when geomatics reconciles water and Zan

“Water and Zan don’t talk to each other. » Founder of the Alisé Géomatique design office, Hélène Durand consistently places her foot in the anthill of urban planners and hydrologists. Today it is delighted to no longer preach in the desert, as illustrated by a recent call for tenders from Greater Lyon: “On the occasion of an update of its mapping of plants in the city, the community is finally showing the “an example of integrating rainwater data into an overall development strategy,” rejoices the geomatician.

Risqu’O, a founding program

On the long road which gradually advances the legitimacy of its approach, the key stage is called Risqu'O. Supported by the Occitanie region in 2019 via its economic development agency Ad'occ, Hélène Durand self-financed 70% of the research work which bears this name, in an open approach joined by the department of Aude, the the public territorial basin establishment Mixed Union of Aquatic Environments and Rivers (EPTB-SMMAR) and the agglomeration of Carcassonne (Aude).

Everyone wanted to learn lessons from the deadly floods of 2018 in Trèbes, by x-raying the neighboring Fresquel watershed (Aude). Using the open source Lizmap software that she helped finalize, the founder ofAlisé Géomatique maps runoff risks based on extremely detailed land use data. Crossed with rain flows, the classification of agricultural areas by type of activity provides precise information, to define the vocation of the soil, with regard to the risks of runoff.

Missed opportunity

However, one actor is missing in this first stage: state services. Hélène Durand regrets this all the more since she had participated, in the years preceding Risqu'O, in the beginnings of the development of the national tool for measuring land use on a large scale: the OCS-GE , official reference in the calculation of artificialization, in the wake of the Climate and Resilience law of August 2021.

This defection contributed to maintaining a hole in the flood risk prevention racketin the absence of exchange between hydrologists and actors in the fight against land artificialization. “Due to a lack of capacity to monitor waterproofing on an intra-plot scale, the OCS-GE lacks robustness in terms of flood risk,” says Hélène Durand.

Pilot scheme in Hauts-de-France

Hence the tactics of Alisé Géomatique, consisting of reduce this plague by relying on territorial projects. Its most recent service concerns the development of a territorial coherence plan (Scot) in the North, where the design office works with a hydrogeologist, alongside the Douais association for the promotion of alternative techniques in terms of rainwater (Adopta), a structure in the swarming phase in the northern half of France.

The question posed by the call for tenders responds exactly to the objectives of Alisé Géomatique: “How can we anticipate the development trajectory, in light of tomorrow's water resources, in the Scot territory? » “The data collected will have made it possible to understand upstream and downstream solidarity beyond the administrative borders of this very populated territory, several times affected by too much and not enough water”testifies Hélène Durand.

Farewell to pipe-centric

In addition to the good use of the tool on a technical level, its satisfaction arises from political management and democratic governance of the territorial project: “Each stakeholder expressed their vision associating water and Zan. We arrive at a 360° diagnosis which covers all the issues: catchment perimeters, trajectory of natural agricultural and forestry areas, waterproofing and urban forms, roads, wastewater treatment capacities, sectors in tension, etc..”

While Risqu'O encountered a lack of immediate response, Hélène Durand looks with hope to what she calls “the end of the pipe-centric approach” in rainwater management. From 2025 to 2030, the 12th programs of water agencies offer, according to her, the opportunity for a change of scalein this register.