Soil traps

Soil traps are structures constructed to harvest soil eroded from the upper slopes of the catchment. The most common types of soil traps are check dams and trenches, built in diversion ditches or waterways.

A check dam slows down the water flow and allows heavier soil particles to settle. The size of the check dam depends on the size of the drainage or gully to be protected. Check dams can be built of Gliricidia stakes, bamboo, loose rocks, logs or other locally available materials.

Trenches are built to trap soil along the waterways and complement the function of check dams. A trench is dug about 1-2 meters above the check dam, at least 0.8 m deep, 1.0 m long and 0.5 m wide. A variation is to construct the trench at the lower portion of the field just above a bund. The purpose is to trap soil and to store water temporarily to increase infiltration.

The accumulated soil in trenches and dams is returned to the field.

Soil traps (A)

Soil traps (B)

Advantages

· Prevents widening and deepening of gullies.
· Promotes the deposition of nutrient-rich, highly fertile sediments.
· Reduces the velocity of runoff in gullies.
· The area where soil accumulates can be used for growing crops.

Limitations

· Requires continuous desilting to prevent overtopping during heavy rains.
· Check dams require regular repair and maintenance.

Factors affecting adoption

Biophysical

Materials for making check dams may be unavailable.

Socioeconomic

Damage to check dams must be repaired and trenches desilted frequently.
Soil traps constructed without the necessary support structures may be ineffective.

Prepared by Kennedy Igbokwe