‘Natural’ rivers, ‘hydromorphological quality’ and river restoration: a challenging new agenda for applied fluvial geomorphology     

Malcolm. D. Newson  Andrew R. G. Large 《地球表面变化过程与地形》2006,31(13):1606-1624

Fluvial geomorphology is rapidly becoming centrally involved in practical applications to support the agenda of sustainable river basin management. In the UK its principal contributions to date have primarily been in flood risk management and river restoration. There is a new impetus: the European Union's Water Framework and Habitats Directives require all rivers to be considered in terms of their ecological quality, defined partly in terms of ‘hydromorphology’. This paper focuses on the problematic definition of ‘natural’ hydromorphological quality for rivers, the assessment of departures from it, and the ecologically driven strategies for restoration that must be delivered by regulators under the EU Water Framework Directive (WFD). The Habitats Directive contains similar concepts under different labels. Currently available definitions of ‘natural’ or ‘reference’ conditions derive largely from a concept of ‘damage’, principally to channel morphology. Such definitions may, however, be too static to form sustainable strategies for management and regulation, but attract public support. Interdisciplinary knowledge remains scant; yet such knowledge is needed at a range of scales from catchment to microhabitat. The most important contribution of the interdisciplinary R&D effort needed to supply management tools to regulators of the WFD and Habitats regulations is to interpret the physical habitat contribution to biodiversity conservation, in terms of ‘good ecological quality’ in rivers, and the ‘hydromorphological’ component of this quality. Contributions from ‘indigenous knowledge’, through public participation, are important but often understated in this effort to drive the ‘fluvial hydrosystem’ back to spontaneous, affordable, sustainable self‐regulation. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Estimating extreme flood magnitude in bedrock-influenced channels using representative reach-based channel resistance data     

G.L. Heritage  A.R.G. Large  B.P. Moon  A.L. Birkhead 《Geografiska Annaler: Series A, Physical Geography》2003,85(1):1-11

Extreme flood events are considered by many researchers to be very important in controlling the development of semi‐arid bedrock‐influenced river systems. Accurate gauging of such events is often impossible, however, as gauges are drowned and often damaged during the event. A methodology for estimating flood discharge for bedrock‐influenced channels is presented that reconstructs hydrometric characteristics of the peak flow and relates these to the roughness character of the river channel in question. The method is evaluated using peak water‐surface slope data relating to the extreme floods of February 2000 along the Sabie and Letaba rivers, located respectively in the Mpumalanga and Northern Provinces, South Africa. The data, in the form of strandline measurements, were taken at hydraulically relevant points along the long profile of both rivers. The resultant data are utilised together with published high flow channel resistance figures, based on the channel morphology of the Sabie and Letaba rivers, to generate peak flow estimates for a number of locations along both rivers. Comparisons are made between the frictional discharge peak flow estimates, velocity‐area and hydrologic estimates of peak flow. These comparisons indicate that the method can produce discharge estimates with an accuracy of ±10% and ± 35% respectively.  相似文献   

Geostatistical analysis of ground‐survey elevation data to elucidate spatial and temporal river channel change     

Adrian Chappell  George L. Heritage  Ian C. Fuller  Andrew R. G. Large  David J. Milan 《地球表面变化过程与地形》2003,28(4):349-370

A digital elevation model (DEM) of a fluvial environment represented landform surface variability well and provided a medium for monitoring morphological change over time. Elevation was measured above an arbitrary datum using a ground‐based three‐dimensional tacheometric survey in two reaches of the River Nent, UK, in July 1998, October 1998 (after flood conditions) and June 1999. A detailed geostatistical analysis of the elevation data was used to model the spatial variation of elevation and to produce DEMs in each reach and for each survey period. Maps of the difference in elevation were produced and volumetric change was calculated for each reach and each survey period. The parameters of variogram models were used to describe the morphological character of each reach and to elucidate the linkages between process and the form of channel change operating at different spatial and temporal scales. The analysis of channel change on the River Nent shows the potential of geostatistics for investigating the magnitude and frequency of geomorphic work in other rivers. A flood modified the channel features, but low magnitude and high frequency flows rationalized the morphology. In spite of relatively small amounts of net flux the channel features changed as a consequence of the reworking of existing material. The blocking of chute entrances and redirection of the channel had a considerable effect on the behaviour of the channel. Such small changes suggested that the distributary system was sensitive to variation in sediment regime. Plots of the kriging variances against sampling intervals were used to quantify the temporal variation in sampling redundancy (ranging between ?11 per cent and +93 per cent). These curves illustrated the importance of bespoke sampling designs to reduce sampling effort by incorporating anisotropic variation in space and geomorphic information on flow regime. Variation in the nugget parameter of the variogram models was interpreted as sampling inaccuracy caused by variability in particle size and is believed to be important for future work on surface roughness. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

An evaluation of neutral and convective planetary boundary-layer parameterizations relative to large eddy simulations   总被引：2，自引：1，他引：2  

Keith W. Ayotte  Peter P. Sullivan  Anders Andrén  Scott C. Doney  Albert A. M. Holtslag  William G. Large  James C. McWilliams  Chin-Hoh Moeng  Martin J. Otte  Joseph J. Tribbia  John C. Wyngaard 《Boundary-Layer Meteorology》1996,79(1-2):131-175

This paper compares a number of one-dimensional closure models for the planetary boundary layer (PBL) that are currently in use in large-scale atmospheric models. Using the results of a large-eddy simulation (LES) model as the standard of comparison, the PBL models are evaluated over a range of stratifications from free convective to neutral and a range of surface shear stresses. Capping inversion strengths for the convective cases range from weakly to strongly capped. Six prototypical PBL models are evaluated in this study, which focuses on the accuracy of the boundary-layer fluxes of momentum, heat, and two passive scalars. One scalar mimics humidity and the other is a top-down scalar entrained into the boundary layer from above. A set of measures based on the layer-averaged differences of these fluxes from the LES solutions is developed. In addition to the methodological framework and suite of LES solutions, the main result of the evaluation is the recognition that all of the examined PBL parameterizations have difficulty reproducing the entrainment at the top of the PBL, as given by the LES, in most parameter regimes. Some of the PBL models are relatively accurate in their entrainment flux in a subset of parameter regimes. The sensitivity of the PBL models to vertical resolution is explored, and substantive differences are observed in the performance of the PBL models, relative to LES, at low resolution typical of large scale atmospheric models.  相似文献   

Microthermometry and geochemistry of fluid inclusions from the Tennant Creek gold-copper deposits: implications for ore deposition and exploration   总被引：1，自引：0，他引：1  

Khin Zaw  D. L. Huston  R. R. Large  T. Mernagh  C. F. Hoffmann 《Mineralium Deposita》1994,29(3):288-300

Gold-copper-bismuth mineralization in the Tennant Creek goldfield of the Northern Territory occurs in pipe-like, ellipsoidal, or lensoidal lodes of magnetite ± hematite ironstones which are hosted in turbiditic sedimentary rocks of Proterozoic age. Fluid inclusion studies have revealed four major inclusion types in quartz associated with mineralized and barren ironstones at Ten nant Creek; (1) liquid-vapour inclusions with low liquid/vapour ratios (Type I), (2) liquid-vapour inclusions with high liquid/vapour ratios or high vapour/liquid ratios and characteristic dark bubbles (Type II), (3) liquid-vapour-halite inclusions (Type III), and (4) liquid-vapour inclusions with variable liquid/vapour ratios (Type V). Type I inclusions are present in the barren ironstones and the unmineralized portions of fertile ironstones, whereas Types II and III inclusions are recognized in fertile ironstones. Trails of Types II and III inclusions cut trails of Type I inclusions. Type I fluid inclusions have homogenization temperatures of 100° to 350 °C with a mode at 200° to 250 °C. Type II inclusions in mineralized ironstones (e.g. Juno, White Devil, Eldorado, TC8 and Gecko K-44 deposits) have homogenization temperatures of 250 °C to 600 °C with a mode of 350 °C. Type I fluid inclusions have a salinity range of 10 to 30 NaCl equiv. wt %. Salinity measurements on fluid inclusions in the mineralized zones gave a range of 10 to 50 NaCl equiv. wt % with a mode of 35 NaCl equiv. wt %. Fluid inclusion studies indicate that the Tennant Creek ironstones were formed from a relatively low temperature and moderately saline fluid, where as gold and copper mineralization was deposited from later hydrothermal fluids of higher temperature and salin ity. Gas analysis indicates the presence of N₂ and CO₂, with very minor CH₄ in Types II inclusions but no N₂ or CH₄ gases in Type I inclusions. Microprobe analysis of the fluid inclusion decrepitates indicates that the inclusions from Tennant Creek contain sodium and calcium as dominant cations and potassium in a subordinate amount. The high temperatures ( 350 °C), high salinities ( 35 NaCl equiv. wt. %) and cation composition of the Tennant Creek ore fluids suggest that the ore fluids were derived from upward migrating heated basinal brines, although contribution from a magmatic source cannot be ruled out. Close association of vapour-rich Type IIb and salt-rich Type III inclusions in the mineralized ironstones (e.g. Juno, White Devil, Eldorado, TC8 and Gecko K-44) indicates heterogeneous trapping of ore fluids. This heterogeneous trapping is interpreted to be due to unmixing (exsolution) of a gas-rich (e.g. N₂) fluid during the upward migration of the metal bearing brines and/or due to degassing caused by reaction of oxidized ore fluids and host ironstones. Fluid inclusion data have important implications regarding the deposition of gold in the ironstones, and may have application in discriminating fertile from barren ironstones.  相似文献   

Gold metallogeny and the copper-gold association of the Australian Proterozoic     

G. J. Davidson  R. R. Large 《Mineralium Deposita》1994,29(3):208-223

Australian Proterozoic gold-producing deposits, emplaced mainly at 1.55–2.00 Ga, are divided into the following categories: (1) iron oxide-dominated, brecciahosted, Cu-U±Au replacement deposits spatially associated with felsic intrusions (273t Au); (2) stratabound Au±Cu-bearing iron formations (152.4t Au); (3) unconformity-style U ±Cu/PGM/Au deposits (53t Au); (4) Iron oxide-dominated Au±Cu mineralisation hosted within elements of ductile deformation (146.7t Au); (5) Broken Hill and volcanic-hosted massive sulphides (150t Au); (6) iron-sulphide-dominated veins and replacement zones spatially related to felsic intrusions (150.7t Au), and (7) iron-sulphide-dominated veins and replacement zones spatially related to elements of regional deformation (159.9t Au). Categories (1) to (4) are mainly confined to Proterozoic rocks, constituting an association in which Au and Cu are commonly present together, with variable amounts of U, Bi, Co, W, Se, Te and REE. Most examples in categories 1–4 fall into either of two groups: Cu-Aumagnetite ±hematite types formed at relatively high temperature (300–450 °C), and Cu-U±Au-hematite types formed at 150–300 °C. We postulate that these ores formed from a common high salinity (15–35 wt. % NaCl equiv.), low total sulphur (a_S = 10^–3 to 10^–2), high fO₂ fluid-type, in which metal transport was dominated by chloride-complexing. The most effective method of metal deposition was fluid mixing, achieving a synchronous decrease in fO₂ and temperature. This unusual oxidised fluid association was favoured in high heat-flow extensional settings containing oxidised and/or oxidised-evaporitic sedimentary sequences. The intrusion of oxidised fractionated granites, which are commonly temporally associated with metal emplacement, acted in some places to heat and focus basinal fluids, and in others was the ultimate source of metals.  相似文献   

Revisiting the influences of parent stock, temperature, and predation on the recruitment of the Northeast Arctic cod stock, 1930-1990     

Pope  John; Large  Philip; Jakobsen  Tore 《ICES Journal of Marine Science》2001,58(5):967-972

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The geochemistry of the sedimentary rocks in the vicinity of the Tom Pb-Zn-Ba deposit, Yukon Territory, Canada     

Duncan Large 《Journal of Geochemical Exploration》1981,15(1-3)

A total of 138 samples of the Devonian sediments in the vicinity of the Tom stratiform Pb-Zn-Ba deposit were analysed for major elements and 16 minor and trace elements by X-ray fluorescence.The geochemistry of the footwall argillites is characterised by a concentration of elements that are typically associated with the detrital resistate minerals and feldspars (e.g. Al₂O₃, Na₂O, K₂O, TiO₂, Ce, Nb, Zr), which are contained within the interbedded silty layers of probable distal turbidite origin.The hanging-wall shales are characterised by high V concentrations. The C-organic data and the V/Cr ratios suggest that sapropelic conditions may have been locally developed in the vicinity of the West zone mineralisation and in the hanging-wall shales. Very high concentrations of Ba were found to be present in the hanging-wall shales (>0.5% Ba).Zn is more widely dispersed than Pb in the sediments around the mineralisation. There is no marked enrichment of Fe, Mn or Cu in the sediments close to the mineralisation.  相似文献   

Numerical investigation of salinity in controlling ore-forming fluid transport in sedimentary basins: example of the HYC deposit, Northern Australia     

Jianwen Yang  Stuart Bull  Ross Large 《Mineralium Deposita》2004,39(5-6):622-631

This paper presents the first hydrogeological model that fully couples transient fluid flow, heat and solute transport associated with the formation of the HYC SEDEX deposit in the McArthur Basin, northern Australia. Numerical results reveal that salinity plays an important role in controlling hydrothermal fluid migration. In particular, it appears that it is the distribution of evaporitic units within a given basin, rather than their absolute abundance, that controls the development of free convection. Relatively saline conditions at the seafloor strengthen the thermally-induced buoyancy force and hence promote free convection of basinal solutions; whereas high salinities at the bottom counteract the thermal function of natural geothermal gradient and suppress the development of convective hydrothermal fluid circulation. In the latter case, higher thermal gradients are required to initiate substantial free convective fluid flow.Numerical experiments also suggest the position of an ore body with respect to its vent system may be controlled by the spatial and temporal salinity distributions in the basin. Vent-distal ore formation, a result of exhalation of brines that are denser than seawater and hence can flow away from the vent region, is promoted by moderate salinity at the seafloor and higher salinity in the aquifer. Vent-proximal ore accumulation, a result of pluming upon exhalation of brines less dense than seawater, is favored by the highest salinity conditions occurring near the level of the seafloor.Editorial Handling: G. Beaudoin  相似文献   

Se and In minerals in the submarine oxidation zone of a massive sulfide orebody of the molodezhnoe copper–zinc massive sulfide deposit,Southern Urals     

N. R. Ayupova  V. V. Maslennikov  V. A. Kotlyarov  S. P. Maslennikova  L. V. Danyushevsky  R. Large 《Doklady Earth Sciences》2017,473(1):318-322

For the first time, extremely high Se and In contents were determined for the pinches of massive sulfide orebodies that are composed of small-clastic layered sulfide sediments transformed during submarine supergenesis. Se (clausthalite and naumannite) and In (roquesite) minerals were found. Hydrothermal chalcopyrite, a significant amount of which is present in the clasts of paleohydrothermal black smoker chimneys, was the source of Se. Most of the amount of In was contributed during dissolution of clasts of hydrothermal sphalerite, which is unstable in the submarine oxidation zone in the presence of oxidized pyrite.  相似文献