Impacts of rainfall features and antecedent soil moisture on occurrence of preferential flow: A study at hillslopes using high-frequency monitoring
Zhenyang Peng, Hongchang Hu, Fuqiang Tian, Qiang Tie, and Sihan Zhao
Department of Hydraulic Engineering, State Key Laboratory of Hydroscience and Engineering, Tsinghua University, Beijing 100084, China
Received: 07 Mar 2016 – Accepted for review: 13 Mar 2016 – Discussion started: 16 Mar 2016
Abstract. In order to evaluate inﬂuences of rainfall features and antecedent soil moisture on occurrence of preferential ﬂow, observation was conducted at 12 sites within a 7-km2 catchment, by applying the high-frequency monitoring approach. Totally 65 rainfall events were selected to compare among sites, and preferential ﬂow was inferred when (i) responses of soil moisture did not follow a linear sequence with depth, or (ii) penetration velocity of wetting front in at least one horizon exceeded the threshold, which was set to be 5–10 times of the saturated hydraulic conductivity of soil matrix at different depths. Results showed that frequency of preferential ﬂow was 40.7 % in average, but varied from 17.9 % to 74.3 % among the sites. Correlations between the frequency and rainfall features, i.e. rainfall amount, duration, maximum and average intensity, were well ﬁtted by logarithmic curves. Rainfall amount, which was most prominently correlated with frequency (R2 = 0.93), was regarded as the dominant driving factor of preferential ﬂow, while average intensity was in second (R2 = 0.90). Antecedent soil moisture was also signiﬁcantly correlated with the frequency. However, this should largely be attributed to the differences of soil moisture among sites, since varying range of soil moisture at a speciﬁc site was not wide enough to inﬂuence the frequency signiﬁcantly. Further examination suggested that topography and surface cover (dead leaves and humus) were the controlling factors of both inﬁltration amount and occurrence of preferential ﬂow, as water was more readily to inﬁltrate into soils and preferential ﬂow was more readily to occur when slope gradient was small and surface cover was thick, while soil moisture was more likely to be a consequence of water storage capacity, rather than an inducer of preferential ﬂow. This knowledge could be helpful in understanding the partitioning of surface runoff and inﬁltration, as well as runoff processes in catchments with complex topography and underlying conditions.
Peng, Z., Hu, H., Tian, F., Tie, Q., and Zhao, S.: Impacts of rainfall features and antecedent soil moisture on occurrence of preferential flow: A study at hillslopes using high-frequency monitoring, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-112, in review, 2016.