted waters and the rest is discharged.
The volume is calculated to ensure that they store a percentage of the water that can not be moved in the treatment stations due to lack of capacity of the sewer network and the sewage treatment plant, and that in the absence of a tank it would go directly to the receiving environment.
In general, to retain around 90% of the pollution that can be discharged we will need an anti-pollution tank that stores the runoff from a rain of between 15 and 25 liters, much less than the rain of last December 2016 that exceeded 200 liters.
In that case, the rains in the field of Cartagena generated runoff in the so-called Rambla de la Maraña of more than 8,000,000 cubic meters of water that crossed the urban core of Los Alcázares.
The Anti-pollution Storm Tank in Los Alcázares should have a volume of around 3,000 m3.
Obviously this tank is not designed to avoid floods, it is easy to observe a difference in capital scale.
And is that these infrastructures are not designed for rains that occur once every 10 years, or as in the case of Los Alcázares last December once every 100 years.
These extraordinary episodes do not impede the function developed by the holding tank of a high percentage of pollution for ordinary rains at the average year scale.
Understanding the utility of a treatment plant when it does not rain, we must also understand that when the rainwater treatment plant has neither the capacity nor the time to treat rainwater, several orders of magnitude higher, and therefore a deposit is required to store said water to be treated later.
As engineers and technicians specialized in this field, we want to advise in an appropriate way to the different social actors so that they have the adequate information at the time of adopting their decisions.
In this case, it is an environment that receives discharges, the Mar Menor, which will not be able to minimize discharges, dispensing with tools as useful as anti-pollution tanks.
Source: UPCT
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