Rill development and soil erosion: a laboratory study of slope and rainfall intensity

A total of 15 rainfall simulation experiments were conducted in a 1 m by 2 m box varying slope (10, 20, 30%) and rainfall intensity (60, 90, 120 mm h^?1). The experiments were performed to study how rill networks initiate and evolve over time under controlled conditions with regard to the treatment variables considered, and to allow for input in a computer simulation model. Runoff and sediment yield samples were collected. Digital elevation models were calculated by means of photogrammetry for several time steps of most experiments. The soil used in the experiments was a basal till derived Cambisol typical for the Swiss Plateau. While significant differences were found for sediment yield, runoff did not vary significantly with treatment combinations. Increasing rainfall intensity had a larger effect on sediment yield than increasing slope. Rill density and energy expenditure decreased with time, suggesting that energy expenditure was a useful parameter to describe the emergence of rill network at the laboratory scale. Copyright © 2010 John Wiley & Sons, Ltd.     

Using beryllium‐7 to monitor the relative proportions of interrill and rill erosion from loessal soil slopes in a single rainfall event

Quantifying the relative proportions of soil losses due to interrill and rill erosion processes during erosion events is an important factor in predicting total soil losses and sediment transport and deposition. Beryllium‐7 (⁷Be) can provide a convenient way to trace sediment movement over short timescales providing information that can potentially be applied to longer‐term, larger‐scale erosion processes. We used simulated rainstorms to generate soil erosion from two experimental plots (5 m × 4 m; 25° slope) containing a bare, hand‐cultivated loessal soil, and measured ⁷Be activities to identify the erosion processes contributing to eroded material movement and/or deposition in a flat area at the foot of the slope. Based on the mass balance of ⁷Be detected in the eroded soil source and in the sediments, the proportions of material from interrill and rill erosion processes were estimated in the total soil losses, the deposited sediments in the flat area, and in the suspended sediments discharged from the plots. The proportion of interrill eroded material in the discharged sediment decreased over time as that of rill eroded material increased. The amount of deposited material was greatly affected by overland flow rates. The estimated amounts of rill eroded material calculated using ⁷Be activities were in good agreement with those based on physical measurements of total plot rill volumes. Although time lags of 45 and 11 minutes existed between detection of sediment being removed by rill erosion, based on ⁷Be activities, and observed rill initiation times, our results suggest that the use of ⁷Be tracer has the potential to accurately quantify the processes of erosion from bare, loessal cultivated slopes and of deposition in flatter, downslope areas that occur in single rainfall events. Such measurements could be applied to estimate longer‐term erosion occurring over larger areas possessing similar landforms. Copyright © 2010 John Wiley & Sons, Ltd.     

Impact of model simplifications on soil erosion predictions: application of the GLUE methodology to a distributed event‐based model at the hillslope scale

In this paper, we analyse how the performance and calibration of a distributed event‐based soil erosion model at the hillslope scale is affected by different simplifications on the parameterizations used to compute the production of suspended sediment by rainfall and runoff. Six modelling scenarios of different complexity are used to evaluate the temporal variability of the sedimentograph at the outlet of a 60 m long cultivated hillslope. The six scenarios are calibrated within the generalized likelihood uncertainty estimation framework in order to account for parameter uncertainty, and their performance is evaluated against experimental data registered during five storm events. The Nash–Sutcliffe efficiency, percent bias and coverage performance ratios show that the sedimentary response of the hillslope in terms of mass flux of eroded soil can be efficiently captured by a model structure including only two soil erodibility parameters, which control the rainfall and runoff production of suspended sediment. Increasing the number of parameters makes the calibration process more complex without increasing in a noticeable manner the predictive capability of the model. Copyright © 2015 John Wiley & Sons, Ltd.     

Geospatially based distributed rainfall‐runoff modelling for simulation of internal and outlet responses in a semi‐forested lower Himalayan watershed

This study presents a Geographic Information System (GIS)‐based distributed rainfall‐runoff model for simulating surface flows in small to large watersheds during isolated storm events. The model takes into account the amount of interception storage to be filled using a modified Merriam ( 1960 ) approach before estimating infiltration by the Smith and Parlange ( 1978 ) method. The mechanics of overland and channel flow are modelled by the kinematic wave approximation of the Saint Venant equations which are then numerically solved by the weighted four‐point implicit finite difference method. In this modelling the watershed was discretized into overland planes and channels using the algorithms proposed by Garbrecht and Martz ( 1999 ). The model code was first validated by comparing the model output with an analytical solution for a hypothetical plane. Then the model was tested in a medium‐sized semi‐forested watershed of Pathri Rao located in the Shivalik ranges of the Garhwal Himalayas, India. Initially, a local sensitivity analysis was performed to identify the parameters to which the model outputs like runoff volume, peak flow and time to peak flow are sensitive. Before going for model validation, calibration was performed using the Ordered‐Physics‐based Parameter Adjustment (OPPA) method. The proposed Physically Based Distributed (PBD) model was then evaluated both at the watershed outlet as well as at the internal gauging station, making this study a first of its kind in Indian watersheds. The results of performance evaluation indicate that the model has simulated the runoff hydrographs reasonably well within the watershed as well as at the watershed outlet with the same set of calibrated parameters. The model also simulates, realistically, the temporal variation of the spatial distribution of runoff over the watershed and the same has been illustrated graphically. Copyright © 2011 John Wiley & Sons, Ltd.     

Two‐dimensional physically based finite element runoff model for small agricultural watersheds: II. Model testing and field application

Mathematical models are useful analysis tools to understand problems in watersheds associated with runoff, and to find solutions through land use changes and best management practices. However, before a model is applied in the field, it must be tested and checked to ensure that the model represents the real world adequately. In this paper, a two‐dimensional physically based finite element runoff model ROMO2D has been verified and validated by comparing the model output with analytic solution under simplified conditions, published data, and field measurements. Calibration of the model was done manually through a multi‐objective calibration procedure, using observed field data. Before going for field validation/application of ROMO2D, analysis was carried out to determine the optimum number of finite elements into which the watershed should be discretized and the size of the time step. A sensitivity analysis of the model was performed using the observed values of watershed parameters. The model was applied to a 1·45 ha agricultural watershed located in the Shiwalik foothills (India) to simulate runoff. The results demonstrated the potential of the model to simulate runoff from small agricultural watersheds for individual storm events with reasonable accuracy. Copyright © 2008 John Wiley & Sons, Ltd.     

Soil production and hillslope transport in mid‐latitudes during the last glacial–interglacial cycle: a combined data and modelling approach in northern Ardennes

The relative efficiency of various hillslope processes through Quaternary glacial–interglacial cycles in the mid‐latitudes is not yet well constrained. Based on a unique set of topographic and soil thickness data in the Ardennes (Belgium), we combine the new CLICHE model of climate‐dependent hillslope evolution with an inversion algorithm in order to get deeper insight into the ways and timing of hillslope dynamics under one such climatic cycle. We simulate the evolution of a synthetic hill reproducing the slope, curvature, and contributing area distributions of the hillslopes of a ~ 2500 km² real area under a simple two‐stage 120‐kyr‐long climatic scenario with linear transitions between cold and warm stages. The inversion method samples a misfit function in the model parameter space, based on estimates of the fit of topographic derivative distributions in classes of soil thickness and of the relative frequencies of the predicted soil thickness classes. Though the inversion results show remarkable convergence patterns for most parameters, no unique solution emerges. We obtain five clusters of good fits, whose centroids are taken as acceptable model solutions. Based on the predicted time series of average denudation rate and soil thickness, plus snapshots of the soil distribution at characteristic times, we discuss these solutions and, comparing them with independent data not involved in the misfit function, we identify the most realistic scenario. Beyond providing first‐order estimates of several parameters that compare well with published data, our results show that denudation rates increase dramatically for a short time at both warm–cold and cold–warm transitions, when the mean annual temperature passes through the [0, ?5 °C] range. We also point to the overwhelming importance of solifluction in shaping hillslopes and transporting soil, and the role of depth‐dependent creep (including frost creep) throughout the climatic cycle, whereas the contributions of simple creep and overland flow are minor. Copyright © 2016 John Wiley & Sons, Ltd.