Runoff characteristics of artificial catchment materials for rainwater harvesting in the semiarid regions of China

Rainwater harvesting is being promoted to solve water problems for agricultural and domestic uses in the semiarid loess regions of China. In recent years, however, the current rainwater harvesting practices are still confined to rural family units to supply household water needs and for very limited supplemental irrigation purposes due to low runoff efficiencies of the limited catchment types and consequently low amount of collected water. The current runoff catchments mainly include rooftops, courtyards, earth and asphalt-paved roads. It is necessary to test artificial catchment treatments to select optimum treatments for large-scale use in the region. This study evaluated runoff characteristics of six surface treatments relative to rainfall amount and intensity and antecedent rainfall during naturally occurring rainfall events in the semi-arid loess regions of northwest China. The surface treatments included two basic types, i.e., earthen (natural loess slope and cleared loess slope) and barrier-type surface treatments (concrete, asphalt--fiberglass, plastic film, and gravel covered plastic film).

The results of the study indicated that runoff and runoff efficiency of the earthen surface treatments were closely related to the rain intensity, while runoff from the asphalt fiberglass, plastic film, gravel-covered plastic film, and concrete surface treatments was more governed by the amount of the rainfall. Asphalt fiberglass had the highest average annual runoff efficiency of 74–81%, followed in decreasing order by the plastic film (57–76%), gravel-covered plastic film (56–77%), concrete (46–69%), cleared loess slope (12–13%), and natural loess slope (9–11%). Antecedent rainfall had an obvious effect on the runoff yield for the cleared loess slope, natural loess slope, and concrete. The threshold rainfall was 8.5, 8.0, and 1.5 mm for the natural loess slope, cleared loess slope, and concrete treatments, respectively, without antecedent rainfall effects and 6.0, 5.0, and 1.2 mm, respectively, with antecedent rainfall effects. Due to the impermeable surface, antecedent rainfall had little effect on the runoff yield for the asphalt fiberglass, plastic film, and gravel-covered plastic film treatments, which had a threshold rainfall of 0.1, 0.2, and 0.9 mm respectively.