**3. Artificial hydrological experimental studies**

Based on intensive literature review, it is found that artificial hydrological experimental studies can be categorised into the following groups with different objectives: (i) runoff and soil erosion processes and response to rainfall pattern, land use type, slope and tillage approach and (ii) nutrient export and response to land use type, slope and rainfall pattern. Now, a summary of the former studies related to these two perspectives is given.

#### **3.1. Impacts of land use and rainfall on runoff processes**

Several parameters are commonly used to describe rainfall-runoff processes, including runoff starting time, share of different runoff components (i.e. surface runoff, interflow at different layers), water residence time, etc. Wang et al. studied the natural rainfall-interflow processes at different soil layers (up layer of 0–40 cm and down layer of 40–110 cm) under natural rainfall condition in hilly region covered with red soil and found that interflow began earlier and had higher value in oiltea camellia than that in resumed field, while the peak fluxes were oppositional; the response time (i.e. lag) of interflow to rainfall and surface runoff increased with increase of soil depth [12]. Based on runoff plot experiments, Yin et al. investigated runoff at different soil layers with respective depth of 30, 60 and 90 cm to the surface with different types of land cover at red soil field slope in Jiangxi province; results showed that grassland cover increased interflow and prolonged interflow duration compared to bare land. Interflow was positively related to rainfall amount, rainfall intensity, rainfall duration and initial infiltrated rainfall, and runoff was mainly affected by rainfall amount at covered field slope while mainly influenced by rainfall intensity at bare field slope [13]. The effects of Bahia grass and its litter on dynamics of soil moisture and water balance were studied using lysimeter in the field slope covered with red soil, and results indicated that surface runoff of bare land was 24.25 times of that with Bahia grass' coverage and 11.78 times of that with Bahia grass' mulching; the effects of ground cover on soil moisture were different between seasons, and different ground covers could increase or decrease soil moisture [14].

structure and vegetation coverage supplemented with necessary engineering measures for soil

Field-Controlled Hydrological Experiments in Red Soil-Covered Areas (South China): A Review

http://dx.doi.org/10.5772/intechopen.70547

191

Xu et al. investigated the characteristics of interflow in the purple soil of field slope under different rainfall intensities and land surface conditions and found that the runoff coefficient and average interflow on undisturbed abandoned lands are 3–15 times and 7–33 times that of bare-cultivated lands, respectively; the difference in runoff generation becomes more evident with increase of rainfall intensity [19]. By the setup through a flow collection system, Liu et al. investigated runoff generation process and found that under condition of small rain, surface runoff and the lag to the flow peak might occur if the soil was dry before the rainfall and surface runoff were primarily controlled by infiltration-excess runoff mechanism [20]. Using rainfall simulation experiments, Zhao et al. assessed different pastures' runoff features under different rainfall intensities, antecedent moisture contents and slope gradients; results showed that ryegrass performs better in delaying time to runoff and reducing runoff coefficient, rainfall intensity and antecedent moisture content as well as gradient that affect runoff

Xie et al. studied the effects of tillage measures, such as down-slope tillage, cross-slope tillage and weed clearing in garden on soil and water conservation using field standard runoff plot method and 5 years' monitored data. Results showed that the order of the test plots from superior to inferior in reducing runoff and sediment loss was cross-slope tillage plot (75.33% and 80.57%), down-slope tillage plot (59.56% and 65.11%), weed clearing plot (21.73% and 38.08%) [22]; the runoff from April to September was more than 85% of the annual total runoff, and the sediment loss was more than 90% of the annual sediment loss; interplanting to increase field covering is an effective measure to prevent water loss and soil erosion, and cross-slope tillage is superior to down-slope tillage [27]. In field slope, Huang investigated the impact of different grass-growing methods on soil erosion and found that no matter which method is used, it can effectively decrease surface runoff and soil losses in comparison to bare pure agricultural land [23]. The reduction impact of land coverage and cultivation methods on runoff generation and sediment load as well as flow velocity by grass coverage in orchard were also reported in many other studies through field slope studies and in situ monitoring [24–26]. Xu et al. assessed the impacts of cultivation method, soil thickness, slope and rainfall intensity on interflow at the region covered with purple soil using artificial rainfall-runoff experiment and found that there was a lag between interflow and surface runoff; runoff generation showed single-modal process with slow variation [27]. Based on automatic monitoring of soil moisture, water potentials and runoff on a typical sloping farmland covered with purple soil, Lv [2013] found that the soils on different sections of sloping farmlands had differential water storage ability, following the order: upslope<middle slope<down slope; with the increase of depth, the water content showed less evident change; rainfall characteristics and soil heterogeneity affected soil water content change and soil water movement pattern; deep subsurface flow of a typical rainfall event showed obvious delay between rainfall and runoff; rainfall events of different intensity had different subsurface runoff coefficient (subsurface runoff coefficient was 53.6% to the large

and water conservation in slope land of red soil in South China.

**3.2. Impacts of slope and tillage on runoff processes**

features [21].

Xie et al. (2014) analysed the characteristics of vertical runoff output in different soil strata on a red soil slope plot under three conditions: vegetation coverage, litter mulch and bare land. The results showed that the total runoff of litter mulch treatment was maximum, followed by the bare land and the vegetation coverage treatment under natural rainfall conditions. Surface runoffs of vegetation coverage and litter mulch treatment were far less than that of the bare land treatment, which were 7.9 and 9.8% of the bare land, respectively. The planted grass and the litter mulch can reduce surface runoff significantly. Interflow of the bare land treatment was the least, which was, respectively, 56.4% of the vegetation coverage and 35.6% of the litter mulch treatments. It demonstrated that both vegetation and litter can increase water seepage. Underground runoff was the main way of runoff output on red soil slope under different treatments, and interflow and surface runoff were directly related to the presence or absence of ground coverage. All different runoff components showed seasonal variation characterized by high runoff in spring and summer, whereas lower runoff in autumn and winter due to temporal change in precipitation [11]. In most studies on groundwater runoff at field slope, the sum of interflow and groundwater flow was considered as a whole without division. In forest watershed, runoff was found to be dominated by groundwater runoff (may be above 39% of the total runoff), while surface runoff had small share (around 1–8% of total runoff) [15, 16].

Xie et al. [2010 b] assessed the effect of runoff reduction through different forest vegetation measures for soil and water conservation in hilly-land area of Jiangxi province using sampleplot and runoff-plot methods; results showed that the interception amount by forest canopy followed the descending order of Pinus elliotii, Masson pine, neddle-broad leaf mixed forest and Chinese chestnut, while the effective interception amount for litter and water holding of soil followed the descending order of Chinese chestnut, neddle-broad leaf mixed forest, Masson pine and Pinus elliotii; the rate of runoff reduction through multilayer vegetation measures was above 90% [28]. Based on statistical analysis on runoff plot experiment in red soil area, Xie et al. [17, 18] found that it was an effective approach to raise the level of vegetation structure and vegetation coverage supplemented with necessary engineering measures for soil and water conservation in slope land of red soil in South China.

Xu et al. investigated the characteristics of interflow in the purple soil of field slope under different rainfall intensities and land surface conditions and found that the runoff coefficient and average interflow on undisturbed abandoned lands are 3–15 times and 7–33 times that of bare-cultivated lands, respectively; the difference in runoff generation becomes more evident with increase of rainfall intensity [19]. By the setup through a flow collection system, Liu et al. investigated runoff generation process and found that under condition of small rain, surface runoff and the lag to the flow peak might occur if the soil was dry before the rainfall and surface runoff were primarily controlled by infiltration-excess runoff mechanism [20]. Using rainfall simulation experiments, Zhao et al. assessed different pastures' runoff features under different rainfall intensities, antecedent moisture contents and slope gradients; results showed that ryegrass performs better in delaying time to runoff and reducing runoff coefficient, rainfall intensity and antecedent moisture content as well as gradient that affect runoff features [21].

#### **3.2. Impacts of slope and tillage on runoff processes**

layers), water residence time, etc. Wang et al. studied the natural rainfall-interflow processes at different soil layers (up layer of 0–40 cm and down layer of 40–110 cm) under natural rainfall condition in hilly region covered with red soil and found that interflow began earlier and had higher value in oiltea camellia than that in resumed field, while the peak fluxes were oppositional; the response time (i.e. lag) of interflow to rainfall and surface runoff increased with increase of soil depth [12]. Based on runoff plot experiments, Yin et al. investigated runoff at different soil layers with respective depth of 30, 60 and 90 cm to the surface with different types of land cover at red soil field slope in Jiangxi province; results showed that grassland cover increased interflow and prolonged interflow duration compared to bare land. Interflow was positively related to rainfall amount, rainfall intensity, rainfall duration and initial infiltrated rainfall, and runoff was mainly affected by rainfall amount at covered field slope while mainly influenced by rainfall intensity at bare field slope [13]. The effects of Bahia grass and its litter on dynamics of soil moisture and water balance were studied using lysimeter in the field slope covered with red soil, and results indicated that surface runoff of bare land was 24.25 times of that with Bahia grass' coverage and 11.78 times of that with Bahia grass' mulching; the effects of ground cover on soil moisture were different between seasons, and different

Xie et al. (2014) analysed the characteristics of vertical runoff output in different soil strata on a red soil slope plot under three conditions: vegetation coverage, litter mulch and bare land. The results showed that the total runoff of litter mulch treatment was maximum, followed by the bare land and the vegetation coverage treatment under natural rainfall conditions. Surface runoffs of vegetation coverage and litter mulch treatment were far less than that of the bare land treatment, which were 7.9 and 9.8% of the bare land, respectively. The planted grass and the litter mulch can reduce surface runoff significantly. Interflow of the bare land treatment was the least, which was, respectively, 56.4% of the vegetation coverage and 35.6% of the litter mulch treatments. It demonstrated that both vegetation and litter can increase water seepage. Underground runoff was the main way of runoff output on red soil slope under different treatments, and interflow and surface runoff were directly related to the presence or absence of ground coverage. All different runoff components showed seasonal variation characterized by high runoff in spring and summer, whereas lower runoff in autumn and winter due to temporal change in precipitation [11]. In most studies on groundwater runoff at field slope, the sum of interflow and groundwater flow was considered as a whole without division. In forest watershed, runoff was found to be dominated by groundwater runoff (may be above 39% of the total runoff), while surface runoff had small share (around 1–8% of total runoff) [15, 16]. Xie et al. [2010 b] assessed the effect of runoff reduction through different forest vegetation measures for soil and water conservation in hilly-land area of Jiangxi province using sampleplot and runoff-plot methods; results showed that the interception amount by forest canopy followed the descending order of Pinus elliotii, Masson pine, neddle-broad leaf mixed forest and Chinese chestnut, while the effective interception amount for litter and water holding of soil followed the descending order of Chinese chestnut, neddle-broad leaf mixed forest, Masson pine and Pinus elliotii; the rate of runoff reduction through multilayer vegetation measures was above 90% [28]. Based on statistical analysis on runoff plot experiment in red soil area, Xie et al. [17, 18] found that it was an effective approach to raise the level of vegetation

ground covers could increase or decrease soil moisture [14].

190 Hydrology of Artificial and Controlled Experiments

Xie et al. studied the effects of tillage measures, such as down-slope tillage, cross-slope tillage and weed clearing in garden on soil and water conservation using field standard runoff plot method and 5 years' monitored data. Results showed that the order of the test plots from superior to inferior in reducing runoff and sediment loss was cross-slope tillage plot (75.33% and 80.57%), down-slope tillage plot (59.56% and 65.11%), weed clearing plot (21.73% and 38.08%) [22]; the runoff from April to September was more than 85% of the annual total runoff, and the sediment loss was more than 90% of the annual sediment loss; interplanting to increase field covering is an effective measure to prevent water loss and soil erosion, and cross-slope tillage is superior to down-slope tillage [27]. In field slope, Huang investigated the impact of different grass-growing methods on soil erosion and found that no matter which method is used, it can effectively decrease surface runoff and soil losses in comparison to bare pure agricultural land [23]. The reduction impact of land coverage and cultivation methods on runoff generation and sediment load as well as flow velocity by grass coverage in orchard were also reported in many other studies through field slope studies and in situ monitoring [24–26]. Xu et al. assessed the impacts of cultivation method, soil thickness, slope and rainfall intensity on interflow at the region covered with purple soil using artificial rainfall-runoff experiment and found that there was a lag between interflow and surface runoff; runoff generation showed single-modal process with slow variation [27]. Based on automatic monitoring of soil moisture, water potentials and runoff on a typical sloping farmland covered with purple soil, Lv [2013] found that the soils on different sections of sloping farmlands had differential water storage ability, following the order: upslope<middle slope<down slope; with the increase of depth, the water content showed less evident change; rainfall characteristics and soil heterogeneity affected soil water content change and soil water movement pattern; deep subsurface flow of a typical rainfall event showed obvious delay between rainfall and runoff; rainfall events of different intensity had different subsurface runoff coefficient (subsurface runoff coefficient was 53.6% to the large rainfall event while the coefficient was only 1.6% to the small rainfall event); the antecedent soil moisture content also significantly affected the runoff coefficient in the vadose zone [20]. In artificially field slope rainfall-runoff experiment, Ding found that under the same rainfall intensity, the share of interflow in the total precipitation increased with rise of runoff plot's slope, while the percentage of the subsurface flow occupying the total precipitation increased with the decrease of rainfall intensity under the same slope gradient [29]. Wang et al. [2017] investigated the effects of tillage practices and slope on runoff and erosion under simulated rainfall in laboratory plots and found that AD (Artificial Digging), AH (Contour Plow) and CP (Contour Plow) can be adopted as a beneficial summer tillage practice for controlling erosion during summer fallow period because it delayed the time to runoff, decreased runoff and sediment, increased infiltration, which in turn promoted rainfall water and soil conservation [30, 31].

In the future, hydrological process at field slope requires more investigation from the following perspectives: (1) improvement of monitoring strategies and methodology. Isotopic method provides an efficient way to reveal hydrological process at field slope, which may improve understanding of hydrological regimes; (2) artificial hydrological experiments may contain certain extent of uncertainty during to heterogeneity in rainfall and physiogeographic condition (e.g. soil type, dryness, porosity), design and installation of long-term in situ experimental study to capture variability of soil water movement at different temporal and spatial scales and (3) development and improvement of modelling tool for simulation and prediction of soil water movement under different climatic condition and catchment characteristics,

Field-Controlled Hydrological Experiments in Red Soil-Covered Areas (South China): A Review

http://dx.doi.org/10.5772/intechopen.70547

193

This work is also supported by the National Natural Science Foundation of China (41501531), the Natural Science Foundation of Jiangsu Province (BK20151062), the Open Research Fund of State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin (China Institute of Water Resources and Hydropower Research, Grant No: IWHR-SKL-201710) and the Science Foundation of Nanjing Institute of Geography and Limnology, Chinese Academy

and Seifeddine Jomaa3

1 Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and

2 State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Nanjing

3 Department of Aquatic Ecosystem Analysis and Management, Helmholtz Centre for

[1] Sidle RC, Hirano T, Gomi T, Terajima T. Hortonian overland flow from Japanese forest plantations – An aberration, the real thing, or something in between? Hydrological

[2] Kaufmann V, Pinheiro A, dos Reis Castro NM. Simulating transport of nitrogen and phosphorus in a Cambisol after natural and simulated intensive rainfall. Journal of

which may assist watershed management for water and soil conservation.

**Acknowledgements**

of Sciences (NIGLAS2014QD07).

Sanyuan Jiang1,2\*, Qiande Zhu2

\*Address all correspondence to: syjiang@niglas.ac.cn

Hydraulic Research Institute, Nanjing, China

Processes. 2007;**21**:3237-3247

Contaminant. 2014;**160**:53-64

Limnology, Chinese Academy of Sciences, Nanjing, China

Environmental Research – UFZ, Magdeburg, Germany

**Author details**

**References**

## **4. Conclusions and outlooks**

This study gave a summary of controlled hydrological experiments using rainfall simulator in China, especially in the red soil-covered region of Jiangxi province, including the design and construction of artificial hydrological experiments, studies and outcomes related to the impacts of slope, land use, tillage, rainfall patterns and antecedent soil moisture on runoff generation and sediment export. Results showed that grass covered slope arable land had lower surface runoff and sediment fluxes, higher subsurface runoff, peak flow, and tailing time relative to bare land; the response of subsurface flow was faster to rainfall and surface runoff from lower to upper layer and lag time increased with increasing soil depth; subsurface runoff had close relationship with rainfall amount, rainfall intensity affected peak subsurface runoff substantially, but did not impact starting time and runoff of subsurface flow; rainfall pattern affected subsurface runoff generation considerably including hydrographs and runoff; precedent soil water content had direct influences on runoff generation and runoff of subsurface flow, characterized by decrease of lag time, increase of runoff and peak flow with increase of precedent soil water content. Runoff plot test is a principal method for research of soil and water conservation and also the main approach of runoff sedimentation measurement. The design of runoff plot should obey the principles of improving the accuracy and decreasing the error of tests, saving construction materials and cutting down project costs, reducing the difficulty of construction and enhancing construction quality, as well as being conducive to post observations and lessening operating costs [31]. Although many studies have been conducted worldwide on soil water movement and transformation on field slopes, most of the former researches were focused on surficial soil water movement in indoor artificial rainfall condition with homogeneous initial soil water content and field slope. Some similar studies have been conducted in the field, however, the studies on infiltration of soil water during rainfall period and its redistribution after the infiltration are not sufficient; most studies do not relate rainfall-infiltration, runoff generation at field slopes, and soil water dynamics; spatial heterogeneity of soil property, hysteresis, surface crust, plant interception, and water uptake by roots were not comprehensively considered. In particular, studies on redistribution and export of surface runoff, interflow and groundwater flow are lacking [32].

In the future, hydrological process at field slope requires more investigation from the following perspectives: (1) improvement of monitoring strategies and methodology. Isotopic method provides an efficient way to reveal hydrological process at field slope, which may improve understanding of hydrological regimes; (2) artificial hydrological experiments may contain certain extent of uncertainty during to heterogeneity in rainfall and physiogeographic condition (e.g. soil type, dryness, porosity), design and installation of long-term in situ experimental study to capture variability of soil water movement at different temporal and spatial scales and (3) development and improvement of modelling tool for simulation and prediction of soil water movement under different climatic condition and catchment characteristics, which may assist watershed management for water and soil conservation.
