WATER MANAGEMENT—A GENERAL REPORT

Abstract

This analysis was undertaken to develop appropriate extreme flood design criteria for a nuclear power plant at Halileh, near Bushehr, Iran, adjacent to the Persian Gulf. Graphical relationships presented provide a convenient means of estimating the probable maximum precipitation and the 2- to 100-year return period rainfall events with durations from 5 min to 24 h. The relationships may be applied for drainage areas up to 25 km². Probable maximum precipitation and 2- to 100-year return period rainfall events were estimated. Precipitation depth-duration relationships were derived.     

Modelling spatially and temporally distributed phenomena: new methods and tools for GRASS GIS

Abstract

The concept of GRASS (Geographic Resources Analysis Support System) as an open system has created a favourable environment for integration of process based modelling and GIS. To support this integration a new generation of tools is being developed in the following areas: (a) interpolation from multidimensional scattered point data, (b) analysis of surfaces and hypersurfaces, (c) modelling of spatial processes and, (d) 3D dynamic visualization. Examples of two applications are given-spatial and temporal modelling of erosion and deposition, and multivariate interpolation and visualization of nitrogen concentrations in the Chesapeake Bay.     

Cryptotephrochronology of the Eemian and the last interglacial–glacial transition in the North East Atlantic

The Eemian interglacial and the onset of the subsequent glacial period serve as the most recent analogue for the natural operation of the climate system during the current interglacial. Pronounced climatic oscillations occurred during this period, but their nature and pattern are poorly understood due to dating limitations and unknown phase relationships between different regions and archives. Tephrochronology offers considerable potential for precise correlation of disparate palaeoclimatic archives preserving evidence of these rapid climatic transitions through the tracing of common isochronous tephra horizons. We outline the identification of three previously unknown cryptotephra horizons within a marine core from the Rockall Trough, North East Atlantic. This sequence preserves a high‐resolution record of this interval and shard size, geochemical heterogeneity and the co‐variance of shard concentrations with ice‐rafted debris data are utilized to demonstrate that primary airfall was the most likely transport and depositional pathway. The main geochemical populations of these horizons have similar transitional alkali major and trace element compositions, suggesting that they were derived from a common Icelandic source, potentially the Öræfajökull volcanic system. These tephra horizons represent additions to the North Atlantic event stratigraphy for this period and tentative correlations to Icelandic terrestrial deposits are proposed for two horizons.     

WEST AFRICAN ENVIRONMENTAL NARRATIVES AND DEVELOPMENT‐VOLUNTEER PRAXIS*

ABSTRACT. Environmental narratives in Africa have been examined in a flurry of publications since the mid‐1990s. In this article we seek to offer insights into the role and motivations of volunteer development workers in perpetuating environmental narratives. We examine the factors that led to the questioning or nonquestioning of environment‐development discourses and their influence, if any, on the actual work undertaken by volunteers. As former development volunteers, we also explore the role that the development‐volunteer experience subsequently played in shaping our own research as academics. Our analysis is based largely on our tenure as U.S. Peace Corps volunteers in Mali from 1987 until 1989 and our later experiences as academics. We draw on our memories, interviews with former colleagues, and training materials to describe how volunteers were introduced to, and encouraged to act on, environmental problems in the West African Sudano‐Sahel. We adopt a reflexive approach to explore briefly how our experiences as volunteers influenced our research and writing as academics.     

Trajectory analysis of the lower Brent Group (Jurassic), Northern North Sea: contrasting depositional patterns during the advance of a major deltaic system

Trajectory analysis is an alternative approach to systems tract analysis in unravelling the sequence stratigraphic development of sedimentary successions. Whereas the latter anticipates a succession of the depositional history in terms of a given order of systems tracts, trajectory analysis combines trajectory classes in any order, thus providing a more flexible interpretation of the depositional evolution with fewer a priori assumptions about the type or the nature of the mechanisms driving sequence development. The overall regressive part of the Brent Delta (Middle Jurassic, Northern North Sea) has been analysed using this approach. The distribution, thicknesses and stacking patterns of facies associations have been analysed to unravel the trajectorial behaviour of the system. In proximal areas (Oseberg domain), thin shoreface/foreshore packages associated with a prograding strandplain are overlain by upper delta-plain (floodplain) and distributary channel deposits. Flat or descending regressive trajectories can explain the stratigraphic development in this area. A short distance to the north (Huldra domain), the presence of thicker shoreface/foreshore packages and lower delta-plain sediments suggests a low-angle ascending regressive trajectory. In more distal areas (Gullfaks and Visund domains), a higher rate of aggradation leads to the development of even thicker shoreface/foreshore packages and the development of lagoons and bays in the lower delta-plain realm. Alternating high- and low-angle ascending regressive trajectories can explain the distal development.     

Using magnetic resonance imaging for experimental analysis of fine‐sediment infiltration into gravel beds

Sedimentologists recognize that development of a fine‐resolution, truly three‐dimensional analytical tool is essential if the internal structure of an opaque material is to be examined. This paper therefore seeks to: (i) test the viability of magnetic resonance imaging for sedimentological research; and (ii) investigate fine‐sediment infiltration into gravel beds. The results of six experiments are analysed quantitatively using Image J post‐processing software. Data indicate that magnetic resonance imaging‐based measurements of particle axes and volumes are comparable with standard laboratory techniques. Furthermore, the technique permits visualization and analysis of differences in the pattern of fine‐sediment infiltration (median particle diameter, d) into a framework of gravel (median particle diameter, D). Data clearly illustrate a siltation process for samples of D/d = 34 and a sealing process for samples of D/d = 7 where the seal is restricted to a depth equal to 2D. This pore‐scale visualization is valuable to the understanding of hydraulic–sediment–habitat interactions.     

Overgrowth Textures, Disequilibrium Zoning, and Cooling History of a Glassy Four-Pyroxene Boninite Dyke from New Caledonia

Pyroxenes in a low-Ca boninite from a dyke show remarkable growthand overgrowth textures and chemical zoning, which are usedto infer crystallization mechanisms and kinetics. The rock comprisesnearly 50 vol.% fresh glass, phenocrysts and glomerocrysts ofclinoenstatite sensu lato ({small tilde}32 vol.%), microphenocrystsof orthopyroxene and Ca-rich clinopyroxene ({small tilde}17vol.%), and microlites of amphibole and oxides ({small tilde}3vol.%). Clinoenstatite, which inverted from protoenstatite,is skeletal with glass and chrome-spinel inclusions and thinovergrowth zones of Ca-rich clinopyroxene and amphibole; thecrystals are occasionally broken. Orthopyroxene is often skeletal,sometimes slightly resorbed with the same inclusions and overgrowthzones. Ca-rich clinopyroxene and amphibole occur mainly in pyroxeneovergrowth zones. Chrome-spinel in contact with glass is overgrownby magnetite-maghemite or amphibole. The rock is andesitic witha high mg-number of 0.78, and is quartz- and strongly hypersthene-and feldspar-normative. The glass is dacitic with an mg-numberof 0.15, strongly quartz- and feldspar-normative, and rich inwater ({small tilde}5.6wt.%). Strong chemical zoning occurs in all minerals, oscillatory zoningoccurring only in clinoenstatite and orthopyroxene. The mg-numberin clinoenstatite sensu lato ranges from 0.95 (clinoenstatitesensu stricto) to 0-68 (clinohypersthene), the largest rangeso far described, and from 0.88 to 0.43 in orthopyroxene. TheWo content of the former (0.21–1.56 with rare higher values)is considerably smaller than and does not overlap that of thelatter (1.36–4.84X Wo generally increasing with Fs. Thecores of both are chromian (up to 0–018 atoms per formulaunit), and Cr falls to or below the detection limit for Fs>25.The Fs-rich zones of clinohypersthene have {small tilde}2wt%A1₂O₃ and (M6wt% TiO₂, whereas those of orthopyroxene reachnearly 10 and 04 wt. %, respectively. Ca-rich clinopyroxenevaries from pigeonite through subcalcic augite and augite toferroaugite, the outer zones reaching 12wt.% A1₂O₃ and 1–8wt% TiO₂. Amphibole is magnesio-hornblende on pyroxene or tschermakitichornblende on oxide. The relative times of nucleation, growth, partial resorption,and fracturing of the crystals were determined from the texturesand the chemistry of the overgrowths. Protoenstatite and chrome-spinelnucleated from the melt and were overgrown in places by allsucceeding minerals. Orthopyroxene nucleated mainly from themelt, whereas the other phases occur only as overgrowths. Orthopyroxenemay show weak resorption at intermediate stages. Protoenstatitecrystals were occasionally broken, the relative times beingshown by the nature of the overgrowths. Minor-element concentrationsvary strongly with the growth stage, chromium soon being usedup in the melt and aluminium and titanium being strongly concentratedin the crystals during the last stages. Plagioclase and quartzare absent because of suppression of their nucleation in a water-richmelt on rapid cooling. Crystallization probably occurred intwo main stages, an early one of moderately fast cooling atlow undercooling probably in a shallow magma chamber (correspondingto the growth of the protoenstatite phenocrysts) and a laterone over a period of less than a day of faster cooling at higherundercooling after uprise and injection into the dyke (correspondingto the fracturing of protoenstatite and growth of the microphenocrystsand microlites).     

Mineral Chemistry of Peridotites from Paleozoic, Mesozoic and Cenozoic Lithosphere: Constraints on Mantle Evolution beneath Eastern China

Major- and trace-element data on the constituent minerals ofgarnet peridotite xenoliths hosted in early Paleozoic (457–500Ma) kimberlites and Neogene (16–18 Ma) volcanic rockswithin the North China Craton are compared with those from thepre-pilot hole of the Chinese Continental Scientific DrillingProject (CCSD-PP1) in the tectonically exhumed Triassic (220Ma) Sulu ultrahigh-pressure (UHP) terrane along its southernmargin. P–T estimates for the Paleozoic and Neogene peridotitexenoliths reflect different model geotherms corresponding tosurface heat flows of 40 mW/m² (Paleozoic) and 80 mW/m² (Neogene).Garnet peridotite xenoliths or xenocrysts from the Paleozoickimberlites are strongly depleted, similar to peridotites fromother areas of cratonic mantle, with magnesium olivine (meanFo_92.7), Cr-rich garnet and clinopyroxene with high La/Yb. Garnet(and spinel) peridotite xenoliths hosted in Neogene basaltsare derived from fertile mantle; they have high Al₂O₃ and TiO₂contents, low-Mg-number olivine (mean Fo_89.5), low-Cr garnetand diopside with flat rare earth element (REE) patterns. Thedifferences between the Paleozoic and Neogene xenoliths suggestthat a buoyant refractory lithospheric keel present beneaththe eastern North China Craton in Paleozoic times was at leastpartly replaced by younger, hotter and more fertile lithosphericmantle during Mesozoic–Cenozoic times. Garnet peridotitesfrom the Sulu UHP terrane have less magnesian olivine (Fo_91.5),and lower-Cr garnet than the Paleozoic xenoliths. The diopsideshave low heavy REE (HREE) contents and sinusoidal to light REE(LREE)-enriched REE patterns. These features, and their highMg/Si and low CaO and Al₂O₃ contents, indicate that the CCSD-PP1peridotites represent a moderately refractory mantle protolith.Details of mineral chemistry indicate that this protolith experiencedcomplex metasomatism by asthenosphere-derived melts or fluidsin Mesoproterozoic, and subsolidus re-equilibration involvingfluids/melts derived from the subducted Yangtze continentalcrust during UHP metamorphism in the early Mesozoic. Tectonicextension of the subcontinental lithospheric mantle of the NorthChina Craton and exhumation of the Sulu UHP rocks in the earlyMesozoic induced upwelling of the asthenosphere. Peridotitessampled by the Neogene basalts represent newly formed lithospherederived by cooling of the upwelling asthenospheric mantle inJurassic–Cretaceous and Paleogene time. KEY WORDS: garnet peridotite xenoliths; North China Craton; lithospheric thinning; Sulu UHP terrane; UHP lithosphere evolution; mantle replacement