“No, water does not flow better through rivers or ravines when there is less vegetation, and those are not clean channels either,” states Pau Fortuño, biologist at the Center for Ecological Research and Forestry Applications (CREAF), bluntly. In this way, the scientist warns that growing in channels and ravines is one of the reasons that complicate the situation in case of large floods of water. Many people think that they are a hindrance to the water running well and can endanger people’s lives when they float in. On the contrary. “What’s more, it has been shown that the pile-ups were cars,” he points out.
Another issue is maintenance work. They are necessary, for example, to prevent the growth of invasive exotic species such as the common reed (Arundo donax), with a “brutal colonization power” and that can cause problems due to the large amount of biomass it generates. If the trees that correspond to them grew in the riverbeds, the cane would not have all the light it needs to grow. “So, by leaving the rivers bare, what we do is encourage this species to grow more and more,” the expert points out.
Taking into account the hydrological functioning of the rivers, adds Fortuño, the correct behavior would be the opposite: letting the native vegetation grow, which is flexible and robust at the same time, purifies the water, controls the sediment, fixes the soil and, at times of floods, contributes to reducing the speed of water and materials arriving from the upper parts of the basin. In floods as devastating as the one that occurred in Valencia, the trees may not be able to stand, no matter how big they are, but “the water will never reach those great speeds and, therefore, that destructive power,” indicates this river specialist. Mediterranean.
The problem is that this type of behavior consisting of leaving naked The river channels continue to be produced in the municipalities because “it is a quick action, which the people ask for and give votes.” In the Mediterranean ravines, through which water does not normally flow and where there are no large forests but there is bushy vegetation, something similar occurs, to which we must add that they are channeled areas, which have been narrowed to the maximum. Also, all kinds.
Channel the river or ravine
“Channeling causes the water to rise more, because it narrows the channel more, the water goes higher and faster, the energy will be greater and where it breaks, jumps or overflows it will be much worse,” explains Alfredo Ollero, professor of Geography. Physics from the University of Zaragoza. In all places where possible it is necessary to give more width to the river and eliminate these channels to make the territory more permeable, he adds. And, if there is no choice but to put the river through a channel, let it be “as wide as possible, because you have to imitate rivers and the way they lower the energy is to widen.”
Ollero is “strongly against” the concept of clearing rivers of vegetation. “Cleaning is removing garbage, dams, weirs, fords, all human obstacles, but not removing sediment or vegetation because it will have serious consequences,” he says. He is also not a fan of hard structures such as the construction of dams, which are used, in addition to storing water, to control floods. “Normally, lamination reservoirs are of no use, because they take up a lot of space and spoil a lot of territory,” he points out. Dams store the water that comes from a flood and drain it progressively, which causes a decrease in damage downstream.
However, Federico Bonet, advisor to the College of Civil Engineers, Canals and Ports and former technical director of the Júcar Hydrographic Confederation (CHJ), maintains that “green” solutions based on nature cannot be applied in all places. He lives in Valencia and affirms that in the Júcar basin, for example, “no significant actions have been carried out for 20 years.” Considers it necessary to prioritize pending actions based on the risk of floods and the damage they may cause. Bonet refers to “defense projects that require a significant investment.” One of them is the connection planned by the CHJ with the new channel of the Turia River, through a green infrastructure.
Bonet indicates that each problem has its solution, and that there are cases in which the toughest infrastructures such as dams or canals are necessary. Among the pending structures, he cites the Marquesado dam, on the Magro River – which in this area has overflowed in several places. It would be located, which on this occasion helped cushion part of the flood, although there were fears for its integrity. Another reservoir, the Montesa reservoir, planned on the Cànyoles river to minimize the risks of flooding in the Costera region and on the banks of the Júcar, has more advanced processing, although it is still unbuilt. And, already in the lower part of the Júcar, a flood plain that overflows when the river carries a lot of water, there is a study to launch an action, in this case more natural, because “being an agricultural area allows it” , specifies the engineer.
