In times of drought, it seems anachronistic to speak of floods. In both cases, we readily speak of " natural disasters ". Admittedly, they are initiated by a meteorological event, but our recklessness in anticipating deserves to qualify these events as "human catastrophe". We justify our inertia by accusing global warming of being the cause of the floods. However, the IPCC recognizes that " it can be said with a high degree of confidence that floods greater than those observed since 1900 have occurred over the past five centuries in northern and central Europe, in the western Mediterranean region and in East Asia ». This undermines the slogan “think global to act local”.
To cope with flooding, it is best to “think local to act local”. We then discover three classic negligence. First, downstream, the insufficient dredging of the mouths. Admittedly, the floods most often evoke small ports in abandoned estuaries. Think of the floods in Quimperlé and Hennebont (January 2001), Abbeville (April 2001), Arles (Dec. 2003), Bayonne (February 2014), and so many others. Port activities justified dredging budgets. This is no longer the case and the siltation of all these estuaries slows down the flow of water… and ecologists are opposed to any work that would upset the underwater flora and fauna. In the middle bed of the rivers, the banks are no longer maintained, trees grow there, are uprooted during floods and constitute real dams by blocking themselves under bridges. Admittedly, there are fewer and fewer local farmers, but too many checks exasperate them: after the floods in Fréjus in 2010, elected municipal officials complained in September 2012 to senators that one of the most problematic points resides in the "ecological police of water". Some operators have even been fined for having maintained the banks, for example by cutting plunging trees!
Upstream, it would be necessary to build precautionary reservoirs. It is on this last point that the problem of floods joins that of droughts. We will not return to cabotage in estuaries, nor to an agriculture that stores a year's harvest in advance or enough to maintain the banks of our rivers. We will therefore have to get used to the idea of investing in basins upstream of our rivers. The creation of basins helps to maintain low water levels in the event of drought. In terms of needs, the water that is not used by man is indeed used to supply all the ecosystems of the planet. As the geographer Ghislain de Marsilly says: “There is no loss: All the water is used by natural ecosystems”.
The importance of maintaining low water levels in rivers at sufficient levels. In Bordeaux, the floods of December 1981 and the frequent low water deficits showed the usefulness of the plan Garonne 2050 to meet the triple objective of limiting flood damage, maintaining low water levels for biodiversity and the natural dredging of the Gironde, and, incidentally, agricultural water allocations negotiated with the parties. The project provides for 415 million m3, of which only 1/5 is for the satisfaction of agricultural needs. Admittedly, the satisfaction of agricultural needs requires public budgets, but all agriculture in the world is indirectly subsidized by subsidized loans, customs protectionism or agrarian development! Where are we on the plan Garonne 2050 published in 2014? Are we condemned to be paralyzed by the ZADists of Sivens who blocked a project of only 1,5 million m3?
Reservoirs also help reduce the risk of flooding. Should we be ashamed of the large lakes built for this purpose between 1960 and 1990 by storing more than 700 million m3 upstream of Paris. They have now become classified natural areas as the common cranes have taken root there. The floods of June 2016 reminded us that they only control 17% of the contributions from the Seine catchment area in Paris. It is still insufficient. When will the necessary construction of the “Bassée tank lockers”, in the region of Marolles sur Seine? Man's control of water is firstly anthropological before being ecological. It forces us to ask ourselves questions: what nature do we want? What relationship do we want between man and nature? Is wilderness good in essence? Is any mastery of nature illegitimate? Geographer Christian Lévêque likes to point out that having a balanced position on these subjects means being able to answer these questions.
Stanislas de Larminat
This article is published from Selection of the day.