Process-based Erosion Model Research Articles

Base flow separation for soil erosion simulation in a granitic forested headwater catchment using a process-based model, GeoWEPP

Distributed erosion models, which simulate the physical processes of water flow and soil erosion, are effective for predicting soil erosion in forested catchments. Although subsurface flow through multiple pathways is dominant for runoff generation in forested headwater catchments, the process-based erosion model, Geo-spatial interface for Water Erosion Prediction Project (GeoWEPP), does not have an adequate subsurface component for the simulation of hillslope water flow. In the current study, the quick flow related to soil erosion during rainfall events is separated from the total hydrograph using base flow separation for GeoWEPP to use direct runoff to predict sediment discharge from a granitic-forested catchment in Japan. Water runoff and sediment discharge also are simulated using the conventional method that reproduces the total hydrograph, and the accuracy of the calculation and estimated erodibility parameters are evaluated. The proposed procedure reproduced the quick-flow runoff during rainfall and the cumulative sediment discharge from the catchment. Simultaneously, the proposed procedure overestimates water runoff during extreme weather events, such as typhoons. The estimated erodibility parameters for the hillslope soil were comparable to those of the surface soil in Japan using both the proposed procedure and the conventional one. Conversely, the channel erodibility obtained from the proposed procedure matched the observed sediment characteristics in the granitic forested catchment. The proposed procedure is a promising method to predict sediment discharge from forested catchments based on the geological features of the catchment.

Detachment rates of purple soil rills affected by subsurface water flow depth

Subsurface water flow, considered as a specific hydrological condition, can couples with overland flow, which likely lead to notable effects on soil detachment process in rills. Clarifying the change in soil detachment rate under different subsurface flow conditions is beneficial to understand the mechanisms of soil erosion and improve process-based erosion model. In this study, the maximum sediment delivery rates at sediment transport capacity were used to determine the conditions when soil detachment rates reached zero. Then, a numerical method (NM) and modified numerical method (MNM) were utilized to estimate the detachment rates through sediment delivery amounts along a rill affected by subsurface water flow depths (5 cm, 10 cm, and 15 cm). The experiments were performed under combined conditions of four slope gradients (5°, 10°, 15°, and 20°) and three flow rates (2, 4, and 8 L min−1). The results showed that the detachment rates could be fitted by a linear function of the sediment concentration computed by the NM and MNM under different subsurface water flow depths. When the depths of subsurface water were 5 cm, 10 cm and 15 cm below the soil surface, soil detachment rates estimated by the NM were approximately 1.23, 1.31 and 1.12 times those obtained by the MNM, respectively. The MNM yielded more reasonable detachment rates than the NM. This method is applicable to estimate detachment rates affected by different subsurface water flow depths. Soil detachment rates of subsurface water flow 5 cm below the surface were similar to those of saturated soil with a 20° slope gradient and a flow rate of 8 L min−1. Soil detachment rate for subsurface water flow at 15 cm below the surface were similar to those of unsaturated soil under low hydrodynamic conditions. The results of this study are helpful to understand the mechanisms of soil erosion affected by subsurface flow and provide a theoretical basis for improving the soil erosion model.

A novel approach to estimating soil yield risk in fire prone ecosystems

Increasing fire activity in the American west heightens the need for natural resource managers to identify where risk associated with post-fire effects is greatest. This is particularly true for water resources, as many headwater forests are at risk for stand replacing fires. However, current methods to model post-fire erosion often have trade-offs between model area and spatial resolution. We introduce a novel approach to combine a process-based erosion model and state-and-transition simulation modeling to estimate post-fire sediment yield and identify areas of high risk. We demonstrate how this method can be applied at three scales: large watershed, sub-watershed, and single fire event. The combination of the erosion model and state-and-transition simulation model allowed us to identify areas of post-fire high sediment yield potential and increased likelihood of fire occurrence. This method can be used by land managers to prioritize pre-fire restoration practices or post-fire rehabilitation actions.

Impact of data sources to DEM construction and application to runoff and sediment yield modelling using LISEM model

The use of interpolated digital elevation models (DEM) obtained from free low-resolution satellite images is a typical solution for soil erosion modelling. However, this method may result in loss of surface details, especially in small catchments. Thus, planialtimetric surveys at the study site may improve quality of terrain description, although it requires high costs and time. Therefore, this study aims to evaluate the impact of two DEM sources on the results of a process-based erosion model. The study was developed in the Lajeado Ferreira creek catchment (1.23 km2) in southern Brazil. Two interpolated 5-m resolution DEM maps obtained from: (i) remote sensing source Shuttle Radar Topography Mission (SRTM), and (ii) field topographic survey with Global Navigation Satellite System using Real Time Kinematic (GNSS/RTK); were used as input in the Limburg Soil Erosion Model (LISEM) to simulate runoff and sediment transport. Two other maps required for modelling were developed from each DEM source: the flow direction and drainage network map. Six monitored rainfall events were calibrated for the variables, timing of peak flow (Qtime), peak flow (Qpeak), surface runoff coefficient (C), total surface runoff volume (Qtotal) and sediment yield (SY). Most variables calibrated were within the acceptable statistical ranges. The Qtime and Qpeak simulated for all events were close to the measured values with minor modification of the input parameters while using GNSS/RTK. However, even in maps with better accuracy of relief description (GNSS/RTK), the erosion parameters adjusted for calibration were not within an acceptable physical limit. For example, soil cohesion values had to be multiplied for at least eight times their original value. Hydrograph and sedimentgraph shapes calibration did not reach a satisfactory statistical level, even with the GNSS/RTK database and the incorporation of relevant features of the landscape based on local observation. Although GNSS/RTK database resulted in gains for some variables calibrated with the LISEM model, the advantages were not significant for the conditions of this study.

Comparing measurements, <sup>7</sup>Be radiotracer technique and process-based erosion model for estimating short-term soil loss from cultivated land in Northern Germany

Due to changing climate and irregular weather patterns, event-based soil loss and sediment yield have become important issues in the agricultural areas. Several mathematical models and prediction methodologies have been used to estimate event-based soil loss and soil redistribution based on soil types, land management, hydrology and local topography. The use of short-lived beryllium-7 as a means of estimating event-based soil erosion/deposition rates has become an alternative to the traditional soil loss measurement methods. A new erosion model taking into account the movement of <sup>7</sup>Be in soils has been presented recently. In order to direct the attention to the potential offered by this technique (measurements and mathematical model), a two-year study was performed at the erosion plots in Müncheberg, Germany, and twelve individual erosion rates were estimated. This paper presents a systematic comparison of the non-steady state <sup>7</sup>Be model with the process-based erosion model EROSION-3D and measured data. The results demonstrate a close consistency between the erosion rates estimated by erosion models and the estimates provided by the <sup>7</sup>Be model and can therefore be seen as a promising contribution to validating the use of this radionuclide to document short-term soil redistribution within the plot and deposited sediment at the bottom of the plot.

FULLY PROBABILISTIC DUNE SAFETY ASSESSMENT USING AN ADVANCED PROBABILISTIC METHOD

In this paper, an advanced probabilistic method - Adaptive Directional Importance Sampling (ADIS) - is used in concert with a process-based dune erosion model - XBeach - to perform a dune safety assessment. The efficiency of the probabilistic method removes the restriction of only using simple empirical dune erosion models for probabilistic calculations. The proposed combination of ADIS and XBeach is able to handle complex cross-shore profiles that empirical dune erosion models cannot, as shown in several case studies.

Modelling soil erosion in a clayey, subsurface-drained agricultural field with a three-dimensional FLUSH model

summary Soil erosion is an important environmental issue in agricultural areas of northern Europe where clayey soils are prevalent. Clayey soils are routinely subsurface drained to accelerate drainage which creates an additional discharge route for suspended sediment. Previously, assessment of the sediment load from clayey fields has been difficult, because process-based models were only able to simulate sediment loads via surface runoff. A new distributed, process-based erosion model was developed and incorporated into the FLUSH modelling system to fulfil this void. The model facilitates simulation of spatially distributed soil erosion on the field surface and sediment loads via surface runoff and subsurface drainflow. Soil erosion on the field surface is simulated with the two-dimensional sediment continuity equation coupled with hydraulic and rain drop splash erosion, sediment settling, and transport capacity processes. Subsurface sediment transport in macropores is described with the three-dimensional advection–dispersion equation. The model was applied to a clayey, subdrained field section (� 3.6 ha) in southern Finland. The results demonstrated the capability of the model to simulate soil erosion and sediment transport in terms of the match between the measured (2669 kg ha � 1 ) and modelled (2196 kg ha � 1 ) sediment loads via surface runoff and the measured (2937 kg ha � 1 ) and modelled (2245 kg ha � 1 ) loads via drainflow during the validation period of 7 months. The model sensitivity analysis pointed out the importance of the flow model parameters in simulation of soil erosion through their control on the division of total runoff into surface runoff and drainflow components. The key parameters in the erosion model were those that affected hydraulic and splash erosion rates. The model application in the experimental field suggested that both hydraulic and splash erosion were the factors behind the sediment losses during the growing season and early autumn, whereas high sediment loads in late autumn were caused by hydraulic erosion due to overland flow in tilled soil.

Prediction of soil detachment in agricultural loess catchments: Model development and parameterisation

The objective of this paper is to derive and parameterise a detachment approach that balances simplicity and necessary process complexity to be implemented in a process-based erosion model applicable at the catchment scale. We proposed a semi-empirical model approach that relates the potential detachment rate by means of a bi-linear combination to the attacking forces of rainfall (characterised as momentum flux of rainfall) and overland flow (characterised as shear stress). The resisting forces against detachment are characterised by two empirical parameters: i) erosion resistance fcrit, which is a threshold of the attacking forces and ii) erodibility parameter p1, which represents the linear increase of detachment once the erosion resistance is overcome. The parameter P2 weights the momentum flux of rainfall against shear stress. The empirical parameters were determined for conventionally tilled loess soils using data sets of rainfall simulation experiments performed in the laboratory and in the field. At first, a data set of laboratory experiments carried out under varying conditions of rainfall and overland flow (published by Schmidt, 1996) but using resembling loess soil samples was used to determine the parameters p1 and P2. Secondly, data from 58 rainfall simulation experiments performed on 24 m2 plots in the Weiherbach catchment (Southwest Germany) were used to parameterise the erosion resistance fcrit under field conditions. We found evidence that cultivation was the first order control of the erosion resistance on conventionally tilled loess soils: crops that are cultivated in rows were strongly susceptible to detachment because runoff is channelled along the intermediate areas of plant rows. For bare soils we found a strong correlation between the erosion resistance, surface roughness and clay content. These results can be used to predict the erosion resistance and regionalise it to the catchment scale as input parameter in a soil erosion model.

Climatic influences on Holocene variations in soil erosion rates on a small hill in the Mojave Desert

A detailed study of a small hill in NE Mojave Desert in eastern California was conducted to elucidate the effect of climate on the variations in soil erosion rates through Holocene. Field surveys and sampling were carried out to obtain information on topography, geomorphology, soil and vegetation conditions, seismic refraction, sediment deposition, and hillslope processes. Integration of this information allowed reconstruction of the hill topography at the end of the Pleistocene, deduction of the evolution of the hill from the end of the Pleistocene to the present, and estimation of total soil losses resulting from various hillslope processes. The estimates are consistent with the premise that early Holocene climate change resulted in vegetation change, soil destabilization, and topographic roughening. Current, very slow, hillslope transport rates (e.g., 5 mm ky −1 by rodent burrowing, a presently important transport form) appear inconsistent with the inferred total soil loss rate (31 mm ky −1). Packrat midden studies imply that the NE Mojave Desert experienced enhanced monsoonal precipitation in the early Holocene, presumably accentuating soil loss. Water erosion on one slope of the hill was simulated using Water Erosion Prediction Project (WEPP), a process-based erosion model, using 4 and 6 ky of precipitation input compatible with an appropriate monsoonal climate and the present climate, respectively. The WEPP-predicted soil losses for the chosen slope were compatible with inferred soil losses. Identification of two time periods within the Holocene with distinct erosion characteristics may provide new insight into the current state of Mojave Desert landform evolution.

Parameter Identifiability for Three Sediment Entrainment Equations

A process-based erosion model is used to study parameterization problems of sediment entrainment equations in overland flow areas. One of the equations for entrainment by flow is developed based on a theory of excess stream power, while the other two relate to excess hydraulic shear. The investigation is conducted in two steps. The first step examines parameter optimization for simulated data sets where the parameter values are known. In the second step, parameter optimization for the most robust equation is examined using experimental data from rainfall simulator plots. Results demonstrate that although the model is capable of estimating total sediment yields with relatively small errors in parameter estimates, the converse is true when the optimization is performed for sediment concentrations. Although sediment yields calculated from simulated sediment concentrations match well with observed data, the parameter estimates generally underestimate sediment concentrations on the rising limb of the sediment graphs, and they overestimate them on the falling limb. This difficulty might be related to structural problems in the model, and unique solutions for parameter estimates cannot be obtained.

Sediment transport capacity and erosion processes: model concepts and reality

Sediment transport capacity, Tc, defined as the maximum amount of sediment that a flow can carry, is the basic concept in determining detachment and deposition processes in current process-based erosion models. Although defined conceptually and used extensively in modelling erosion, Tc was rarely measured. Recently, a series of laboratory studies designed to quantify effects of surface hydrologic conditions on erosion processes produced data sets feasible to evaluate the concept of Tc. A dual-box system, consisting of 1·8 m long sediment feeder box and a 5 m long test box, was used. Depending on the relative magnitudes of sediment delivery from feeder and test boxes, five scenarios are proposed ranging from deposition-dominated to transport-dominated sediment regimes. Results showed that at 5 per cent slope under seepage or 10 per cent slope under drainage conditions, the runoff from the feeder box caused in the additional sediment transport in the test box, indicating a transport-dominated sediment regime. At 5 per cent slope under drainage conditions, deposition occurred at low rainfall intensities. Increases in slope steepness, rainfall intensity and soil erodibility shifted the dominant erosion process from deposition to transport. Erosion process concepts from the Meyer–Wishmeier, Foster–Meyer and Rose models were compared with the experimental data, and the Rose model was found to best describe processes occurring during rain. A process-based erosion model needs to have components that can represent surface conditions and physical processes and their dynamic interactions. Copyright © 1999 John Wiley & Sons, Ltd.

Sediment transport capacity and erosion processes: model concepts and reality

Sediment transport capacity, Tc, defined as the maximum amount of sediment that a flow can carry, is the basic concept in determining detachment and deposition processes in current process-based erosion models. Although defined conceptually and used extensively in modelling erosion, Tc was rarely measured. Recently, a series of laboratory studies designed to quantify effects of surface hydrologic conditions on erosion processes produced data sets feasible to evaluate the concept of Tc. A dual-box system, consisting of 1·8 m long sediment feeder box and a 5 m long test box, was used. Depending on the relative magnitudes of sediment delivery from feeder and test boxes, five scenarios are proposed ranging from deposition-dominated to transport-dominated sediment regimes. Results showed that at 5 per cent slope under seepage or 10 per cent slope under drainage conditions, the runoff from the feeder box caused in the additional sediment transport in the test box, indicating a transport-dominated sediment regime. At 5 per cent slope under drainage conditions, deposition occurred at low rainfall intensities. Increases in slope steepness, rainfall intensity and soil erodibility shifted the dominant erosion process from deposition to transport. Erosion process concepts from the Meyer–Wishmeier, Foster–Meyer and Rose models were compared with the experimental data, and the Rose model was found to best describe processes occurring during rain. A process-based erosion model needs to have components that can represent surface conditions and physical processes and their dynamic interactions. Copyright © 1999 John Wiley & Sons, Ltd.

An examination of the relationship between erodibility parameters and soil strength

Erosion rate of soil by the impact of raindrops and overland flow of water is often considered to be affected by the shear strength of surface soil. Physically based erosion models indicate a link between defined erodibility parameters and soil strength. The objectives of this paper are to determine erodibility parameters with the process-based erosion model GUEST for a. krasnozem soil of two contrasting strengths, and to examine the influence of soil strength on erodibility parameters. Soil beds of width 1 m and length 5.8 m, with and without compaction, were exposed to simulated, constant rate rainfall. A range of slopes was used. Detachment trays of width 300 mm and downslope length 200 mm containing soils of identical strength were placed at the same slope and exposed to the same rain in order to determine the effects of rainfall-driven processes alone on erosion. Soil strength was measured with a hand vane tester and a pocket penetrometer to determine whether compaction was effective in modifying soil strength. Temporal variation in sediment concentrations (c) for the large soil beds and detachment trays was measured for each slope and soil strength. The settling velocity characteristic of soil, with and without exposure to rain, was determined with the modified bottom withdrawal tube technique. Values of c decreased with increase in soil strength. The relationship between c and slope was influenced by soil strength in a manner consistent with the theoretical expectation of the role of soil strength in controlling erosion. Rilling during erosion was absent only when the soil was compacted. The average settling velocity of the soil exposed to rain (i.e. its depositability) was significantly lower than for the same soil not subjected to rain, indicating a breakdown of soil aggregates as a result of raindrop impact. Rainfall detachability parameters (estimated with GUEST) Were lower when soil strength was high. Runoff-driven erodibility parameters, namely the specific energy of entrainment (J), increased and the approximate erodibility parameter (�) decreased with increase in soil strength. The Variation in these erodibility parameters with soil strength was consistent with the theory implemented in GUEST. Detailed analysis of the relative contribution of rainfall- and runoff-driven processes to c at varying stream powers and soil strengths indicated that, at high soil strength, uncertainty in the values of J and � is high because of the higher contribution to c of rainfall-driven rather than runoff-driven processes. The adequacy of in situ measurement of soil strength as an indicator of soil erodibility is discussed in relation to the results presented.

Determining Erodibility Parameters from Rangeland Field Data for a Process-Based Erosion Model

ABSTRACT T</emph >he forms of the sediment continuity equation used in process-based erosion prediction models do not allow for direct analytical solution for soil erodibility parameters for the case when performing rills is not practical or desirable. Therefore, erodibility parameters cannot be calculated from rangeland field erosion data using simple regression unless simplifying assumptions are made which may compromise the accuracy of the parameter estimates. This study developed an optimization technique for determining erodibility parameters from rangeland field data for use in a three parameter steady-state erosion model, and evaluated the method's effectiveness. Model response to variation of the erodibility parameters was also evaluated. Estimated erodibility parameter values characterized the measured data adequately. Model response surface shapes did not indicate problems in terms of parameter identifiability, strong interdependence or sensitivity.