Permeable Rock Dams

A permeable rock dam is a water harvesting technique where flooding rain water is collected in valley bases or other depressions to irrigate crops later/elsewhere, filling in gullies, controlling water flows, increasing crop production and reducing soil erosion.. Permeable rock dams are long and relatively shallow to reduce erosion while accumulating silt and distributing water. They comprise of long low rock walls with smooth crests so that water can spread to avoid overflow from the dam. However, this technology is site specific; it cannot be practiced in areas where there are no rocks/stones and means of transporting these building materials. The impoundment of silt prior to runoff entering a watercourse can be beneficiary to downstream users and can contribute to improved water quality in the catchment

Technical Application

To effectively implement Permeable Rock Dam practices, the following steps should be carried out:

Step 1: Consider constructing a permeable rock dam across relatively wide and shallow valleys.
Step 2: Permeable rock dams should consist of long, low rock walls with level crest along full length although farmers should consider central spillways where water course has cracks.
Step 3: The dam should be between 50-300m in length and 1m in height within a gully.
Step 4: Consider making the dam wall flatter on the downslope side than on the upslope side.
Step 5: A foundation of small stones should be set in the trench.
Step 6: An apron of large rocks is essential to split the erosive force of the overflow.
Step 7: Downstream banks of the water stream should be shielded by stone pitching to prohibit the increase of the gully.

Return on Investment Realisation Period

Crop Production

Fodder Production

Farm Income

Household Workload

Food Security