Works and techniques to slow down water
At the scale of a farm, it is possible to design a number of structures whose objective is to slow down and help water infiltration. These structures should be implemented in addition to classical agroecological techniques (in particular cover crops, addition of organic matter, etc.), in order to first reduce the runoff coefficient on the plot.
Measurement of flows and topography
Before installing any structure, it is essential to start by conducting a topographic analysis of the land, identify the flows (maximum volumes) and the runoff coefficient (and the soil infiltration capacity).
The topographic analysis will determine where to place infrastructures (identification of swales and key points), and the flow analysis will decide the sizing and type of infrastructure.
Green and blue corridors, machinery circulation
When designing these infrastructures, it is important to anticipate the passage of machinery but also animals. Water circuits are upstream of circulation in Yeomans' permanence scale, and if a road or a ruminant crossing must cut a ditch, it will not be effective for long.
Infrastructures
The list below is not exhaustive.
Keylines
Keylines are the “softest” infrastructures after the implementation of cover crops and allow water infiltration along contour lines. The keyline aims to distribute the quantities of infiltrated water between the swale (the natural water runoff path) and the ridges. Keylines can be repeated regularly and it is possible to sow perennial plants in the cracking line to let their roots infiltrate the created space (shrubs with small fruits).
Fascines (torrent corrections)
Fascines are wooden or stone structures that slow down water flow in a stream. They are the equivalent of beaver dams, and fascines must be wide enough to prevent water from running off on either side. Fascines are easy to implement and help break the speed of a violent flow (torrent) which otherwise could create ruts and gully erosion.
See the article on fascines.
Swales
Swales are ditches that follow contour lines. Water stagnates in the swale until fully infiltrated, and they are not intended for storage. Swales can be more or less wide and have indentations (sort of separations every 3 or 4 m in the swale to prevent water circulation along the swale). Swales are intended to be grassed, or even planted with perennial species, with gentle slopes that will help maximize water infiltration capacity.
Ponds and hillside reservoirs
Unlike swales, ponds are intended to retain water for later use (irrigation or watering). They are subject to regulation and require prior declaration.
Adaptive solutions
In some cases, structures that can adapt according to the season can be implemented (swales with sluice gates (traps), including concepts of connected sluice gates that open and close depending on the water needs at each point of the plot), but it is wise not to play sorcerer's apprentice with water and always start with basic agroecological levers (cover crops, organic matter inputs, etc.) and only then, to correct problems, consider this type of arrangement.
