**3. Water monitoring and sample collection system**

The artificial rainfall simulation testing ground is approximately 300 m<sup>2</sup>

**Figure 7.** The experimental variant slope soil tank in Beijing Normal University.

m, installed with the height of 5.2 m [9, 10].

222 Hydrology of Artificial and Controlled Experiments

**Figure 8.** The experimental slope-adjustable soil tank in Hohai university.

rainfall simulators, which have various combinations of types of sprayer, water pressure, and rainfall intensity. Every trough rainfall simulator has three swayed sprinklers, spacing at 1.1

The slope-adjustable soil tank is made of welding steel plates splitting into two parts of the main tank and overflow tank in State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering of Hohai University (**Figure 8**). The two tanks are connected by four holes at the bottom. Effective volume of main tank measures 12 m long × 3 m wide × 1.5 m deep, while that of overflow tank measures 1.5 m long × 10 m wide × 6.2 m deep. The whole tank is divided into two 1.5-m-wide parts, varying from 0 to 30° under the drive of hydraulic pressure. The decision of its size is optimized profoundly after referencing international

, concluding 15 trough

**Rainfall monitoring system:** Rainfall gauges are installed uniformly, recording the average value as rainfall intensity of the whole rainfall. The dataset is collected by computer automatically with 0.1 mm of precision. Laser rainfall intensity monitor is installed in Experimental Hall of Water and Soil Process of IGSNRR. It is composed of an array of laser transmitters and receivers. It achieves the rain non-touch measurement using orthogonally multiplexed laser beams according to the light attenuation law. The measurement error is less than 2%.

**Discharge monitoring system:** A simple and effective artificial flow measurement is applied for the monitoring system. Because water flows out from pipe, the discharge can be measured using a volume-known container and a stopwatch at the outlet.

**Soil water potential monitoring system:** The method of automatic collection of soil water potential is to transfer soil water potential (kPa) measured by negative pressure meter into electronical signals (mV) and then transfer analog signals into digital signals through A/D converter inputting the computer. Finally, the signals mentioned above are translated into soil negative pressure value based on mV-negative pressure relationship after calibration. The computer gives commands and instructions getting through specialized microcontroller and makes choice between sections and channels, to realize sample automation.

**Water and soil collection system:** Surface water collection system has a simple mechanism. Runoff flows into sampling bottles through water pipe collected at regular intervals. Collecting soil water corporates with soil water vacuum extraction device, which distils soil samples in a vacuum and then condensates water using liquid nitrogen.

The set of system consisting of various monitoring devices can develop runoff generation mechanism of different underlying surface, movement law of soil water, pollution law of nonpoint source pollution, migration and transformation law of pollution in soil, soil erosion law, and landslide formation mechanism.

#### **4. Main results**

Under the condition of experimental variant slope soil tank, some studies on hydrological physical mechanism experiment can be conducted, for example, rainfall-runoff formation under conditions of different rainfall intensity, surface slope and underlying surface, the law of surface water-biowater-groundwater cycle and transformation, pollution on migration, and transformation in unsaturated soil water. The margins tank has been used in the past to examine the characteristics of two-dimensional mudflows, the gully formation by turbidity currents [11], and the feasibility of using jets to manage sediments in a combined sewer overflow storage reservoir. The experimental soil tank can also be used to analyze the soil infiltration feature during rainfall [12, 13] and hydrodynamic mechanism of soil erosion [14] in Institute of Soil and Water Conservation, lateral downslope unsaturated flow in Hohai University [15], soil water movement using gamma ray in Xi'an University of Technology [5, 16], and rainfall-runoff relationship for different rainfall intensities in Institute of Geography [17]. Solute transport experiments have used tank arrangements for various purposes, including migration of infiltrated NH4 and NO<sup>3</sup> in a soil and groundwater system [18], bioavailable phosphorus loss in runoff [19], and enrichment mechanisms of phosphorus [20].

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#### **5. Conclusion**

The successful study of variant slope soil tank with artificial rainfall simulation system provides a basic foundation for hydrological and aquatic environmental experiment research under controlled conditions. After the operation of several years, this system has a reliable performance and stable manifestation. It is of great importance for studying rainfall-runoff relationship, establishment of conceptual hydrological model, migration and transformation of pollution material in soil water environment, and soil erosion and sediment yield study.

#### **Acknowledgements**

This work was financially supported by Key Program of National Natural Science Foundation of China (Grant No. 41730749) and CAS Key Technology Talent.

#### **Author details**

Lihu Yang1,2\*, Simin Qu<sup>3</sup> , Yifan Wang<sup>3</sup> and Xianfang Song1,2

\*Address all correspondence to: yanglihu@igsnrr.ac.cn

1 Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China

2 University of Chinese Academy of Sciences, Beijing, China

3 College of Water Resources and Hydrology, Hohai University, Nanjing, China
