The origin of the ponds
During the last great ice ages, the Dombes was covered in glaciers. Gradually the ice retreated forging a gently undulating relief and depositing clay-based sediments in its wake. Clay becomes impermeable when wet, retaining water. This characteristic is important for creating a pond. Men have been able to use the particularities of the Dombes soil and relief to set up the ponds.
A man-made creation
They built earthen dykes to retain rainwater and also dug numerous ditches to circulate the water.
Numerous structures such as empellements and ébies (overflows) were built to manage and direct the water, to avoid flooding when there is too much water.
The thou of a pond
At the edge of every pond in the Dombes region is a Thou. But what is the thou and what is it used for?
The thou, often made of stone or concrete, is a kind of sluice that can be opened to slowly empty the water from the pond. It works a bit like a washbasin plug. When the thou is opened, the pond empties through the drainage ditch.
Water management
The pond water comes from rainwater. To manage the water, ditches have been created to collect rainwater and allow water to circulate from one pond to another.
The ponds are therefore often connected to each other and form a veritable network.
Ponds are organized according to the topography of the land. Some are higher than others.
To move water from one to the other, the lowest pond has to be emptied and then the thou of a pond further upstream is opened to let the water flow.
Water circulation and proper management are very important as they serve to save and reuse water, a very precious commodity in the Dombes, several times over.
A dry pond
An emptied pond doesn’t have to be refilled. It can be left without water for a year, a dry phase (assec) during which work can be carried out in and around the pond. The section is cleaned to remove the muddy earth that has gradually settled over the years and which hinders fishing. Structures such as the thou and water inlets are inspected and repaired if necessary. It is also during this dry period that the farmer can sow cereals in the pond: oats and especially corn. These two activities, checking the structures and farming, help to maintain, sanitize and enrich the pond.
The one-year dry periods alternate with phases of the pond being in water. The duration of these wet periods has increased over time, from 2-3 years to 4-5 years.
