**1. Introduction**

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Soil erosion is a common global environmental problem and undermines sustainable devel‐ opment in various economies and societies. Detailed information about changes in surface roughness during the whole soil erosion process remains limited, however, due to practical difficulties in obtaining direct soil microrelief measurements (Huang, 1998) and a lack in systematic research. The Chinese Loess Plateau is one of the most severely eroded regions in the world, which has created many environmental problems along the lower reaches of the Yellow River. Despite this, however, very little erosion-based research has been conducted on the Loess Plateau. Erosion and runoff processes are influenced mainly by soil surface characteristics such as soil surface roughness, cohesion, and granular stability. Among these characteristics, soil surface roughness is a key parameter (Gómez, and Nearing, 2005; Mir‐ zaei et al., 2008), and is used to describe the variation in surface elevation across a field. The soil surface micro-topography or roughness is strongly influenced by agricultural activities, together with soil properties and climate. The term soil roughness was used to describe dis‐ turbances or irregularities in the soil surface at a scale which was generally too small to be captured by a conventional topographic map or survey. Soil surface roughness is an impor‐ tant parameter in understanding the mechanisms of soil erosion by water and wind. Many erosion related surface processes, such as depression water storage, raindrop or wind shear detachment, and sediment transport have characteristic lengths in millimeter scales. Thus, soil surface roughness resulting from small scale elements is important in understanding these processes and their spatial variation (Huang and Bradford, 1990). Soil surface rough‐ ness determines the storage of water on the soil surface and may indirectly influence its in‐ filtration capacity. The velocity of overland flow is controlled by the hydraulic resistance of the soil surface. Soil surface roughness affects the organization of the drainage pattern on

© 2012 Zheng and He; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Zheng and He; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

the field and the catchments scale, which in turn may have important implications for the spatial distribution of sediment sources and sinks. Conversely, some of these processes af‐ fect surface roughness. Most of the literature on soil surface roughness focusing on its math‐ ematical description and on how it changes under rainfall(Linden and Van doren,1986; Römkens and Wang,1987; Lehrsch et al,1988; Bertuzzi et al.,1990).Soil surface roughness sig‐ nificantly impacts runoff and sediment generation under rainfall in several different ways.

assure to fill to be homogeneous and close natural state through randomization method. Be‐ fore the rainfall, the soil mechanical composition was measured by the pipette method, and

Rainfall/erosion methods in this lab study were similar to those described by Zheng et al. (2007). The soil box was adjusted at 150 slope gradient and then placed under a rainfall sim‐ ulator with oscillating nozzles. Rainfall high was 2.7 m and effective rainfall area approxi‐

rainfall intensities were rated before testing. The uniformity of rainfall was up to 0.90. De‐ velopment of micro-relief was monitored by recording soil surface at the beginning and at the end of the experiments, using the non-contact profile laser scanner measuring instru‐ ment specified and calculated (Zheng,2007). The maximum range of detectable elevation dif‐ ferences was approximately 500 mm. Surface relief was measured point by point in a regularly spaced grid. The maximum scanning area was 2 m. The surface roughness was measured for each soil box before the rainfall and after the rainfall separately with non-con‐

Simulated rainfall for each replication of a treatment were divided into the single rainfall in‐ tensity and the combined rainfall intensity, the parameters of single rainfall intensity respec‐ tively were 0.68 mm/min and 1.50 mm/min, the parameter of combined rainfall intensity is 0.68 mm/min,1.00 mm/min and 1.50 mm/min. The above experiments had three repeats. Each experiment started on a freshly prepared surface for each replication of a treatment.

The four artificial management measures were designed according to the local agriculture cus‐ tom in Loess Plateau, because agriculture management measures were mainly artificial man‐ agement. The four artificial management measures were the raking cropland (PM), the artificial hoe (CH), the artificial dig (TW) and the contour slope (DG).They were used to simulate differ‐ ent types of soil surface roughness separately, the straight slope (CK) was taken to the control.

The amounts of splash erosion were collected through the hanging splash erosion board and measured by the oven drying method. The width to the hanging splash erosion board was 1m and the height was 0.5m.The hanging splash erosion board was installed in the middle

At the same time, raindrops of every rainfall were collected to calculate raindrop diameter. Raindrop diameter was measured through the color spot method according the B.Z.Dou

*d* =0.356*D* 0.712 (1)

of the soil box was to be used to collect splashing soil during the experiments(Fig.1).

et.al (Dou and Zhou,1982; Zheng and Gao,2000), the formula was as following:

The rainfall simulation duration were depended on the change of soil surface.

. This experiment used the constant rainfall intensity, therefore, different

Change of Soil Surface Roughness of Splash Erosion Process

http://dx.doi.org/10.5772/51278

103

the soil bulk density was measured by the ring sampler method.

mately was 20 m2

tact the profile laser scanner.

**2.3. Management treatments**

**2.4. Splash erosion**

**2.2. Rainfall simulations and soil surface roughness measurement techniques**

It was one kind of erosion phenomenon which the raindrop strikes the soil surface to create the soil particle dispersion and the leap moves for the splash erosion. It was one of the important components to soil erosion (Wang et al,1997, 1999; Zhao and Wu,2001; Liu and Wu,1996;Wu, 1999; Wu and Zhou,1994). The kinetic energy which the raindrop dropped from airborne was the higher than that of sheet flow and erosion sediment during the rainfall runoff for the differ‐ ent soil surface (Huang,1983). According to the observation data of some researches, the soils of bare land by the raindrop scattered were 10 times than those of the laminar flow scoured (Cai et al,1998). Many authors have studied the effect of rainfall on soil surface roughness and developed models to describe the change of soil surface roughness. Some researches obtained the simple forecast model of soil surface roughness (Johson et al,1979; Onstad,1984; Steichen, 1984). Later, the widely accepted concept of decreasing roughness with increasing amount of rainfall or rainfall energy may not always be appropriate. After 63 mm of rainfall the surface was crusted and surface roughness was decreased. However, an additional 92 mm of rainfall appeared to have a higher roughness value (Huang and Bradford,1992).

The objective of this study was to focus on the relationship between soil surface roughness and splash erosion. First, soil surface roughness affected on splash erosion under the condition of rainfall. Second, how was the change of soil surface roughness during the period of rainfall?
