Over the course of a century, an immense effort transformed the Landes de Gascogne region in southwestern France. Workers dug approximately 40,000 kilometers of ditches—equivalent to the distance from Earth to the Moon—to drain the marshy landscape. This massive drainage project, initiated by a Napoleonic law from June 19, 1857, was promoted by engineer Jules Chambrelent. The law mandated the systematic digging of ditches to drain the land before planting pines, which led to the forest expanding from 100,000 to over a million hectares in a century. This transformation altered the natural function of the soil, which once acted like a sponge, absorbing and slowly releasing water. Today, the extensive ditch network, expanded in the 20th century, drains rainfall too quickly into the Adour and Leyre rivers, increasing the risk of sudden floods. In the mid-19th century, the Landes de Gascogne was a vast area of wet heaths, bogs, and marshes where water often stagnated, making agriculture difficult and life challenging for residents. Engineer Jules Chambrelent proposed a radical solution: breaking the compact layer of alios, a rock that prevents water from seeping into the ground, and implementing a systematic drainage plan. By 1855, 20,000 hectares had already been drained and planted with pines under his direction before the law was passed. The law had both sanitation and political goals, aiming to convert traditional pastoral lands into forest monocultures that were more profitable for the state and large landowners. The maritime pine, a resilient species that can grow in poor and acidic soils, was selected to occupy the newly drained areas. However, local historians note that drainage in the Landes did not begin with the 1857 law. Shepherds had long used traditional drainage ditches, known locally as jales, barrades, or crastes. The law industrialized and expanded drainage on an unprecedented scale, leading to the disappearance of iconic water areas such as the Orx pond. The ditch network completely changed the way water functioned across the entire Landes region, directing it directly toward the Adour and Leyre rivers instead of allowing it to stagnate or infiltrate slowly. This change caused the Landes massif to lose its natural sponge-like function, which once absorbed heavy rains and released them gradually. A drained forest now allows water to flow almost as quickly as it falls. As autumn approaches in the Southwest, the ditches that were designed to quickly dry the soil now drain rainfall with remarkable efficiency but with limited control, increasing the risk of sudden downstream floods. The DFCI (Forest Defense against Fire) notes that the current drainage network was significantly expanded and modernized during the 20th century. Recent studies on the Landes massif suggest targeted hydrological restoration efforts, aiming to restore the soil’s ability to retain some water to reduce the most severe effects of heavy rainfall. This approach avoids filling all ditches or flooding the area, which would be impractical and dangerous due to the increased fire risk on wet and unstable soil. The transformation of the Landes de Gascogne from a wet heathland to a dry pine forest illustrates how political, technical, and economic decisions can permanently reshape a landscape and alter its relationship with water. The Landes massif still bears the marks of this ambitious project, raising questions about how much a territory can be transformed without compromising its ability to manage nature’s extremes.