GIS Based Distributed Model for Soil Erosion and Rate of Sediment Outflow from Catchments

A spatially distributed rainfall–runoff–soil erosion model capable of handling catchment heterogeneity in terms of landuse, soil, slope, and rainfall has been developed and applied to data from several catchments. The model operates on a cell basis and accepts distributed inputs from a raster geographic information system (GIS). The catchment digital elevation model is used in the model to generate drainage paths from each of the discretized cells to the catchment outlet in proper hydrologic order. Following the computational hydrological sequencing thus derived, the mechanics of overland flow are modeled using a finite volume based numerical solution of the diffusion wave approximation of the St. Venant equations and the process of soil erosion is modeled using a numerical solution of the sediment continuity equation with appropriate auxiliary equations. The spatial information for each cell of the catchment was generated using digital analysis of satellite data and published information by making use of commercially available image processing and raster GIS packages. Results of model application on several catchments indicate that the model can compute temporal distribution of the sediment outflow rate at the catchment outlet for storm events reasonably well. The cell-based structure of the model also allows for computation of the spatial distribution of computed variables such as the amount of soil erosion.     

Laboratory Simulation of Urban Runoff and Estimation of Runoff Hydrographs with Experimental Curve Numbers Implemented in USEPA SWMM

The prognostic capabilities of a lumped hydrologic modeling approach may be complicated by routing and connectivity among infiltrative and impervious surfaces. We used artificial rainfall to generate runoff from impervious and bare soil boxes arranged in series to simulate different extents and connectivity of impervious surfaces under different moisture conditions for pervious areas. Curve numbers were calculated from observed rainfall and runoff data, compared with published values, and used in the curve number infiltration algorithm in the U.S. EPA Storm Water Management Model 5 (USEPA SWMM5) to generate runoff hydrographs. Experimental curve numbers were higher than tabular USDA values, ranging from 91 to 96. Simulations of infiltration and runoff response with experimental curve numbers showed overall good agreement with observed data, although SWMM5 was unable to re-create early term infiltration patterns, and simulated runoff lagged observed, which is attributed to implicit accounting for soil moisture and other assumptions of the SWMM5 curve number application. Our results highlight some prospects for the use of curve numbers in modeling infiltration and runoff.     

Case Study of a Full-Scale Evapotranspiration Cover

The design, construction, and performance analyses of a 6.1?ha evapotranspiration (ET) landfill cover at the semiarid U.S. Army Fort Carson site, near Colorado Springs, Colo. are presented. Initial water-balance model simulations, using literature reported soil hydraulic data, aided selection of borrow-source soil type(s) that resulted in predictions of negligible annual drainage ( ? 1?mm/year). Final construction design was based on refined water-balance simulations using laboratory determined soil hydraulic values from borrow area natural soil horizons that were described with USDA soil classification methods. Cover design components included a 122?cm thick clay loam (USDA), compaction ? 80% of the standard Proctor maximum dry density (dry bulk density ～ 1.3?Mg/m3), erosion control measures, top soil amended with biosolids, and seeding with native grasses. Favorable hydrologic performance for a 5?year period was documented by lysimeter-measured and Richards’-based calculations of annual drainage that were all <0.4?mm/year. Water potential data suggest that ET removed water that infiltrated the cover and contributed to a persistent driving force for upward flow and removal of water from below the base of the cover.     

Aerial Assessment of Ephemeral Gully Erosion from Agricultural Regions in the Pacific Northwest

Soil erosion from agricultural areas continues to be problematic in terms of both financial and environmental measures. Ephemeral gullies contribute to the soil loss both by the volume of sediment eroded from the gullies and because they act as delivery channels for surface erosion. High resolution aerial imagery was used to quantify the amounts and locations of ephemeral gullies in the subbasins of the Potlatch River system. Areal ephemeral gully erosion rates varied from 33.6?mt/km2 (0.15 U.S. t/acre) in the Big Bear Creek Subbasin to 88.4?mt/km2 (0.39 U.S. t/acre) in the Middle Potlatch Creek Subbasin representing 2.3–7.7% of the total surface sediment load. An erosion potential index was proposed to assist resource managers predict gully locations at the watershed scale using readily available remote sensing and geographic information system layers.     

Study of Spatial and Temporal Processes of Soil Erosion on Sloping Land Using Rare Earth Elements As Tracers

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Upland Erosion Modeling in a Semihumid Environment via the Water Erosion Prediction Project Model

The major water quality impairment in the midwest United States is sediment eroded from agricultural lands. Yet, few understand the spatial and temporal variability of erosion, or soil erosion dynamics, in relation to precipitation, topography, land management, and severe events. The objectives of this paper are to (1) develop a methodology for estimating long-term spatial soil erosion and water runoff losses and (2) explore issues in applying an established physical-based process model, Water Erosion Prediction Project (WEPP), to a large area by establishing a prototype system for the state of Iowa. This study for the first time provides a comparison of the model predictions against long-term measurements of the sediment delivery ratio (SDR) in the South Amana Catchment of the Clear Creek Watershed (CCW), a heavily instrumented watershed that is roughly 10 times the maximum WEPP fold size. To further examine the performance of WEPP in a semihumid environment, such as the CCW, where runoff and raindrop impact to erosion may be significant, the SDR was plotted as a function of the runoff coefficient, defined as the runoff/rainfall ratio. In addition, the WEPP predictions are compared against the statistical relation of SDR vs. runoff coefficient developed by Piest et al. in 1975) for watersheds in Iowa. It is shown that WEPP follows the trend shown by Piest et al. quite closely and performs well for continuous simulations extended up to 300?years.     

A methodological approach for estimating turbidity in a river

During the operations of purging and disposal of sediments of a reservoir it is necessary to know the values of turbidity in the river downstream in natural condition, in the absence of dams or river training works. The paper shows that under these conditions the ratio of the average values of sediment discharge to the annual maximum value of water discharge is a function of the average annual turbidity. Turbidity can be considered as representative synthetic index of the climatic conditions, the lithological features and the land cover of the basin, and the geometric characteristics of the river network. The proposed relationship of sediment discharge as a function of water discharge were validated on the basis of data collected from different Italian regions that have very different morphological, geo-lithological and rainfall features and that are characterised by a basin area changing between a few dozen and thousands of square kilometres. The results can be considered satisfying.     

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.     

Worldwide Residential Soil Regulatory Guidance Values for Chlorinated Ethenes

Surface soil contamination is often regulated by using guidance values that specify the maximum amount of pollutant that can be present without prompting a regulatory response. In the United States, there are at least 88 value sets, and another 35 worldwide, that provide guidance for at least one chlorinated ethene. Trichloroethene is the most commonly regulated chlorinated ethene (118 values) and may be the most commonly regulated synthetic organic surface soil contaminant. Cis- and trans-1,2-dichloroethene are the least regulated chlorinated ethenes. Overall, there are 617 guidance values for specific chlorinated ethenes plus another 32 for mixed isomers of dichlorethene. This analysis explores the origin, magnitude, and form of the variability of these values. Results indicate that values span from 4.9 to 6.6 orders of magnitude and follow distributions similar to lognormal random variables. However, distributions include value clusters similar to values advocated by the U.S. Environmental Protection Agency (USEPA) or the Canadian Council of Ministers of the Environment (CCME). Although only 9.5% of the regulatory guidance values (RGVs) are identical to USEPA or CCME values, 55% of these fall within the uncertainty bounds estimated for USEPA risk models. Results suggest that stronger national leadership and reduced risk model uncertainty could be effective in reducing the RGV variability of chlorinated ethenes.     

Modified vegetation-erosion dynamics model and its application in typical watersheds in the Loess Plateau

The vegetation-erosion model was applied in three typical watersheds of hilly and gully area in the Loess Plateau in northwestern China to study the dynamic relations between vegetation coverage and soil erosion rate and various stresses. The model was improved by introducing rainfall and runoff factors. Then the modified model was applied in the Luergou and Luoyugou watersheds. The calculation results with the modified model were compared with the results of the original model. The precisioos of simulated vegetation coverage and soil erosion rate with the modified model were greatly improved compared with the original model. Soil erosion rate reduced with increasing vegetation coverage and the human disturbance caused high soil erosion.     

Comparison of Long-Term Observed Sediment Trap Efficiency with Empirical Equations for Coralville Reservoir, Iowa

Trapping efficiency (TE) is defined as the percent of particles that are retained within an impoundment. TE can vary from ? 0% indicating no sediment is retained or is lost, to 100% where all the sediment is retained. In this paper a high quality, long-term data set (32?years) was used to demonstrate that annual sediment trap efficiencies for a run of the river impoundment are variable. For water years 1973–2005, annual trap efficiencies for Coralville Reservoir ranged from 5.6 to 95.8%, with a mean of 74.7% and a median of 79.9%. Overall trap efficiency for the entire period was determined to be 80.3% and a detention time of 12.4?days. A comparison of the observed long-term TE was done against different empirical TE equations that are commonly used (Brown, Brune, Churchill, Dendy, Heinemann, & USDA/Summit Co., Water District). The Churchill equation provided the best fit of the empirical trap efficiency equations (TEC = 79.1%); all other empirical TE relationships underestimated the observed trap efficiency with errors ranging from 13.7 to 33.1%. Bathymetric data show that since 1958 the reservoir has lost 11% of its flood storage capacity, and over 62% of its normal pool capacity. For the time studied (1973–2005) the loss of storage is estimated to correspond to 16.9×109?kg of sediment deposited in the reservoir, resulting in an annual sedimentation rate of 5.3×108?kg?year?1.     

Integrated Methodology of Design for Construction Site Sedimentation Basins

The performance of four sedimentation basins (SBs) at a Pennsylvania Department of Transportation I-99 highway construction site was evaluated based on their particle removal ability. Suspended solids data from the basins indicated poor particle removal, peaks in suspended solid concentration that correlated with rainfall peaks and possibility of sediment resuspension. The current Pennsylvania Department of Environmental Protection basis for basin design is the allocation of 28?m3 (1,000?ft3) of sediment storage zone and 140?m3 (5,000?ft3) of drainage zone per disturbed acre of the drainage basin. Overflow rate, which is a scientific basis for particle removal, is currently not considered in the design of basins. This paper presents a methodology for developing an integrated design for SBs, applying rainfall probability plots to determine an appropriate basin settling volume. The revised universal soil loss equation is used to identify sediment zone volume, and an overflow rate is determined to design basin surface area. The method presented is a comprehensive procedure for designing SBs with flexibility to choose the extent of particle removal and runoff capture, and to vary construction costs.     

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.     

Evaluation of Different Seed Mixtures for Grass Establishment to Mitigate Soil Erosion on Steep Slopes of Railway Batters

Unpredictable rainstorms can pose greater risks of soil erosion on newly formed unprotected railway batters. A bioengineering approach consisting of revegetation can be an effective tool for soil-erosion control. Perennial species, such as buffel grass, are preferred for durability of vegetation cover in the arid and semiarid tropics. However, it takes a longer time to establish buffel than annual species such as Japanese millet (JM). A replicated plot-scale field trial consisting of different proportions of grass-seed mixtures of buffel and JM was conducted on railway-batters slope in the semiarid tropics of central Queensland, Australia. A supplementary automated drip irrigation system was set up to aid seed germination and early establishment of the grass cover. JM alone or JM-dominated seed mixtures significantly reduced soil erosion during the earlier stages. For example, during the second sampling interval (SI), which occurred 63?days after seeding, JM alone reduced soil erosion by 50% (20.2?versus 10.21??t/ha) in comparison to the sole buffel. This trend began to shift as the growth of buffel commenced at the latter stages. By the end of the 11 months, erosion from all seeded plots was not significantly different among the plots with more than 90% soil-loss reduction in comparison to the bare scenario, resulting in more than 60% grass cover. Results suggested that a monoculture of JM or JM-dominated seed mixture with buffel grass could be an effective bioengineering approach for revegetation of railway batters for protection against soil erosion. Quick establishment owing to faster seed germination, seedling establishments, and growth-producing sizable canopy cover developed by JM in the early stage of batter could reduce soil erosion in comparison to a sole crop of slow-growing perennial species buffel. The established vegetation self-regenerated and responded dynamically and naturally to changing conditions of the railway batter within a year, after which JM started to die back.     

Porcine linkage and cytogenetic maps integrated by regional mapping of 100 microsatellites on somatic cell hybrid panel

Recently two main genetic maps [Rohrer et al. Genetics 136, 231 (1994); Archibald et al. Mamm. Genome 6, 157 (1995)] and a cytogenetic map [Yerle et al. Mamm. Genome 6, 175 (1995)] for the porcine genome were reported. As only a very few micro-satellites are located on the cytogenetic map, it appears to be important to increase the relationships between the genetic and cytogenetic maps. This document describes the regional mapping of 100 genetic markers with a somatic cell hybrid panel. Among the markers, 91 correspond to new localizations. Our study enabled the localization of 14 new markers found on both maps, of 54 found on the USDA map, and of 23 found on the PiGMaP map. Now 21% and 43% of the markers on the USDA and PiGMaP linkage maps respectively are physically mapped. This new cytogenetic information was then integrated within the framework of each genetic map. The cytogenetic orientation of the USDA linkage maps for Chromosomes (Chrs) 3, 8, 9, and 16 and of PiGMaP for Chr 8 was determined. USDA and PiGMaP linkage maps are now oriented for all chromosomes, except for Chrs 17 and 18. Moreover, the linkage group "R" from the USDA linkage map was assigned to Chr 6.     

Sediment and Metals Modeling in Shallow River

It is a challenge to apply coupled hydrodynamic, sediment process, and contaminant fate and transport models to the studies of surface water systems. So far, there are few published modeling studies on sediment and metal transport in rivers that simulate storm events on an hourly basis and use comprehensive data sets for model input and model calibration. The United States Environmental Protection Agency (USEPA) in 1997 emphasized the need for credible modeling tools that can be used to quantitatively evaluate the impacts of point sources, nonpoint sources, and internal transport processes in 1D/2D/3D environments. A 1D and time-dependent hydrodynamic, sediment, and toxic model, within the framework of the 3D Environmental Fluid Dynamics Code (EFDC), has been developed and applied to Blackstone River, Mass. The Blackstone River Initiative (USEPA) in 1996, a multiyear and multimillion-dollar project, provided the most comprehensive surveys on water quality, sediment, and heavy metals in the river, and served as the primary data set for this study. The model simulates three storm events successfully. The river flow rates are well calculated both in amplitude and in phase. The sediment transport and resuspension processes are depicted satisfactorily. The concentrations of sediment and five metals (cadmium, chromium, copper, nickel, and lead) during the three storm events are also simulated very well. Numerical analyses are conducted to clarify the impacts of contaminant sources and sediment resuspension processes on the river. While point sources are important to sediment contamination in the river, other sources, including nonpoint sources from watershed and bed resuspension, were found to contribute significantly to the sediment and metals in the river. Point sources alone cannot account for the total metals in the river. The model presented in this paper can be a useful tool for studying sediment and metals transport in shallow rivers and for water resource management.     

Experimental Investigation of the Hydraulic Erosion of Noncohesive Compacted Soils

This paper presents the results of a laboratory investigation whose purpose was to evaluate the effects of compaction on the erodibility of cohesionless soils. By means of a recently developed flume experiment, sediment erosion rates and incipient motion, as a function of shear stress, average velocity, and dry density, have been determined for three compacted sand and gravel mixtures. A preliminary comparison of the incipient motion values shows that granular soils compacted at the Proctor optimum have a higher resistance to free surface flow erosion than those compacted at lower and higher densities. This leads one to infer that the Proctor optimum, generally used as a standard for construction, might also be an optimum for hydraulic resistance and stability. Additional comparison of the experimental data with two commonly used incipient motion criteria also suggests that Yang’s criterion is a better predictor of soil detachment than the Shields-Yalin criterion.     

八一至泽当公路水土流失环境影响初步研究

在详细了解八一至泽当公路工程及工程区自然环境情况的基础上,结合工程前期设计成果,依照水土保持有关法律及规范,界定了本工程水土流失防治责任范围和防治分区,预测了工程建设可能产生的水土流失及危害,并提出了相应的分区防治措施建议。     

Shear Strength of Compacted Soil under Infiltration Condition

Landslides in residual soil slopes are commonly induced by rainfall infiltration. These residual soils are typically in an unsaturated state with negative pore-water pressures or matric suctions since the groundwater tables in steep slopes are often deep. The net normal and shear stresses of the soil remain essentially constant during rainwater infiltration into the slope. Failure of the slope during rainfall can be primarily associated with the decrease in the matric suction of the soil. The objective of the study was to investigate the strength and deformation characteristics of a residual soil of the Bukit Timah Granitic Formation during infiltration that leads to slope failure. There were two modified direct shear apparatuses used. One apparatus was used for the determination of shear strength under controlled suction conditions while the other apparatus was used for shearing-infiltration tests. The shearing-infiltration test results were compared with the shear strength values obtained from the shearing tests under constant suction. The shearing-infiltration test results indicate a close relationship between the decreasing matric suction and the increasing displacement rate of the soil specimen. At the initial part of the infiltration process, there is a rapid reduction in matric suction that is accompanied by little movement in the soil. When failure of the soil is imminent, the soil movement will accelerate.     

降雨条件下植物修复分层尾矿土壤重金属迁移的模拟分析

为探究分层土壤中重金属铜迁移对地下水的污染规律,通过土柱淋滤试验方法模拟表层植被、不同降雨强度、不同淋滤液pH条件下分层修复尾矿土壤中重金属铜的纵向迁移规律。结果表明,重金属铜会因为淋滤作用在分层土壤中纵向迁移,各土柱出水口淋出液的重金属铜浓度从上到下呈增加趋势,淋出液中重金属铜浓度随土壤中重金属铜浓度的增加而增加;当淋滤液pH<7时,各土柱出水口淋出液的pH值从上到下呈增加趋势;表层植被、降雨强度及淋滤液pH对淋出液中重金属铜的浓度有影响;在适宜降雨强度范围内,淋出液重金属铜的浓度随淋滤强度增大而增大;表层覆有植被的土柱降雨淋滤后各出水口（除溢流口外）的淋出液重金属浓度较大;当淋滤液pH<7时,各出水口淋出液的重金属浓度随淋滤液pH值的减小而增大,酸性淋滤液会在一定程度上促进淋出液重金属的析出。研究结果为控制实际尾矿库土壤污染和地下水污染提供理论基础。