Quantifying periglacial erosion: insights on a glacial sediment budget,Matanuska Glacier,Alaska

Glacial erosion rates are estimated to be among the highest in the world. Few studies have attempted, however, to quantify the flux of sediment from the periglacial landscape to a glacier. Here, erosion rates from the nonglacial landscape above the Matanuska Glacier, Alaska are presented and compare with an 8‐yr record of proglacial suspended sediment yield. Non‐glacial lowering rates range from 1·8 ± 0·5 mm yr^?1 to 8·5 ± 3·4 mm yr^?1 from estimates of rock fall and debris‐flow fan volumes. An average erosion rate of 0·08 ± 0·04 mm yr^?1 from eight convex‐up ridge crests was determined using in situ produced cosmogenic ¹⁰Be. Extrapolating these rates, based on landscape morphometry, to the Matanuska basin (58% ice‐cover), it was found that nonglacial processes account for an annual sediment flux of 2·3 ± 1·0 × 10⁶ t. Suspended sediment data for 8 years and an assumed bedload to estimate the annual sediment yield at the Matanuska terminus to be 2·9 ± 1·0 × 10⁶ t, corresponding to an erosion rate of 1·8 ± 0·6 mm yr^?1: nonglacial sources therefore account for 80 ± 45% of the proglacial yield. A similar set of analyses were used for a small tributary sub‐basin (32% ice‐cover) to determine an erosion rate of 12·1 ± 6·9 mm yr^?1, based on proglacial sediment yield, with the nonglacial sediment flux equal to 10 ± 7% of the proglacial yield. It is suggested that erosion rates by nonglacial processes are similar to inferred subglacial rates, such that the ice‐free regions of a glaciated landscape contribute significantly to the glacial sediment budget. The similar magnitude of nonglacial and glacial rates implies that partially glaciated landscapes will respond rapidly to changes in climate and base level through a rapid nonglacial response to glacially driven incision. Copyright © 2009 John Wiley & Sons, Ltd.     

Drucker-Prager系列屈服准则在稳定分析中的应用研究

Drucker-Prager（下简称D-P）系列屈服准则作为Mohr-Coulomb（下简称M-C）准则的修正模型在岩土工程中得到了广泛的使用。然而采用不同的D-P系列屈服准则可能会得到差距较大的结果,因此,选用合适的D-P系列屈服准则十分重要。在研究了D-P系列屈服准则与M-C准则之间的对应关系之后,指出D-P系列屈服准则对应的Lode角取值较为有限,难以反映出材料在丰富受力状态下的M-C准则屈服强度,将其取值范围扩大至－30°～30°,并以某边坡和向家坝泄12坝段抗滑稳定分析为例,对如何选用合适的D-P系列屈服准则这一问题进行了研究,提出了具体的选择方法。研究结果表明,只要选用的D-P系列屈服准则对应的Lode角能反映影响边坡和坝基稳定的关键部位的受力状态,就能够得到较好的结果,将D-P系列屈服准则对应的Lode角取值范围扩大至－30°～30°也是必要的。     

灌溉与施氮对黑河中游新垦沙地春小麦生长特性、耗水量及产量的影响

在黑河中游边缘绿洲新垦沙地设计大田试验,研究了不同灌溉量(估算春小麦生育期需水量的0.6、0.8、1.0倍)与施氮量(0、140、221和300 kg/hm2)对春小麦生长特性、耗水量及产量的影响.结果表明,灌溉与施氮对春小麦植株高度产生一定的影响,但其效果不明显.高灌溉量加大作物的耗水量,春小麦全生育期,高灌溉处理的耗水量比中等灌溉处理与低灌溉处理分别增加16.68%与36.88%.当施氮量小于221 kg/hm2时,增加施氮量可以提高地上部干物质量、单位面积粒数、单穗粒重与产量,从而提高水分利用效率(WUE);当施氮量大于221 kg/hm2时,高施氮量使大量干物质滞留于营养器官,导致成熟前物质的转移不充分,同时在土壤水分亏缺的条件下,高施氮处理加重干旱胁迫,从而使221 kg/hm2处理的地上部干物质量(4 159 kg/hm2)、单位面积粒数(3 774)、单穗粒重(259.42 mg)、产量(2 132.83 kg/hm2)与WUE(3.85 kg·mm-1·hm-2)在各施氮处理中最高.地上部干物质量、籽粒产量及产量构成要素随灌溉量的增加而增加.低灌溉处理的WUE显著高于中等灌溉处理与高灌溉处理处理,中等灌溉处理与高灌溉处理之间的WUE差异不显著.结果表明,低灌溉处理(春小麦全生育期灌溉量378 mm)与221 kg/hm2施氮是黑河中游边缘绿洲新垦沙地农田可以获得相对较高的经济产量与高WUE的最佳组合.     

渗透系数衰减时矿坑涌水量与开采深度的关系

给出了在岩石渗透性随深度衰减条件下,二维稳定流巷道涌水量的解析解。对巷道涌水量与巷道位置深度的关系,不同水平巷道涌水量以及矿坑总涌水量随开采深度的变化关系进行了理论分析。最后用平顶山矿突水资料进行了验证。      

Hydrological and sediment yield response to summer rainfall in a small high Arctic watershed

In cold regions, the response and related antecedent mechanisms that produce flood flows from rainfall events have received limited study. In 2007, a small watershed at Cape Bounty, Melville Island, Nunavut, was studied in detail during the melt season. Two rainfall events on June 30 and July 22, totalling 9·2 and 10·8 mm, respectively, represented significant contributions to seasonal discharge and sediment transport in a year with a low winter snowpack. The precipitation events elevated discharge and suspended sediment concentrations to twice the magnitude of the nival melt, and generated the only measurable downstream lacustrine turbidity current of the season. In two days, rainfall runoff transported 35% of the seasonal suspended sediment load, in contrast to 29% transported over the nival freshet. The magnitude and intensity of the rain events were not unusual in this setting, but the rainfall response was substantial in comparison with equivalent past events. Exceptional temperatures of July 2007 generated early, deep permafrost thaw, and ground ice melt. The resultant increase in soil moisture amplified the subsequent rainfall runoff and sediment transport response. These results demonstrate the importance of antecedent moisture conditions and the role of permafrost active layer development as an important factor in the rainfall runoff and sediment transport response to precipitation events. Copyright © 2009 John Wiley & Sons, Ltd.     

An investigation of lag times for rainfall–runoff–sediment yield events in small river basins / Une analyse des temps de réponse d'événements pluie–débit–transport solide au sein de petits bassins versants

Abstract

River basin lag time (LAG), defined as the elapsed time between the occurrence of the centroids of the effective rainfall intensity pattern and the storm runoff hydrograph, is an important factor in determining the time to peak and the peak value of the instantaneous unit hydrograph, IUH. In the procedure of predicting a sedimentgraph (suspended sediment load as a function of time), the equivalent parameter is the lag time for the sedimentgraph (LAG_s ), which is defined as the elapsed time between the occurrence of the centroids of sediment production during a storm event and the observed sedimentgraph at the gauging station. Results of analyses of rainfall, runoff and suspended sediment concentration event data collected from five small Carpathian basins in Poland and from a 2.31-ha agricultural basin, in central Illinois, USA have shown that LAG_s was, in the majority of cases, smaller than LAG, and that a significant linear relationship exists between LAG_s and LAG.     

A conceptual model of water yield effects from beetle‐induced tree death in snow‐dominated lodgepole pine forests

In regions of western North America with snow‐dominated hydrology, the presence of forested watersheds can significantly influence streamflow compared to areas with other vegetation cover types. Widespread tree death in these watersheds can thus dramatically alter many ecohydrologic processes including transpiration, canopy solar transmission and snow interception, subcanopy wind regimes, soil infiltration, forest energy storage and snow surface albedo. One of the more important causes of conifer tree death is bark beetle infestation, which in some instances will kill nearly all of the canopy trees within forest stands. Since 1996, an ongoing outbreak of bark beetles (Coleoptera: Scolytidae) has caused widespread mortality across more than 600,000 km² of coniferous forests in western North America, including numerous Rocky Mountain headwaters catchments with high rates of lodgepole pine (Pinus contorta) mortality from mountain pin beetle (Dendroctonous ponderosae) infestations. Few empirical studies have documented the effects of MPB infestations on hydrologic processes, and little is known about the direction and magnitude of changes in water yield and timing of runoff due to insect‐induced tree death. Here, we review and synthesize existing research and provide new results quantifying the effects of beetle infestations on canopy structure, snow interception and transmission to create a conceptual model of the hydrologic effects of MPB‐induced lodgepole pine death during different stages of mortality. We identify the primary hydrologic processes operating in living forest stands, stands in multiple stages of death and long‐dead stands undergoing regeneration and estimate the direction of change in new water yield. This conceptual model is intended to identify avenues for future research efforts. Copyright © 2012 John Wiley & Sons, Ltd.     

Spatial scale dependency issues in the application of the Modified Universal Soil Loss Equation (MUSLE)

ABSTRACT

The MUSLE is used within hydrological models to estimate sediment yields from catchments of various sizes, but the spatial scale dependency issues associated with estimating the MUSLE parameters have not been adequately addressed. In the absence of detailed observed data on both hydrological response and sediment yield, some analytical approaches and hypothetical examples are presented to identify the key issues. The results suggest that methods used to estimate both the erosivity and topographic factors are scale dependent, particularly if a lumped or semi-distributed modelling approach is used. The conclusion is that spatial scale dependencies will add to the uncertainties inherent in the use of the MUSLE if not carefully understood and appropriately addressed. One suggested approach is to apply the erosivity equation to a fixed (small) representative area and then scale up to the total catchment, an approach that recognizes the variability of averaged parameters across different spatial scales.     

2D modelling of a dry joint masonry wall retaining a pulverulent backfill

This work focuses on an analysis of dry joint retaining structures based on yield design theory: the stability of the masonry is assessed using rigid block and shear failure mechanisms in the wall and its backfill. An application of this simulation on 2D scale‐down brick and wood models is then addressed, showing close agreement between theoretical predictions and experimental results. Further development on this work, including application of this theory on dry‐stone retaining walls, is discussed as a conclusion. Copyright © 2009 John Wiley & Sons, Ltd.     

Gene Expression Programing for Estimating Suspended Sediment Yield in Middle Euphrates Basin,Turkey

Gene expression programing (GEP) is used to estimate the suspended sediment yield (SSY) in Euphrates River. SSY is considered to be a function of (i) discharge and (ii) time‐lagged discharge and SSY. The proposed models were trained to extrapolate natural stream data collected from five stations in Middle Euphrates Basin. A detailed sensitivity analysis is done to select the time‐lagged discharge and sediment yield variables. GEP implicitly evaluates the contribution of each independent variable on the fitness of candidate solution and eliminates the variable having no contribution. In this study, all input variables are observed to be included in the proposed GEP models, which prove the significance of each variable. Also, standard and modified sediment rating curves and regression‐based formulae are developed for the five stations. In verification, the estimations of GEP formulae agree well with the measured ones. The GEP models are evaluated by the results of the rating curves and regression formulae. In general, the GEP formulae give better results compared to the rating curves and regression‐based formulae.