An approximate analytical solution for describing surface runoffand sediment transport over hillslope

Soil and water loss from farmland causes&nbsp;land degradation&nbsp;and water pollution, thus continued efforts are needed to establish mathematical model for quantitative analysis of relevant processes and mechanisms. In this study, an approximate analytical solution has been developed for overland flow model and sediment transport model, offering a simple and effective means to predict overland flow and erosion under natural rainfall conditions. In the overland flow model, the flow regime was considered to be transitional with the value of parameter&nbsp;&beta;&nbsp;(in the kinematic wave model) approximately two. The change rate of unit discharge with distance was assumed to be constant and equal to the runoff rate at the outlet of the plane. The excess rainfall was considered to be constant under uniform rainfall conditions. The overland flow model developed can be further applied to natural rainfall conditions by treating excess rainfall intensity as constant over a small time interval. For the sediment model, the recommended values of the runoff erosion calibration constant (cr) and the splash erosion calibration constant (cf) have been given in this study so that it is easier to use the model. These recommended values are 0.15 and 0.12, respectively. Comparisons with observed results were carried out to validate the proposed analytical solution. The results showed that the approximate analytical solution developed in this paper closely matches the observed data, thus providing an alternative method of predicting runoff generation and sediment yield, and offering a more convenient method of analyzing the quantitative relationships between variables. Furthermore, the model developed in this study can be used as a theoretical basis for developing runoff and&nbsp;erosion control&nbsp;methods.</span

An approximate analytical solution for describing surface runoff and sediment transport over hillslope

Soil and water loss from farmland causes land degradation and water pollution, thus continued efforts are needed to establish mathematical model for quantitative analysis of relevant processes and mechanisms. In this study, an approximate analytical solution has been developed for overland flow model and sediment transport model, offering a simple and effective means to predict overland flow and erosion under natural rainfall conditions. In the overland flow model, the flow regime was considered to be transitional with the value of parameter beta (in the kinematic wave model) approximately two. The change rate of unit discharge with distance was assumed to be constant and equal to the runoff rate at the outlet of the plane. The excess rainfall was considered to be constant under uniform rainfall conditions. The overland flow model developed can be further applied to natural rainfall conditions by treating excess rainfall intensity as constant over a small time interval. For the sediment model, the recommended values of the runoff erosion calibration constant (c(r)) and the splash erosion calibration constant (c(f)) have been given in this study so that it is easier to use the model. These recommended values are 0.15 and 0.12, respectively. Comparisons with observed results were carried out to validate the proposed analytical solution. The results showed that the approximate analytical solution developed in this paper closely matches the observed data, thus providing an alternative method of predicting runoff generation and sediment yield, and offering a more convenient method of analyzing the quantitative relationships between variables. Furthermore, the model developed in this study can be used as a theoretical basis for developing runoff and erosion control methods. (C) 2018 Elsevier B.V. All rights reserved

Experimental Study on the Mechanisms of Soil Water-Solute- Heat Transport and Nutrient Loss Control

The release and migration of nutrients, pesticides, and other chemicals in the runoff from agricultural lands is not only an economic loss but a threat to the quality of our surface and groundwater. In contrast to pollution from point sources, pollution from non-point sources is often low in intensity but high in volume. The development of a physically based model to simulate the transport of soil solutes would provide a better understanding of transport mechanisms and assist in the development of effective methods to control the loss of nutrients from soils and the pollution of waterways. As a result, numerous studies have been conducted in this area. But due to the soil genesis and human activity, the process is very complex, which can have a great impact on soil water movement, solute transport, as well as nutrient loss. In this study, we determined water movement and solute and heat transport through columns of disturbed soil samples. We also carried out simulated rainfall experiments on an artificial slope to study the nutrient loss

Evaluation of the Heat Pulse Ratio Method for Measuring Soil Water Flux

Soil water flux is an important hydrologic parameter, yet few techniques for measuring it in situ are available. Here we evaluate the heat pulse ratio method for measuring water flux. We conducted heat pulse measurements of flux in packed columns of sand, sandy loam, and silt loam soil. Water fluxes were calculated from the data following both a traditional temperature increase difference method and a new temperature increase ratio method. Both methods yielded similar estimates of flux, agreeing to within 0.84 cm h−1 on average. The low flow detection limits for both methods were also similar and ranged from 0.1 to 0.4 cm h−1However, the ratio method was superior in that it permitted simpler calculations, reduced the number of required parameters by four, and exhibited two to three times greater precision. We found strong linear relationships (r 2 ≥ 0.98, standard error \u3c 0.4 cm h−1) between estimated and imposed water fluxes up to 40 cm h−1 However, the slopes of these relationships were less than one, ranging from 0.739 for the sand to 0.224 for the sandy loam. These slopes indicate that the sensitivity was less than predicted by the standard conduction–convection model. We have not discovered the cause of these errors, but we did find that the errors could not be explained by increasing the magnitude of the conduction term in the model as has been previously suggested. Instead, the errors could be explained by reducing the magnitude of the convection term. This finding can help direct future research efforts to improve the accuracy of the ratio method

Evaluation of Hydraulic Parameters Obtained by Different Measurement Methods for Heterogeneous Gravel Soil

Knowledge of soil hydraulic parameters for the van Genuchten function is important to characterize soil water movement for watershed management. Accurate and rapid prediction of soil water flow in heterogeneous gravel soil has become a hot topic in recent years. However, it is difficult to precisely estimate hydraulic parameters in a heterogeneous soil with rock fragments. In this study, the HYDRUS-2D numerical model was used to evaluate hydraulic parameters for heterogeneous gravel soil that was irregularly embedded with rock fragments in a grape production base. The centrifugal method (CM), tensiometer method (TM) and inverse solution method (ISM) were compared for various parameters in the van Genuchten function. The soil core method (SCM), disc infiltration method (DIM) and inverse solution method (ISM) were also investigated for measuring saturated hydraulic conductivity. Simulation with the DIM approach revealed a problem of overestimating soil water infiltration whereas simulation with the SCM approach revealed a problem of underestimating water movement as compared to actual field observation. The ISM approach produced the best simulation result even though this approach slightly overestimated soil moisture by ignoring the impact of rock fragments. This study provides useful information on the overall evaluation of soil hydraulic parameters attained with different measurement methods for simulating soil water movement and distribution in heterogeneous gravel soil

Effect of surface stone cover on sediment and solute transport on the slope of fallow land in the semi-arid loess region of northwestern China

In the semi-arid loess region of northwestern China, use of stone and gravel as mulch has been an indigenous farming technique for improving crop production for over 300 years. However, systematic studies on the effects of stone covers on soil and water conservation have been rarely conducted, except for a few investigations and documentations on the stone cover effects on erosion and solute transport in such a highly erodible loess region. Materials and methods We experimentally examined the effects of surface stone cover on sediment erosion and solute transport using the water-scouring method on sloping land in a semi-arid region in China, which had been left fallow with alfalfa (Medicago sativa) for 3 years. All covered stones rested on the soil surface, and none were partly or completely embedded in the soil surface layer. Stone cover percentages were classified into three groups: 0% (no stone cover, the control treatment), 5.1%, and 20.8%. Two sizes of stones, SCA (7.6 x 7.6 cm) and SCB (18.4 x 18.4 cm), were used in the treatment of 5.1% stone cover. A dye method was used to measure flow velocities in the experiments. Each stone treatment had one replicate. Results and discussion The surface cover by stones influenced soil erosion processes, runoff generation, and solute transport. Runoff rate and sediment yield decreased as stone cover percentages increased from zero (no stone cover) to 20.8%. The effect of stone sizes on the runoff was not significant, whereas stone size type SCA caused lower sediment yield than SCB at the same stone cover percentage of 5.1%. Likewise, water flow velocity and the Froude numbers also decreased with increasing stone cover percentage. The Manning roughness increased with increasing stone cover percentage, ranging from 0.0296 to 0.0579 m(-1/3) s. But the Reynolds numbers among different stone cover percentages and sizes remained nearly the same with a small variation from 483 to 486. Conclusions The study implied that stone cover percentage and size have important influences on sediment and solute concentration in runoff. Surface-covering stones reduced the velocity of runoff, increased surface roughness, decreased sediment yield in runoff, and consequently reduced the quantities of solute release from soil surface

Effects of Surface Mulching on the Growth and Water Consumption of Maize

This study provides understandings of the effect of mulching on the growth, development, and water consumption of dry maize. Parameters including soil temperature, soil water-filled pore space (WFPS), water storage capacity, water consumption, grain yield, water-use efficiency, and biomass yields were followed and analyzed by applying straw mulching (SM), gravel mulching (GM), and plastic film mulching (FM). The results show that the soil temperature (0&ndash;20 cm) throughout the whole observation period (2011&ndash;2013) was significantly increased by applying GM and FM, while SM reduced the soil temperature. SM increased the WFPS, while FM and GM showed no significant effect. SM and FM increased the soil water storage and water-use efficiency in the early stages of maize growth (from sowing to vegetative growth) compared with using GM. With the progress of time, fewer differences between all treatments were observed. Water consumption of the three treatments was in the order of SM &lt; FM &lt; GM, indicating that SM was the most effective in preventing water evaporation. The resulting yields of corn also varied. Compared with the control, FM significantly increased the yields by 1.7, 0.5, and 2.2 ton/ha in the tested three years, respectively. In contrast, GM showed no significant difference in the three years, and SM showed no significant difference in 2011 and 2012 but increased the yield by 2.2 ton/ha in 2013. FM is shown to be an effective method for increasing the yields of corn for the studied region, GM is not recommended, and SM is the most effective in improving the water availability in the soil, while its effect on corn yields needs to be further explored

Chloride transport in undisturbed soil columns of the loess Plateau

In soils containing preferential flow paths, both water and solute can move preferentially, bypassing much of the soil matrix. The object of this study was to examine the effect of preferential solute transport in Changwu (loamy soil) soil and Ansai soil (sandy soil) containing macroporosity. Miscible displacement experiments were conducted with 5 undisturbed soil columns (19.45 cm diameter, 43.5 cm long). Breakthrough curves (BTC's) of Chloride were measured under water-saturated steady flow conditions. The data were simulated using three conceptual models. The results show that two-flow region model described the preferential solute transport much better than the two-region model and the convection dispersion equation (CDE), especially there were humps in the tailing side. Moreover, distinct double peaks were apparent with the increase of pore water velocity in a loamy soil column. In addition, high pore water velocity and small mass transfer coefficient between the two-flow regions enhanced the development of double BTC peaks