El Miramon ForestThe riverbank, one of San Sebastián's green lungs, has opened two new rainwater retention ponds that are now fully operational. These structures have been built in the streams of Pakea and Altzaerreka and are considered key components within the city's natural drainage system.
With this intervention, the City Council of Donostia / San Sebastián reinforces its strategy to deal with episodes of heavy rainsincreasingly frequent, and improve the management of the water that reaches the Urumea riverThe project combines flood protection criteria with a clear commitment to environmental quality and landscape integration within the forest environment.
A strategic project for the natural drainage of the city
The new retention ponds have been designed as key points of the natural drainage system in San Sebastián, taking advantage of the network of irrigation channels in the Miramon forest. Its main function is to regulate peak flows during storms, preventing water from suddenly reaching the lower areas of the city.
As explained by the Councillor for Maintenance and Urban Services, Carlos GarciaThe intervention pursues a very specific dual purpose: on the one hand, reduce the risk of flooding in particularly sensitive areas such as the environment of Anoeta and the neighborhood of AmaraOn the other hand, limiting the volume and load of towing that ends up flowing into the Urumeathus contributing to preserving the quality of the river's water.
The City Council emphasizes that these ponds do not function as permanent reservoirs, but as temporary retention infrastructure which remain practically empty under normal conditions. They only partially fill when heavy rainfall occurs, retaining some of the flow and releasing it more gradually.
In this way, the Miramon forest is consolidated as a multifunctional spaceIn addition to its recreational and ecological value, it plays a relevant role in the city's adaptation to climate change and extreme rainfall events.
Details of the ponds in the Pakea and Altzaerreka regattas
In the regatta of Pakea A retention pond has been constructed with a maximum capacity of 480 cubic metersIt is located downstream from a pedestrian footbridge and just before the underground section under the road. GI-20, a particularly sensitive point when the flow rate increases suddenly.
Pakea's structure has been configured in such a way that allows the passage of the usual ecological flow without altering the normal course of the regatta. It only comes into operation during periods of heavy rain, at which time it acts as a buffer that retains some of the water, controlling flooding and preventing the pedestrian walkway and nearby areas from becoming inundated.
In the case of AltzaerrekaThe pond is larger, with a maximum retention volume of 901 cubic metersIt has been located upstream of the underground tunnel. Miramon roada busy route close to bike pathwhich also benefits from this additional protection against overflows.
This second pond is specially designed for to retain water flows These barriers are installed during periods of extraordinary rainfall, protecting both the bike lane and adjacent areas. This reduces the risk of damage to infrastructure and improves the safety of pedestrians and cyclists who use these routes daily.
Both actions have been designed to adapt to the morphology of the regattas, so that the hydraulic function It is combined with the conservation of the landscape and environmental values ​​of the surroundings, using appropriate materials such as Bentonite for pondsavoiding overly rigid or visually aggressive solutions.
Integration into the landscape and respect for the urban forest
One of the most carefully considered aspects of the project has been the landscape integration of the new infrastructure in the Miramon forest. Solutions such as the following have been used for this purpose: vegetated breakwaterwhich allows for the stabilization of slopes and channels while simultaneously promoting colonization by native plant species such as juncus acutus.
During the execution of the works, the following have been established strict limitations on the use of heavy machinery In order to avoid damage to existing vegetation and forest soil, the intervention has been planned so that access, stockpiling, and earthmoving are kept to the absolute minimum.
The City Council emphasizes that the work on the Pakea and Altzaerreka regattas has been carried out respecting the character of an urban forest Miramon, avoiding unnecessary logging and prioritizing the protection of established habitats. This philosophy aligns with European policies that promote nature-based solutions for water management in urban environments.
In addition to reducing the risk of flooding, ponds can exert a complementary ecological function by creating small temporary wetlands that, although not their main objective, can be beneficial for certain invertebrates and birds associated with riparian environments and for plant species such as Aquatic Mentha.
Investment, deadlines and support from European funds
The construction of these retention ponds has involved a total investment of 821.800 Euros, an amount that the City Council considers justified by the direct impact on the flood safety and the associated environmental improvement. Some official documents specify the figure more precisely, placing it around 821.800,57 Euros.
The work has been completed within approximately three monthsThis significantly reduced the initially planned five-month timeframe. This acceleration of the work has allowed the infrastructure to be operational before the periods of greatest risk of heavy rainfall, minimizing disruption for the neighborhood and users of the Miramon forest.
The technical project has been drafted by the company Girder Engineers commissioned by the City Council's Department of Maintenance and Urban Services. The action is part of the municipal strategy called "Sustainable environmental management of rainwater and streams in Donostia-San Sebastián", which articulates different measures to improve the hydrological behavior of the city.
This strategy was selected in 2022 by the Biodiversity FoundationThe project was funded by the Ministry for Ecological Transition and the Demographic Challenge, through a specific call for proposals for climate change adaptation projects. Thanks to this funding, the project has been able to be financed with European funds NextGeneration EU, framed within the European Union's Recovery and Resilience Facility.
Technology and continuous monitoring of hydraulic behavior
Beyond the physical works, the City Council has opted to incorporate monitoring technology in the new ponds. Both infrastructures have level sensors which allow continuous monitoring of the hydraulic behavior of the Pakea and Altzaerreka streams.
These devices make it easier to have real time data This information is particularly useful for improving preventative management, anticipating potential problems, and optimizing future actions related to sustainable urban drainage.
The combination of retention works with telematic monitoring systems is part of a growing trend in Europe towards solutions of green and blue infrastructure supported by digital tools. In this way, cities like San Sebastián are moving towards more resilient and adaptive water management models.
In the medium and long term, the data collected by the sensors can also be used to evaluate the actual performance of the ponds, comparing the design forecasts with the observed behavior, and adjusting, if necessary, the criteria applied in similar future projects.
With the commissioning of the retention ponds in the Miramon ForestSan Sebastián takes another step in modernizing its natural drainage system, combining discreet, landscape-integrated hydraulic works with European-funded control technology. The result is an intervention that helps reduce the risk of flooding in areas such as Amara and Anoeta, protects the quality of the Urumea River, and reinforces the role of the urban forest as an ally against the impacts of climate change in the city.
