Reduction in interrill sediment transport by rolled erosion control systems

Rolled erosion control systems (RECS) reduce detachment and transport of sediment by mitigating the basic processes of run-off and erosion (e.g., splash detachment, interrill transport, run-off velocity, surface crusting). Despite the variety of products available in the market today, only limited research has been conducted on their influence on erosion subprocesses. This study addresses some of the limitations of previous research by using laboratory rainfall simulation to study rainsplash sediment redistribution, run-off, total interrill sediment transport, and aggregate size transport from an erodible Vertisol. Three 3-h rainfall simulations were conducted on a 20° slope at a rainfall intensity of ≈100 mm h⁻¹ on (1) a bare soil control, (2) four predominately natural RECS, and (3) four synthetic RECS. Data indicate that all products significantly reduced run-off (enhanced infiltration), and decreased interrill sediment transport compared to the bare soil control. However, it was observed that several products (C125, Curlex I, Geojute, SC150BN, TB1000, and P300) were statistically more effective than PECMAT and TerraJute. Finally, preferential transport of selected aggregate fractions was examined. Cover percentage, three-dimensionality, and drapability were identified as favorable physical attributes for mitigating erosion processes.     

Quantification of seasonal sediment and phosphorus transport dynamics in an agricultural watershed using radiometric fingerprinting techniques

Purpose

Phosphorus (P) is a limiting nutrient for most US Midwestern aquatic systems and, therefore, increases of P, through point or non-point sources (NPS) of pollution such as agriculture, causes eutrophication. Identifying specific NPS contributions (e.g., upland vs. stream channels) for sediments and P is difficult due to the distributed nature of the pollution. Therefore, studies which link the spatial and temporal aspects of sediment and P transport in these systems can help better characterize the extent of NPS pollution.

Materials and methods

Our study used fingerprinting techniques to determine sources of sediments in an agricultural watershed (the North Fork of the Pheasant Branch watershed; 12.4 km² area) in Wisconsin, USA, during the spring, summer, and fall seasons of 2009. The primary sources considered were uplands (cultivated fields), stream bank, and streambed. The model used fallout radionuclides, ¹³⁷Cs, and ²¹⁰Pb_xs, along with total P to determine primary sediment sources. A shorter-lived fallout radioisotope, ⁷Be, was used to determine the sediment age and percent new sediments in streambed and suspended sediment samples (via the ⁷Be/²¹⁰Pb_xs ratio).

Results and discussion

Upland areas were the primary source of suspended sediments in the stream channels followed by stream banks. The sediment age and percent new sediment for the streambed and suspended sediments showed that the channel contained and transported newer (or more recently tagged with ⁷Be) sediments in the spring season (9–131 days sediment age), while relatively old sediments (165–318 days) were moving through the channel system during the fall season.

Conclusions

Upland areas are the major contributors to in-stream suspended sediments in this watershed. Sediment resuspension in stream channels could play an important role during the later part of the year. Best management practices should be targeted in the upland areas to reduce the export of sediments and sediment-bound P from agricultural watersheds.     

Process-based modelling of erosion,sediment transport and reservoir siltation in mesoscale semi-arid catchments

Purpose

To support scientifically sound water management in dryland environments a modelling system has been developed for the quantitative assessment of water and sediment fluxes in catchments, transport in the river system, and retention in reservoirs. The spatial scale of interest is the mesoscale because this is the scale most relevant for management of water and land resources.

Materials and methods

This modelling system comprises process-oriented hydrological components tailored for dryland characteristics coupled with components comprising hillslope erosion, sediment transport and reservoir deposition processes. The spatial discretization is hierarchically designed according to a multi-scale concept to account for particular relevant process scales. The non-linear and partly intermittent run-off generation and sediment dynamics are dealt with by accounting for connectivity phenomena at the intersections of landscape compartments. The modelling system has been developed by means of data from nested research catchments in NE-Spain and in NE-Brazil.

Results and discussion

In the semi-arid NE of Brazil sediment retention along the topography is the main process for sediment retention at all scales, i.e. the sediment delivery is transport limited. This kind of deposition retains roughly 50 to 60 % of eroded sediment, maintaining a similar deposition proportion in all spatial scales investigated. On the other hand, the sediment retained in reservoirs is clearly related to the scale, increasing with catchment area. With increasing area, there are more reservoirs, increasing the possibility of deposition. Furthermore, the area increase also promotes an increase in flow volume, favouring the construction of larger reservoirs, which generally overflow less frequently and retain higher sediment fractions. The second example comprises a highly dynamic Mediterranean catchment in NE-Spain with nested sub-catchments and reveals the full dynamics of hydrological, erosion and deposition features. The run-off modelling performed well with only some overestimation during low-flow periods due to the neglect of water losses along the river. The simulated peaks in sediment flux are reproduced well, while low-flow sediment transport is less well captured, due to the disregard of sediment remobilization in the riverbed during low flow.

Conclusions

This combined observation and modelling study deepened the understanding of hydro-sedimentological systems characterized by flashy run-off generation and by erosion and sediment transport pulses through the different landscape compartments. The connectivity between the different landscape compartments plays a very relevant role, regarding both the total mass of water and sediment transport and the transport time through the catchment.     

Linking temporal scales of suspended sediment transport in rivers: towards improving transferability of prediction

Journal of Soils and Sediments - Suspended sediment (SS) transport in rivers is highly variable, making it challenging to develop predictive models that are applicable across timescales and rivers....     

Model of sediment transport in an irrigation furrow

A new equation describing the transport of sediments by waterflows in irrigation furrows was developed. The equation was verified using the results of field studies on irrigated sierozems. The absolute relative error was 9%, and the coefficient of correlation was 0.92.     

Generalized equations of sediment discharge for assessing the erosion and transport capacities of shallow surface flows

On the basis of existing sediment discharge equations, their generalized and simplified forms were given for assessing and predicting the rill erosion of soils. The substantiation and parameterization of the generalized equations were performed for calculating the limit transport capacity of shallow water-sand flows from experimental data. Examples of calculations were given to illustrate the procedure for determining the hydraulic parameters of flows and the limit discharges of sandy sediments.     

Effect of slope borders in reducing splash erosion during sediment transport by rain-induced overland flow

Splash erosion plays a vital role in the loss of eroded materials. Unlike those in slope central areas, laterally ejected splashed materials in slope border areas cannot be replenished easily because slope edges prevent splash erosion particles from entering the slope. Thus, splashed materials in slope border areas are less than those in slope central areas because of the lack of source areas for splash-eroded materials. However, this phenomenon, called the slope border effect, has received minimal attention by researchers. The partially missing splash erosion induced by the slope border effect on sediment transport was investigated to understand the slope erosion mechanism further in this paper. A modified soil pan divided into four areas, namely, central erosion test area (length = 100 cm, width = 35 cm, depth = 45 cm), border erosion test area (length = 100 cm, width = 35 cm, depth = 45 cm), splash compensate border area (length = 110 cm, width = 30 cm, depth = 45 cm) and splash collection area (length = 100 cm, width = 2.5 cm, depth = 45 cm) was used to monitor diffusion and splash erosion under simulated rainfall. Results showed that the splash detachment rate increased with the increase in slope but initially decreased and then increased with the increase in rainfall intensity. The runoff rate and diffuse erosion rates for complete splash erosion (SE) treatments were higher than those without partial splash erosion (SE_L). Under low rainfall erosive power and runoff transport capacity (e.g., 5° slope and 60 mm h⁻¹), the transported clay in SE treatments was approximately 2% more than that in SE_L treatments. This amount changed to more than 2% sand under high rainfall and runoff erosive power. However, the mass fraction accounted for by silt particles in the sediments of the SE_L treatments was more than that in the SE treatments. Thus, the partially missing splash erosion can weaken the selective transport ability of runoff for sediments. The effect of missing partial splash erosion on diffuse erosion was enhanced with an increase in erosive power. The results of our paper will provide insights into the effect of the boundary effect zone of slope on soil erosion and its related mechanisms.     

黄土高原径流侵蚀功率输沙模型的改进

水土流失对流域生态危害严重,输沙量模拟和预测可以为流域水土流失防治提供依据,因此精确的输沙模型是流域水土流失治理的重要工具。为了精确模拟变化环境下黄土高原年输沙量,该研究基于黄土高原19个水文站的径流和输沙数据,通过随机森林变量重要性度量方法评估年径流侵蚀功率、淤地坝指数、淤地坝相对指数、归一化植被指数、不透水地面积等因子对流域年输沙量的影响,使用非线性最小二乘法估算年输沙模型参数,对比分析不同因子组合的年输沙模型精度,提出适用性较强的黄土高原年输沙模型,据此开展年输沙量变化贡献率分析。结果表明：1）以幂函数形式构建的仅含径流侵蚀功率单因子输沙模型精度与流域面积有显著的负相关关系,相关系数为-0.505（P<0.05）,模型精度随着流域面积增大而下降,在大于7 000 km2的流域适用性较差;2）年径流侵蚀功率、淤地坝指数及不透水地面积因子组合建立的多因子年输沙模型在黄土高原适用性最佳,模型在率定期NSE平均值为0.84,RMSE平均值为0.21亿t,在验证期纳什系数平均值为0.79,均方根误差平均值为0.27亿t。3）影响研究流域年输沙量变化的因素依次是：年径流侵蚀功率、不透水地面积和淤地坝指数。研究可以为黄土高原不同区域水土流失防治和生态治理工作提供理论支撑。     

Soil erosion and carbon dynamics

Accelerated erosion involves preferential removal of soil organic carbon (SOC) because it is concentrated in vicinity of the soil surface and has lower density than the mineral fraction. The SOC transported by water runoff is redistributed over the landscape and deposited in depressional sites where it is buried along with the sediments. However, the fate of the SOC transported, redistributed and deposited by erosional processes is a subject of intense debate. Sedimentologists argue that SOC buried with sediments is physically protected, and that depleted in the eroded soil is replaced through biomass production. Thus, they argue that the erosion–sedimentation process leads to globally net SOC sequestration of 0.6–1.5 Gt C/year. In contrast, soil scientists argue that: (i) a large portion of the SOC transported by water runoff comprises labile fraction, (ii) breakdown of aggregation by raindrop impact and shearing force of runoff accentuates mineralization of the previously protected organic matter, and (iii) the SOC within the plow zone at the depositional sites may be subject to rapid mineralization, along with methanogenesis and denitrification under anaerobic environment. Whereas, tillage erosion may also cause burial of some SOC, increase in soil erosion and emission of CO₂ from fossil fuel combustion are net sources of atmospheric CO₂. Soil scientists argue that soil erosion may be a net source of atmospheric CO₂ with emission of 1 Gt C/year. It is thus important to understand the fate of eroded SOC by measuring and monitoring SOC pool in eroded landscape as influenced by intensity and frequency of tillage operations and cropping systems.     

Soil erosion prediction and sediment yield estimation: the Taiwan experience

Estimating watershed erosion using geographic information systems coupled with the universal soil loss equation (USLE) or agricultural non-point source pollution model (AGNPS) has become a recent trend. However, errors in over-estimation often occur due to the misapplication of parameters in the equation and/or model. Because of poor slope length calculation definitions for entire watersheds, the slope length factor is the parameter most commonly misused in watershed soil loss estimation. This paper develops a WinGrid system that can be used to calculate the slope length factor from each cell for reasonable watershed soil loss and sediment yield estimation.     

上方来水来沙对浅沟侵蚀产沙及水动力参数的影响

 浅沟侵蚀是黄土高原重要的侵蚀类型,上方汇水对坡面浅沟侵蚀具有重要的影响。采用野外放水冲刷试验,定量分析26°坡耕地在上方来水量为5、10和15L/min时对坡下方浅沟侵蚀产沙及其水动力参数的影响。结果表明：上方来水的汇入使浅沟水流流速明显增大,雷诺数、弗劳德数、水流功率和剪切力分别增大33%～76%、21%～47%、29%～72%和18%～42%,阻力系数减少11%～13%,导致浅沟侵蚀产沙量明显增大;除流速和弗劳德数外,其余水动力参数随放水时间的延长呈递增趋势;上方来水使浅沟侵蚀产沙量相对增量与水流功率和剪切力相对增量均呈幂函数关系。     

Soil erosion and sediment dynamics in the Anthropocene: a review of human impacts during a period of rapid global environmental change

Journal of Soils and Sediments - Humanity has been modifying the planet in a measurable way for thousands of years. Recently, this influence has been such that some feel we are in a new geological...     

伊朗土壤侵蚀及河流泥沙研究

土壤侵蚀使水土资源流失,河道泥沙淤积,严重制约着区域生态、社会、经济的发展。伊朗地处干旱、半干旱气候带,土壤侵蚀严重,河流泥沙问题突出,已成为影响该国经济社会发展的主要环境问题之一。通过介绍伊朗土壤侵蚀和泥沙淤积的基本情况,并对该国有关土壤侵蚀及河流泥沙方面的研究和治理成果进行总结,提出未来研究的趋势和相关建议,以期为伊朗和我国的水土保持及泥沙治理提供参考。     

坡面流输沙能力与土壤可蚀性参数对细沟土壤侵蚀过程影响的有限元计算模型研究

土壤侵蚀预报模型对于定量评价水土保持效果,合理制定水土保持措施等具有重要意义。细沟侵蚀模型是土壤侵蚀预报模型的重要组成部分。本研究建立了一个以物理概念为基础的细沟侵蚀预报模型,模型包括水流连续性方程、水流动力学方程和泥沙运移方程;同时,模型改进了部分参数的计算方法,以线性形式的水流输沙能力计算方法取代原有的对数形式方法,将土壤最大剥蚀率用于土壤可蚀性参数的计算;采用有限元方法对模型进行顺序求解;Visual C++语言数值计算程序被用来模拟细沟侵蚀产沙变化过程,并进行了一系列室内试验验证该数学模型、模型参数及数值计算方法。结果表明,模型预测值和实测值具有很好的一致性,改进的模型参数计算方法能够准确地反映土壤可蚀性参数与水流输沙能力对细沟侵蚀过程的调控作用。     

Monitoring and analysis of suspended sediment transport dynamics in the Carapelle torrent (Southern Italy)

In Northern Puglia watershed's high rates of suspended sediment loads occur along the hydrographic network during intense rainfall events. In order to monitor this phenomenon an automated station, equipped with a turbidity probe, has been set up in the Carapelle torrent.     

Soil erosion risk mapping with new datasets: An improved identification and prioritisation of high erosion risk areas

The numerous estuarine, marshy and marine ecosystems along the coastline of Mauritius Island are potential sinks for sediment especially during intense rainfall events when delivery ratios are high at basin outlets. For sustainable environmental management, soil and water conservation measures are needed, as these will better protect the cultivated lands and aquatic ecosystems from the damages associated with excessive soil loss and sediment deposition. Conservation program usually requires focusing available resources on a limited number of priority action areas. Such areas typically have the highest erosion risk and are connected to aquatic ecosystems. An erosion risk mapping model has been applied in this work to find the priority action areas of Mauritius and new datasets representing rainfall erosivity and topographic factors were used compared to a previous application of the same model. Rainfall erosivity was mapped with Fournier Index instead of rainfall depth. The topographic effect was mapped using a function combining slope length and slope gradient (LS) and was based on the unit contributing area algorithm along with land parcels effect. These new datasets improved the erosion risk mapping and the identification and prioritisation of high erosion areas. The prioritisation was done at basin and subbasin scales and considered the location of wetlands. This enabled the identification of basins and subbasins with the greatest erosion risk and towards which conservation measures can be directed for protecting lands on-site and wetlands off-site from environmental damages.     

Improving precision in sediment source and erosion process distinction in an upland catchment,south-eastern Australia

Analysis of sediment sources is an important component in the development of catchment sediment budgets and in determining links between erosion from sources and sediment delivery to catchment outlets. In this study ¹³⁷Cs and ²¹⁰Pb_ex were used to determine surface and sub-surface source contributions of fine sediment in a small upland headwater catchment (1.6 km²) in south-eastern Australia. The findings from this analysis are employed in an adjustment procedure to better differentiate sediment source erosion processes by utilising channel survey and erosion pin data. This improved the precision of estimates of sediment-source erosion-process contributions from hillslopes and channel/gully walls. A mean of 74% of in-channel deposits and suspended sediment exiting the study catchment was derived from sub-surface sources and when adjusted for erosion process this increased to 81%, which may be attributed to channel and gully wall erosion alone. Net erosion of the channel floor was low and constitutes only a small part of the total channel source input to sediment flux. Variability in sediment source contributions within the catchment was high, with rapid transition from hillslope to channel source dominance of sediment flux with distance downstream in the study catchment.