Baoyuan Liu

Calibration of the LISEM model for a small loess plateau catchment

The Limburg Soil Erosion Model (LISEM) soil erosion model was calibrated for a 2-km2 catchment on the Chinese Loess Plateau. The most important calibration factors were saturated conductivity and Mannings n. Calibration on catchment discharge was done by using the discharge peak (timing and discharge) followed by an adjustment for the total discharge to obtain the correct amount of sediment output. The results showed that LISEM can be successfully calibrated for a Loess Plateau catchment, and that small runoff events need to be calibrated separately from large runoff events. A separate calibration might even be needed for each event. The model performance was also evaluated using catchment wide spatially distributed data on rill erosion. Rill erosion intensity was mapped in the field and compared to spatial patterns of erosion predicted by LISEM. The simulated erosion patterns do show some resemblance with mapped erosion patterns in a general sense but they are very different in detail. The cause for this can be found in the extremely steep slopes and abrupt slope changes in the catchment. Some of the process descriptions in LISEM are not intended for such an environment, while the grid based kinematic wave routing cannot cope with the abrupt changes in flow conditions. The effects of this are amplified by inaccuracies in the input data and the DEM. For topographically complex catchments it will be very difficult to obtain data that are good enough for an accurate simulation of erosion patterns. This limits the use of a model such as LISEM as a predictive tool for future events. Simulation of different land use scenarios is less problematic, if a known event is used for all scenario simulations.

Discharge and sediment measurements at the outlet of a watershed on the Loess plateau of China

A dam and weir system was constructed to measure the discharge of water and sediment from a selected small catchment on the Loess plateau in China. The aim of the system described here was to collect data on discharge and sediment content during occasional summer storms. These data can be used for calibrating and validating the LISEM erosion model. A V-notch weir was selected since it can measure a wide range of discharges. The measurement structure was equipped with an ultrasonic sensor to measure the water level. The system automatically switched on as soon as rain had been detected and the water level data were stored when a certain level threshold was surpassed. As a back-up system a flow meter was used, while a local farmer had also been hired to manually record water level during events. Sediment content of the runoff was determined on samples taken by an automatic sampler and a local farmer took additional samples. The system operated from April 1998 until September 2000. In this period, six events occurred and data could be collected during five of those. The data were corrected to make them useful for comparison with erosion simulation results. The collected data show that runoff only occurs during high-intensity rainstorms that produce more than about 11 mm of rain.

Modelling water flow and sediment processes in a small gully system on the Loess Plateau in China

Abstract A single gully system was selected in a small agricultural watershed on the Loess Plateau of China with the objective of measuring and then simulating water and sediment transport and defining alternative land uses to reduce discharge and soil loss. The gully had a total length of about 40 m and was about 30 m wide. The watershed feeding the gully occupied about 1950 m 2 (including the gully itself). The gully bottom had a slope of about 32–40°, whereas the gully walls were from 40° to over 60°. Soil water content and water and sediment discharge were measured automatically. The physically based hydrological and soil erosion model LISEM was used to calculate water and sediment discharge. Calibration has been carried out for one event, by adjusting the saturated conductivity values. Validation was performed for two additional runoff events. Calibration results show reasonably comparable hydrographs between measured and calculated discharge. LISEM could be calibrated on the hydrograph quite satisfactorily using the saturated conductivity as a calibration factor. Also, validation of LISEM for two other runoff events showed reasonably good results. The calibration on total soil loss also shows good results. For the validation runs, these results are poor, probably due to limitations of the measurement equipment and the incapability of the model to simulate small events. Scenario analyses showed that forest, as an alternative land use for the gully bottom, will result in significantly lower water and sediment. This strongly supports the implementation of the reforestation policy recently suggested and activated by the central government of the P.R. China.

Intensive water content and discharge measurement system in a hillslope gully in China

Abstract An automatic monitoring system was constructed to intensively study the water–profile–runoff interactions during rain events, of a hillslope gully. The system was installed on the Loess plateau in the Shaanxi province in northern China. The primary goal was to obtain a better understanding of soil erosion processes in this district to aid in better management. To accomplish this, infiltration and runoff data for running, calibrating and validating the LISEM erosion model was needed. The system presented here consisted of 29 Time Domain Reflectometry (TDR) water content sensors that monitored the water content variation in time. Sensors were installed in different subsystems throughout the gully geometry such as in the cropland surrounding the gully, in some gully slopes and in the gully floor. At the outflow point of the gully, an H-flume was installed in order to measure the actual discharge of the gully system and to measure directly the sediment concentration in the discharge. The monitoring system was programmed in this way so that more measurements were recorded when a rainstorm occurred. Installation took place in April 1998 and it was used until September 2000. In 1998, five major rain events were recorded, which generated runoff and erosion, in 1999 and 2000 only one. Cropland measurements showed high water contents and high infiltration rates all through the measuring period and also showed a strong reaction to precipitation. The sidewalls of the gully showed much lower water contents where only very shallow parts showed some infiltration during rain showers, while steep parts of the gully, such as pipes and vertical walls, showed an extremely low water content and practically no water content variation with time. Simulation results confirmed the suspicion that these areas are an important source for Hortanian overland flow within the gully system. Model simulations further showed that most of the sediment being eroded from the gully system was coming from rills and smaller gullies being cut into the main gully bottom. Saturation excess overland flow proved to be dependent on the characteristic of the rain event as well as on the water content of the soil at the beginning of the event.

Using contour lines to generate digital elevation models for steep slope areas: a case study of the Loess Plateau in North China

In soil erosion models digital elevation models (DEMs) play an important role. Most interpolations from contour lines fail to address multi-value cells (MVCs) problems and therefore find it difficult to deal with steep slopes. These interpolation methods randomly assign a single value for MVCs and use this value in interpolation for nearby cells. This approach is very inaccurate. The frequency of MVCs and the problem caused by them was investigated, and the errors created by using the random values for MVCs was analyzed in this paper. A special treatment for MVCs and practical solution to create more accurate interpolation cell values in DEM building was developed. The new approach involves storing additional information of contour lines that go through the MVCs, such as maximum height and minimum height values, and the cardinal orientation relationship of the contour lines. A special MVC filter kernel was developed to decide the appropriate elevation value for interpolation. The computation method is based on raster data. An area on the Loess Plateau in North China was selected as an example to demonstrate the problems of the previously common used approach and to show results of the new method.

Soil loss tolerance in the black soil region of Northeast China

Soil loss tolerance (T) is the maximum rate of annual soil erosion that is tolerated and still allows a high level of crop productivity to be sustained economically and indefinitely. In the black soil region of Northeast China, an empirically determined, default T value of 200 (t/km2·a) is used for designing land restoration strategies for different types of soils. The objective of this study was to provide a methodology to calculate a quantitative T for different black soil species. A field investigation was conducted to determine the typical soil profiles of 21 black soil species in the study area and a quantitative methodology based on a modified soil productivity index model was established to calculate the T values. These values, which varied from 68 t/km2·a to 358 t/km2·a, yielded an average T value of 141 t/km2·a for the 21 soil species. This is 29.5% lower than the current national standard T value. Two significant factors that influenced the T value were soil thickness and vulnerability to erosion. An acceptable reduction rate of soil productivity over a planned time period of 1% is recommended as necessary for maintaining long-term sustainable soil productivity. Compared with the currently used of regional unified standard T value, the proposed method, which determines T using specific soil profile indices, has more practical implications for effective, sustainable management of soil and water conservation.

Increasing trends in rainfall-runoff erosivity in the Source Region of the Three Rivers, 1961–2012

As the head source of the two longest rivers in China and the longest river in Southeast Asia, the East Qinghai-Tibetan Plateau (QTP) is experiencing increasing thaw snowmelt and more heavy precipitation events under global warming, which might lead to soil erosion risk. To understand the potential driving force of soil erosion and its relationship with precipitation in the context of climate change, this study analyzed long-term variations in annual rainfall-runoff erosivity, a climatic index of soil erosion, by using the Mann-Kendall statistical test and Theil and Sens approach in the Source Region of the Three Rivers during 1961-2012. The results showed the followings: (i) increasing annual rainfall-runoff erosivity was observed over the past 52years, with a mean relative trend index (RT1) value of 12.1%. The increasing trend was more obvious for the latest two decades: RT1 was nearly three times larger than that over the entire period; (ii) more precipitation events and a higher precipitation amount were the major forces for the increasing rainfall-runoff erosivity; (iii) similar rising trends in sediment yields, which corresponded to rainfall-runoff erosivity under slightly increasing vegetation coverage in the study area, implied a large contribution of rainfall-runoff erosivity to the increasing sediment yields; and (iv) high warming rates increased the risk of soil destruction, soil erosion and sediment yields. Conservation measures, such as enclosing grassland, returning grazing land to grassland and rotation grazing since the 1980s, have maintained vegetation coverage and should be continued and strengthened.

Estimation of USLE crop and management factor values for crop rotation systems in China

Abstract Soil erosion on cropland is a major source of environmental problems in China ranging from the losses of a non-renewable resource and of nutrients at the source to contamination of downstream areas. Regional soil loss assessments using the Universal Soil Loss Equation (USLE) would supply a scientific basis for soil conservation planning. However, a lack of information on the cover and management (C) factor for cropland, one of the most important factors in the USLE, has limited accurate regional assessments in China due to the large number of crops grown and their complicated rotation systems. In this study, single crop soil loss ratios (SLRs) were collected and quantified for 10 primary crops from past studies or reports. The mean annual C values for 88 crop rotation systems in 12 cropping system regions were estimated based on the combined effects of single crop SLRs and the percentage of annual rainfall erosivity (R) during the corresponding periods for each system. The C values in different cropping system regions were compared and discussed. The results indicated that the SLRs of the 10 primary crops ranged from 0.15 to 0.74. The mean annual C value for all 88 crop rotation systems was 0.34, with a standard deviation of 0.12. The mean C values in the single, double and triple cropping zones were 0.37, 0.36 and 0.28, respectively, and the C value in the triple zone was significantly different from those in single and double zones. The C values of dryland crop systems exhibited significant differences in the single and triple cropping system regions but the differences in the double regions were not significant. This study is the first report of the C values of crop rotation systems in China at the national scale. It will provide necessary and practical parameters for accurately assessing regional soil losses from cropland to guide soil conservation plans and to optimize crop rotation systems.

Estimating rainfall erosivity by incorporating seasonal variations in parameters into the Richardson model

Rainfall erosivity is an important climatic factor for predicting soil loss. Through the application of high-resolution pluviograph data at 5 stations in Huangshan City, Anhui Province, China, we analyzed the performance of a modified Richardson model that incorporated the seasonal variations in parameters α and β. The results showed that (1) moderate to high seasonality was presented in the distribution of erosive rainfall, and the seasonality of rainfall erosivity was even stronger; (2) seasonal variations were demonstrated in both parameters α and β of the Richardson model; and (3) incorporating and coordinating the seasonality of parameters α and β greatly improved the predictions at the monthly scale. This newly modified model is therefore highly recommended when monthly rainfall erosivity is required, such as, in planning soil and water conservation practices and calculating the cover-management factor in the Universal Soil Loss Equation (USLE) and Revised Universal Soil Loss Equation (RUSLE).

Influence of soil and water conservation measures on soil fertility in the Beijing mountain area

Soil and water conservation (SWC) measures can be adopted to conserve soil and water and improve soil fertility. The degree to which SWC measures improve soil fertility is affected by the type of SWC measure, soil type, climate, etc. The purpose of this study was to study the effect of the main SWC measures implemented in the Beijing mountain area on soil fertility. Six runoff plots, including a fish pit (fallow) (FPF), fish pit (Platycladus orientalis L. Franco) (FPP), narrow terrace (fallow) (NTF), narrow terrace (Juglans regia L.) (NTJ), tree pan (Juglans regia L.) (TPJ), and fallow land (FL), were established to analyze the differences in soil fertility in the Beijing mountain area. Soil samples were collected in 2005 and 2015 from the six runoff plots. Soil particle size; soil total nitrogen (TN), total phosphorous (TP), total potassium (TK), alkali-hydrolysable nitrogen (Ah-N), available P (Av-P), and available K (Av-K); and soil organic matter (SOM) were measured. The soil integrated fertility index (IFI) was calculated. The results showed that the soil nutrient content and IFI significantly decreased from 2005 to 2015 in the FL plot and significantly increased in the five runoff plots with SWC measures. Compared to the other runoff plots with SWC measures, the FPP plot more significantly improved the soil nutrient content and IFI. The TN, Ah-N, Av-K, SOM, and IFI in the FPP plots increased by 98%, 113%, 61%, 69 and 47%, respectively, from 2005 to 2015. The IFI for the FPP, NTJ, and TPJ exceeded the average IFI of the farmland soil in the study region. The results indicated that the combination of engineering practices and vegetative measures effectively improved soil fertility. These results may be helpful for selecting SWC measures, land-use planning and monitoring and assessing soil fertility.