Minimize floods by imitating nature

Could the tragedy that Valencia is experiencing have been avoided? And from now on, what needs to be done to prevent future floods in a context of increasingly frequent extreme events? «When it comes to an exceptional flood like in this case there will always be some damage, but we must try to minimize the risk, especially in built areas by improving soil infiltration. Measures must also be applied upstream and agricultural and forest lands should be sponged, river spaces expanded and riverside vegetation increased. It is about reducing as much as possible those peaks of water drag that function like a tsunami,” says Carles Ibáñez, scientific director of the Center for Climate Resilience (CRC), who points out the case of the Mississippi, which has had channels parallel to the river since 1927 to prevent New Orleans from flooding.

The College of Civil Engineers, Canals and Ports recalls that in 2007, and in collaboration with the Júcar Confederation, a flood risk management plan was made for the Rambla del Poyo – one of those that has now overflowed. –, and solutions were reached that from an economic point of view “were perfectly viable, but were never implemented. Among them are a upstream reforestation plan; the construction of a set of micro-dams to reduce runoff and in the flood zone, the establishment of green corridors to collect the water and redirect it to the new channel of the Turia. Furthermore, as published this week In 2001, the National Hydrological Plan was approved, which included the construction of a dam in Cheste, just a few kilometers before the area affected by DANA. The dam disappeared from public plans after the withdrawal of the Hydrological Plan during the Zapatero government.

Beyond improving or applying warning systems and educating, the first thing is not to build in flood zones, say Ecologistas en Acción. In Valencia, Alicante and Murcia alone there are 280,000 homes in floodplains. «It is urgent to force the immediate adaptation of municipal plans to the Mapping of Flood Zones and Preferential Flow Zones and to the effective fulfillment of the obligation to inform the purchase and sale of homes of their location in flood-prone areas”, they say. The organization is also one of the many organizations that ask for clearer adaptation measures in the face of events of this type: “Urgent and more forceful mitigation policies (reduction of emissions, conservation of biodiversity and ecosystems) and adaptation are necessary.” to climate change. Something that the IPCC has been insisting on since 2022.

Gray and green works

The adaptation covers a wide catalog of solutions: «Very simple works can help evacuate large quantities of water that are naturally dammed simply by facilitating its exit into its natural channels. From the elevation of infrastructure or equipment to the creation of controlled temporary flooding zones, very useful in those cases in which the system of motes or flood protection dikes is exceeded by the floods, at which time, these motes or Overtopped dams become counterproductive,” says Rosa Arce, member of the Water, Energy and Climate Change Commission of the College of Civil Engineers, Canals and Ports. And it is that «The classic means based on putting cement, cleaning ravines are falling short and we must take another leap with solutions based on nature,” says the director of the CRC.

The Netherlands suffered a wave of floods during the 1990s. After them, the government implemented an extensive program of measures that aimed to leave “room for the river.” The works began in 2007 and concluded in 2018. There were 30 projects aimed at restoring the flood plain of four of the Rhine, the Meuse, the Waal and the Ijssel, so that they could overflow safely. It included creating water buffer zones, relocating levees, increasing the depth of lateral channels and constructing flood diversions.

From Holland to Spain

Miriam García, director of Landlab, an architecture studio in Barcelona specialized in resilient urban projects, points out the difference between the Dutch example and the solutions that are being adopted in some Spanish locations. «The Netherlands is below sea level and very used to working with floods, but as much as it is an inspiring example, we cannot apply everything that is successful in other places. You have to take into account the particularity of Spain, in the Mediterranean cities you have to work between aridity and floods. Here there are two types of effects or impacts of climate change: those that have to do with increased temperatures and those that have to do with river and maritime flooding. For the first type, cities would have to be greened and heat island effects reduced. And in the second case it means more control over the water cycle to transform cities into sponges. For this, there are many measures that can be applied to retain water that can later be used to fill aquifers or irrigate. Cities have more autonomy to make decisions but when it comes to rivers or coasts there are several administrations involved that have to coordinate. What we see is that in general not much is being done.

There are several examples in Spain that nature-based solutions are capable of minimizing flood damage. The La Marjal flood park was the first in the country; It was inaugurated in 2015 and was planned after the floods of 2007. It was built near San Juan beach in an old marshland area and now the full urban center. The flood zone is capable of absorbing 45,000 m3 of water.

He Zaragoza water park It is another example of intervention; in this case on the left bank of the Ebro River. It takes advantage of an already existing forest, expands it and manages it “offering space for overflow and natural filtration to the river. The river forest has been reduced, over centuries, to make room for agriculture. The Park returns a good part of the surface of the meander to the riverside forest,” says the Aldayjover architecture studio. For its part, the Barcelona Superillas project included this type of solutions for water management. Enric Grandados Square, For example, it has a naturalized garden and an urban water drainage system that prevents up to 85% of surface runoff.

A dune for Benidorm

►If we talk about the coast “it must be adapted to maritime storms. Cement boardwalks can be replaced with natural dune systems or pine forests can be installed to help fix the water. On the coast these projects are more linked to natural spaces. There are no projects in cities,” says Miriam García from the Landlab architecture studio.

That is, precisely, one of the proposals for the city of Benidorm, one of the main tourist destinations in Spain and which, “however, due to its location in an area prone to especially intense storms, has suffered damage several times, especially on the promenade and surrounding areas. In order to mitigate this phenomenon, the creation of a dune with vegetation that acts as a barrier between the water and the city’s infrastructure, capable of containing a flood of at least three meters, has been proposed. To protect the beach from erosion caused by river flooding, the implementation of vegetated sand dams is proposed to channel the flow of water from the ravines. A cobblestone is placed to reduce the speed of the flow and the promenade is provided with pebbles to limit the combined action of river and coastal flooding,” explains engineer Rosa Arce.