Flood frequency analysis of southern Africa: II. Identification of regional distributions

Abstract

Regional frequency analysis of annual maximum flood data comprising 407 stations from 11 countries of southern Africa is presented. Forty-one homogeneous regions are identified. The L-moments of the observed data indicate that the possible underlying frequency distributions are Pearson type 3 (P3), lognormal 3-parameter (LN3), General Pareto (GPA) or General Extreme Value (GEV). Simulation experiments for the selection of the most suitable flood frequency procedure indicate that Pearson type 3/Probability Weighted Moments (P3/PWM) and log-Pearson type 3/Method of Moments (LP3/MOM) are suitable procedures for the region.     

Updating the Phase 1 habitat map of Wales, UK, using satellite sensor data

The Phase 1 Survey is the most comprehensive and widely used national level map of semi-natural habitats in Wales. However, the survey was based largely on field survey and was conducted over several decades, before being completed in 1997. Given that resources for a repeat survey were limited, this study has used an object-orientated rule-based classification implemented within eCognition of multi-temporal satellite sensor data acquired between 2003 and 2006 to map semi-natural habitats and agricultural land across Wales, thereby allowing a progressive update of the Phase 1 Survey. The classification of objects to Phase 1 habitat classes was undertaken in two steps; firstly the landscape of Wales was divided into objects using orthorectified SPOT-5 High Resolution Geometric (HRG) reflectance data (10 m spatial resolution) and Land Parcel Information System (LPIS) boundaries. A rule-base was then developed to progressively discriminate and map the distribution of 105 sub-habitats across Wales based on time-series of SPOT HRG, Terra-1 Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Indian Remote Sensing Satellite (IRS) LISS-3 data, derived datasets (e.g., vegetation indices, fractional images) and ancillary information (e.g., topography). The rules coupled knowledge of ecology and the information content of these remote sensing data using a combination of thresholds, Boolean operations and fuzzy membership functions. A second rule-base was then developed to translate the more detailed sub-habitat classification to Phase 1 habitat classes. Indicative accuracies of the revised Phase 1 mapping, based on comparisons with the later Phase 2 survey (for selected habitats), were >80% overall and typically between 70% and 90% for many classes. Through this exercise, Wales has become the first country in Europe to produce a national map of habitats (as opposed to land cover) through object-orientated classification of satellite sensor data. Furthermore, the approach can be adapted to allow continual monitoring of the extent and condition of habitats and agricultural land.     

Rugose corals from the Upper Ordovician Sholeshook Limestone of southwest Wales with an assessment of the coral affinities and biofacies

Limestone horizons of Upper Ordovician (Katian) age in southwest Wales contain diverse fossil faunas including rugose corals. The existence of Ordovician Rugosa in Wales was first reported by Murchison in the 1830s, but since then hardly any specimens have been documented systematically until this present study. Newly collected material from the area around Llanddowror (Carmarthenshire) has now confirmed the diversity of rugose corals in the Sholeshook Limestone (Katian age), an arenaceous limestone originating from the shelf edge of the palaeocontinent Avalonia. The majority of the specimens are preserved as moulds. This means that in many instances preservation of the fossils was insufficient for specific identification; nevertheless, it was possible to document a diverse rugose coral fauna, including Helicelasma, probable Grewingkia and Kenophyllum, and a potential early mucophyllid. While associated with considerable difficulties, as some diagnostic features of Rugosa are not visible in moulds, it is demonstrated here that the work with such specimens can result in faunal information which would otherwise be unobtainable. An assemblage of rugose and tabulate corals in the Sholeshook Limestone can be differentiated from a similar assemblage in the neighbouring Robeston Wathen Limestone which has a slightly different lithology. The fauna has strong similarities with other Avalonian (Irish, English, Belgian) as well as Baltic (Estonian and Norwegian) rugose coral faunas. Copyright © 2012 John Wiley & Sons, Ltd.     

Sequence stratigraphy of the upper Millstone Grit (Yeadonian,Namurian), North Wales

The upper Millstone Grit strata (Yeadonian, Namurian) of North Wales have been studied using sedimentological facies analysis and sequence stratigraphy. These strata comprise two cyclothems, each containing prodelta shales (Holywell Shale) that pass gradationally upwards into delta‐front and delta‐plain deposits (Gwespyr Sandstone Formation). The deltas formed in shallow water (<100 m), were fluvial‐dominated, had elongate and/or sheet geometries and are assigned to highstand systems tracts. Two delta complexes with distinctive sandstone petrographies are identified: (1) a southerly derived, quartzose delta complex sourced locally from the Wales‐Brabant Massif, and (2) a feldspathic delta complex fed by a regional source(s) to the north and/or west. The feldspathic delta complex extended further south in the younger cyclothem. A multistorey braided‐fluvial complex (Aqueduct Grit, c. 25 m thick) is assigned to a lowstand systems tract, and occupies an incised valley that was eroded into the highstand feldspathic delta complex in the younger cyclothem. A candidate incised valley cut into the highstand feldspathic delta complex in the older cyclothem is also tentatively identified. Transgressive systems tracts are thin (<5 m) and contain condensed fossiliferous shales (marine bands). The high‐resolution sequence stratigraphic framework interpreted for North Wales can be readily traced northwards into the Central Province Basin (‘Pennine Basin’), supporting the notion that high‐frequency, high‐magnitude sea‐level changes were the dominant control on stratigraphic architecture. Copyright © 2007 John Wiley & Sons, Ltd.     

Ordovician Intrusive-related Gold-Copper Mineralization in West-Central New South Wales, Australia

Three major types of Ordovician intrusive-related gold-copper deposits are recognized in central-west New South Wales, Australia: porphyry, skarn and high sulphidation epithermal deposits. These deposits are mainly distributed within two Ordovician volcano-intrusive belts of the Lachlan Fold Belt: the Orange-Wellington Belt and the Parkes-Narromine Belt. Available isotopic age data suggest that mineralization of the three types of deposits is essentially coeval with the Ordovician intrusive rocks (480-430 Ma).Porphyry gold-copper deposits can be further divided into two groups. The first group is associated with monzonite showing shoshonitic features, represented by Cadia and Goonumbla. The second group is associated with diorite and dacite, including the Copper Hill and Cargo gold-copper deposits. Gold skarn is associated with Late Ordovician (430-439 Ma) monzonitic intrusive complexes in the Junction Reefs area (Sheahan-Grants, Frenchmans, and Cor-nishmens), Endeavour 6, 7 and 44, Big and Little Cadia     

Late Quaternary solifluction sheets in the British uplands

Solifluction sheets are large-scale and extensive valley-floor and valley-side landforms developed widely in the British Isles from mass-wasting of glacial and periglacial sediments during late-glacial times. We describe their geographical distribution and review the processes that have led to their development. We use data from the Cheviot Hills, the one site in the British Isles where sedimentology and optically stimulated luminescence dating have been combined, to assess their age and nature of deposition. We also present data from central Wales where a new mapping and resistivity survey has reconstructed the nature of valley-side solifluction sheets. We explore the relative lack of recent research on these landforms and argue that solifluction sheets represent a clear example of how upland geomorphological systems have responded to late-glacial climate change. We end by identifying a number of areas where research on these enigmatic features could be focussed, including better understanding of their distribution, sedimentology and age.     

坦比地区正断层位移模式探讨

本文通过对坦比地区上古生界中正断层位移的研究,提出本区海西—印支期正断层的三种主要位移模式:锥形、梯形和锯齿形,以及两种复合类型:锥-梯形,梯-锥形。此外,笔者还对造成断裂位移模式复杂化的两种主要因素——岩性变化与剖面效应进行了探讨。     

REGIONAL WATER MANAGEMENT: AN ASSESSMENT OF INSTITUTIONS IN ENGLAND AND WALES1

Water management institutions vary in comprehensiveness, level of governmental intervention, and basis of geographic delimitation. In 1973 the British Parliament created ten integrated water authorities in England and Wales based on river basins. They are responsible for all aspects of the water industry and are virtually the sole providers of water services. In 1983 Parliament reorganized the governing boards of the authorities along corporate lines. Evaluation of the British institutional arrangement and performance suggests that the comprehensive regional water authorities facilitate efficiency, effectiveness, and adequate technology, but that they limit representation of legitimate local and public interests and poorly accommodate existing governmental units.     

Social justice in coastal erosion management: The temporal and spatial dimensions

Coastal erosion management is primarily based on economic considerations (cost-benefit analysis). From the perspective of social justice (as a particular expression of the wider concept of human rights), however, several arguments can be advanced regarding public intervention in coastal defence management when private property is threatened by coastal erosion. In this paper we examine these arguments at both the short-term local scale and the long-term large spatial scale and consider the merits of inclusion of a social justice dimension in coastal erosion management. The coast provides a range of resources that benefit society as a whole. Coastal residents and property owners face a direct financial loss from coastal erosion but the general public also stands to incur losses other than purely financial if it there is public intervention for the benefit of these property owners. The arguments for public intervention are strongest at the local and short-term scales but they weaken (and even reverse) at geographically larger and longer time scales. At larger scales, the costs to society increase as intergenerational equity, non-coastal residents, climate and sea level change, and the environment are considered. Because of the intensity of interest involved at the local level, we argue that the necessary hard decisions must be made nationally if a sustainable policy is to be adopted. Social justice considerations provide a potential improvement on the traditional economic cost/benefit-based decision-making process of coastal erosion management but they only contribute to sustainability if viewed at the national level.     

The present-day stress field of New South Wales,Australia

The Australian continent displays the most complex pattern of present-day tectonic stress observed in any major continental area. Although plate boundary forces provide a well-established control on the large-scale (>500 km) orientation of maximum horizontal stress (S_Hmax), smaller-scale variations, caused by local forces, are poorly understood in Australia. Prior to this study, the World Stress Map database contained 101 S_Hmax orientation measurements for New South Wales (NSW), Australia, with the bulk of the data coming from shallow engineering tests in the Sydney Basin. In this study we interpret present-day stress indicators analysed from 58.6 km of borehole image logs in 135 coal-seam gas and petroleum wells in different sedimentary basins of NSW, including the Gunnedah, Clarence-Moreton, Sydney, Gloucester, Darling and Bowen–Surat basins. This study provides a refined stress map of NSW, with a total of 340 (A–E quality) S_Hmax orientations consisting of 186 stress indicators from borehole breakouts, 69 stress measurements from shallow engineering methods, 48 stress indicators from drilling-induced fractures, and 37 stress indicators from earthquake focal mechanism solutions. We define seven stress provinces throughout NSW and determine the mean orientation of the S_Hmax for each stress province. The results show that the S_Hmax is variable across the state, but broadly ranges from NE–SW to ESE–WNW. The S_Hmax is approximately E–W to ESE–WNW in the Darling Basin and Southeastern Seismogenic Zone that covers the west and south of NSW, respectively. However, the present-day S_Hmax rotates across the northeastern part of NSW, from approximately NE–SW in the South Sydney and Gloucester basins to ENE–WSW in the North Sydney, Clarence-Moreton and Gunnedah basins. Comparisons between the observed S_Hmax orientations and Australian stress models in the available literature reveal that previous numerical models were unable to satisfactorily predict the state of stress in NSW. Although clear regional present-day stress trends exist in NSW, there are also large perturbations observed locally within most stress provinces that demonstrate the significant control on local intraplate sources of stress. Local S_Hmax perturbations are interpreted to be due to basement topography, basin geometry, lithological contrasts, igneous intrusions, faults and fractures. Understanding and predicting local stress perturbations has major implications for determining the most productive fractures in petroleum systems, and for modelling the propagation direction and vertical height growth of induced hydraulic fractures in simulation of unconventional reservoirs.