黄土地区梁峁坡的坡地特征与土壤侵蚀

本文指出黄土地区梁峁坡的坡角主要分布在14°—28°之间,特征坡角的上限相当于黄土的内摩擦角,下限相当于内摩擦角的0.45倍。黄土地区的坡地形态可分为直形坡、凸形坡、凹形坡、复合形坡和阶梯形坡等五种类型。土壤侵蚀主要受坡地形态和坡度的控制,侵蚀量随着坡度的增大而增加,坡度大于15°时,侵蚀量突增,坡面冲刷加剧,26°达极大值,此后冲刷作用减弱,重力侵蚀逐渐显著,至45°侵蚀达到最大值,以后又趋减弱。     

Factors influencing the formation of shallow landslides in the Boston Mountains of northwest Arkansas,USA

Slope failures cause billions of dollars of damage annually and put human lives at risk. This study employed field measurements and observations to provide the framework for laboratory simulations to investigate the effects of environmental characteristics on slope stability in the highly fractured bedrock region of the Boston Mountains, northwest Arkansas. Field measurements, to determine characteristics and possible controls of 10 shallow slope failures along an interstate highway, revealed that slope failures occurred within a relatively narrow range of slope angles (17–36°) and in loamy soils. Based on field observations, flume experiments were conducted to investigate the relationships between soil texture, slope angle, bedrock fractures, soil compaction, and slope instability. Time to failure differed (p < 0.05) among treatment combinations. Generally, slopes composed of loam were more stable than slopes composed of sand. Time to failure decreased more on slopes of 15–20° than on slopes of 20–25°. Flume slopes with sod cover never failed. This study provided a methodology for using field analyses of slope failures to guide laboratory experiments and demonstrated that complex interactions among environmental factors work to stabilize or compromise steep (>20°) slopes.     

花岗岩不同土地利用类型坡地水土流失特征*

利用福建省安溪水土保持试验站的实测资料,对花岗岩不同土地利用类型坡地的水土流失特征进行了初步研究,试验结果说明,坡地只要有一定的植被覆盖和适当的坡地工程,水土流失均可得到控制.松耕使坡耕地土壤侵蚀力急剧下降,必须加强夏季园面覆盖.建议利用USLE进行土壤侵蚀预测时,未扰动自然课露坡地C取值0.1-0.3.实测结果显示,香根草带和牧草覆盖均有良好的保持水土效益,与山边沟工程结合,可以在较陡坡地果园开发中替代梯田台地进行推广.     

乔木的斜向支撑效能及其坡面稳定意义

以滇中地区的松林为例,初步定量探讨了乔木对顺坡有的浅层土壤的斜向支撑作用。研究,树根可能提供的锚固力可达０．６９ｋＮ;在有效的锚固作用下,单株树干的支撑力（抗滑力）最高为０．４２ｋＮ,平均为０．１７ｋＮ;受斜向支撑作用的影响,本来不稳定的浅层松散物质的稳定性系数Ｆ值,由０．５４提高到１．１０,使坡面成为稳定斜坡。如果在特定条件下,树根的锚固力全部转化为支撑力,坡面的Ｆ值可以达到２．８２。     

RATES OF SLOPE DECLINE,TALUS GROWTH AND CLIFF RETREAT ALONG THE SHOMYO RIVER IN CENTRAL JAPAN: A SPACE‐TIME SUBSTITUTION APPROACH

On the basis of a space–time substitution, rates of cliff retreat and talus development overthe pasttens ofthousands of years were quantified for valley‐side slopes along the Shomyo River with a known rate of waterfall recession. Detailed profiles of the valley‐side slopes were obtained at 19 sites along the river by map reading and field survey, and the morphologic characteristics of the slopes were then measured. By combining the locations of the slopes with the recession rate of Shomyo Falls, it is estimated that the growth rate of the talus slope is 3.9–7.2 mm/yr, the rate of decline of the cliff is 2.0–4.0 × 10^?4 deg/yr, and the retreat rate of the cliff top is 6.2–11.6 mm/yr.     

Response of small mid-mountain rivers to human impact with particular reference to the last 200 years; Eastern Sudetes, Central Europe

In the mid-mountains of Central Europe relict forms of periglacial morphogenesis occur, including debris slope covers. However, the Holocene forest succession limited sediment transfer towards valley systems.The eastern, mid-mountain part of the Sudetes, characterised by a dense stream network and by the local occurrence of metallic and gold ores, was already settled by humans in early medieval times. Timber from the forested slopes was used to produce charcoal and streams acted as energy sources for smelting plants and smithies. Agriculture developed on less inclined slopes. Temporal clearances on steep slopes and replacement of primeval beech forest by spruce trees, influenced water circulation on slopes. The exposed slope covers were transferred to valley floors during high precipitation events. Consequently, they were selectively redeposited within the floodplain, changing the former channel pattern, especially at confluences. The introduction of cultivation on slopes triggered intense soil erosion so that agricultural terraces were built in order to prevent surface wash. The terraces are often strengthened with stone walls up to 4.5 m high. Terraces acted as ‘sediment traps’, storing the washed material within the slope. The layers of fine-grained colluvial sediments, which can be linked with agriculture, cover the older, debris slope covers. The colluvium is especially thick at the terrace edges. Despite the protective role of terracing, part of the washed material was transferred to valleys, often becoming overbank deposits, covering older gravel and boulder alluvium. The decline of iron ore exploitation and processing, at the beginning of the 19th century, together with agricultural withdrawal, which was especially radical after the 2nd World War, resulted in successive renaturalisation of the environment being followed by slope stabilisation and deepening of bigger river channels.The results led to the conclusion that a strong human impact on the slope–valley system in the mid-mountain part of the Eastern Sudetes influenced changes in the dynamics and morphology of small rivers to a much higher extent than the climate variations, especially during the Little Ice Age.     

Thermal Regime of Rock and its Relation to Snow Cover in Steep Alpine Rock Walls: Gemsstock,Central Swiss Alps

Snow cover influences the thermal regime and stability of frozen rock walls. In this study, we investigate and model the impact of the spatially variable snow cover on the thermal regime of steep permafrost rock walls. This is necessary for a more detailed understanding of the thermal and mechanical processes causing changes in rock temperature and in the ice and water contents of frozen rock, which possibly lead to rock wall instability. To assess the temporal and spatial evolution and influence of the snow, detailed measurements have been carried out at two selected points in steep north‐ and south‐facing rock walls since 2012. In parallel, the one‐dimensional energy balance model SNOWPACK is used to simulate the effects of snow cover on the thermal regime of the rock walls. For this, a multi‐method approach with high temporal resolution is applied, combining meteorological, borehole rock temperature and terrain parameter measurements. To validate the results obtained for the ground thermal regime and the seasonally varying snowpack, the model output is compared with near‐surface rock temperature measurements and remote snow cover observations. No decrease of snow depth at slope angles up to 70° was observed in rough terrain due to micro‐topographic structures. Strong contrasts in rock temperatures between north‐ and south‐facing slopes are due to differences in solar radiation, slope angle and the timing and depth of the snow cover. SNOWPACK proved to be useful for modelling snow cover–rock interactions in smooth, homogenous rock slopes.     

SPATIAL AND TEMPORAL PATTERNS OF TALUS ACTIVITY – A LICHENOMETRIC APPROACH IN THE STUBAIER ALPS,AUSTRIA

Lichenometric measurements using Rhizocarpon ssp. were carried out on 20 talus slopes in the cirques of the Finstertal valley (Austria) at an elevation of 2300–3000 m a.s.l. The aim was to assess activity patterns on selected slopes and between the slopes of the study area, to find evidence of rockfall pulses in the last centuries and to calculate rockwall retreat rates. A calibration curve was derived from five sites of known age and adapted to the prevailing size of talus boulders. We measured the five largest lichens on more than 300 boulders and the percentage coverage of Rhizocarpon‐free clasts on more than 1000 test fields. Most of the investigated talus cones are characterized by moderate rockfall supply, with the apex being more active than the talus foot and moderate redistribution by avalanche and debris flows. Considerably enhanced activity was found under rockwalls influenced by permafrost, particularly on the north faces at an elevation of >2600 m a.s.l. At currently moderately active sites, boulder falls seem to have been slightly more frequent in the late nineteenth and first half of the twentieth century. In positions where permafrost is expected in the rockwalls, a weak maximum in the late nineteenth century and highly active present‐day conditions were found, the latter being assigned to current permafrost melt. Rockwall retreat rates derived from lichen coverage are between 400 and 1500 mm/ka which is in good concurrence with talus volume assessments, but higher than the rates derived from direct rockfall measurements. The rates derived from lichen coverage have to be taken with caution as the effects of debris redistribution are hard to quantify.     

VASCULAR PLANTS OF MOUNTAIN TALUS SLOPES,MT. RAE AREA,ALBERTA, CANADA

The vascular flora of talus slopes in the Mt. Rae area, Canadian Rocky Mountain Front Ranges, is discussed in the context of edaphic and geomorphic conditions. Thirteen talus slopes were sampled systematically for the presence of vegetation, and vascular plants were identified to the species level. Such talus slopes are generally considered relatively sterile and too unstable for the development of distinctive flora. The presence of vegetation is usually taken as an indicator of slope stability. A total of 77 species with boreal and arctic affinities was identified. Most plants display growth forms suitable to the unstable and xeric talus substrate with Schroeter's Schuttstrecker and Schuttdecker forms being most common. Although areal coverage by plants is sparse, a large number of species with morphological characteristics suitable for the talus environment suggests that the presence of plants should not be regarded as an absolute indicator of slope stability. Rather, these plants may represent a long-term equilibrium assemblage characteristic of active talus slopes in a mountain environment.     

Revisiting William Morris Davis and Walther Penck to Propose a General Model of Slope ‘Evolution’ in Deserts

Based on research from slopes on rhyolite domes of known age formed over a million‐year continuum in eastern California, a classic geomorphic debate is reconsidered and a general model of desert slope development proposed. This study examines steep (～25° to ～35°) boulder‐dominated slopes that include well, varnished, vertically oriented colluvial deposits. Such deposits are common throughout the arid southwestern United States. Basic field and isotopic dating methods are combined with two surface‐dating techniques, cosmogenic chlorine‐36 and rock varnish microlaminae, to produce a detailed slope development history with broad implications for geomorphic theory that includes the unresolved geomorphic debate between Walther Penck and William Morris Davis. Slopes in this study are dominated by the on‐going desert slope processes of debris flows and in‐situ grain disintegration as evidenced by active debris flow features, terminal Pleistocene ages of microlaminae, and chlorine‐36 ages progressively younger than potassium‐argon ages for slope genesis. Results also indicate that slopes retreat in a parallel fashion as postulated by Penck. Furthermore, the deposits do not exhibit significant changes in grain size, shape, or angularity from genesis to ～0.6 Ma but change markedly after that time possibly indicating a geomorphic threshold between ～0.6 and ～1 Ma, or episodic erosional events throughout the mid to late Pleistocene.     

IMPACTS OF DIFFERENT TYPES OF LAND USE ON PROCESSES OF SOIL AND WATER LOSS OVER PURPLE SOIL SLOPELAND

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横断山脉的地形气候利用与橡胶树北移

横断山南端是我国成功种植橡胶树的地区,其生产性植胶北界可达北纬24°,海拔高度可达1000米左右,因而成为世界高纬度、高海拔植胶地区。本文即以此为例,探讨地形气候利用与橡胶树北移的关系。     

The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia

The role of post-Little Ice Age (LIA) Neoglacial retreat on landslide activity is investigated in 19 alpine basins along the upper Lillooet River Valley, British Columbia. We examine how Neoglacial scouring and glacial recession have modified hillslope form and slope stability, and construct a decision-making flowchart to identify landslide hazards associated with glacial retreat. This work is based on field mapping, GIS analysis, statistical associations between landslides and terrain attributes, and a comparison between Neoglaciated and non-Neoglaciated terrain within each basin.The bedrock landslide response to glacial retreat varies appreciably according to lithology and the extent of glacial scour below the LIA trimline. Valleys carved in weak Quaternary volcanics show significant erosional oversteepening and contain deep-seated slope movement features, active rock fall, rock slides, and rock avalanches near glacial trimlines. Basins in stronger granitic rock rarely show increased bedrock instability resulting from post-LIA retreat, except for shallow-seated rock slides along some trimlines and failures on previously unstable slopes. In surficial materials, landslides associated with post-LIA retreat originate in till or colluvium, as debris slides or debris avalanches, and are concentrated along lateral moraines or glacial trimlines.Significant spatial association was also observed between recent catastrophic failures, gravitational slope deformation, and slopes that were oversteepened then debuttressed by glacial erosion. Eight out of nine catastrophic rock slope failures occurred just above glacial trimlines and all occurred in areas with a previous history of deep-seated gravitational slope movement, implying that this type of deformation is a precursor to catastrophic detachment.     

不同坡角公路路基流场的风洞实验

根据内蒙古S315一级公路黑风口路段风沙危害现状,基于风洞模拟实验,采用毕托管测定不同坡角路基模型断面的风速,通过对流场分布、风速廓线及风速减弱率的分析探讨沙漠公路风沙危害的形成机理。结果表明：坡角对路基两侧的积沙范围和风蚀强度有重要影响。风速一定时,坡角越大,路基两侧积沙范围越大,与之对应的防护范围也应加大。路基坡角一定时,路基背风侧积沙范围随风速增大整体可能呈扩大趋势,坡角越大,扩大趋势越不明显,导致大量沙粒堆积在背风坡脚附近,这就需在坡角较大的公路背风侧多设置几道阻沙栅栏和固沙方格来降低风速、防治沙害。风沙流对迎风坡脚和迎风坡肩的风蚀作用最强,在实际应用中,应重点对这两个部位进行工程砌护,以防路基塌陷造成交通事故威胁公路安全运营。     

Tree-ring evidence linking late twentieth century changes in precipitation to slope instability,central New York state,USA

The Burtonsville landslide in central New York, USA, is a kilometer-scale rotational block failure in glacial till that was likely initiated by incision of the adjacent Schoharie Creek. Although the timing of initial failure is unknown, relatively fresh scarps and tilted surfaces suggest that movement is post-glacial and active. The river currently erodes the toe slope and it removed significant material during flooding associated with Hurricane Irene (August 2011). We retrieved tree cores from 111 trees across the landslide to reconstruct modern movement and block tilting as it related to moisture conditions in the region. Our data show that trees across the slide are in sync with respect to the stress response indicated by reaction wood. The magnitude of response to slope instability, as inferred from eccentric growth, has varied considerably across the site. We hypothesize that macropore development during the driest periods, and the differential rate at which water has reached subsurface failure planes, has caused the observed slope instability. The combination of a wetter precipitation regime and slope instability leads to higher sediment loads in the adjacent stream and serves as a useful analogy for similar watersheds in the region.     

Erosion of strip-mine spoil in Iowa and its implications for erosion models

Spoil banks of abandoned strip mines in southern Iowa are composed of crushed shale and are sufficiently acid and steep to preclude the establishment of vegetation over decades. Rates of sheetwash erosion were studied for different slope components by using erosion pin arrays over a three year period. Small watersheds lacking gully development were monitored simultaneously with sediment traps and additional erosion pin arrays. The frequenct of small landslides was estimated throughout the mine and one landslide was captured in a sediment trap, permitting some quantification of this component of erosion. Slopes affected by landslides erode at a rate about four times greater than areas not affected by landslides and sediment from landslides contributes approximately 11% of the total material delivered to interbank basins (excluding sediment from gully erosion which was not quantified in this study).Rates of sheetwash erosion are rapid, with denudation proceeding at 1.5–2.8 cm yr⁻¹. However, the slope angle has little influence on rates of erosion and we evaluate the difficulties in applying predictive models, such as the USLE, to these conditions. The slopes appear to be undergoing parallel retreat at their angle of repose (about 33°).     

黄土丘陵沟壑区典型小流域土地持续利用案例研究

本文选择我国水土流失最为严重的黄土丘陵沟壑区作为研究地区,通过野外调查、土地利用填图,结合区域国民经济发展规划提出了4种基本土地利用规划方案附加2种保护性耕作措施;开展了生态适宜性、经济可行性和社会可接受性评价。提出:在得到大量外部经济支持的前提下,应积极实行15°以上的坡耕地全部退耕还林还草的方案,其中在中等坡度的地区(15°-25°)应发展果园和经济林;若缺少外部强有力的经济支持,该区土地利用调整应逐步开展,短期内(约0-5年),建议坡度大于25°的坡耕地逐步退耕还林还草,其中,坡度大于25°,地形条件较好的地区应种植果园和经济林;中期(约5-10年),坡度大于20°的黄土地区应逐步退耕还林还草,其中坡度介于20°-25°之间的地区应转变为果园和经济林;10年之后,建议大于15°的坡耕地全部转变为其他用途,其中坡度介于15°-25°的黄土地区应转变为果园和经济林,坡度大于25°的地区转变为林地/灌丛和草地     

三峡水库淹没区农业人口安置问题的几点意见

长江三峡淹没区农业人口就近安置的设想,梯田建设,进一步探索解决问题的途径,试验研究的序幕等几个方面提出了自己的看法们应注意的问题。     

Nature and Dynamics of an Active Block Stream, Kunlun Pass, Qinghai Province, People's Republic of China

Active block streams are common on the slopes of mountains on the northern, drier portion of the Qinghai-Xizang (Tibetan) Plateau. Between 1990 and 1995, the authors studied a block stream northeast of the crest of the Kunlun Pass at latitude 35°50’N, longitude 94°05’ E. It occurs on a 31° slope facing southwest at 4800 m altitude and consists of a 15 cm layer of blocks moving downslope over a sandy loam of lacustrine origin. The blocks are derived from both frost shattering of exposed bedrock and by ejection of blocks from the till capping the hill. No water flows in the block stream and its surface is level with the surrounding slope. Mean annual air temperature is –6°C and mean annual precipitation is about 320 mm. The few plants growing between the blocks exhibit elongated stems and/or roots, indicating movement of the upper layers of blocks relative to the underlying materials. Average mean annual downslope movement of the surface blocks ranges up to 95 cm but varies both across the block stream and also along its long axis. The blocks are gradually extending further downslope. Comparison of movement of lines painted on stones in summer and winter shows that most of the movement occurs in winter. The stones usually rotate randomly as they move, probably by sliding on ice. There is no obvious sorting or rounding of the blocks during movement downslope. The deposits produced differ from talus/scree sediments as they have a dip of less than the maximum angle of rest of dry sediment (c. 33°) and also show no sorting downslope. The movement of material takes place predominantly in winter, rather than in summer and the deposits occur in areas of negligible snow cover. Ground temperatures suggest exceptionally rapid temperature changes under the blocks, indicating air exchange in the voids. Mean ground temperatures in the loams beneath the blocks are about 7°C colder than in the adjacent soils. Winter snow covers are noticeably absent, and summer precipitation is often in the form of snow, which soon melts. Permafrost is present beneath the block stream but is absent in the sandy loam soils. The ground is also moister beneath the blocks. It appears that the surface blocks tend to slide downslope on the icy surface of the underlying blocks, perhaps aided by water from melting snow. This and the lack of sorting by clast size clearly differentiates them from talus slopes or avalanche deposits.     

Conceptual model of sediment processes in the upper Yuba River watershed, Sierra Nevada, CA

This study examines the development of a conceptual model of sediment processes in the upper Yuba River watershed; and we hypothesize how components of the conceptual model may be spatially distributed using a geographical information system (GIS). The conceptual model illustrates key processes controlling sediment dynamics in the upper Yuba River watershed and was tested and revised using field measurements, aerial photography, and low elevation videography. Field reconnaissance included mass wasting and channel storage inventories, assessment of annual channel change in upland tributaries, and evaluation of the relative importance of sediment sources and transport processes. Hillslope erosion rates throughout the study area are relatively low when compared to more rapidly eroding landscapes such as the Pacific Northwest and notable hillslope sediment sources include highly erodible andesitic mudflows, serpentinized ultramafics, and unvegetated hydraulic mine pits. Mass wasting dominates surface erosion on the hillslopes; however, erosion of stored channel sediment is the primary contributor to annual sediment yield. We used GIS to spatially distribute the components of the conceptual model and created hillslope erosion potential and channel storage models. The GIS models exemplify the conceptual model in that landscapes with low potential evapotranspiration, sparse vegetation, steep slopes, erodible geology and soils, and high road densities display the greatest hillslope erosion potential and channel storage increases with increasing stream order. In-channel storage in upland tributaries impacted by hydraulic mining is an exception. Reworking of stored hydraulic mining sediment in low-order tributaries continues to elevate upper Yuba River sediment yields. Finally, we propose that spatially distributing the components of a conceptual model in a GIS framework provides a guide for developing more detailed sediment budgets or numerical models making it an inexpensive way to develop a roadmap for understanding sediment dynamics at a watershed scale.