Anàlisi cost-benefici per la implementació de sistemes urbans de drenatge sostenible (SUDS) al municipi de La Garriga

Abstract

Nowadays a large part of Catalonia’s sewer systems are combined sewer systems, which means that they are deriving the rain water and the wastewater together into the Wastewater Treatment Plants (WWTP). These systems were considered as problematical, furthermore if the city has an old sewer system like La Garriga. During heavy rainfall events when the conduits’ capacity is reached, there is a wastewater outfall through the outlets. The polluted water flows directly into the river. This causes high contamination with heavy metals, nutrients, pesticides and other compounds which became a negative impact for the environment. One way to achieve the reduction or to avoid these wastewater outfalls is to implement Sustainable Urban Drainage Systems (SUDS) with the aims to maximize the infiltration of the ground water to recycle it into the natural water cycle, to reduce the volume of water which flows into the conduits, to minimize the urban flooding and reduce the urban damages consequently. If we complement SUDS with storm tanks we can achieve better results related with the number and the volume of outfalls and attenuate the flow peaks created for the rain events. The purpose of this final work is creating or designing four possible scenarios with SUDS complemented with storm tanks for evaluate the efficiency of the scenarios on the current model. We started the project ENDERUS in 2014 with a calibrate model of La Garriga’s sewer system developed in ICRA (Institut Català de Recerca de l’Aigua) with the SWMM program (Strom Water Management Model). Subsequently, the dates are transferring into KOSIM, which is a software for continuously simulation, by Institut für technische-wissenschaftliche Hydrologie GmbH (Itwh) from Germany to built this four scenarios and run simulations to quantify and evaluate all the parameters related with outfalls and runoff-models of La Garriga. The last part of this study is selecting the best scenario, which presents the best percentages, values until 40% of reduction in the volume and number of outfalls, the peak of the flows increase 0.5m3/s, and other improvements we will obtain if we choose this scenario. Finally, we made out an approximated budget (10.905.750€) for the implementation of 20% of SUDS in each area and built two storm tanks with 1500m3 of volume, to give a approximate inversion for the city of La Garriga