|Alternating series of ‘shelves’ and ‘risers’ characterize bench terraces. They are usually developed on relatively steep slopes (15-55%) with deep soils that allow this type of landscaping. Bench terraces help to store water and by reducing runoff and by capturing sediment they also prevent soil erosion. Therefore, by using this technique more water can be made available for the plants which, in turn, increases the agricultural production.
In bench terraces the riser (steeper ascending slope) is often reinforced with stones and/or vegetation cover. When the bench is made slightly inward sloping, water storage increases, and soil protection is improved. In arid areas, conservation bench terraces are preferred. In such cases, the distance between terraces is increased and a portion of the sloping land is left to act as catchment area. The runoff generated by the catchment area will nourish the plants placed immediately above the riser wall.
The construction of bench terraces is labour or equipment intensive. The bench terraces must be laid carefully on the contours – so that the hydraulic pressure is evenly spread. The design starts with a careful survey and pegging of the contour lines. This process can be carried out with an A-frame level or a water tube level. Consequently, the cut and fill areas are defined, and the excavation is performed. Care is taken to preserve the upper layer of the soil that holds most of the nutrients. The construction must start from the lower level of the field and then proceed upwards. Thereafter the newly created riser can be reinforced with locally available stones. When required, ditches and drains must be dug to dispose excess water.
Conservation bench terraces should be considered as water harvesting techniques, as they allow the generation of additional runoff. They should be planned according to plant requirements and climatic features of the area.