The situation of Valencia in the Turia flood plain, on flat terrain and under a mountain range from which water arrives at high speed, poses a risk for the city that has been identified for years; In addition to the overflowing of the Turia in 1957, the Júcar also caused floods in 1982 and there is a list of more than 20 events that have occurred since the 14th century. These weeks there has been a lot of talk and debate about cleaning channels, urbanization in flood zones, dams and other water management measures. Some of these issues have even slipped into the questions of the Spanish Teresa Ribera’s exam before the European Parliament. And the images of puents clogged by reeds or streets full of remains of this species have been common during the flood. José Javier Sanchis Bretones, from Algemesí, reported on television a few days ago that in August 2023 and in July of this year he wrote to the Júcar Hydrographic Confederation (CHJ) to address the cleaning of the Magro river bed that runs through his town. and that joins the Júcar River at its terminus, and it has not been the only one to do so, farmers associations like Asaja have also complained about this. The war of responsibilities over who should carry out the cleaning is still in force, but should we intervene by cleaning channels or not? The answer: it depends where and it depends on what.
In the case of cane, it must be clarified that it is an invasive species, “arundo donax”, subject to various river eradication programs. The Ministry of Ecological Transition itself finances a program, Caña a la cane, to eradicate this species in the lower part of the Júcar. “The objective – says the project website – is to reduce the impact of high probability floods in the municipalities of the lower river basin with actions such as the management and control of invasive species and the recovery of native vegetation.”
If we talk about vegetation in general, things change. Ernest Blade, professor of Hydrological Engineering, professor at the Higher Technical School of Civil Engineering, Canals and Ports of Barcelona of the Polytechnic University of Catalonia and director of the Research Institute in River Dynamics and Hydrological Engineering clarifies that «Not cleaning in headwater areas has advantages because it helps the water go slower, which means that the flood effect is delayed. Yes, not cleaning can have a counterproductive effect when a lot of vegetation accumulates in certain points such as bridges. It is an issue that must be analyzed basin by basin because each torrent has its characteristics and its population. At the head it is better not to clean and in low areas it is usually convenient. For Rafa Seiz, WWF water policy coordinator, he says that it is precisely the vision we have of rivers that explains events like these. «The natural functioning of a river does not make cleaning necessary, but since we have installed bridge infrastructure, it may be necessary to clean to unclog areas covered by concrete. Dead vegetation must be promptly cleaned there. In Valencia there has been a problem of accumulation in specific points, but not due to native vegetation. The river tends to be considered a rapid drainage channel; In these cases the speed is accelerated because there is nothing to stop the progress and, in addition, the floods are concentrated because the river has no room to expand. “The idea of having a channel that moves water from one place to another is an old, engineering vision that does not take into account the environmental benefits of rivers.” The recipe then is to remove the excess cane, replace it with native vegetation and not leave the river empty of obstacles wherever possible. “With this erroneous idea of leaving the channels bare, we encourage the cane to grow more and more,” notes a report from the Center for Ecological Research and Forestry Applications these days.
Dams that reduce damage
The Forata or Buseo dams have played their role in this crisis. Forata, which flows into the Magro River, drained 1,000 m³/s at times during the rains. Before the episode, it was at 73.93% of its capacity and the water reached 379.20 meters out of a total of 384. Buseo also discharged up to 1,900 m3/sg at the Vilamarxant point, when “its usual flow is 5 m3/sg. The fear that it would reach its limit and a possible collapse forced water to be poured,” El Levante publishes. Before being almost exceeded, it was at 12% of its capacity, this medium points out. In fact, The dam now leaks in five places. «The dams have to have a regulation of flows that enter and leave. In an episode like this you do not have the ability to stop the flooding, you have to open and drain it to avoid endangering the stability of the structure. The damage of a collapse would be greater. We saw it in Tous during the dam break,” says Ernest Blade. The failure of this large dam on the Júcar River caused a flood with a peak of 16,000 m3/second in the year 82.
In addition to the role of existing dams, these weeks reference has been made to the approach of construction of a dam in Cheste in the National Hydrological Plan, approved in 2001 and annulled in 2005. The president of the Association of Civil Engineering Civil Engineering Engineers, José Trigueros, stated these days in the media that “this infrastructure would have mitigated the flood, although it did not could have completely stopped the flood” and urged public decision-makers to “stop cursing when talking about reservoirs, dams or canals.” Ignacio Escuder, a dam expert at the Institute of Water and Environmental Engineering of the Polytechnic University of Valencia, recalled in a recently held event that there is, in fact, a new dam planned in the general flood risk plans of the Confederation.
On the other hand, Europe’s 2030 plan, which says that at least 25,000 kilometers of rivers must be freed, continues to generate controversy. The Dam Removal organization recalls that Spain has eliminated 241 barriers on water courses in Spain, although the vast majority are small weirs. “Large dams were planned in the 1920s and now there is a global trend towards the retraction of these infrastructures,” says Ernest Blade, who also explains: “What happens upstream influences downstream. Large dams, in general, usually help avoid flooding downstream if they are properly managed, but they also have an impact on the territory. Large dams have two main uses: electricity and irrigation, and building more large dams is unfeasible, because the ideal sites are already occupied. As for weirs, there is now a tendency to eliminate them because the activities they served no longer exist: for example, powering small factories or irrigation. They represent a barrier to the ecosystem. These weirs also have little impact in terms of preventing flooding and laminating water,” he says.
The WWF technician adds: «It is difficult to answer what would have happened if more dams had been built without modeling. Given the exceptional nature of the episode, I don’t know if they would have been useful. From a purely environmental point of view, dams are not necessary, because they are a barrier that has consequences on the ecosystem and the dynamics of the territory. They represent an almost permanent interruption of the downstream flow. “Sometimes it is smaller than what would be expected downstream and when it is released it is much larger.” For her part, Annelies Broekman, member of Creaf’s Water and Global Change research group, also remembers that most dams have problems with clogging and excess sediment. «There is a pilot in the Ebro to make a bypass to remove sludge and take them downstream, but it is experimental. The dams have been made for irrigation and hydroelectric production, but they hardly function to laminate the avenues. Furthermore, we cannot think about floods without thinking about droughts and dams drying out the landscape. Despite the copious rains, the reservoirs in Catalonia are only 33% full; We have not come out of the drought. We must rethink the culture of the last century. Some dams cannot be removed, but nature gives us better services; “an aquifer works better than a reservoir,” he says.
A future for Valencia
Zero risk does not exist, but, in addition to avoiding building around the river, these weeks voices have been heard calling for investing in the improvement and maintenance of hydraulic infrastructure and changing water management by coexisting gray or engineering solutions with others based on in nature. «We have good climate information and to reduce the consequences of floods it is necessary that the channels are not occupied by houses, industrial or commercial warehouses, roads, train tracks or retaining walls and that rivers have banks wide enough to grow and decrease without endangering the population,” says Annalies Broekman, who recalls that similar problems can occur in other areas – as we see these days with the new Dana that crosses the Peninsula.
«Everything that has been seen in this flood confirms what we already know. Looking to the future, it is necessary not to build, but also to move what can be done and adapt and protect what cannot, in addition to doing natural restoration work. Rigid infrastructures that were thought to be good no longer guarantee the function for which they were designed. It gives a false sense of security. “These walls are built for flows that can no longer be assured now.”.
The false security that comes with hiding riverbeds
Has the time come to rethink our way of seeing rivers? In some cases the water torrents have been covered with concrete, causing the channels to pass under the cities. In a context of climate change, those consulted consider that the old solutions, in some cases, give us a false sense of security. Human beings have a short lifespan and, although the historical information is there, we forget that water always wants to return to the path it followed. «Excessive channeling of a river or covering torrents in urban areas is disastrous. When channeling is done, it is done for a probability or return period, but there can always be episodes in which a greater flow circulates than was thought during the design and that will always happen. If the work is covered, the day it passes the water will pass over it. Renaturalizing, as long as it is not just gardening work and involves river restoration and giving more space to rivers, reduces the risk of flooding. This and avoiding hard pipes is usually positive,” says Ernest Blade from the UPC.