**2. Material and Methods**

#### **2.1. Soil and soil box design**

Experiments were carried out at the Northwest AF University Soil Erosion Research Labora‐ tory,Yangling town,China. The soil was collected from the topsoil soil (0-20cm) in Yangling town. Basic properties of soil were following (Table 1).


**Table 1.** Particle size distribution (0—20cm) of experimental soil.

Four iron boxes of 2.0 m×1.0 m×0.5 m were used in the rainfall simulation study. Air-dried top soil was passed through a 10mm sieve to insure homogeneity and placed in every ero‐ sion box with an area of 2m2 . The soil bulk density was controlled to 1.08 g cm-3 in order to 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 the soil bulk density was measured by the ring sampler method.

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

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‐ mately was 20 m2 . This experiment used the constant rainfall intensity, therefore, different 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‐ tact the profile laser scanner.

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

#### **2.3. Management treatments**

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.

#### **2.4. Splash erosion**

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. 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).

**2. Material and Methods**

102 Research on Soil Erosion Soil Erosion

**2.1. Soil and soil box design**

sion box with an area of 2m2

town. Basic properties of soil were following (Table 1).

**Table 1.** Particle size distribution (0—20cm) of experimental soil.

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?

Experiments were carried out at the Northwest AF University Soil Erosion Research Labora‐ tory,Yangling town,China. The soil was collected from the topsoil soil (0-20cm) in Yangling

**Particle size/ (%)** > 0.25mm 0.25—0.05mm 0.05—0.01mm 0.01—0.005mm 0.005—0.001mm < 0.001mm 0.12 2.70 41.13 6.88 12.89 36.28

Four iron boxes of 2.0 m×1.0 m×0.5 m were used in the rainfall simulation study. Air-dried top soil was passed through a 10mm sieve to insure homogeneity and placed in every ero‐

. The soil bulk density was controlled to 1.08 g cm-3 in order to

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

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

$$d = 0.356D^{0.712} \tag{1}$$

where d is the raindrop diameter of every rainfall (mm), D is the color spot diameter (mm).

**Tillage practice Rainfall intensity/**

0.68

0.68

0.68

0.68

0.68

Under the rainfall intensity of 0.68 mm/min: *R* 1/*R* 0=49261E-3.3451 r=0.817 n=15

Straight slope (CK)

Raking cropland (PM)

Artificial hoe (CH)

Artificial dig (TW)

Contour slope (DG)

**Table 2.** Change of soil surface roughness on the single rainfall intensity.

method of statistics and analysis. The results followed:

Under the rainfall intensity of 1.50 mm/min: *R* 1/*R* 0=2×106

rainfall(cm), E is the total kinetic energy of raindrop (J/cm2

The same bellow.

Burwell (1969) and Steichen (1984).

the increasing rainfall intensity.

**intensity**

**mm·min-1 R0/cm R/cm R/R0**

1.50 0.193 0.960

1.50 0.268 1.115

1.50 0.732 1.036

1.50 0.874 1.077

1.50 1.707 1.045

0.235 1.169

Change of Soil Surface Roughness of Splash Erosion Process

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

105

0.246 1.024

0.654 0.926

0.701 0.864

1.576 0.965

E-4.2309 r=0.836 n=15

min), n is the sample number.

0.201

0.240

0.706

0.812

1.633

Note: *R* 0-soil surface roughness before rainfall, cm*R*- soil surface roughness after rainfall, cm.

Relationships between rainfall energy and soil surface roughness were obtained by the

where *R* 1 is the soil surface roughness after rainfall(cm), *R* 0 is the soil surface roughness before

They had the power function relationship between the change of the soil surface roughness and kinetic energy of raindrop under the different rainfall intensities. Soil surface roughness decreased with the increasing kinetic energy of raindrop. The results had the consistent with

The combined rainfall intensity was be simulated in order to clear about the change and nature of soil surface roughness. The changing characteristics of soil surface roughness were different for the different slopes under the combined rainfall intensity (Table.3). The changing characteristics of soil surface roughness increased first, and then decreased, and increased finally with the increasing rainfall intensity on the CK slope. However, the changing characteristics of soil surface roughness increased on the PM slope, and the change of soil surface roughness increased first and then decreased on other slopes with

**3.2. Changing characteristics of soil surface roughness under the combined rainfall**

**Figure 1.** Collecting board of splash erosion.
