Measured Sediment Yield Research Articles

도시유역에 대한 토사유출량 모의기법 적용성 검토

국내 도시화 시험유역에 대한 기존 토사유출공식의 적용 가능성을 검토하기 위해 도시 시험유역의 실측자료와 모의기법 적용결과를 비교.분석하였다. 적용된 토사유출량 산정 모의공식으로는 개정범용토양손실공식(RUSLE - Revised Universal Soil Loss Equation), 수정범용토양손실공식(MUSLE - Modified Universal Soil Loss Equation)을 활용하였다. 시험유역은 유역면적 약 3.81 <TEX>$km^2$</TEX>로 면적대비 56 % 정도가 도로 및 포장 등으로 도시화가 진행된 도시 시험유역을 선정하여 자동 강우 및 수위계측기를 이용하여 지난 3년간 연속적으로 수문자료를 축적하였다. 또한 계측지점에서의 유출량별 소류사 및 부유사 실측을 통하여 유량-유사량 관계곡선을 개발한 후 호우사상별 유역으로 부터의 토사유출량을 산정하였다. 실측된 강우 및 유량 자료를 활용하여 모의한 토사유출량과 실측한 토사유출량을 비교한 결과 RUSLE를 적용한 모의결과가 실측 토사유출량과 근접한 결과를 제시하였으나 상관계수가 낮아 적용에 세심한 주의가 요구됨을 알 수 있었다. 반면, 실제 유출수문곡선을 MUSLE기법에 적용하여 모의한 토사유출량과 실측 토사유출량의 상관관계는 우수한 예측결과를 보였으나 보정계수의 적용이 필요함을 확인하였다. Field measured sediment yield from an experimental urbanized basin was compared with the predicted sediment yields with RUSLE (Revised Universal Soil Loss Equation), and MUSLE (Modified Universal Soil Loss Equation). The experimental basin is 3.1km2 in area and fifty six percent of the total area had been urbanized. The hydrological data have been measured with T/M at the outlet of the experimental basin. Runoff from the basin and rainfall depth of the basin were measured every minute. Bed load and suspended load were also measured for a given flow rate. Runoff rating curves and sediment rating curve were developed for the last three years. RUSLE showed scattered prediction results but the average of the prediction values was close to the measured one. Meanwhile, MUSLE showed linear correlation between the measured sediment yield and predicted one with high correlation coefficient. But MUSLE predicts high values than the real one. Therefore, adjustment is necessary to apply MUSLE in estimation of sediment yield from the experimental urbanized basin.

Investigating the effects of afforestation on soil erosion and sediment mobilisation in two small catchments in Southern Italy

Annual soil losses in southern Italy can exceed 100–150 t ha− 1 year− 1. Where erosion on agricultural land is particularly severe, land use change and afforestation are frequently seen as the most appropriate means of reducing erosion risk. However, the overall effectiveness of afforestation in reducing soil erosion remains uncertain, due to the poor development of the forest cover in some areas, leading to significant areas with sparse tree cover, and the erosional impact of forest harvesting, which commonly involves clearcutting. The study reported here addresses this uncertainty and focuses on two small catchments (W2 and W3) located in Calabria, southern Italy, for which measurements of suspended sediment yield are available. Both the catchments originally supported a rangeland vegetation cover and they were planted with eucalyptus trees in 1968. Currently, only catchment W3 supports a continuous forest cover. In catchment W2 the forest cover is discontinuous and there is a significant area of the catchment (ca. 20%) where the tree cover is sparse and the vegetation cover is dominated by natural grasses. Two additional erosion plots were established within catchment W2 in 1991, in order to explore the effect of the density of the tree cover on soil erosion. Information on the sediment yields from the two catchments and the plots for 10 storm events that occurred during the period December 2005–December 2006 and associated information on the 137Cs and excess 210Pb of the sediment, have been used to investigate the effectiveness of afforestation in reducing sediment mobilisation and net soil loss from the catchments involved. The results demonstrate that the areas of greatest soil loss are associated with the slopes where the tree cover is discontinuous, and that forest harvesting by clearcutting causes significant short-term increases in sediment mobilisation and sediment yield. These findings, which are consistent with previous work undertaken within the same area, emphasize the importance of vegetation cover density in influencing rates of soil loss in the study catchments. The study also provided a useful demonstration of the potential for using measurements of the 137Cs and 210Pbex content of sediment, in combination with more traditional sediment monitoring, to investigate sediment sources and to compare the sediment dynamics of catchments subjected to different land management practices.

Comparison between a Soft and Crisp Geographic Boundary of the Soil Texture Component in Hydrologic Models

This note is based on the generally accepted fact that soil boundaries are usually gradual rather than abrupt, and this is followed by an application of fuzzy set theory to what are already known to be diffuse boundaries. Sediment yield measurements are used to describe the control condition against which the fuzzy and conventional boundaries are assessed. In terms of the K factor, the fuzzy boundary representation showed less difference (up to 16.8%). The Nash–Sutcliff coefficient of efficiency and the root mean square error for the fuzzy boundary are 0.96 and 1.3× 10−3 , respectively, whereas those for the conventional boundary are 0.76 and 3.4× 10−3 , respectively. The estimation by the soil erosion model shows that the fuzzy representation of geographic boundary is more accurate than the conventional method. But the difference between erosion predictions using conventional boundaries and fuzzy boundaries is relatively small.

Slope Interrupter Best Management Practice Experiments on a Tilting Soil Bed with Simulated Rainfall

This paper documents an experimental study conducted to evaluate the performance of two commonly used sediment treatment control products, albeit with contrasting treatment technologies: a fiber roll or wattle (i.e., three-dimensional filter) and a perforated pipe wrapped by a pervious geosynthetic material (i.e., boundary filter). Emphasis was placed on (1) simulating field conditions and (2) describing performance via runoff, sediment yield, and particle-size measurements. Scaling problems typically associated with erosion experiments were minimized by using standard-size products (not scaled models) and a large-scale erosion bed with overhead rainfall simulators, with which dominant forms of soil erosion and sediment transport were attained. The results indicate that the experimental procedures and measurements utilized are appropriate for quantifying the erosion control performance of the products tested. In particular, the measurements revealed the important role of installation quality on BMP performance. Results also indicate that the magnitudes of peak discharge and total runoff from compacted, bare soils on steep slopes can approach values typical of highly impervious surfaces.

Hydrologic and Erosion Models to Assess Land Use and Management Practices Affecting Soil Erosion

We developed a new, coupled, hydrologic-erosion model and a targeted field data-collection program to quantify hillslope soil erosion rates and sediment yield in semiarid regions. While the methodology has a wide range of actual and potential applications, we use military training activities as an example. The methodology is applied at the Yakima Training Center (YTC) in south central Washington, USA where most erosion and transport occurs during extreme events of short duration, often associated with rapid rain-induced snowmelt on frozen soil. The distributed hydrologic and soil erosion modeling system is used to simulate continuous water balance and soil thermal state throughout all seasons of the year. We estimated surface runoff and sediment yield for relatively undisturbed areas as well as from roads, firebreaks, and vehicle tracks associated with training activities at the study site. Field data were collected on over 100 hillslope profile transects across the YTC to parameterize, test, and evaluate the linked modeling system. We successfully validated the modeling system against several databases, upland sediment delivery to stream networks, and measured sediment yield from 12 sedimentation ponds within the YTC. The simulation results are superior to those from a currently used model, which help to illustrate applicability of the presented erosion prediction technology.

A Statistical Sediment Yield Prediction Model Incorporating the Effect of Fires and Subsequent Storm Events1

Abstract: Alluvial fans are continuously being developed for residential, industrial, commercial, and agricultural uses in southern California. Development and alteration of alluvial fans need to consider the possibility of mud and debris flows from upstream mountain watersheds affected by fires. Accurate prediction of sediment yield (or hyper‐concentrated sediment yield) is essential for the design, operation, and maintenance of debris basins to safeguard properly the general populace. This paper presents a model for the prediction of sediment yields that result from a combination of fire and subsequent storm events. The watersheds used in this analysis are located in the foothills of the San Gabriel Mountains in southern California. A multiple regression analysis is first utilized to establish a fundamental statistical relationship for sediment yield as a function of relief ratio, drainage area, maximum 1‐h rainfall intensity and fire factor using 45 years of data (1938‐1983). In addition, a method for multi‐sequence sediment yield prediction under fire conditions was developed and calibrated using 17 years of sediment yield, fire, and precipitation data for the period 1984‐2000. After calibration, this model was verified by applying it to provide a prediction of the sediment yields for the 2001‐2002 fire events in southern California. The findings indicate a strong correlation between the estimated and measured sediment yields. The proposed method for sequence sediment yield prediction following fire events can be a useful tool to schedule cleanout operations for debris basins and to develop an emergency response strategy for the southern California region where plentiful sediment supplies exist and frequent fires occur.

Field evaluation of the Hillslope Erosion Model (HEM) in Iran

The development of improved soil erosion and sediment yield predictions technology is required to provide watershed stakeholders with the tools they need to evaluate the impact of various management strategies to plan for the optimum use of the land. In this paper, the Hillslope Erosion Model (HEM) was applied to predict the sediment yield from two sets of plots that represented open grazing and manually harvested treatments in Talesh rangelands, Guilan Province, Iran. The model performance was evaluated by comparing predicted and measured sediment yield in standard plots resulting from 24 natural rainfall events. The results showed that the calibration of the default value of erodibility parameter did not improve the initial efficacy of the model, while the development of an appropriate regression function was required to obtain accurate estimates on sediment yield from the study plots. The results of the analyses showed the potential of the model to predict sediment yield for the open grazing and cultivated treatments with coefficients of determination of 0.96 and 0.98, and estimation errors of 20.78% and 47.00%, respectively. The predicted results therefore showed that the HEM could be used as a major tool to estimate sediment yield at plot scale in rangelands.

Predicting postfire sediment yields at the hillslope scale: Testing RUSLE and Disturbed WEPP

High‐severity wildfires can increase hillslope‐scale sediment yields by several orders of magnitude. Accurate predictions of postfire sediment yields are needed to guide management decisions and assess the potential impact of soil loss on site productivity and downstream aquatic resources. The Revised Universal Soil Loss Equation (RUSLE) and Disturbed WEPP are the most commonly used models to predict postfire sediment yields at the hillslope scale, but neither model has been extensively tested against field data. The objectives of this paper are to (1) compare predicted sediment yields from RUSLE and Disturbed WEPP against 252 plot years of data from nine fires in the Colorado Front Range; and (2) suggest how each model might be improved. Predicted and measured sediment yields were poorly correlated for RUSLE (R2 = 0.16) and only slightly better correlated for Disturbed WEPP (R2 = 0.25). Both models tended to over‐predict sediment yields when the measured values were less than 1 Mg ha−1 yr−1 and to under‐predict higher sediment yields. Model accuracy was not improved by increasing the soil erodibility (K) factor in RUSLE and was only slightly improved by slowing the vegetative recovery sequence in Disturbed WEPP. Both models much more accurately predicted the mean sediment yields for hillslopes grouped by fire and severity (R2 = 0.54 to 0.66) than for individual plots. The performance of RUSLE could be improved by incorporating an erosivity threshold and a nonlinear relationship between rainfall erosivity and sediment yields. The performance of WEPP could be improved by reducing the effective hydraulic conductivity in sites that have recently burned at high severity. The results suggest that neither model can fully capture the complexity of the different controlling factors and the resultant plot‐scale variability in sediment yields.

Spatially distributed modelling of soil erosion and sediment yield at regional scales in Spain

Initiated by the need to quantify erosion rates and the impacts of global changes on erosion, several attempts have been made to apply erosion models at regional scales. However, these models have often been directed towards on-site soil erosion estimates, emphasising sheet and rill erosion processes, and disregarding gully erosion, channel erosion and sediment transport. These models are therefore of limited use for the assessment of sediment yield, off-site impacts of erosion, and for the development of environmental management to control these impacts at regional scale. This study analyses and compares three spatially distributed models for the prediction of soil erosion and/or sediment yield at regional scales: the WATEM-SEDEM model that is based on the empirical Revised Universal Soil Loss Equation (RUSLE) in combination with a sediment transport equation, the physics-based Pan European Soil Erosion Risk Assessment model (PESERA), and a newly developed Spatially Distributed Scoring model (SPADS). The three models were applied to 61 Spanish drainage basins and model predictions were evaluated against data on measured reservoir sedimentation rates. Global data sets on land use, climate, elevation and soil characteristics were used as model input for WATEM-SEDEM and SPADS, whereas published soil erosion estimates of PESERA at 1 km 2 resolution were used directly. SPADS and WATEM-SEDEM provided best results after separate calibration for basins with a Sediment Delivery Ratio (SDR) higher than 5% and those with an SDR lower than 5%. In this way, SPADS explained 67% of variation in sediment yield, while WATEM-SEDEM explained 48% of the variation. PESERA represents a promising alternative to the use of empirical models at the regional scale as it can be applied to very diverse environments with little calibration. However, PESERA provides soil erosion rates and not sediment yield estimates. For most basins PESERA soil erosion rates vary between fifty and close to zero percent of total sediment yield. Two major factors may explain this discrepancy between modelled soil erosion rates and measured sediment yield. First, it may be that PESERA underestimates soil erosion under Mediterranean conditions, although PESERA soil erosion rates are of the same order of magnitude as erosion rates measured in erosion plot studies. Second, gully-, river channel erosion and sediment transport processes may be much more important than sheet- and rill erosion for regional scale sediment yield in these environments. These issues therefore require further attention in future model development. Although spatially lumped models provide better predictions of sediment yield at the basin scale, and while validation of the predicted spatial patterns of sources and sinks of sediment requires further research, spatially distributed models are expected to be of value to support management decisions regarding the assessment of on-site and off-site impacts of erosion at the regional scale.

Vegetation Cover Plays the Most Important Role in Soil Erosion Control

To obtain, characteristics and behaviors of soil erosion phenomena, to control it's harms and reduce it's risks, realistic data from soil erosion rates are necessary. Mean while, measuring soil erosion rates particularly in large scale is a time consuming and expensive task. Moreover, spatial and temporal changes of soil erosion increase this problem. Therefore, to find out a certain way of creating capable methods which easily and quickly be able to estimate soil erosion rate, is quite logical. So, different models are widely used, but, may be the most important consideration with this regard is that, these models should be previously, tested and adopted to defined areas to stop probability of causing some huge and meaningful errors. Therefore, to achieve the above mentioned aim, different methods are used. Anyway, conditions which resulted to create a suitable model, should be considered in a defined area where, model is applied, unless, model application can leads to huge risks. This study is an attempt with this refer, that is, with comparing measured soil loss rates and predicted soil erosion rates from a defined catchment area, created a reasonable relationship between them and achieved the main aim of the study. That is, one of the small upland catchments of Emam kandi of Urmia with 75 ha area which is part of the Urmia lake catchment area and under layned by calcareous parent material, is selected as a study site. Selected catchment has natural pasture and has closured during the recent years. To calculate sediment yield the following processes were done: first, estimating the volume of trapped sediments, then, surveying the catchment area, for calculating sediment yield. Measured sediment yield is 6.19 t ha(-1) year(-1) which leads to soil loss rate of 13.76 t ha(-1) year(-1) by using Sediment Delivery Ratio (SDR). Also, inside the measurement of sediment yields and calculation of soil loss rates, two models of MUSLE and PSIAC were used respectively after exclosure and before exclosure to predict soil loss rates. Predicted soil loss rates by MUSLE and PSIAC respectively are 12.80 and 26.5 t ha(-1) year(-1). Finally, Comparisons and statistical analysis and scientific discussions were made.

Conformity of MUSLE Estimates and Erosion Plot Data for Storm-Wise Sediment Yield Estimation

In this study, the conformity of mathematical model of the MUSLE for the estimation of storm-wise sediment yield in plots was examined at Matash Ranch in northern Iran. For the measurement of sediment yield, three plots were established within each openly grazed and manually harvested area. The MUSLE model was applied through determining the entire required inputs for the study plots of 24 storm events, which occurred during the study period from May to September 2004. The quantity results were then statistically compared using paired t-Test analysis. The results of the study verified the disability of the model in sound prediction of sediment yield on storm basis for the study area. Additionally, a high level of agreement beyond 86% was found between estimated and measured sediment yield which created the possibility of comparative evaluation of the effects of different land use managerial approaches on sediment yield in the study area.

Estimating spatial distribution of soil loss over Seyhan River Basin in Turkey

Summary The purpose of this study was to investigate the spatial distribution of annual soil loss in Seyhan River Basin using USLE model. A geographic information system (GIS) was used to generate maps of the USLE factors which are rainfall erosivity (R), soil erodibility (K), slope length and steepness (LS), cover (C) and conservation practices (P) factors. By integrating these maps in GIS, spatial distribution of soil loss over the Seyhan River Basin was obtained. Annual average soil loss for the Seyhan River Basin was 16.38 t ha−1 y−1. Annual soil loss more than 200 t ha−1 y−1 in pixel level was in the southern region, while the northern region showed the lower annual values. These results are verified by comparing sediment yield measurements in the basin. An area about 198.25 km2 (0.96%) experiences extremely severe erosion risk, which needs suitable conservation measures to be adopted on a priority basis. The spatial distribution of erosion risk classes estimated 61.03% very low, 8.76% low, 23.52% moderate, 4.03% severe and 1.70% very severe. Thus, the USLE model was used in a GIS environment to identify regions susceptible to water erosion and needing immediate soil conservation planning and application in the Seyhan River Basin in Turkey.

Development and application of a GIS-based sediment budget model

Accelerated erosion and increased sediment yields resulting from changes in land use are a critical environmental problem. Resource managers and decision makers need spatially explicit tools to help them predict the changes in sediment production and delivery due to unpaved roads and other types of land disturbance. This is a particularly important issue in much of the Caribbean because of the rapid pace of development and potential damage to nearshore coral reef communities. The specific objectives of this study were to: (1) develop a GIS-based sediment budget model; (2) use the model to evaluate the effects of unpaved roads on sediment delivery rates in three watersheds on St. John in the US Virgin Islands; and (3) compare the predicted sediment yields to pre-existing data. The St. John Erosion Model (STJ-EROS) is an ArcInfo-based program that uses empirical sediment production functions and delivery ratios to quantify watershed-scale sediment yields. The program consists of six input routines and five routines to calculate sediment production and delivery. The input routines have interfaces that allow the user to adjust the key variables that control sediment production and delivery. The other five routines use pre-set erosion rate constants, user-defined variables, and values from nine data layers to calculate watershed-scale sediment yields from unpaved road travelways, road cutslopes, streambanks, treethrow, and undisturbed hillslopes. STJ-EROS was applied to three basins on St. John with varying levels of development. Predicted sediment yields under natural conditions ranged from 2 to 7 Mg km −2 yr −1, while yield rates for current conditions ranged from 8 to 46 Mg km −2 yr −1. Unpaved roads are estimated to be increasing sediment delivery rates by 3–6 times for Lameshur Bay, 5–9 times for Fish Bay, and 4–8 times for Cinnamon Bay. Predicted basin-scale sediment yields for both undisturbed and current conditions are within the range of measured sediment yields and bay sedimentation rates. The structure and user interfaces in STJ-EROS mean that the model can be readily adapted to other areas and used to assess the impact of unpaved roads and other land uses sediment production and delivery.

Modelling soil erosion and sediment yield at a catchment scale: the case of Masinga catchment, Kenya

AbstractDevelopment of improved soil erosion and sediment yield prediction technology is required to provide catchment stakeholders with the tools they need to evaluate the impact of various management strategies on soil loss and sediment yield in order to plan for the optimal use of the land. In this paper, a newly developed approach is presented to predict the sources of sediment reaching the stream network within Masinga, a large‐scale rural catchment in Kenya. The study applies the revised universal soil loss equation (RUSLE) and a developed hillslope sediment delivery distributed (HSDD) model embedded in a geographical information system (GIS). The HSDD model estimates the sediment delivery ratio (SDR) on a cell‐by‐cell basis using the concept of runoff travel time as a function of catchment characteristics. The model performance was verified by comparing predicted and measured plot runoff and sediment yield. The results show a fairly good relationship between predicted and measured sediment yield (R2=0·82). The predicted results show that the developed modelling approach can be used as a major tool to estimate spatial soil erosion and sediment yield at a catchment scale. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Effect of different land use on soil erosion in the pre-alpine fringe (North-East Italy): Ion budget and sediment yield

Data concerning ion budget from rainfall, runoff and soil loss measurements from two experimental plots located in North-East Italy, under different land cover (beech forest and vineyard, respectively), are reported.The chemical composition of rainfall, soil solution and runoff was determined to study the solute cycle within the soil, and the relationships between water, soil and vegetation. The forest ecosystem is more prone to acidification than the agricultural one; the elemental concentration of runoff water is considerably lower than that of soil solution.Comparing the ion input (rainfall) and output (runoff) at the two sites, it was possible to estimate the ion budget in the two soil-vegetation systems. The runoff amount and the ion balance are related to rainfall volumes and composition; the measured runoff under vineyard is 59% in comparison to the one under beech.The soil loss at the two experimental sites (170 kg/ha and 132 kg/ha, respectively) is quite limited. The measured sediment yield of the two catchments (0.24–0.19 t/ha/year, respectively) is consistent with data reported for native forests of western Europe.Comparing rainfall and soil loss at the two sites proved that maintenance of some form of land cover is advisable if runoff and erosion are to be minimized.In the European context, where the most important consequences of erosion are sedimentation downstream and loss of productivity, this type of data will yield valuable information for the understanding of such processes occurring at catchment scale, and will help policy-makers develop appropriate programs for the territory safeguard.

Spatial patterns of soil erosion and deposition in two small, semiarid watersheds

This work investigates spatial patterns of hillslope erosion and sediment yields in a semiarid ecosystem considering influences of vegetation, slope, rocks, and landscape morphology. The 137Cs inventories were measured on one shrub and one grassed watershed in southeastern Arizona. Calculated mean erosion rates in eroding areas were 5.6 and 3.2 t ha−1 yr−1, and net erosion rates for the entire watershed, including depositional areas, were 4.3 and nearly 0 t ha−1 yr−1 for the shrub and grass watersheds, respectively, over the past four decades. Differences in hillslope erosion rates between the two watersheds were apparently due to vegetation: while on the shrub site, runoff pathways were unobstructed, on the grass site, runoff was obstructed by vegetation patches and litter. Hillslope erosion rates within the watersheds were not correlated to slope gradient or curvature but were correlated to rocks in the upper soil profile. These results are interpretable in terms of slope‐velocity equilibrium wherein overland flow velocities became independent of slope gradient because of differential rock cover, which evolved as a result of preferential erosion of fine material on the steeper slopes prior to 137Cs deposition. Watershed morphology and channel incision controlled sediment yield. Most of the eroded soil was deposited in swales of the grassed watershed. Most of the soil eroded in the shrub watershed was exported from the watershed outlet by way of a well‐incised channel system. The study shows that measurement of sediment yield from a watershed can be a poor indicator of erosion taking place within the watershed.

A review of the measurement of sediment yield in different scales

The present review paper has the objective of presenting and briefly discussing the state-of-the-art papers on sediment yield (SY) measurement. About 80 publications are referred to, representing all continents, and more than 30 countries. It is observed that SY measurement technique is a much stronger function of temporal than of spatial resolution. Annual average SY data of 364 catchments are summarized. Global data presents no trend concerning catchment area and the same behavior is observed for the continents, except for Africa, which presents a consistent decrease of SY with increasing area. A graphical representation of the spatial and temporal applicability of the different SY measurement techniques is shown.

Predicting soil erosion and sediment yield at the basin scale: Scale issues and semi-quantitative models

Basin sediment yield is the product of all sediment producing processes and sediment transport within a basin. Consequently, the prediction of basin sediment yield should take into consideration all different erosion and sediment transport processes. However, traditional physics-based, conceptual, and empirical or regression models have not been able to describe all these processes due to insufficient systems knowledge and unfeasible data requirements. Therefore, the applicability of these models at the basin scale is troublesome. This paper first illustrates the relation between basin area, dominant erosion processes, and sediment yield by a combination of measured sediment yield at different spatial scales in Mediterranean environments. This clearly reveals that soil erosion rates measured at one scale are not representative for sediment yield at another scale level. Second, the most important semi-quantitative models developed for erosion and sediment yield assessments at the basin scale are reviewed. Most of these models use environmental factors to characterise a drainage basin in terms of sensitivity to erosion and sediment transport. Six of the nine models discussed (PSIAC, FSM, VSD, Gavrilovic, CSSM, WSM) include sheet-, rill-, gully, bank erosion, landslides, and connectivity, at least partly, in the assessment of basin sediment yield. The low data requirements and the fact that practically all significant erosion processes are considered makes them especially suited for estimating off-site effects of soil erosion. The other three models (EHU, CORINE, FKSM) focus mainly on sheet and rill erosion and provide quantitative descriptions of the sensitivity to erosion at basin or even regional scales. These models thus focus mainly on on-site problems of soil erosion. Most of the semi-quantitative models might benefit from a more quantitative description of factors used to characterise the basin. Though an equilibrium should be found between the extra effort and increase in model performance, the increased availability of spatially distributed topographic data as well as high-resolution satellite imagery will probably make this feasible in the near future.

Runoff and soil loss from bench terraces. 2. An event‐ based erosion process model

SummaryDespite widespread bench terracing of rainfed hillsides in upland West Java, soil loss rates remain high. This paper reports measurements of sediment yield from terrace risers and beds and from terrace units made during three consecutive rainy seasons. The results demonstrate that soil loss from the terraces occurs in two stages: rainfall‐driven transport by splash and shallow overland flow (wash) from the terrace riser and bed to a central drain is followed by a combination of onward wash transport of fine sediment and entrainment by runoff of coarser sediment deposited in the drain. A model (TEST: Terrace Erosion and Sediment Transport) was developed, describing these processes as a function of vegetation and soil surface cover and the presence of a layer of deposited sediment. The model was calibrated using some of the measured sediment yield data and subsequently tested by simulating the remaining data. The results were satisfactory and modelled fractions of sediment transported by splash, wash and flow‐driven runoff transport generally compared well with observed fractions of fine and coarse particles in eroded sediment from the various plots.

GIS와 USLE를 이용한 아산만 유입 유사량 추정

본 연구는 아산만으로 유입되는 유사량을 추정하기 위하여 Landsat-5 TM 위성영상과 NGIS 수치자료를 이용하여 대상유역의 기본도와 USLE 주제도를 구축하고, 범용토양유실공식(USLE)을 이용하여 아산만 유역의 토양유실량을 추정하였다. 유사운송비와 포착률을 이용하여 아산만으로 유입되는 유사량을 추정하였으며, 이를 농업기반공사의 배수갑문 관리자료와 환경부의 담수호 부유물 측정자료로부터 구한 실측 유사량과 비교하였다. USLE와 유사운송비, 포착률을 이용해 추정된 값과 실측 유입유사량을 비교한 결과, 아산호의 경우 연평균 추정치는 5,665tonnes/yr, 실측치는 12,937tonnes/yr, 삽교호의 경우 추정치는 6,765tonnes/yr, 실측치는 12,395 tonnes/yr 으로 나타났다. Geographic Information System (GIS) combined with Universal Soil Loss Equation (USLE) was used to estimate the soil erosion of Asan Bay experiment watershed in Korea. Spatial data for each USLE factors were obtained from the Landsat-5 TM remote sensing images and 1/25,000 scale digital contour maps. Sediment yield to Asan Bay was estimated by the sediment delivery ratio and trap efficiency. The estimated sediment yield was compared with observed on the Asan and Sapgyo estuary sub-watershed within Asan Bay experimental watershed for the period from 1981 to 2000. The calculated total annual sediment yields from Asan and Sapgyo estuary sub-watershed to Asan Bay were 5,665tonnes/yr and 6,766tonnes/yr, respectively. The measured sediment yields were 12,937tonnes/yr and 12,395tonnes/yr, respectively on an average.