Evaluating and comparing methods of sinkhole susceptibility mapping in the Ebro Valley evaporite karst (NE Spain)

Multiple sinkhole susceptibility models have been generated in three study areas of the Ebro Valley evaporite karst (NE Spain) applying different methods (nearest neighbour distance, sinkhole density, heuristic scoring system and probabilistic analysis) for each sinkhole type separately (cover collapse sinkholes, cover and bedrock collapse sinkholes and cover and bedrock sagging sinkholes). The quantitative and independent evaluation of the predictive capability of the models reveals that: (1) The most reliable susceptibility models are those derived from the nearest neighbour distance and sinkhole density. These models can be generated in a simple and rapid way from detailed geomorphological maps. (2) The reliability of the nearest neighbour distance and density models is conditioned by the degree of clustering of the sinkholes. Consequently, the karst areas in which sinkholes show a higher clustering are a priori more favourable for predicting new occurrences. (3) The predictive capability of the best models obtained in this research is significantly higher (12.5–82.5%) than that of the heuristic sinkhole susceptibility model incorporated into the General Urban Plan for the municipality of Zaragoza. Although the probabilistic approach provides lower quality results than the methods based on sinkhole proximity and density, it helps to identify the most significant factors and select the most effective mitigation strategies and may be applied to model susceptibility in different future scenarios.     

Geomorphology of coal seam fires

Coal fires occur in underground natural coal seams, in exposed surface seams, and in coal storage or waste piles. The fires ignite through spontaneous combustion or natural or anthropogenic causes. They are reported from China, India, USA, South Africa, Australia, and Russia, as well as many other countries. Coal fires lead to loss of a valuable resource (coal), the emission of greenhouse-relevant and toxic gases, and vegetation deterioration. A dangerous aspect of the fires is the threat to local mines, industries, and settlements through the volume loss underground. Surface collapse in coal fire areas is common. Thus, coal fires are significantly affecting the evolution of the landscape. Based on more than a decade of experience with in situ mapping of coal fire areas worldwide, a general classification system for coal fires is presented. Furthermore, coal seam fire geomorphology is explained in detail. The major landforms associated with, and induced by, these fires are presented. The landforms include manifestations resulting from bedrock surface fracturing, such as fissures, cracks, funnels, vents, and sponges. Further manifestations resulting from surface bedrock subsidence include sinkholes, trenches, depressions, partial surface subsidence, large surface subsidence, and slides. Additional geomorphologic coal fire manifestations include exposed ash layers, pyrometamorphic rocks, and fumarolic minerals. The origin, evolution, and possible future development of these features are explained, and examples from in situ surveys, as well as from high-resolution satellite data analyses, are presented. The geomorphology of coal fires has not been presented in a systematic manner. Knowledge of coal fire geomorphology enables the detection of underground coal fires based on distinct surface manifestations. Furthermore, it allows judgments about the safety of coal fire-affected terrain. Additionally, geomorphologic features are indicators of the burning stage of fires. Finally, coal fire geomorphology helps to explain landscape features whose occurrence would otherwise not be understood. Although coal fire-induced thermal anomalies and gas release are also indications of coal fire activity, as addressed by many investigators, no assessment is complete without sound geomorphologic mapping of the fire-induced geomorphologic features.     

Sinkholes (Dolines) in lateritised sediments, western Sturt plateau, Northern Territory, Australia

Sinkholes up to 50 m diameter and 15 m deep are developed in the lateritised Mullaman (Lower Cretaceous) quartzitic and argillaceous beds of the western Sturt Plateau, in the monsoonal north of the Northern Territory, Australia. Some sinkholes are degraded and of some antiquity: though their age is not precisely known, they formed during the late Cenozoic following the uplift and desiccation of the latertte. Others are fresh and a few have formed in living memory. Some sinkholes may be due to collapse of the Mullaman beds into voids in the underlying Cambrian limestone, but most have evolved wholly within the highly siliceous Mullaman beds, which have been dissolved or altered, creating either voids or compartments filled with uncosolidated material. Subsequent water-table lowering and collapse of the overlying beds into the low-density zones caused the formation of sinkholes.Fractures have significantly influenced the location, pattern and detailed plan shape of sinkholes. Sinkholes also occur within and at the margins of old drainage lines. The water table stood higher in the late Pleistocene, bringing alkaline groundwaters into contact with the country rock. A late Cenozoic fall in regional water table caused slacking or disaggregation. Litter derived from a Eucalyptus-dominated woodland facilitated iron mobilisation. Biogenic agents may have accelerated the weathering of the silica, silicates and iron oxides of which the country rock and laterite are largely composed.     

Rainfall-driven Episodic Flood Events: are they a major factor in moulding New South Wales arid land vegetation patterns?

Episodic high rainfall has been proposed as an important factor in perennial species recruitment but flooding based on rainfall at a distance from the site has received little attention. Although such flood events in arid Australia are rare, studies of the ephemeral Olary Creek indicate that occasional floods can also have a high impact on the vegetation and landscape. During February 1997, a high-rainfall event caused flooding in the Olary Creek. One branch of the creek created a terminal lake within mallee vegetation on Nagaela Station in far-western New South Wales. The flood path of Olary Creek and this terminal lake allow study of the importance of rainfall-driven flood events in shaping vegetation in arid environments. This paper reports (i) the response of arid land plant species to high-rainfall-driven episodic flood events and (ii) how grazing pressure from native and introduced herbivores can impact on native species response.

A systematic study was conducted to understand the botanical composition in flooded and control areas based on 25 m² fenced and unfenced plots subjected to flooding and non-flooding. For 6 years following flooding, species richness in the flooded area was twice that of unflooded areas. In particular, 27 native species from 13 families were recorded both in the enclosed and open plots located in the flooded area. Over the study period nine species: Brachyscome ciliaris, Helichrysum leucopsidium, Vittadinia cuneata, Casuarina pauper, Maireana sedifolia, Salsola kali, Sclerolaena obliquicuspis, Eremophila sturtii and Eucalyptus foecunda germinated only in the flooded enclosed plots. Further, 11 exotic species from five families were recorded in the flooded (both enclosed and open) plots over the study period. Knowledge gained from this study will contribute to management strategies for arid land vegetation.     

广州夏茅村岩溶塌陷灾害特征及防治对策

通过对广州夏茅村岩溶塌陷进行地质勘察,系统探讨了当地的地质环境条件、岩溶塌陷的灾害特征、岩溶发育条件和岩溶塌陷的形成原因。结果表明,区内第四系覆盖土层厚度大且分布不均,土洞大量发育,隐伏可溶岩的富水性好,溶洞发育;同时,覆盖层内的松散岩类孔隙水与下伏灰岩裂隙溶洞水之间的水力联系密切,含水砂层内地下水位的改变会直接引起下伏灰岩裂隙溶洞水的水位波动,构成岩溶塌陷的水动力因素;钻孔桩施工时钻孔揭穿覆盖层内土洞顶部的黏性土层盖板,造成盖板上部的细砂及淤泥流入土洞,是岩溶塌陷的直接触发因素。在此基础上,提出建立岩溶分布区的地下水动态长期监测网,对岩溶塌陷地段进行灌浆处理,是根治夏茅村岩溶塌陷的主要有效途径。     

Modeling spatiotemporal patterns of building vulnerability and content evacuations before a riverine flood disaster

In this paper, a spatiotemporal framework is developed for identifying building vulnerabilities and content evacuations during riverine flooding events. This work investigates the spatiotemporal properties required to trigger building contents evacuations in the floodplain during a flood event. The spatial properties for building risks are based on topography, flood inundation, building location, building elevation, and road access to determine five categories of vulnerability, vulnerable basement, flooded basement, vulnerable first-floor, flooded first-floor, and road access. Using this framework, a model designed to track the spatiotemporal patterns of building evacuations is presented. The model is based upon real-time flood forecast predictions that are linked with building properties to create a model that captures the spatiotemporal ordering of building vulnerabilities and building content evacuations. Applicable to different communities at risk from flooding, the evacuation model is applied to a historical flood for a university campus, demonstrating how the defined elements are used to derive a pattern of vulnerability and evacuation for a campus threatened by severe flooding.     

暴雨内涝情景下城市消防服务可达性的精细化评估

为了揭示城市暴雨内涝灾害对应急响应服务功能的影响,论文基于高精度城市洪涝模型(FloodMap)和增强型两步移动搜寻法(E2SFCA),对暴雨内涝灾害影响下上海市中心城区消防服务可达性进行精细化评估。研究结果表明：① 百年一遇暴雨内涝情景下,内涝最严重时积水深度超过50 cm的淹没范围整体呈现“西高东低”分布态势,淹没总面积约1.5 km²,可导致471条路段(约占路网全长5.11%)通行受阻。② 上海市中心城区消防服务可达性的空间差异比较显著,大体呈现出由黄浦江两岸向西北和东南方向递减态势,但在一天中的不同时段,可达性空间格局变化并不明显。③ 与正常天气条件相比,暴雨内涝情景下不可达单元(250 m×250 m)数量显著增多,夜间低峰、早高峰、白天平峰和晚高峰时段分别增加36.32%、35.89%、39.07%和32.01%;从暴雨内涝的过程(全程120 min)上看,在雨峰后半段((30, 45] min)不可达单元数量最多,消防服务可达性的空间差异程度最大。④ 消防服务可达性表现出一定程度的空间集聚特征,其中高值聚集区(“高—高”型)主要位于黄浦江两岸以及浦西边缘地区,低值聚集区(“低—低”型)主要位于西北和西南区域,这2类聚集区呈“团块状”分布,而“高—低”型和“低—高”型集聚均不显著。⑤ 研究区内消防服务可达性与需求的空间失配现象(“低需求—高可达”或“高需求—低可达”)较为明显,而暴雨内涝会加剧空间失配问题。研究结果可为提升城市洪涝灾害管理与应急响应服务的精细化水平提供科学依据。     

Determination of ice thickness, subice topography and ice vol-ume at Glacier No. 1 in Tien Shan, China by ground penetrating radar

We describe a radio-echo sounding (RES) survey for the determination of ice thickness, subglacial topography and ice volume of Glacier No. 1 , in Tien Shan, China, using ground-penetrating radar (GPR). Radar data were collected with 100-MHz antennas that were spaced at 4 m with a step size of 8 m. The images produced from radar survey clearly show the continuity of bedrock echoes and the undulation features of the bedrock surface. Radar results show that the maximum ice thickness of Glacier No. 1 is 133 m, the thickness of the east branch of Glacier No. 1 averages at 58. 77 m while that of the west branch of Glacier No. 1 averages at 44. 84 m. Calculation on ice volume indicates that the ice volume of the east branch of Glacier No. 1 is 51. 87 × 106 m3 and that of the west branch of Glacier No. 1 is 20. 21 × 106 m3. The amplitude of the undulation of the bedrock surface topography revealed by radar profiles is larger than that of the glacier surface topography, indicating that the surface relief does     

A LiDAR-based flood modelling approach for mapping rice cultivation areas in Apalit,Pampanga

Majority of rice cultivation areas in the Philippines are susceptible to excessive flooding owing to intense rainfall events. The study introduces the use of fine scale flood inundation modelling to map cultivation areas in Apalit, a rice-producing municipality located in the province of Pampanga in the Philippines. The study used a LiDAR-based digital elevation model (DEM), river discharge and rainfall data to generate flood inundation maps using LISFLOOD-FP. By applying spatial analysis, rice cultivation zone maps were derived and four cultivation zones are proposed. In areas where both depth and duration exceed threshold values set in this study, varieties tolerant to stagnant flooding and submergence are highly recommended in Zone 1, where flood conditions are least favorable for any existing traditional lowland irrigation varieties. The study emphasizes that a decline in yield is likely as increasing flood extents and longer submergence periods may cause cultivation areas for traditional irrigated lowland varieties to decrease over time. This decrease in yield may be prevented by using varieties most suitable to the flooding conditions as prescribed in the rice zone classification. The method introduced in this study could facilitate appropriate rice cultivation in flood-prone areas.     

Columbia Mountain landslide: late-glacial emplacement and indications of future failure, Northwestern Montana, USA

The well preserved and undissected Columbia Mountain landslide, which is undergoing suburban development, was studied to estimate the timing and processes of emplacement. The landslide moved westward from a bedrock interfluve of the northern Swan Range in Montana, USA onto the deglaciated floor of the Flathead Valley. The landslide covers an area of about 2 km², has a toe-to-crown height of 1100 m, a total length of 3430 m, a thickness of between 3 and 75 m, and an approximate volume of 40 million m³. Deposits and landforms define three portions of the landslide; from the toe to the head they are: (i) clast-rich diamictons made up of gravel-sized angular rock fragments with arcuate transverse ridges at the surface; (ii) silty and sandy deposits resting on diamictons in an internally drained depression behind the ridges; and (iii) diamictons containing angular and subangular pebble-to block-sized clasts (some of which are glacially striated) in an area of lumpy topography between the depression and the head of the landslide. Drilling data suggest the diamictons cover block-to-slab-sized bedrock clasts that resulted from an initial stage of the failure.The landslide moved along a surface that developed at a high angle to the NE-dipping, thinly bedded metasediments of the Proterozoic Belt Supergroup. The exposed slope of the main scarp dips 30–37°W. A hypothetical initial rotational failure of the lower part of a bedrock interfluve may have transported bedrock clasts into the valley. The morphology and deposits at the surface of the landslide indicate deposition by a rock avalanche (sturzstrom) derived from a second stage of failure along the upper part of the scarp.The toe of the Columbia Mountain landslide is convex-west in planview, except where it was deflected around areas now occupied by glacial kettles on the north and south margins. Landsliding, therefore, occurred during deglaciation of the valley while ice still filled the present-day kettles. Available chronostratigraphy suggests that the ˜1-km thick glacier in the region melted before 12,000 ¹⁴C years BP—within 3000 years of the last glacial maximum. Deglaciation and hillslope failure are likely causally linked. Failure of the faceted interfluve was likely due tensile fracturing of bedrock along a bedding-normal joint set shortly after glacial retreat from the hillslope.Open surficial tension fractures and grabens in the Swan Range are limited to an area above the crown of the landslide. Movement across these features suggests that extensional flow of bedrock (sackung) is occurring in what remains of the ridge that failed in the Columbia Mountain landslide. The fractures and grabens likely were initiated during failure, but their morphologies suggest active extension across some grabens. Continued movement of bedrock above the crown may result in future mass movements from above the previous landslide scarp. Landslides sourced from bedrock above the scarp of the late-glacial Columbia Mountain landslide, which could potentially be triggered by earthquakes, are geologic hazards in the region.     

A groundwater vortex hypothesis for mima-like mounds, Laramie Basin, Wyoming

Mima-like mounds in the Laramie Basin occur where: (1) impervious bedrock (shale) is at a shallow depth (∼ 2–5 m); (2) bedrock is overlain by a thin veneer (∼ 1–4 m) of alluvial gravels; and (3) a strong argillic/calcic or petrocalcic soil caps the landform, typically a terrace. Active and inactive mounds contain churned materials, including pebbles derived from adjacent/subjacent units. The mounds are circular in plan view and lens- or funnel-shaped in cross-section. The strong intermound (premound) soil collapses beneath the mound, is entirely or partly destroyed at its base, or is truncated at the mound edge. Stratigraphic relationships on the youngest terrace of the Laramie River indicate that the inactive mounds are Holocene in age.Sodium concentrations (used as a tracer) in mound material and adjacent/subjacent units suggest that the mounds rotate counterclockwise. This movement may be driven by free spiral vortices (low hydraulic head) in confined (artesian) groundwater flow in alluvium between shallow bedrock and strong surface soil. The vortices (similar to water draining from a bathtub or a whirlpool in a river) may result from enlargements, constrictions, or changes in permeability of the aquifer — or meandering of groundwater flow. Groundwater, dissolved ions, and materials in suspension, or through friction and turbidity, then would move from adjacent high-hydraulic head areas into and down the vortex. In effect, the high head (intermound) areas would act as a pump whereas the vortex (which would form a mound) would act as a turbine — responding, therefore, to energy transformations between groundwater velocity and pressure according to the Bernoulli principle and Newton's Second Law of Motion. Soil or sediment, incapable of being fully moved into and down the vortex, would amass at the land surface as a circular mound that in cross-section would have a lens or funnel (turbine) shape. Computer modelling shows that mounds tend to form over deep bedrock and thick alluvium.The groundwater vortex hypothesis can account for the building of the mound higher at its center, the circular plan view and lens (or funnel) shape in cross-section, the inward spiral of sodium, the churned character of mound material, and the collapse (or truncation) of soils and other units beneath and along mound edges. The hypothesis, however, must not be applied to all other Mima or mima-like mounds, unless vortex motion can be determined and if stratigraphic similarities can be demonstrated.     

Accounting for variability in commercial flood damage estimation

Flooding in the business district of Kempsey, New South Wales, Australia, in 2001 allowed the collection and analysis of commercial flood damage data. Analysis indicated that direct losses were significant, totalling A$2.5 million. Data were variable owing to differences in the vulnerability of businesses to flood damage, differences in the impacts of the hazard upon businesses and survey uncertainty. Little direct relationship was found between direct commercial damage and over-floor water depth. Simple averaging and stage-damage curve loss estimation methods ignore the large variability present and result in inaccurate estimation of direct commercial damage. Probability loss estimation methods account for the variability present by assessing the chance of loss values occurring at specified depths of over-floor flooding.     

Age and hydrological significance of lichen limits on sandstone river channels near Sydney,Australia

Trimmed lichen communities (lichen limits) are abrupt changes from a lichen community to a scoured bare rock surface and have been used to determine bankfull channel capacity on bedrock channels and their response to the combined disturbances of flow regulation and climate change. They can also be used to set flushing flows in bedrock channels. In sandstone gorges of the Nepean River, Australia, the crustose lichen, Lecidea terrena Nyl, was common at both gorge and cemetery (sandstone headstones) sites, enabling construction of growth curves for above and below dam areas. Growth curves were used to date lichen colonisation of sandstone surfaces in rivers. The oldest, highest lichen limit at all sites represented the pre‐flow regulation lichen community because its characteristics above and below Nepean Dam were similar and were trimmed to a level that produced consistent discharges across a range of catchment areas. They corresponded to return periods of less than 2 years on the annual maximum series and was developed during the flood‐dominated regime (FDR) of 1857–1900. Lichen limits form by the phycobiont dominating the mycobiont and hence degrading lichen thalli due to water inundation causing weak or dead thalli to be scrubbed from the rock surface. Trimming to the unregulated lichen limit represents a small flood of frequent occurrence appropriate for flushing bedrock channels. A lower lichen limit was only found below a diversion weir and was formed by frequent dam spills between 1950 and 1952 during an extraordinary wet period at the start of the FDR between 1949 and 1990. Lichens colonised exposed sandstone between the level of frequent flows from 1949 to 1952, and the high lichen limit. On the Avon River, an additional lower limit reflected a massive downward shift in flow duration following the start of interbasin diversions to Wollongong in 1962.     

辽河三角洲湿地景观的水文调节与防洪功能

以辽河三角洲为对象论述了湿地景观的水文功能,重点研究湿地蓄水容量与苇田蒸发散、湿地水更新率、稻田水量平衡等湿地的水文调节功能及人类活动的影响;探讨了湿地水文调节功能的价值估算,三角洲地下含水层的调洪功能;并根据辽河三角洲湿地的景观生态特征和在防洪中的功能,将湿地景观划分出5个功能区,为制定合理的景观规划,为促进三角洲地区的可持续发展服务。     

天山1号冰川厚度和冰下地形探测与冰储量分析

通过对天山乌鲁木齐河源 1号冰川的雷达回波探测 ,清晰地揭示出冰川底部冰 /岩界面的位置及其起伏变化特征 ,显示出雷达波对山地冰川良好的穿透能力和对冰下地形的高分辨能力 ,冰川雷达测厚的误差小于 1 .2 %。研究结果显示 ,1号冰川东支冰川平均厚度为 5 8.77m ,西支冰川平均厚度为 44.84m ,冰体厚度最大值发育于冰川中部趋于主流线位置。冰川冰储量计算表明 ,东支冰储量为 0 .0 5 1 868km3,西支冰储量为 0 .0 2 0 2 1 0km3。表面和底部地形有明显差异 ,主要因冰川动力过程对基岩强烈的地貌作用所致 ,意味着冰床的起伏地形对冰川浅层冰体的运动过程影响不显著。     

METHOD FOR RECOGNIZING LOCAL BEDROCK INFLUENCE ON DRIFT PLAINS*

Analysis of topographic and bedrock surface data from 41 sites 23.3 km² (9 m²) within Midwestern areas glaciated during the Late Wisconsinan identifies an average drift thickness-maximum bedrock relief transition equation for the presence or absence of bedrock surface influences on topographic detail. For sites with average drift thicknesses between 15 and 35 m, the transition occurs when average drift thicknesses exceed 0.5 maximum bedrock relief + 10 m. This equation may provide a practical tool in searching for buried bedrock valleys.     

A GIS-based method for flooded area calculation and damage evaluation

Using geographic information system to study flooded area and damage evaluation has been a hotspot in environmental disaster research for years. In this paper, a model for flooded area calculation and damage evaluation is presented. Flooding is divided into two types: ‘source flood’ and ‘non-source flood’. The source-flood area calculation is based on seed spread algorithm. The flood damage evaluation is calculated by overlaying the flooded area range with thematic maps and relating the result to other social and economic data. To raise the operational efficiency of the model, a skipping approach is used to speed seed spread algorithm and all thematic maps are converted to raster format before overlay analysis. The accuracy of flooded area calculation and damage evaluation is mainly dependent upon the resolution and precision of the digital elevation model (DEM) data, upon the accuracy of registering all raster layers, and upon the quality of economic information. This model has been successfully used in the Zhejiang Province Comprehensive Water Management Information System developed by the authors. The applications show that this model is especially useful for most counties of China and other developing countries.     

粤西河流阶地的分布与特征

依据广东西部超过18条河流、39处河流阶地、至少35个14C、热释光的冲积层测龄数据等情况,可知粤西最多有4级河流阶地(不包括湛江组和北海组阶地);多数河流最高阶地靠近现代主河床分布,深切曲流中有河流阶地,反映近数十万年来河床改道不大;西江在封开有广东高度最高(76 m)的河流阶地,而广东高度最高的地下河阶地是111 m,大致显示出地面与地下剥蚀强度的差异;通常山区河流长度越大,河漫滩和河流阶地的高度越大,河流阶地的级数和级别也常增加;在河流上游的下段和中游的上段,河流阶地的高度最大且级数也最多;在晚更新世之前与后,河谷中下游地区的新构造运动趋势由上升变为稳定或沉降;连滩盆地是广东全新世构造沉降最典型的山间盆地。     

A GIS-based method for flooded area calculation and damage evaluation

1 IntroductionFlooding simulation and damage evaluation has attracted attention in environmental disaster research fields for many years. Since the 1990s, especially in recent years, using geographic information systems (GIS) technology and its powerful functions of spatial analysis and visualization to simulate and display flooded area and to evaluate disaster damage has become a research hotspot. Most of the papers involved in this field are from hydraulic and hydrologic point of view and b…     

Karst and karstification in gypsiferous beds in Mathiesondalen, Central Spitsbergen, Svalbard

Recent karst forms in gypsiferous beds are reported from Mathiesondalen in Central Spitsbergen, where several sinkholes (dolines) and swallow holes have been formed after the deposition of Holocene raised beach sediments. The bedrock of the area is mostly interbedded gypsum/anhydrite and dolomites of the Carboniferous Ebbadalen Formation.