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

Investigation of runoff generation processes and response to changes in catchment characteristics (e.g. land use, soil type, slope, etc.), tillage practice and climate pattern (e.g. rainfall intensity and rainfall duration) is important for understanding of the hydrological cycle and developing land management practices for water and soil conservation. Field and indoor artificial hydrological experiments provide an efficient way for the study of the above processes. This study gave a summary of artificial hydrological experiments using rainfall simulator in China, especially in the red soil-covered region of Jiangxi province. Experiment setting for field and indoor artificial hydrological experiments were introduced; the water balance, runoff components (i.e. surface runoff, subsurface runoff at different depths), runoff amount and relationship to rainfall events were studied and assessment of land coverage and tillage practices on soil and water conservation were conducted. Based on the literature review, it implies that hydrological process at field slope requires more investigation in the following aspects: (1) improvement of monitoring strategies and methodology and isotopic method may be used to improve understanding of hydrological regimes, (2) developing long-term in situ experimental study to analyse soil water movement at different temporal and spatial scales and (3) developing and improving modelling of soil water movement

Monitoring Water Turbidity Using Remote Sensing Techniques

In the present work, the use of optical cameras for turbidity measurements is tested on the Bode River in Germany, which is one of the best-instrumented catchments in Central Germany with a long-term time series on water quantity and quality. Four trap cameras have been installed on monitored cross-sections with the aim to explore the potential of RGB indices for the description of water turbidity. A description of the experimental setup and some preliminary results are introduced

Hysteretic sediment fluxes in rainfall-driven soil erosion

Hysteresis patterns of different sediment particle sizes were studied via a detailed laboratory study and modelling. Seven continuous rainfall events with stepwise- varying rainfall intensities (15, 30, 45, 60, 45, 30 and 15 mm\,h\textsuperscript{-1}, each 20 min duration) were conducted using a 5-m\,$\times$\,2-m erosion flume. Flow rates and sediment concentration data were measured using flume discharge samples, and interpreted using the Hairsine and Rose (HR) soil erosion model. The total sediment concentration and concentrations of seven particle size classes ( 1000 $\mu$m) were measured. For the total eroded soil and the finer particle sizes (< 2, 2-20 and 20-50 $\mu$m), there was a clockwise pattern in the sediment concentration versus discharge curves. However, as the particle size increased, concentrations tended to vary linearly with discharge. The HR model predictions for the total eroded soil and the finer particle size classes (up to 100 $\mu$m) were in good agreement with the experimental results. For the larger particles, the model provided qualitative agreement with the measurements but concentration values were different. In agreement with previous investigations using the HR model, these differences were attributed to the HR model’s assumption of suspended sediment flow, which does not account for saltation and rolling motions

Functional Multi-Scale Integration of Agricultural Nitrogen-Budgets Into Catchment Water Quality Modeling

Funding Information: The work is supported by the TERENO and MOSES projects, Helmholtz Association. The authors highly acknowledge the data from the Extended Static Fertilization Experiment at Bad Lauchst?dt and the State Institute for Agriculture and Horticulture Saxony-Anhalt. The authors also thank the German Weather Service, the Federal Institute for Geosciences and Natural Resources and the State Agency for Flood Protection and Water Management Saxony-Anhalt for the model setup data. The authors thank the Editor Harihar Rajaram and two anonymous reviewers for their constructive comments. Open access funding enabled and organized by Projekt DEAL.Peer reviewedPublisher PD

Hysteretic sediment fluxes in rainfall-driven soil erosion: Particle size effects

A detailed laboratory study was conducted to examine the effects of particle size on hysteretic sediment transport under time-varying rainfall. A rainfall pattern composed of seven sequential stepwise varying rainfall intensities (30, 37.5, 45, 60, 45, 37.5 and 30 mm h‑1), each of 20-mins duration, was applied to a 5-m × 2-m soil erosion flume. The soil in the flume was initially dried, ploughed to a depth of 20 cm and had a mechanically smoothed surface. Flow rates and sediment concentration data for seven particle size classes ( 1000 µm) were measured in the flume effluent. Clockwise hysteresis loops in the sediment concentration versus discharge curves were measured for the total eroded soil and the finer particle sizes ( 1000 µm). Overall, it is found that hysteresis varies amongst particle sizes and that the predictions of the HR model are consistent with hysteretic behavior of different sediment size classes

Estimation of rainfall-driven soil erosion from different rainfall intensities, exposed areas and initial soil conditions

The factors influencing the rain-splash soil erosion include rainfall characteristics, area exposed to raindrops and soil properties. Understanding of these factors and of their interactions is crucial for better predictions of soil erosion yields. To this end, laboratory flume experiments were conducted varying the precipitation rate, the fraction of exposed soil area and initial soil conditions. The discharge rate and concentrations of individual size classes were measured at the flume outlet. These data were used to investigate the dependence of soil sediment yield on the precipitation rate, area exposed and soil initial conditions. In particular, we examined the role of these factors on predicting experimental results based on a prototype experiment. Results revealed that estimates of the concentrations of individual size classes, taking the area-based approach into account, reproduce satisfactorily the measured data at steady state. It was also found that, under carefully controlled conditions, this proportionality (to area of exposed soil) holds for the entire erosive event. These findings, in terms of sediment concentrations of individual size classes, generalized previous results for the total sediment concentration. At short times, most sediment size classes have an early concentration peak, which was found not to be proportional to the area exposed and effective rainfall rate. Rather, short time behaviour is mainly controlled by the soil antecedent conditions, such as surface roughness, bulk density and soil moisture. For predictions based on precipitation rate, results showed that erosion rates based on a prototype were within a factor two of measured rates. Overall, the results indicate that, for a given soil, experimental data based on a given rainfall rate can be used as a crude estimator of the steady rate of erosion for a different rainfall rate

The Hairsine-Rose Soil Erosion Model: Analysis for Total Sediment Concentration

The Hairsine-Rose (HR) model considers rainfall- and shear-driven erosion of the soil bed, overland transport and sediment deposition. Here, we consider the model for rainfall-driven erosion. The model takes account of the different erodabilities of the original soil and deposited material, as well as onsidering the spatial and temporal behaviour of the different sediment sizes in the eroded bed. This latter feature is crucial, as different grain sizes are transported differently due to the wide range of possible settling velocities. Nevertheless, many experiments, both in the laboratory and the field, measure only total sediment concentrations of eroded material (e.g., at the outlet of a laboratory erosion flume). The HR model equations were summed to obtain a model for total sediment concentration (HRTS model). It was found that the HRTS model includes as a parameter an integral term that gives rise to a closure problem. Consequently, in general solutions must be found by (numerical) iteration in which, essentially, discretization leads to calculation of the sediment size classes in the standard HR model. Nevertheless, we show that accurate approximations can be produced by exploiting the behaviour of the model’s predictions of the deposition of previously eroded material, also known as the shield layer. That is, for circumstances where the spatial dependence of this layer can be neglected (e.g., erosion of a uniform bed by constant rainfall), the shielding of the original soil by the deposited layer can be estimated a priori. Based on this estimate, closed-form solutions for the total sediment eroded can be deduced, from which the transport of any given sediment size class can be calculated. We present closed-form approximations, which compare very well with numerical solutions of the HR model, and which are directly applicable to experiments in which the total sediment concentrations in runoff are measured

Parameter Changes from Upscaling of a Local Scale, Process-Based Erosion Model

Soil erosion affects agricultural productivity, the natural environment and infrastructure security. Soil loss and its associated impacts are important environmental problems. Consequently, model-based predictions of erosion are beneficial for a variety of applications. Process-based erosion models are used to forecast sediment transport concentration as it varies temporally and spatially. Of these, the one-dimensional Hairsine-Rose model describes multiple particle size classes, rainfall detachment, flow-driven entrainment and deposition. This model has been evaluated for different experiments, and has been shown to reliably explain experimental data in a consistent manner. It is common on both the hillslope and laboratory scales to apply one-dimensional erosion models even though the overland flow and sediment transport is two-dimensional. One-dimensional parameter determinations, which are based typically on outflow data, implicitly average the two-dimensional flow. Here we compare experimentally and numerically this averaging process for the Hairsine-Rose model. For this purpose, laboratory experiments were performed using different configurations of the 2 m × 6 m EPFL erosion flume. The flume was divided into 4 smaller flumes, with widths of 1 m, 0.5 m, and 2 × 0.25 m, but otherwise identical. A series of experiments was to provide data sets for analysis by the Hairsine-Rose model. After running the experiments, the amount of the eroded sediment in each subplot was assessed by comparing the temporal variation of eroded mass to evaluate the effect of, and sensitivity to, transverse width on erosion dynamics. The surface elevation changes due to erosion were examined to provide further understanding of the erosion data. A high resolution laser scanner provided details of the soil surface in the form of digital terrain maps before and after the experiment. This method presents a promising way for identification of spatial distribution pattern of eroded soil. In addition, we ran simulations using a fully two dimensional implementation of the Hairsine-Rose model for erosive flows with varying topography with spatially dependent flow and erosion input parameters to produce both outflow hydrographs and suspended sediment graphs. The data were integrated transversely and, as for the experimental data, the one-dimensional Hairsine-Rose model was used to fit the integrated data and so provide parameter estimates to compare with the two-dimensional input values