Contour trenching

Contour trenching is an agricultural technique that can be easily applied in arid sub-Sahara areas to allow for water, and soil conservation, and to increase agricultural production.

Technique

Trenches can be artificially digged along the contour lines. Water flowing down the hill is retained by the trench, and is infiltrating the soil below.

Between two trenches crops can benefit during the growing season (when there is less rain) from the subsoil water reserve gathered during the rainy season.

Advantages

Immediate advantages are the following:

• The rain water does not immediately run off the hill,
• Water does not evaporate uselessly
• The water balance is enhanced
• Crops do not suffer later on from water shortage,
• Fertile soil particles are not lost by water and wind erosion.

Implementation

Depending on the slope of the hill, the parallel trenches can be closer or further from one another.

Manually digged trenches are smaller. Machine digged trenches can be deeper. The dimensions, and the format of the trench should correspond to the local climate and soil conditions. The trench should be big enough to keep all the water; no water should spoil over the downhill border. The upside of the trench should be protected against erosion, by means of e.g. grass, shrubs, or fabric.

See also

• Groundwater recharge