Soft-riser bench terrace design for the hilly loess region of Shaanxi Province, China

Abstract

Reconfiguration of hillside fields into terraces is regarded as one of the key techniques for water and soil conservation in mountainous regions. On slopes exceeding 75°, traditional techniques of terracing are difficult to apply as terrace risers (i.e. backslopes), if not reinforced, are so abrupt that they collapse under gravity alone, thus damaging the terrace. To improve reconfiguring of hillside fields into terraces, holistic techniques of soft-riser bench terrace engineering, including revegetation with trees and planting of grasses on terrace riser slopes, were tested between 1997 and 2001 in Xiabiabgou watershed, Yan’an, Shaanxi Province, China. A “working with nature” engineering approach was employed, terrace riser slopes of 45°, similar to the pre-existing slope of 35°, were employed to reduce gravity erosion radically. Based on concepts of biodiversity and principles of landscape ecology, terrace benches, bunds and risers were planted with trees, shrubs, forage grasses, and crops, serving to generate a diverse array of plants, a semi-forested area and to stabilize terrace bunds and risers. Soft-riser bench terrace design made it possible to reduce hazards arising from gravity erosion significantly, and reduce the costs of individual terrace riser construction and maintenance to 73.93% and 49.68%, respectively, of costs under traditional techniques. Such a construction allowed an enrichment and concentration of nutrients in the soil of the terrace bunds and risers, providing an ideal environment for a range of plants to grow and develop. The terrace riser can be planted with a drought-resistant plants ranging from forage grasses to trees. This terrace riser vegetation will turn the exposed terrace bunds and risers existing under traditional techniques into plant-covered belts, great green ribbons decorating the farmland, and contributing to the enhancement of the landscape's biology.