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Much hill country in New Zealand has been converted from indigenous forest to pastoral agriculture, resulting in increased soil erosion. Following a severe storm that hit the Manawatu–Wanaganui region in 2004 and caused 62,000 landslides, the Horizons Regional Council have implemented the Sustainable Land Use Initiative (SLUI), a programme of widespread soil conservation. We have developed a New Zealand version (SedNetNZ) of the Australian SedNet model to evaluate the impact of the SLUI programme in the 5850 km2 Manawatu catchment. SedNetNZ spatially distributes budgets of fine sediment in the landscape. It incorporates landslide, gully, earthflow erosion, surficial erosion, bank erosion, and flood-plain deposition, the important forms of soil erosion in New Zealand. Modelled suspended sediment loads compared well with measured suspended sediment loads with an R2 value of 0.85 after log transformation. A sensitivity analysis gave the uncertainty of estimated suspended sediment loads to be approximately plus or minus 50% (at the 95% confidence level). It is expected that by 2040, suspended sediment loads in targeted water management zones will decrease by about 40%. The expected decrease for the whole catchment is 34%. The expected reduction is due to maturity of tree planting on land at risk to soil erosion. The 34% reduction represents an annual rate of return of 20% on 20 million NZ$ of investment on soil conservation works through avoided damage to property and infrastructure and avoided clean-up costs.

In coarse-grained, unsaturated soils, heavy rainstorms may cause either shallow landslides or superficial soil erosion. The triggering of both of these phenomena is related to infiltration, runoff and overland flow, which are key processes requiring investigation. In particular, the quantitative estimates of the sediment yield at the outlet of mountain basins requires suitable physically based modelling. In this paper, the available approaches to soil erosion analysis are first reviewed, and the capabilities and limitations of a physically based model are then evaluated through a case study of two small mountain basins. The results obtained are in good agreement with those in the literature and with specific field data from a test area. Specifically, for distinct, realistic rainfall scenarios, soil suction is found to be a key factor in the spatial–temporal evolution of infiltration and runoff inside a mountain basin, and soil suction and rainfall intensity greatly influence the total peak discharge of water and sediments. The maximum volumetric concentration of sediments transported by water to the outlet of a mountain basin is found to be primarily related to the basin's specific morphometry.

The relationships among rainfall, runoff, and sediment delivery are significant in predicting soil erosion and in evaluating the benefits of watershed management practices (WMP) on the hilly-gully regions of the Loess Plateau. Hydrologic data (1987 to 2010) were analyzed for variations in precipitation, runoff, and sediment delivery at annual and event scale. These data were obtained from the Qiaozi East watershed (QE) and the Qiaozi West watershed (QW) with and without WMP, respectively. Results indicated that the runoff coefficients of the watersheds decreased significantly, although the runoff coefficient of QE was less than half of that of QW. Sediment delivery decreased more in QE than in QW mainly because of the increase in vegetation cover in both watersheds. In QE, the relationship between runoff and sediment delivery did not change significantly from 1987 to 2006, although the variation was significant from 2007 to 2010. In QW, the relationship between runoff and sediment delivery was not notably altered from 1987 to 2010. This finding suggested that vegetation practices and engineering measures on the hillslope did not strongly affect the relationship between runoff and sediment delivery in the watersheds. But the construction of check dams reduced gully erosion and the suspended sediment concentration. Hence, control practices for gully erosion significantly influenced the relationship between runoff and sediment delivery. This study suggests that a combination of hillslope and gully erosion control practices effectively reduces erosion and sediment delivery in the hilly-gully regions of the Loess Plateau.

The aim of this study is to quantify the impact of climate change on soil loss at catchment scale at high temporal and spatial resolution. Simulations were performed for one example catchment in Saxony/Germany. The study is based on the B2 IPCC-scenario and model outputs of three models: ECHAM4-OPYC3 (general circulation model), WETTREG (statistical downscaling climate model) and EROSION 3D as a process-based soil erosion model. Soil loss was simulated for the future time period from 2031 to 2050. Results were compared to soil loss based on 20 years of measured precipitation from 1981 to 2000. The results of the simulations with EROSION 3D allow the quantification of the impacts of climate change on erosion rates. The impact of the expected increase of precipitation intensities leads to a significant increase of soil loss by 64% by 2050. Expected changes in land use due to changed crop rotation, and the influence of a shifted harvest are taken into account in the scenario studies. The impacts of land use, soil management and soil properties on soil loss are higher than the effects of the changed precipitation patterns.

High suspended sediment loads and the resulting turbidity can impact the use of surface waters for water supply and other designated uses. Changes in fluvial sediment loads influence material fluxes, aquatic geochemistry, water quality, channel morphology, and aquatic habitats. Therefore, quantifying spatial and temporal patterns in sediment loads is important both for understanding and predicting soil erosion and sediment transport processes as well as watershed-scale management of sediment and associated pollutants. A case study from the 891 km 2 Cannonsville watershed, one of the major watersheds in the New York City water supply system is presented. The objective of this study was to apply Soil and Water Assessment Tool-Water Balance (SWAT-WB), a physically based semi-distributed model to identify suspended sediment generating source areas under current conditions and to simulate potential climate change impacts on soil erosion and suspended sediment yield in the study watershed for a set of future climate scenarios representative of the period 2081–2100. Future scenarios developed using nine global climate model (GCM) simulations indicate a sharp increase in the annual rates of soil erosion although a similar result in sediment yield at the watershed outlet was not evident. Future climate related changes in soil erosion and sediment yield appeared more significant in the winter due to a shift in the timing of snowmelt and also due to a decrease in the proportion of precipitation received as snow. Although an increase in future summer precipitation was predicted, soil erosion and sediment yield appeared to decrease owing to an increase in soil moisture deficit and a decrease in water yield due to increased evapotranspiration.

Soil surface roughness has a strong influence on runoff and erosion, affecting surface storage capacity, water flow routing and velocity, and modifying runoff rates. It also reduces soil detachment by raindrops and the shear effect of water flow on the soil surface. In arid and semiarid ecosystems, biological soil crusts (BSCs) commonly appear in clearings between plants. Depending on the dominant component in the BSC community, the roughness of the soil surface may vary considerably, changing the hydrologic and erosive response of the soil. The aim of this study is to determine the effect of physical and biological crusts on soil surface roughness and their influence on runoff and erosion. For this purpose, we set up open plots containing different BSC types and treatments and recorded runoff and total erosion from all the events for 18 months. Micro-topographic indexes were calculated from high-resolution digital surface models of the plots built from terrestrial laser scanner height data. After comparing different spatial resolutions and indexes, we concluded that only the local Random Roughness index in a 40-mm moving window provided a precise estimation of the roughness induced by BSCs, though it did not have a direct effect on runoff response. The best relationship between microtopography and runoff on biologically crusted soils was found for surface storage capacity, which appears as a powerful predictor of the runoff coefficient on long temporal scales. Sediment yield was not well predicted by any of the micro-topographic indexes studied. The only index that was significantly related to sediment yield was the local Random Roughness in a 40 mm moving window, but even this explained only a third of the erosion variance.

Rainfall events on steep hillslopes can cause both soil erosion and shallow landslides. These processes interact with each other and need to be studied in an integrated way to understand hillslope sediment yields. The main aim of this research is to study post-failure sediment yield following landslides that alter local slope gradients. A laboratory flume under a rainfall simulator was used to quantify erosion and shallow landslides in fine-grained silty loess soils. The flume was divided into an upper and a lower section; the slopes of which could be altered. A total of 12 experiments were conducted on slopes ranging from 35° to 47° in the upper and 5° to 10° in the lower flume sections. Shallow landslides were triggered in four of the 12 experiments. Sediment and runoff were collected from the flume outlet every minute during landslides and every 10 min before and after landslides. Changes in the soil slope after landslides occurred were recorded. Results showed that peak sediment yields were related to landslide occurrence and proximity to the outlet. Post-failure reduction in sediment yields was related to the evolution of the hillslope after slope failures. A simple rule-based soil redistribution model of runout distance was validated using the experimental results. The Water Erosion Prediction Project (WEPP) model was used to simulate runoff and soil erosion during pre- and post-failure rainfall events. Predicted runoff rates and sediment yields using WEPP were in good agreement with those measured in both pre- and post-failure events, indicating that the model can be used successfully as part of an integrated approach to modeling sediment yields in landslide-prone landscapes.

An increasing number of studies have indicated that soil erosion, sediment redistribution and water discharge during the Holocene have varied greatly under influence of environmental changes. In this paper we have used a modeling approach to study the driving forces for soil erosion and sediment redistribution on the one hand, and water discharge on the other hand, during the Holocene for the Belgian Dijle catchment. Soil erosion and sediment redistribution was modeled using the spatially distributed Watem/Sedem model. Several scenarios of past land use and climate were used to model soil erosion, colluvial sedimentation and sediment export to the fluvial system, and those scenarios were combined with a sensitivity analysis. Modeling results are validated based on an available time differentiated field-based sediment budget. Water discharge was modeled using the spatially distributed STREAM model with a daily time step. The model was calibrated based on contemporary discharge data. The results indicate that soil erosion has increased between the early Holocene and the current situation by ca. 9% due to climatic variations, and by ca. 6000% due to changes in land use. The average discharge has increased by ca. 7%, mainly due to land use changes, and the discharge also shows more peaks. The decrease in cropland area and increase in built up area since 1775 CE has resulted in a decrease in soil erosion and in a further increase in discharge, showing the difference in sensitivity of both processes to land use changes.

Soil erosion is a major environmental problem threatening the sustainable development of the Chinese Loess Plateau. Distributed soil erosion models can be used for studying erosion patterns in relation to alternative land-use conditions, identifying sediment sources, and hence guiding soil and water conservation planning. In this study, we used the WATEM/SEDEM model to predict annual erosion patterns with respect to land-use change within a typical hilly catchment in the Loess Plateau. Soil erosion rates derived from (137)Cs measurements in a nearby catchment were used to calibrate the model. The model's performance was assessed by comparing the simulated erosion pattern with the field observations, based on the model efficiency (ME), relative root mean square error (RRMSE) and kappa statistics. It was found that the WATEM/SEDEM model performs poorly in predicting erosion amounts for each raster cell used for the modeling, but is more reliable in predicting the spatial pattern of erosion. For the entire catchment, the land-use conversions between 1990 and 2005 reduced soil erosion, largely due to the Grain-for-Green project initiated by the Chinese central government. We also compared the contribution of specific land-use types to soil erosion reduction, and addressed the possible influences of land-use policy upon soil erosion. (C) 2010 Elsevier B.V. All rights reserved.

This paper reports the mapping of monthly soil erosion risk on Mauritius which was carried out using GIS, decision rules and readily available data namely, monthly rainfall depth, soil types, slope and land cover. Slope and soil were first combined to produce soil erosion susceptibility followed by land cover to produce erosion sensitivity, and then rainfall to produce erosion risk. The high erosion areas of the Island have been extracted from the soil erosion risk maps, whereby these areas can face land degradation problems and can be responsible for sediment discharge into wetlands located at the outlet of drainage basins. As such, drainage basins have been delineated using automatic catchment delineation tools and their percentage of high erosion areas computed. Basins with the greatest percentage of high erosion areas and particularly those that directly have a wetland at the outlet can be given priority for soil and water conservation efforts. The mapping reported in this paper can be adapted to other countries which need an erosion assessment for the identification of high erosion areas and priority action areas.

Fire can alter sediment sources and transport rates in river basins, changing landforms and aquatic habitats and degrading downstream water quality. Variability in the response between environments, between fires, and with time since fire makes predicting the catchment-scale effect of individual fires difficult. This study applies the fallout radionuclides 137Cs and 210Pbxs to trace the sources and transport of fine sediment through a river network following a wildfire of moderate to extreme severity in the 629-km2 eucalypt-forested Nattai River water-supply catchment near Sydney, Australia. The tracer analysis showed that post-fire erosion caused a switch in fine (

Slope–channel coupling and in-channel sediment storage can be important factors that influence sediment delivery through catchments. Sediment budgets offer an appropriate means to assess the role of these factors by quantifying the various components in the catchment sediment transfer system. In this study a fine (

Landscapes in southeastern Australia have changed dramatically since the spread of European colonisation in the 19th century. Due to widespread forest clearance for cultivation and grazing, erosion and sediment yields have increased by a factor of more than 150. In the 20th century, erosion and sediment yield were reduced again due to an increasing vegetative cover. Furthermore, during the last decades, thousands of small farm dams were constructed to provide drinking water for cattle. These dams trap a lot of sediment, thereby further reducing sediment delivery from hillslopes to river channels. Changes in sediment delivery since European colonisation are documented in sediment archives. Within this study, these changing rates in hillslope erosion and sediment delivery were modelled using a spatially distributed erosion and sediment delivery model (WATEM/SEDEM) that was calibrated for Australian ecosystems using sediment yield data derived from sedimentation rates in 26 small farm dams. The model was applied to the Murrumbidgee river basin (30,000 km 2 ) under different land-use scenarios. First, the erosion and sediment yield under pre-European land-use was modelled. Secondly, recent land-use patterns were used in the model. Finally, recent land-use including the impact of farm dams and large reservoirs was simulated. The results show that the WATEM/SEDEM model is capable of predicting the intensity of the geomorphic response to changes in land-use through time. Changes in hillslope erosion and hillslope sediment delivery rates are not equal, illustrating the non-linear response of the catchment. Current hillslope sediment supply to the river channel network is predicted to be 370% higher compared to the pre-European settlement period, yet farm dams have reduced this back to 2.5 times the pre-19th century values. The role of larger reservoirs is even more important as they have reduced the current sediment supply downstream to their pre-European values, thus completely masking the increased hillslope erosion rates from land-use change. However, the model does so far not include valley widening and sediment storage in river systems. Therefore, modelled rates of sediment delivery are lower than observed values.

The response of erosion and sediment export to past land-use change has been studied in four agricultural areas of Europe. Three of these areas were subject to land abandonment or de-intensification and one to intensification of land-use practices. Erosion and sediment yield were modeled using the WaTEM/SEDEM model, which combines the RUSLE equation with a sediment routing algorithm. Spatial relationships between the RUSLE C-factor (i.e. land-use) and other erosion and sediment export-determining factors (slope, soil erodibility and distance to rivers) were investigated, as these account for non-linearity in the response of erosion and sediment export to land-use change. Erosion and sediment export have decreased enormously in the de-intensified areas, but slightly increased in the intensively cultivated area. The spatial pattern of land-use change in relation to other erosion and sediment export-determining factors appears to have a large impact on the response of soil erosion and sediment export to land-use change. That the drivers of abandonment of arable land and erosion coincide indicates that de-intensification leads to a more favourable landscape pattern with respect to reduction of erosion and sediment export. This mechanism applies not only within the study areas, but also among the European study areas where the process of intensification of some areas and de-intensification of others might result in an overall decrease of erosion and sediment yield through time. (C) 2007 Elsevier B.V. All rights reserved.

Soil erosion by water is one of the major causes of land degradation in Lebanon. The problem has not yet been treated in detail although it affects vast areas. This study elaborates a model for mapping soil erosion risk in a representative area of Lebanon at a scale of 1:100,000 using a spatial database and GIS. First, three basic maps were derived: (1) runoff potential obtained from mean annual precipitation, soil-water retention capacity and soil/rock infiltration capacity; (2) landscape sensitivity based on vegetal cover, drainage density and slope; and (3) erodibility of rock and soil. Then two thematic maps were derived: potential sensitivity to erosion obtained from the runoff potential and landscape sensitivity maps, and erosion risk based on the potential erosion and erodibility maps. The risk map corresponds well to field observations on the occurrence of rills and gullies. The model used seems to be applicable to other areas of Lebanon, constituting a tool for soil conservation planning and sustainable management.

One of the main aims of geomorphology is to understand how geomorphic processes change topography over long time scales. Over the last decades several landscape evolution models have been developed in order to study this question. However, evaluation of such models has often been very limited due to the lack of necessary field data. In this study we present a topography based hillslope erosion and deposition model that is based on the WATEM/SEDEM model structure and works on a millennial time scale. Soil erosion, transport and deposition are calculated using slope and unit contributing area. The topography is iteratively rejuvenated by taking into account modelled erosion and deposition rates, thereby simulating topographic development backwards in time. A first attempt has been made to spatially evaluate the model, using detailed estimates for historical soil erosion and sediment deposition volumes, obtained from an augering campaign in a small catchment in the Belgian Loess Belt. The results show that the model can simulate realistic soil redistribution patterns. However, further research is necessary in order to deal with artificial flaws that cause routing problems and significantly influence results. Common problems and issues related to this type of backward modelling are also discussed.

In many developing countries, sustainable land management and water resources development are threatened by soil erosion and sediment-related problems. In response to such threats, there is an urgent need for improved catchment-based erosion control and sediment management strategies. The design and implementation of such strategies require data on erosion rates and understanding of the factors that control the delivery of sediment through the catchment system. In this study, reservoir sedimentation and corresponding catchment attribute data were used to investigate the major factors controlling sediment yield variability in a mountainous dryland region of northern Ethiopia. Sediment yield data were acquired for representative 11 catchments above reservoirs. Geomorphological and anthropogenic catchment attributes were extracted for each reservoir from different sources including digital elevation models, satellite images and field surveys. Different statistical analyses such as Pearson's correlation, principal components and multiple regression were implemented to analyze the relationship between sediment yield and catchment characteristics and to determine the major factors controlling the variability of sediment yield. The results show that terrain form, gully erosion, surface lithology, and land cover explain most of the variability in sediment yield among the catchments. The implications of the results, for relevant management intervention targeted at ameliorating the major causative factors of erosion, are also outlined.

Traditional vegetative techniques to control gully development rely mainly on the effects of above ground biomass, whereas little attention has been given to the role of below ground biomass. Yet, in a context where above ground biomass may temporarily or spatially disappear (e.g. due to fire or grazing), roots can play an important role in protecting soil against erosion. Few studies have investigated the impacts of roots of natural vegetation (such as grass) on the resistance of topsoils in concentrated flow erosion zones, although grasses grow in many environments. Therefore, the objective of this study is to investigate the impact of root density and root length density of grass on the erodibility of root-permeated saturated topsoils. Three plots were established on a sandy loam. Their treatments were (1) bare, (2) low density drilled grass and (3) high density drilled grass, simulating different root densities. After one month, topsoil samples were taken and subjected to concentrated flow using a hydraulic flume in the laboratory. Slope, flow discharge, mean velocity, water temperature and sediment concentration were measured. Root density and root length density values were assessed. Relative soil detachment rates and mean flow shear stresses were calculated. The results indicate a negative exponential relation between the relative soil detachment rate and root density as well as root length density, independent of the applied flow shear stresses. However, the best relationship fitting the data is the Hill curve, indicating that relative soil detachment rates decrease to very low values (0.05) with an increase in root density from 0 to 4 kg m − 3 or root length density from 0 to 400 km m − 3 . A comparison between the effects of vegetation cover on sheet and rill erosion rates and those of the root area ratio of grass roots on relative soil detachment rates reveals that grass roots are very effective in reducing soil detachment rates. The equations obtained can be used to predict the effect of grass roots on soil erosion rates during concentrated runoff and to evaluate the ability of roots to increase topsoil resistance against erosion by concentrated flow. Calculations of relative erosion rates using the equations from the RUSLE and WEPP models indicate that the observed trend is better predicted with the RUSLE model and the WEPP model for croplands than with the WEPP model for rangelands.

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.

Geomorphological research has played an important role in the development and implementation of soil erosion assessment tools. Because policy and management approaches include the use of soil erosion assessment tools, soil erosion research directly affects the public in terms of providing information on natural hazards and human impacts, and also as the basis for regulatory policy on land management. For example, soil loss calculations and geomorphological expertise are used to support soil conservation planning, both through agricultural legislation that defines maximum tolerable soil loss rates, and through federal and local legislation that requires soil erosion controls on many construction sites. To be useful for decision makers, soil erosion models must have simple data requirements, must consider spatial and temporal variability in hydrological and soil erosion processes, and must be applicable to a variety of regions with minimum calibration. The growing use of erosion models and Geographic Information Systems (GIS) in local to regional scale soil and water conservation raises concerns about how models are used. This has prompted interest in methods to assess how models function at management scales and with the types of data that are commonly available to users. A case study of a GIS-based soil erosion assessment tool using the process-based Water Erosion Prediction Project (WEPP) shows that using commonly available data rather than research grade data can have (predictably) a significant impact on model results. If model results are then used in management decisions, it is critical to assess whether the scale and direction of variation in results will affect management and policy decisions. Geomorphologists provide unique perspectives on soil erosion and can continue to affect policy through soil erosion research. This research should focus on fundamental processes, but equally important is continued development and evaluation of models that are matched to real world data availability, geomorphic settings, and information needs. D 2002 Elsevier Science B.V. All rights reserved.

The importance of the inherent resistance of soil to erosional processes, or soil erodibility, is generally recognized in hillslope and fluvial geomorphology, but the full implications of the dynamic soil properties that affect erodibility are seldom considered. In Canada, a wide spectrum of soils and erosional processes has stimulated much research related to soil erodibility. This paper aims to place this work in an international framework of research on water erosion processes, and to identify critical emerging research questions. It focuses particularly on experimental research on rill and interrill erosion using simulated rainfall and recently developed techniques that provide data at appropriate temporal and spatial scales, essential for event-based soil erosion prediction. Results show that many components of erosional response, such as partitioning between rill and interrill or surface and subsurface processes, threshold hydraulic conditions for rill incision, rill network configuration and hillslope sediment delivery, are strongly affected by spatially variable and temporally dynamic soil properties. This agrees with other recent studies, but contrasts markedly with long-held concepts of soil credibility as an essentially constant property for any soil type. Properties that determine erodibility, such as soil aggregation and shear strength, are strongly affected by climatic factors such as rainfall distribution and frost action, and show systematic seasonal variation. They can also change significantly over much shorter time scales with subtle variations in soil water conditions, organic composition, microbiological activity, age-hardening and the structural effect of applied stresses. Property changes between and during rainstorms can dramatically affect the incidence and intensity of rill and interrill erosion and, therefore, both short and long-term hillslope erosional response. Similar property changes, linked to climatic conditions, may also significantly influence the stability and resilience of plant species and vegetation systems. Full understanding of such changes is essential if current event-based soil erosion models such as WEPP and EUROSEM are to attain their full potential predictive precision. The complexity of the interacting processes involved may, however, ultimately make stochastic modelling more effective than physically based modelling in predicting hillslope response to erodibility dynamics.