Debris flood risk assessment for Mosquito Creek, British Columbia, Canada

Mosquito Creek drains a 15.5 km² watershed on the North Shore Mountains north of Vancouver, British Columbia, Canada, and flows through the densely urbanized District and then City of North Vancouver. Previous studies determined that the creek is subject to debris floods (hyperconcentrated flows). The National Research Council of Canada is applying multi-hazard risk assessment procedures for various regions in B.C. and chose Mosquito Creek as one of its target areas. As part of its natural hazard management plan, the District of North Vancouver (DNV) requested an assessment of debris flood hazards and associated risk to life. Using a combination of empirical methods, dendrochronology and some judgment, BGC Engineering Inc. assessed debris flood hazard extent, velocity and depth for estimated 100-, 200-, 500- and 2,500-year debris flow return periods. Based on the results from the hazard assessment, risk for individuals and groups living within the hazard area, including residential homes and a fire hall, was estimated. Compared to risk tolerance criteria accepted on an interim basis by the DNV, we estimate that societal risk exceeds tolerable standards and that individual risk exceeds tolerable standards for 10 homes. The results from the risk to loss of life study have prompted DNV to implement a series of risk reduction measures including installation of a debris containment net and watershed restoration measures.     

On the Relationship Between Killing-Yano Tensors and Electromagnetic Fields on Curved Spaces

The existence of skew symmetric Killing-Yano (KY) tensors of order 2 has been investigated on curved spaces. The integrability conditions of KY tensor including Carter's algebraic relation of symmetric tensor with electromagnetic field have been transcribed in Newman-Penrose formalism. The KY bivectors are classified according to their nullity in electrovac space-times. It is shown that the non-null (or null) electromagnetic field implies to the existence of non-null (or null) KY tensor. Thus Collinson's theorems on the existence of KY tensors on vacuum space-times have been generalized on electrovac space-times. Chandrasekhar's theorem on vacuum type D space-times has also been generalized on the existence of non-null KY tensor on electrovac type D or non-vacuum type D space-time filled with dust. All theorems presented here have been strengthened by giving examples for known space-times. It is also shown that most of KY tensors discussed here are eigen-KY-bivectors of the respective curvature tensors.     

A test of independence for stratigraphic sequences with respect to embedded Markov chains

Identification of cyclic sequences gives valuable insight into depositional associations of stratigraphic facies. An embedded Markov chain is a reasonable general model for facies transitions. But a model with independent random occurrences of facies is not an appropriate null hypothesis to be tested to show the presence of cycles because of definitional restriction in transition observations to only those between different facies. This is a common stratigraphic situation and the problem has been raised recently by several authors. We present here a test statistic for null hypothesis derived from the concept of partial independence and inherent to the model of embedded Markov processes.     

Mass Transport in a Thin Layer of Bi-Viscous Mud Under Surface Waves

The mass transport in a thin layer of non-Newtonian bed mud under surface waves is examined with a two-fluid Stokes boundary layer model. The mud is assumed to be a bi-viscous fluid, which tends to resist motion for small-applied stresses, but flows readily when the yield stress is exceeded. Asymptotic expansions suitable for shallow lluid layers are applied, and the second-order solutions for the mass transport induced by surface progressive waves are obtained numeri-cally. It is found that the stronger the non-Newtonian behavior of the mud, the more pronounced intermittency of the flow. Consequently, the mass transport velocity is diminished in magnitude, and can even become negative (i. e. , oppo-site to wave propagation) for a certain range of yield stress.     

Lateglacial vegetation development in Denmark – New evidence based on macrofossils and pollen from Slotseng,a small-scale site in southern Jutland

This paper presents the first unambiguous terrestrial palaeoecological record for the late glacial “Bølling warming” in Denmark. Pollen and macrofossil stratigraphies from pre-Bølling to 10,800 cal yr BP are presented from a small kettle hole in Southwest Denmark, during which the lake basin developed from an immature stage after the deglaciation to complete infilling in the early Holocene. Results show that the recently deglaciated landscape bore a discontinuous vegetation of pioneer plants. After the Bølling warming, an open Dryas octopetala-Betula nana community developed with Helianthemum oelandicum. Subarctic species were dominant and local successions were probably delayed by relatively unstable and infertile soils. There is no indication of a climate cooling during the period corresponding to the Older Dryas, but the occurrence of several drought tolerant and steppe species indicates that the period was relatively dry. In the Allerød period the Dryas-B. nana vegetation was initially replaced by an open Salix and grass dominated vegetation and some 400 years later, the first tree birches were documented presumably occupying moist and sheltered soils while drier land remained open. In the Younger Dryas period trees disappeared and the vegetation became open again and dominated by subarctic species. Following climate warming at the Younger Dryas–Holocene transition a shrub community of Empetrum and Juniperus developed. After approximately 200 years it was replaced by birch forest. Overall, the late-glacial vegetation cover had a more open and patchy character than inferred from previous pollen studies as assessment of the vegetation succession based on macrofossil evidence is essential. The inferred general vegetation development corresponds well with results of other studies in the region. Canonical ordinations (RDA) indicate that vegetation changes at the landscape scale during the Lateglacial period were driven by changes in climate, soils and competition for light.     

Preliminary Studies of Soils in North-East Greenland between 74° and 75° Northern Latitude

Jakobsen, Bjarne Holm: Preliminary Studies of Soils in North- East Greenland between 74° and 75° Northern Latitude. Geografisk Tidsskrift 92:111–115. Copenhagen 1992.

The geography of soils has been studied in north-east Greenland between latitudes 74° and 75° N. The study ranges from the outer coast to the interior of the ice-free land area. Well-drained soils show a characteristic sequence determined by the east-west climatic gradient. Fossil soil characteristics and secondary formed features supply information on the palaeoclimate.     

Commercial hunting activities in the Greenland Sea: The impact of the European blubber industry on East Greenland Inuit societies/Optically Stimulated Luminescence dating of Inuit settlement structures in coastal landscapes of Northeast Greenland

Geografisk Tidsskrift—Danish Journal of Geography 110(2):357–363, 2010

Geografisk Tidsskrift—Danish Journal of Geography 110(2):365–371, 2010     

River flow time series prediction with a range-dependent neural network

Abstract

Artificial neural networks provide a promising alternative to hydrological time series modelling. However, there are still many fundamental problems requiring further analyses, such as structure identification, parameter estimation, generalization, performance improvement, etc. Based on a proposed clustering algorithm for the training pairs, a new neural network, namely the range-dependent neural network (RDNN) has been developed for better accuracy in hydrological time series prediction. The applicability and potentials of the RDNN in daily streamflow and annual reservoir inflow prediction are examined using data from two watersheds in China. Empirical comparisons of the predictive accuracy, in terms of the model efficiency R² and absolute relative errors (ARE), between the RDNN, back-propagation (BP) networks and the threshold auto-regressive (TAR) model are made. The case studies demonstrated that the RDNN network performed significantly better than the BP network, especially for reproducing low-flow events.     

基于多尺度的老采空区上方建筑物变形分析及预报

老采空区上方地表变形是一个具有复杂性、突然性和长期性等显著特点的非线性过程。在老采空区上方建设生活或服务设施时,必须对老采空区上方地基稳定性和残余变形情况进行评价和预测。基于多尺度经验模态分解（EMD）,提出了老采空区上方地表建筑物稳定性分析及预测新方法。通过实例研究,证实采用多尺度经验模态分解可获得老采空区上方地表建筑物的动态变形细部信号。对各分解尺度进行分析能更准确有效地评价原始数据所反映的建筑物变形特征和进行变形机制研究。同时,实例计算也证实,采用考虑多尺度特征的预测模型可获得比传统方法更优的变形预报精度,为更科学地评价老采空区建筑物稳定性提供理论依据。     

半无限平面问题的相对位移

通过Flamant和Melan的解析解答、Mindlin解答的积分蜕化公式以及有限元数值分析计算结果,展示了在半无限平面问题中线荷载作用方向位移解答的不确定性。线荷载作用方向没有绝对位移,只有相对位移,但相对位移会随着与位移约束参考点距离的增大而增大,或随着线荷载在垂直于半平面方向分布长度的增大而增大,不具收敛性。这意味着,在解析和数值分析中,纯粹的半平面问题的位移解答具有多值性,因此,将岩土工程问题作为半空间问题进行分析是必要的。