Use of fused airborne scanning laser altimetry and digital map data for urban flood modelling

Flood modelling of urban areas is still at an early stage, partly because until recently topographic data of sufficiently high resolution and accuracy have been lacking in urban areas. However, digital surface models (DSMs) generated from airborne scanning laser altimetry (LiDAR) having sub‐metre spatial resolution have now become available, and these are able to represent the complexities of urban topography. This paper describes the development of a LiDAR post‐processor for urban flood modelling based on the fusion of LiDAR and digital map data. The map data are used in conjunction with LiDAR data to identify different object types in urban areas, though pattern recognition techniques are also employed. Post‐processing produces a digital terrain model (DTM) for use as model bathymetry, and also a friction parameter map for use in estimating spatially distributed friction coefficients. In vegetated areas, friction is estimated from LiDAR‐derived vegetation height, and (unlike most vegetation removal software) the method copes with short vegetation less than ～1 m high, which may occupy a substantial fraction of even an urban floodplain. The DTM and friction parameter map may also be used to help to generate an unstructured mesh of a vegetated urban floodplain for use by a two‐dimensional finite element model. The mesh is decomposed to reflect floodplain features having different frictional properties to their surroundings, including urban features (such as buildings and roads) and taller vegetation features (such as trees and hedges). This allows a more accurate estimation of local friction. The method produces a substantial node density due to the small dimensions of many urban features. Copyright © 2007 John Wiley & Sons, Ltd.     

Evaluating the effect of scale in flood inundation modelling in urban environments

Cellular‐based approaches for flood inundation modelling have been extensively calibrated and evaluated for the prediction of flood flows on rural river reaches. However, there has only been limited application of these approaches to urban environments, where the need for flood management is greatest. Practical application of two‐dimensional (2D) flood inundation models is often limited by computation time and processing power on standard desktop PCs when attempting to resolve flows on the high‐resolution grids necessary to replicate urban features. Consequently, it is necessary to evaluate the effectiveness of coarse grids to represent flood flows through urban environments. To examine these effects, LISFLOOD‐FP, a 2D storage cell model, is applied to hypothetical flooding scenarios in Greenfields, Glasgow. Grid resampling techniques in GIS software packages are evaluated and a bilinear gridding technique appears to provide the most accurate and physically intuitive results. A gridding method maintaining sharp elevation changes at building interfaces and neighbouring land is presented and estimates of the discretization noise associated with the coarse resolution grids suggest little improvement over current gridding methods. The variation in model results from the friction sensitivity analysis suggests a non‐stationary response to Manning's n with changing model resolution. Model results suggests that a coarse resolution model for urban applications is limited by the representation of urban media in coarse model grids. Furthermore, critical length scales related to building dimensions and building separation distances exist in urban areas that determine maximum possible grid resolutions for hydraulic models of urban flooding. Copyright ©, 2008 John Wiley & Sons, Ltd.     

Microstructures of phosphatic porcelain from sintering to vitrification: Evidence from sherds excavated in Charleston,South Carolina

Eight phosphatic porcelain sherds recovered from various historical sites in Charleston were analyzed by electron microprobe. Some sherds contain sulfur (2.3–3.1wt.% SO₃); others contain only traces of this component. The analytical data suggest that the sulfurous sherds are Bow porcelain (London, Bowcock period, ca. 1755–1769). The origin(s) of the low‐S samples remains unidentified; one compositionally resembles “gold‐anchor period” (phosphatic) Chelsea porcelain (London, ca. 1756–1769) but its decoration is inconsistent with known wares produced by this factory during that era. The degree of vitrification is highly variable, particularly among the SO₃‐poor samples. The melt phase is strongly enriched in incompatible elements (Ti, Fe, Na, K). The phosphate phase [calcined bone ash (hydroxyapatite)] in poorly vitrified samples hosts minute melt blebs, but remains porous. With increasing vitrification, these melt blebs increase in size and begin to coalesce, ultimately forming ameboid patches up to ∼10 μm in diameter. In the most vitrified samples, the coalesced melt “leaks” into the matrix, leaving behind a phosphate phase that lacks pores and melt and has a lower CaO/P₂O₅ ratio (=2.7, molecular proportions) than either hydroxyapatite (3.3) or β‐whitlockite (3.0). The two varieties of phosphate occur in some poorly vitrified samples, suggesting the recycling of high‐fired wasters (as “grog”) in their ceramic pastes. Melt compositions vary with contiguous mineralogy, accounting for their divergence from the ternary eutectic in the Ca₃(PO₄)₂‐CaAl₂Si₂O₈‐SiO₂ system. The resorption of phosphate by the matrix melt virtually precludes recognition of anorthite formed by the “non‐phosphate glass equation.” © 2011 Wiley Periodicals, Inc.     

Responding to the consequences of uncertainty in geographical data

The presence of uncertainty in geographical data has the potential to expose users to undesirable consequences in their decision making. Accordingly, our efforts to understand uncertainty seek to (a) avoid the use of data that are not suitable for their intended purpose (that is, data whose consequences are unacceptable), (b) to reduce any undesirable consequences to an acceptable level, and (c) to devise ways of living with undesirable data when the adverse consequences caused by poor data do not alter our ultimate decision choice. To assist this task, we propose an approach where the adverse consequences of uncertainty caused by the use of unsuitable geographical data are expressed in terms of risk. In this paper we first show that risk management offers geographical data users a range of options for responding to the adverse consequences of data uncertainty, and secondly we present and discuss the various risk response options.     

Benthic changes during 10 years of organic enrichment by McMurdo Station, Antarctica

A benthic habitat along the coast of McMurdo Station in the Ross Sea, Antarctica is enriched by sewage from the station and altered by hydrocarbons and heavy metals in an adjacent historic dumpsite. We report on 10 years of change in the benthic communities from 1988 to 1998 and compare enrichment effects at Australia's Casey Station, East Antarctica. Despite being 14 km apart, reference communities upcurrent and downcurrent of McMurdo Station remained closely similar over time, dominated in all years by a tube building polychaete, Spiophanes tcherniae. The community bordering McMurdo Station was generally a third as abundant as communities at the reference sites over the decade of sampling, although diversity was as high or higher, except in the most contaminated areas. In 1992, organic enrichment of the outfall community intensified and within the year, the opportunistic polychaetes Aphelochaeta sp., Ophryotrocha notialis, Capitella perarmata, and Leitoscoloplos kerguelensis became dominant. Since 1996, two of the three enriched communities have increased in resemblance to the reference communities. Given the observed responsiveness of the benthos to the outfall so far, further changes are anticipated within the year following implementation of sewage treatment in 2003. Organic enrichment by McMurdo Station has had a greater impact on benthic community structure than at Australia's Casey Station.     

Ore deposits associated with mafic magmas in the Kaapvaal craton

Mafic and ultramafic magmatism played an important role in the 3.5 Ga long history of the Kaapvaal craton. The oldest (3.5 Ga) greenstone belts contain mafic and ultramafic volcanics that erupted in an oceanic environment, probably in oceanic plateaus. Then followed a series of continental flood basalts, from the ∼3.4 Ga old Commondale and Nondweni sequences, to the 180 Ma Karoo basalts. The history was dominated, however, by the emplacement, 2.1 Ga ago, of the Bushveld complex, an enormous layered ultramafic-mafic-felsic intrusion. Three types of ore deposits might be found in such a sequence: Ni-Cu-Fe sulfides in komatiites of the greenstone belts; “Noril'sk-type” Ni-Cu-PGE deposits in the Karoo and other flood basalts; and deposits of Cr, platinum-group elements (PGE) and V in the Bushveld and other layered intrusions. Only the latter are present. It is tempting to attribute the absence of komatiite-hosted deposits to the specific character of the ultramafic rocks in Kaapvaal greenstone belts, which are older that the 2.7 Ga komatiites that host deposits in Australia, Canada and Zimbabwe, and are of the less-common “Al-depleted” type. However, a review of mantle melting processes found no obvious connection between the character of the mantle melts and their capacity to form ore deposits. The lack of this type of deposit may be due to differences in the volcanic environment, or it may be fortuitous (the Barberton and other belts are small and could fit into deposit-free parts of the much larger Australian or Canadian belts). Still more puzzling is the absence of Noril'sk-type deposits. The Karoo and older flood basalt sequences appear to contain all the important elements of the volcanic sequences that host the Siberian deposits. It is now recognised that these deposits formed through the segregation of sulfide from magma flowing rapidly through conduits en route from deeper magma chambers to the surface. An exploration approach aimed at understanding the fluid dynamics of such systems seems warranted. Although the Bushveld intrusion has been studied for decades and its deposits are taken as type examples of magmatic mineralisation, the origin of its PGE deposits remains unclear. Opinion is divided on the relative importance of sulfide segregation from magma filling a large chamber at the time of emplacement, and the scavanging of PGE from fluids circulating through cumulates at a late magmatic stage. Answers to these questions may come from studies designed to gain a better understanding of the mechanisms through which the magma chamber filled and solidified. Received: 15 September 1996 / Accepted: 7 January 1997