Effect of ground cover on splash and sheetwash erosion over a steep forested hillslope: A plot-scale study Afshin Ghahramani a, ⁎, Yoshiharu Ishikawa b , Takashi Gomi c , Katsushige Shiraki d , Shusuke Miyata e a United Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Japan b Institute of Symbiotic Science and Technology, Tokyo University of Agriculture and Technology, Japan c Department of International Environmental and Agriculture Science, Tokyo University of Agriculture and Technology, Japan d Graduate School of Agriculture, Tokyo University of Agriculture and Technology, Tokyo, Japan e Disaster Prevention Research Institute, Kyoto University, Japan abstract article info Article history: Received 30 June 2009 Received in revised form 26 November 2010 Accepted 30 November 2010 Keywords: Splash erosion Sheetwash Overland runoff Sediment transportation Forested steep hillslope The contributions and relationships of erosion by splash and overland flow over a steep slope in a Japanese beech forest in plots with different percentages of ground cover were examined. Three erosion plots (2 m wide × 5 m long) with average understory coverage of 1%, 45%, and 94% were installed. Sediment transported by rain splash and by overland flow was sampled separately. For the plots with sparse, moderate, and high understory coverage, the average proportions of splash soil to total soil erosion during the monitoring period were 16%, 32%, and 18%, respectively. A significant correlation between the amount of splash soil and precipitation was found in the plots with 1% and 45% understory coverage, whereas no statistical relationship was identified for the plot with high understory coverage. At the sparse ground cover plot showing the largest sediment movement, the contribution of splash transport decreased with increasing precipitation. The amount of sheetwash erosion was significantly correlated with the amount of splash soil under the condition of sparse ground cover. This relationship was more pronounced during high precipitation events and the rainy season. Splash contribution to the sediment transport was in the range of 0.8%–76.7%, 2.8%–81% and 2.1%–60.8% for plot with high, moderate and low ground cover, respectively. The sparse ground cover showed the largest variation of splash and sheetwash contribution in soil erosion. This variability was due to variation in ground cover and soil surface wetness condition which led to a variation of detachment and non-linear relationship of sheetwash splash. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Understanding soil detachment by precipitation drops is an important first step in clarifying soil erosion processes on hillslopes (e.g. Young and Wiersma, 1973; Abrahams and Parsons, 1991; Van Dijk et al., 2003; Kinnell, 2005). Numerous studies have indicated that soil erosion processes involve detachment by both falling raindrop impacts and overland runoff, followed by the movement of detached particles by shallow overland runoff (Meyer et al., 1975; Nearing et al., 1989; Kinnell and Wood, 1992; Kinnell and Cummings, 1993; Zhang et al. 1998; Foster, 1990; Huang, 1998; Foster, 1982, 1984; Morgan, 2001; Nord and Esteves, 2005). Complex interactions of splash erosion, overland flow erosion, and other factors may affect erosion processes. Particles detached by raindrops can be transported by splashing or overland flow. For interrill erosion, overland flow during moderate precipitation may not have enough flow depth and consequently enough power to break down the cohesive force between soil particles and then transport detached particles (Emmanuel and Dunne, 2003). Furthermore, although the subject of fewer studies, sediment movement by splashing has also been found to be important in the interrill erosion process of forested steep landscapes (Miura et al., 2003). Sidle et al. (2007) showed that a significant amount of storm water movement occurred in the near-surface soil layer of a forested hillslope with sparse ground cover (Gc). Sparse cover could result from inappropriate forest management or overgrazing of understory vegetation by domestic or wild animals. When overland flow is very shallow, not only soil detachment but also splash-induced soil movement (sediment transport by the splash mechanism) may play significant roles in the sediment transport of the hillslope. Further- more, in cases of shallow overland flow, the flows are often not Catena 85 (2011) 34–47 ⁎ Corresponding author. United Graduate School of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8, Saiwai-cho, Fuchu-shi, Tokyo 183-8509, Japan. Tel.: +81 80 3257 2929; fax: +81 42 367 5826. E-mail address: 50008953802@st.tuat.ac.jp (A. Ghahramani). 0341-8162/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.catena.2010.11.005 Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena