Characterisation of sea-water intrusion in the Pioneer Valley, Australia using hydrochemistry and three-dimensional numerical modelling     

A. D. Werner  M. R. Gallagher 《Hydrogeology Journal》2006,14(8):1452-1469

Sea-water intrusion is actively contaminating fresh groundwater reserves in the coastal aquifers of the Pioneer Valley, north-eastern Australia. A three-dimensional sea-water intrusion model has been developed using the MODHMS code to explore regional-scale processes and to aid assessment of management strategies for the system. A sea-water intrusion potential map, produced through analyses of the hydrochemistry, hydrology and hydrogeology, offsets model limitations by providing an alternative appraisal of susceptibility. Sea-water intrusion in the Pioneer Valley is not in equilibrium, and a potential exists for further landward shifts in the extent of saline groundwater. The model required consideration of tidal over-height (the additional hydraulic head at the coast produced by the action of tides), with over-height values in the range 0.5–0.9 m giving improved water-table predictions. The effect of the initial water-table condition dominated the sensitivity of the model to changes in the coastal hydraulic boundary condition. Several salination processes are probably occurring in the Pioneer Valley, rather than just simple landward sea-water advancement from “modern” sources of marine salts. The method of vertical discretisation (i.e. model-layer subdivision) was shown to introduce some errors in the prediction of water-table behaviour.  相似文献   

Remediation of piled foundations against lateral spreading by passive site stabilization technique   总被引：2，自引：0，他引：2  

Ahmet Pamuk  Patricia M. Gallagher  Thomas F. Zimmie 《Soil Dynamics and Earthquake Engineering》2007,27(9):864-874

Physical modeling tests were conducted on pile foundations to measure the seismic performance of a new ground improvement technology, called passive site stabilization, for use on sites susceptible to liquefaction and liquefaction-induced lateral spreading. The method involves the slow injection of a low-viscosity stabilizer in conjunction with the natural groundwater flow. The effectiveness of the treatment using dilute colloidal silica as the stabilizer was tested by two centrifuge models that simulated soil–pile interaction of a 2×2 end-bearing pile group embedded in a multilayer soil deposit of 10-m thickness. The models utilized a laminar box and involved gently inclined soil profiles with and without the applied soil improvement. Response of the pile groups and the lateral spreading behaviors of the treated and untreated soil under a simulated base shaking were investigated and compared. The results showed that treatment with dilute colloidal silica stabilizer minimized permanent lateral deformations and reduced the liquefaction potential of the soil. Significant reductions occurred in the measured pile bending moments and axial forces because the layer treated with dilute colloidal silica did not liquefy. Thus, the technique can be an alternative to traditional methods of ground improvement.  相似文献   

Progressive changes in the morphology of fluvial terraces and scarps along the Rappahannock River,Virginia     

Steven M. Colman 《地球表面变化过程与地形》1983,8(3):201-212

Progressive geomorphic changes in the flight of fluvial terraces along the Rappahannock River, Virginia, provide a framework for analysing the effect of time on landforms. The oldest terrace is probably no younger than early Quaternary, and the youngest major fill terrace probably correlates with the high sea level of the last major interglacial. A uranium-series date of 187,000 yr has been obtained on coral from marine sediments related to this terrace. Indices of terrace preservation, especially drainage densities and area to perimeter ratios, show systematic changes with terrace age. Hence, these variables appear to satisfactorily indicate relative age, and could perhaps be used to estimate actual ages if suitably calibrated. The morphology of scarps formed by entrenchment of the fluvial terraces is more variable than analogous morphology of fault scarps and wave-cut bluffs. However, measurements of the fluvial scarps clearly indicate that for a given terrace age, higher scarps tend to have steeper slopes, and that for a given scarp height, older scarps tend to have gentler slopes. The terrace forms themselves are preserved for at least several million years. Depositional features such as bars and channels with l–3m of relief are preserved on terraces on the order of 10⁵ yr old. Scarps related to the formation of terraces of this age are well preserved and have slopes of about 6–8 degrees where the scarp height is about 5 m. The preservation of fluvial landforms and scarps suggests that, if fault scarps comparable to these features were commonly formed by earthquakes in low relief areas of the eastern United States, many should be recognizable.  相似文献   

Abrupt deglaciation on the northeastern Tibetan Plateau: evidence from Lake Qinghai   总被引：4，自引：0，他引：4  

Xiuju Liu  Steven M. Colman  Erik T. Brown  Andrew C. G. Henderson  Josef P. Werne  Jonathan A. Holmes 《Journal of Paleolimnology》2014,51(2):223-240

We inferred the climate history for Central Asia over the past 20,000 years, using sediments from core QH07, taken in the southeastern basin of Lake Qinghai, which lies at the northeastern margin of the Tibetan Plateau. Results from multiple environmental indicators are internally consistent and yield a clear late Pleistocene and Holocene climate record. Carbonate content and total organic carbon (TOC) in Lake Qinghai sediments are interpreted as indicators of the strength of the Asian summer monsoon. Warm and wet intervals, associated with increased monsoon strength, are indicated by increased carbonate and TOC content. During the glacial period (~20,000 to ~14,600 cal year BP), summer monsoon intensity remained low and relatively constant at Lake Qinghai, suggesting cool, dry, and relatively stable climate conditions. The inferred stable, cold, arid environment of the glacial maximum seems to persist through the Younger Dryas time period, and little or no evidence of a warm interval correlative with the Bølling–Allerød is found in the QH07 record. The transition between the late Pleistocene and the Holocene, about 11,500 cal year BP, was abrupt, more so than indicated by speleothems in eastern China. The Holocene (~11,500 cal year BP to present) was a time of enhanced summer monsoon strength and greater variability, indicating relatively wetter but more unstable climatic conditions than those of the late Pleistocene. The warmest, wettest part of the Holocene, marked by increased organic matter and carbonate contents, occurred from ~11,500 to ~9,000 cal year BP, consistent with maximum summer insolation contrast between 30°N and 15°N. A gradual reduction in precipitation (weakened summer monsoon) is inferred from decreased carbonate content through the course of the Holocene. We propose that changes in the contrast of summer insolation between 30°N and 15°N are the primary control on the Asian monsoon system over glacial/interglacial time scales. Secondary influences may include regional and global albedo changes attributable to ice-cover and vegetation shifts and sea level changes (distance from moisture source in Pacific Ocean). The abruptness of the change at the beginning of the Holocene, combined with an increase in variability, suggest a threshold for the arrival of monsoonal rainfall at the northeastern edge of the Tibetan Plateau.  相似文献   

Kelp gulls prey on the eyes of juvenile Cape fur seals in Namibia     

AJ Gallagher  ER Staaterman  N Dreyer 《African Journal of Marine Science》2015,37(3):411-414

The kelp gull Larus dominicanus is an abundant and highly successful avian predator and scavenger that breeds along the coastline in the Southern Hemisphere, ranging from Antarctica to the tropics. On account of its dietary breadth, wide-ranging foraging strategies, and acclimation to modified landscapes, this species has received considerable attention within the seabird literature over the past 40 years. Furthermore, owing to its ready habituation to human-dominated environments, the species has been used as a bio-indicator of habitat modification. Here we describe new predatory behaviours of the kelp gull on a larger-bodied sympatric mammal species, the Cape fur seal Arctocephalus pusillus pusillus, along the coast of Namibia, and discuss our findings as they relate to food web dynamics and behavioural plasticity.  相似文献   

On atmospheric radiative feedbacks associated with climate variability and change     

R. A. Colman  L. I. Hanson 《Climate Dynamics》2013,40(1-2):475-492

Using the method of radiative ‘kernels’ an analysis is made of water vapour, lapse rate and ‘Planck’ (uniform vertical temperature) long wave feedbacks in models participating in the World Climate Research Program (WCRP) Coupled Model Intercomparison Project phase 3 (CMIP3). Feedbacks are calculated at climate change timescales from the A1B scenario, and at three ‘variability’ timescales from the corresponding preindustrial experiments: seasonal, interannual and decadal. Surface temperature responses show different meridional patterns for the different timescales, which are then manifest in the structures of the individual feedbacks. Despite these differences, mean water vapour feedback strength in models is positive for all models and timescales, and of comparable global magnitude across all timescales except for seasonal, where it is much weaker. Taking into consideration the strong positive lapse rate feedback at seasonal timescales, combined water vapour/lapse rate feedback is indeed similar across all timescales. To a good approximation, global water vapour feedback is found to be well represented by the temperature response along with an assumption of unchanged relative humidity under both variability and climate change. A comparison is also made of model feedbacks with reanalysis derived feedbacks for seasonal and interannual timescales. No strong relationships between individual modelled feedbacks at different timescales are evident: i.e., strong feedbacks in models at variability timescales do not in general predict strong climate change feedback, with the possible exception of seasonal timescales. There are caveats on this (and other) findings however, from uncertainties associated with the kernel technique and from, at times, very large uncertainties in estimating variability related feedbacks from temperature regressions.  相似文献   

The South Pacific Convergence Zone in CMIP5 simulations of historical and future climate   总被引：3，自引：1，他引：2  

Josephine R. Brown  Aurel F. Moise  Robert A. Colman 《Climate Dynamics》2013,41(7-8):2179-2197

The South Pacific Convergence Zone (SPCZ) is evaluated in historical simulations from 26 Coupled Model Intercomparison Project Phase 5 (CMIP5) models, and compared with previous generation CMIP3 models. A subset of 24 CMIP5 models are able to simulate a distinct SPCZ in the December to February (DJF) austral summer, although the position of the SPCZ in these models is too zonal compared with observations. The spatial pattern of SPCZ precipitation is improved in CMIP5 models relative to CMIP3 models, although the spurious double ITCZ precipitation band in the eastern Pacific is intensified in many CMIP5 models. All CMIP5 models examined capture some interannual variability of SPCZ latitude, and 19 models simulate a realistic correlation with El Niño–Southern Oscillation. In simulations of the twenty-first century under the RCP8.5 emission scenario, no consistent shift in the mean position of the DJF SPCZ is identified. Several models simulate significant shifts northward, and a similar number of models simulate significant southward shifts. The majority of CMIP5 models simulate an increase in mean DJF SPCZ precipitation, and there is an intensification of the eastern Pacific double ITCZ precipitation band in many models. Most models simulate regions of increased precipitation in the western part of the SPCZ and near the equator, and regions of decreased precipitation at the eastern edge of the SPCZ. Decomposition of SPCZ precipitation changes into dynamic and thermodynamic components reveals predominantly increased precipitation due to thermodynamic changes, while dynamic changes lead to regions of both positive and negative precipitation anomalies.  相似文献   

The Great Dun Fell Experiment 1995: an overview     

K. N. Bower  T. W. Choularton  M. W. Gallagher  R. N. Colvile  K. M. Beswick  D. W. F. Inglis  C. Bradbury  B. G. Martinsson  E. Swietlicki  O. H. Berg  S. -I. Cederfelt  G. Frank  J. Zhou  J. N. Cape  M. A. Sutton  G. G. McFadyen  C. Milford  W. Birmili  B. A. Yuskiewicz  A. Wiedensohler  F. Stratmann  M. Wendisch  A. Berner  P. Ctyroky  Z. Galambos  S. H. Mesfin  U. Dusek  C. J. Dore  D. S. Lee  S. A. Pepler  M. Bizjak  B. Divjak 《Atmospheric Research》1999,50(3-4)

During March and April of 1995 a major international field project was conducted at the UMIST field station site on Great Dun Fell in Cumbria, Northern England. The hill cap cloud which frequently envelopes this site was used as a natural flow through reactor to examine the sensitivity of the cloud microphysics to the aerosol entering the cloud and also to investigate the effects of the cloud in changing the aerosol size distribution, chemical composition and associated optical properties. To investigate these processes, detailed measurements of the cloud water chemistry (including the chemistry of sulphur compounds, organic and inorganic oxidised nitrogen and ammonia), cloud microphysics and properties of the aerosol and trace gas concentrations upwind and downwind of the cap cloud were undertaken. It was found that the cloud droplet number was generally strongly correlated to aerosol number concentration, with up to 2000 activated droplets cm⁻³ being observed in the most polluted conditions. In such conditions it was inferred that hygroscopic organic compounds were important in the activation process. Often, the size distribution of the aerosol was substantially modified by the cloud processing, largely due to the aqueous phase oxidation of S(IV) to sulphate by hydrogen peroxide, but also through the uptake and fixing of gas phase nitric acid as nitrate, increasing the calculated optical scattering of the aerosol substantially (by up to 24%). New particle formation was also observed in the ultrafine aerosol mode (at about 5 nm) downwind of the cap cloud, particularly in conditions of low total aerosol surface area and in the presence of ammonia and HCl gases. This was seen to occur at night as well as during the day via a mechanism which is not yet understood. The implications of these results for parameterising aerosol growth in Global Climate Models are explored.  相似文献   

A Model of Ground Water Discharge from an Unconfined Coastal Aquifer   总被引：5，自引：1，他引：4  

Michael A. Robinson  Daniel L. Gallagher 《Ground water》1999,37(1):80-87

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