SLU news

New advice on how to create stable agricultural ditches

Published: 20 March 2020
A ditch in agricultural land recently maintained, with a tree by the horizon, photo.

Agricultural ditches degrade over time and risk becoming unstable. In a new doctoral thesis, Daniel Avilés has proposed methods for identifying soils that are sensitive to erosion and mass movements. The thesis also describes that soil vegetation helps to stabilise ditches.

The degradation of agricultural ditches is often due to soil erosion, which can cause mass movement (bank failure) when the toe of the bank is eroded, or the slope of the bank is too steep. Soil eroded or displaced by mass movement is reducing the drainage capacity and increasing the need for maintenances of the ditches.

–Today, there is a great lack of knowledge on how to easily identify soils that are susceptible to erosion and bank failure, says Daniel.

Where should maintenance work be prioritized?

Deciding where to prioritise expensive maintenance work in agricultural ditches is a difficult task. As there may be multiple sources of instability, for example soil erosion and soil mass movements, it can be problematic to determine which indicators should be considered. This information is important for making decisions regarding possible stresses caused by water flow that should be considered when designing ditches.

Methods for assessing the soil resistance to detachment and the stability of ditches to mass movements were presented

In a new doctoral thesis, Daniel Avilés presents a method to evaluate how easily a soil can be detached by the action of the water flowing in the ditch.  A cohesive strength meter (CSM) was used to measure how resistant a soil is to detachment compared with other soils. The measurements can be used to compare soils within an area and to identify ditch segments that are more prone to erosion and thus require more maintenance work. In addition, these measurements can be used to relate a soil’s strength to possible hydraulic pressures that may occur in a ditch, says Daniel.

– I also investigated the stabilising role of vegetation in increasing ditch bank stability. Even a thin layer of soil with roots could be enough to stabilise ditch banks against mass movement. This indicates that, during maintenance work, vegetation on ditch banks should be left in place whenever possible or at least plant roots should be left in the soil. This will make the ditch banks more resistant to erosion by flowing water and to mass movement, says Daniel.

Daniel Avilés will defend his doctoral thesis ”Soil erosion and mass movement in agricultural drainage ditches” on the 15th of April. Read more about Daniel Avilés' defence here.