Effect of ground cover on splash and sheetwash erosion over a steep forested hillslope: A plot-scale study
Research Highlights
► Separate measurements of rain splash and sheetwash erosion. ► Measurements were carried out under natural rainfall conditions. ► Clarifying the effect of ground cover on hillslope soil erosion mechanisms (sheet wash and splash). ► Quantitatively clarifying the importance of rain splash and sheet wash erosion. ► Conceptualization of downslope rain splash erosion processes.
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. Furthermore, in cases of shallow overland flow, the flows are often not uniform. Therefore, to examine erosion processes, it is necessary to clarify the importance of splash and sheetwash erosion (transported sediment by unconcentrated overland flow) by sampling each process separately. Recent laboratory experiments have advanced our understanding of the physics of splashing (Furbish et al., 2007, Ma et al., 2008). However, knowledge of splashing on steep forested hillslopes is limited. Although previous studies have examined relationships among various rainfall indices, overland runoff, ground cover, and soil erosion (Marston, 1952, Cerdà, 1998, Cantón et al., 2001), and Miyata et al. (2009) recently increased our knowledge of ground cover effects on hillslope erosion processes, few studies have examined splash and sheetwash erosion separately (within an event) with regard to their relationships to rainfall, runoff, and ground cover as well as their relationship to each other.
In forested landscapes, ground cover reduces soil erosion and overland flow (Marston, 1952, Hattori et al., 1992, Zhou et al., 2002, Miura et al., 2002, Miura et al., 2003, Kawana et al., 1963, Murai and Iwasaki, 1975, Murai and Iwasaki, 1976, Yoshimura et al., 1981, Yoshimura et al., 1982). Because the size distribution of throughfall drops is greater under the canopy (Chapman, 1948, Tsukamoto, 1966, Nanko et al., 2006) rain splash erosion could be an important erosion mechanism. But still there is not enough knowledge of soil erosion in interrill area of forest floor (Miyata et al., 2009).
There are previous studies of ground cover effect on soil erosion, but those were not examining splash and sheetwash process separately. Miura et al. (2003) reported the dominance of splash in mass transport of steep forested hillslope without separating splash and sheetwash erosion.
There are laboratory or field experiments with simulated rainfall that examined splash and sheetwash erosion by comparing the results of experimental sets which one of rainfall or overland runoff was isolated (e.g. Hudson, 1957, Ziegler et al., 2000, Rouhipour et al., 2006). It is rare to find previous works on separate sampling of splash and sheetwash by field experiments under natural rainfall. Though Young and Wiersma (1973) in a laboratory experiment with simulated rainfall sampled splash and sheetwash separately on a low slope (9%). Sutherland et al. (1996) in a laboratory experiment with small plots (0.18 m2) separated splash and sheetwash on slopes up to 20°. Separately studying splash and sheetwash with regard to ground cover effect was neglected in previous researches of field experiment on natural hillslopes (Hattori et al., 1992, Miura et al., 2002, Miura et al., 2003, Kawana et al., 1963, Murai and Iwasaki, 1975, Murai and Iwasaki, 1976, Yoshimura et al., 1981, Yoshimura et al., 1982, Miyata et al., 2009).
It is commonly accepted that downslope sediment splash transport is high over steep slopes. Although now the contribution of splash in sediment transport processes is well known, we do not know what is the quantitative contribution of splash and sheetwash in total sediment transport in our study area. How are their relationships and variations with changing of ground cover?
The objectives of this study were to examine a) sediment production by rain splash erosion in relation to totally produced sediment to show relative importance of splash erosion, b) the relationship between splash and sheetwash erosion, and c) the function of forest floor cover over a steep hillslope in relation with splash and sheetwash mineral soil material movement.
We conducted field monitoring of soil erosion by splash and sheetwash mechanisms under natural precipitation in steep hillslope plots with different percentages of ground covers (including understory vegetation and litter). To examine the interaction between splash and sheetwash, we sampled and measured splash and sheetwash soil material separately. The relationships of storm precipitation characteristics and overland flow to splash and sheetwash erosion were investigated to identify factors affecting soil loss from the plots. The findings of this study will provide more knowledge of splash contribution to sediment transport over steep forested landscapes in which ground cover is sparse due to forest management or overgrazing by animals. Clarifying the relative importance of splash and sheetwash can help to get a better evaluation of steep hillslope erosion. Various classes of understory coverage were examined to identify the role of the forest floor in soil erosion and the results can be applied to soil conservation planning and modeling.
Section snippets
Methods and materials
A number of experiments have already been applied to measure soil detachment rate and splash transportation by raindrops. These methods mainly involved the use of cups and trays. Salles and Poesen (2000) used a splash cup technique in a laboratory experiment to determine the mass of detached sediment. Nanko et al. (2008) also used cups to measure the rate and mass of splash erosion. Van Dijk et al. (2003), in a study in West Java, Indonesia, measured the splash mass and rate on terrace beds and
Characteristics of precipitation
During the monitoring period from May to November 2007–2009 for plot 3 and May to November 2007 and May to August 2008 for plots 1 and 2, total precipitation of 2007, 2008 and 2009 was 1980 mm, 2275 mm and 2042 mm respectively, 64%, 38% and 28.7% of which occurred in the typhoon season from July to November respectively for 2007, 2008 and 2009. Intense and heavy precipitations (1264 mm, 862 and 587 mm of total precipitation for 2007–2009) were recorded during typhoons. Large storm events occurred
Conclusion
Plot-scale contributions and relationships of sheetwash and splash soil erosion on a steep forested hillslope were investigated during 2007 to 2009. In the field monitoring, we sampled erosion by rain splash and overland flow separately. The findings of this study are summarized as follows: (1) Considerable soil splash transport occurred in hillslopes with sparse understory vegetation. (2) The contribution of splash transport to total sediment movement mainly depended on vegetation and litter
Acknowledgments
This study was partially funded by the Kanagawa Prefecture Natural Environmental Center. We appreciate four anonymous reviewers and the editor, for their comments. We thank the graduate students of Tokyo University of Agriculture and Technology, Laboratory of soil erosion and hydrology for their assistance through field works.
References (63)
- et al.
Hydrological erosion response of a badlands system in semiarid SE Spain
J. Hydrol.
(2001) A simple approach to soil loss prediction: a revised Morgan–Morgan–Finney model
Catena
(2001)- et al.
Evaluating the influence of canopy species and meteorological factors on throughfall drop size distribution
J. Hydrol.
(2006) - et al.
Estimation of soil splash detachment rates on the forest floor of an unmanaged Japanese cypress plantation based on field measurements of precipitation drop sizes and velocities
Catena
(2008) - et al.
A simplified hillslope erosion model with vegetation elements for practical applications
J. Hydrol.
(2002) - et al.
Splash and wash dynamics: an experimental investigation using an Oxisol
Geoderma
(1996) - et al.
Hydrological impacts of reafforestation with eucalypts and indigenous species: a case study in southern China
For. Ecol. Manage.
(2002) - et al.
Resistance to overland flow on desert pavement and its implications for sediment transport modeling
Water Resour. Res.
(1991) - et al.
Interrill soil erosion processes and their interaction on low slopes
Earth Surf. Process. Landforms
(2007) - et al.
Runoff and soil loss response to vegetation removal in a semiarid environment
Soil Sci. Soc. Am. J.
(1997)
The influence of geomorphological position and vegetation cover on the erosional and hydrological processes on a Mediterranean hillslopes
Hydrol. Process.
Sediment concentration in interrill flow: interactions between soil surface conditions, vegetation and rainfall
Earth Surf. Process. Landforms
Size of raindrops and their striking force at the soil surface in a red pine plantation
Eos Trans. AGU
Contribution à l'étude de l'érosion par le splash
Z. Geomorphol.
Effects of rainfall, vegetation, and microtopography on infiltration and runoff
Water Resour. Res.
A rain splash transport equation assimilating field and laboratory measurements
J. Geophys. Res.
Studies of raindrop erosion
Agric. Eng.
Sediment detachment by rain power
Water Resour. Res.
Modelling the erosion process
Process-based modelling of soil erosion by water on agricultural land
In Soil Erosion on Agricultural Land
Mathematical simulation of upland erosion by fundamental erosion mechanics
Rain splash of dry sand revealed by high-speed imaging and sticky paper splash targets
J. Geophys. Res.
The formation and characteristics of splash following raindrop impact on soil
J. Soil Sci.
Effect of water depth on soil detachment caused by raindrop impact
Effect of forest floor coverage on reduction of soil erosion in Hinoki plantations (in Japanese with English summary)
Bull. For. Prod. Res. Inst.
Sediment regimes under different slope and surface hydrologic conditions
Soil Sci. Soc. Am. J.
Progress report on experiments at Henderson Research Station 1953–1956
Rhod. Agric. J.
Studies on protection of forest soil in hinoki stands at Owase. I. Experiment of reducing surface soil loss in hinoki plantations (in Japanese)
Trans. Annu. Meet. Jpn. For. Soc.
Soil cohesion as affected by time and water-content
Soil Sci. Soc. Am. J.
Raindrop-impact-induced erosion processes and prediction: a review
Hydrol. Process.
Soil slope gradient interactions in erosion by rain-impacted flow
Trans. Am. Soc. Agric. Eng.
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