Effects of rainfall and terracing-vegetation combinations on water erosion in a loess hilly area, China.

Terracing and vegetation restoration are the basic measures to protect soil from water erosion and to combat land degradation. However, long-term quantitative evaluation on the erosion control benefits of different terracing techniques and vegetation types are still insufficient, particularly under variable rainfall. The aim of this article, therefore, is to evaluate the coupling effects of different terracing-vegetation combinations and rainfall types (RTs) on runoff retention and erosion reduction in a loess hilly catchment of China. Six types of terracing-vegetation combinations, including leveled benches-C. microphylla (LM), fish-scale pits-P. orientalis (FO), leveled ditches-P. armeniaca (LA), zig terraces-P. orientalis (ZO), fish-scale pits-P. tabulaeformis (FT), zig terraces-P. tabulaeformis (ZT) and the corresponding plots with same vegetation cover and non-terracing measures were designed and monitored. Based on five consecutive years of monitoring data, 69 rainfall events causing runoff and erosion were observed. Rainfall eigenvalues, including rainfall amount (RA), maximum 10-min intensity (I), maximum 30-min intensity (I) and rainfall duration (RD) dominated water erosion processes. Surface runoff and sediment reduction benefits differed with different terracing techniques. Mean runoff coefficients (R) among all kinds of terracing-vegetation combinations were FT > LM > FO > LA > ZO > ZT, while mean soil loss rates (E) among all kinds of combinations were FT > FO > LM > LA > ZT > ZO. ZT showed the highest mean runoff reduction (44.03%), while ZO generated the highest sediment reduction (39.08%). The worst performance was observed in FT. With regards to the results, it is necessary to select the optimal terracing-vegetation measures for erosion control based on the dominant rainfall eigenvalues in different areas. Overall, ZT, ZO and LA combinations are recommended, while uncertainty was detected in combinations with fish-scale pits. Suitable terracing-vegetation measures should be selected after considering the micro-relief construction, the optimization of plant disposition and the efficiency of water erosion reduction. Management should focus on the construction standards, the threshold of resisting erosion for each terracing measure, and timely maintenance of the terraces.