How the village of Colomieu mitigated flood and drought risks through water infiltration

In less than three years, the residents of Colomieu transformed their fields and paths into natural sponges, limiting overflows of the Bresse River and maintaining soil moisture during dry summers. This collective effort, born out of concern for increasingly violent spring floods and summers where wells run dry, mobilized over a hundred volunteers and relied on satellite data to identify areas where water flows most rapidly.

Water infiltration: how the village reshaped its territory

The first step was to map the catchment basin using Copernicus images, which offer a 10-meter resolution and allow for identification of impermeable soils and concentrated runoff zones. By crossing these observations with ECMWF model predictions, farmers were able to target critical points for infiltration trenches and retention ponds. The work, done with shovels and cement mixers, created over 150 meters of gently sloping ditches filled with local vegetation and gravel to slow flow.

Meanwhile, a network of soil moisture sensors connected to a local server allowed real-time monitoring of the impact of new structures. The data was analyzed using a predictive model based on a neural network trained with regional rainfall history and flow measurements. This model, hosted on an open-source platform, indicated that infiltration could reduce the peak discharge of the river by 30% during an hour of 20mm rain, according to the latest simulations.

Scientific basis of infiltration

Infiltration relies on the soil's ability to absorb water when it has a porous structure and vegetation cover that protects aggregates. In compacted soil, pores are reduced, preventing water penetration and forcing it to flow rapidly into watercourses, increasing flood risk. By creating gravel-filled ditches and replanting local species, Colomieu residents increased surface porosity and reduced compaction. This "diffuse recharge" allows water to infiltrate gradually, reach groundwater reserves, and slowly release during drought periods.

The process also relies on the principle of soil storage capacity, which depends on texture, organic matter content, and depth of horizons. By increasing permeable surface area, the village added approximately 1,500 m³ of stored water in the subsurface, equivalent to 15 days of average rainfall for the area, according to the model.