Real-Time River Level Monitoring Using GPS Heighting

This paper presents the current progress of the River Level Monitoring using GPS Heighting (RiGHt) project. The aim of the project is to develop an integrated system to allow the continuous monitoring of river heights using a buoy equipped with Global Positioning System (GPS) and satellite communications and using Geographical Information System (GIS) techniques. ? 2000 John Wiley & Sons, Inc.     

Sub-grid scale parameterisation of 2D hydrodynamic models of inundation in the urban area

This paper presents preliminary results from a study considering the parameterisation of coarse-grid 2D flood models to take into account sub-grid scale flow patterns occurring in the urban area. A simulation of a severe flood in an urbanized coastal floodplain is first run using a fine grid that can resolve the flow around and between buildings. Next, the same model is run again using the same underlying topography, although stripped from any buildings, and a set of 7 values of the roughness parameter (Manning’s n), all larger than (or equal to) the value used in the original run. A further set of simulations is carried out using a five-fold increased grid cell size. It is found that while it may be possible to model the overall effects of the buildings using strongly increased roughness parameter values, using a coarse grid otherwise has implications related to the loss of information about the site topography that results in flood flow routes being incorrectly modelled.     

Fluid venting and seepage at accretionary ridges: the Four Way Closure Ridge offshore SW Taiwan

Within the accretionary prism offshore SW Taiwan, widespread gas hydrate accumulations are postulated to occur based on the presence of a bottom simulating reflection. Methane seepage, however, is also widespread at accretionary ridges offshore SW Taiwan and may indicate a significant loss of methane bypassing the gas hydrate system. Four Way Closure Ridge, located in 1,500 m water depth, is an anticlinal ridge that would constitute an ideal trap for methane and consequently represents a site with good potential for gas hydrate accumulations. The analysis of high-resolution bathymetry, deep-towed sidescan sonar imagery, high-resolution seismic profiling and towed video observations of the seafloor shows that Four Way Closure Ridge is and has been a site of intensive methane seepage. Continuous seepage is mainly evidenced by large accumulations of authigenic carbonate precipitates, which appear to be controlled by the creation of fluid pathways through faulting. Consequently, Four Way Closure Ridge is not a closed system in terms of fluid migration and seepage. A conceptual model of the evolution of gas hydrates and seepage at accretionary ridges suggests that seepage is common and may be a standard feature during the geological development of ridges in accretionary prisms. The observation of seafloor seepage alone is therefore not a reliable indicator of exploitable gas hydrate accumulations at depth.     

The stream hydrology response of converting a headwater pasture catchment to Pinus radiata plantation

ABSTRACT

The planting of degraded land with tree plantations may be effective at improving land use sustainability and profitability but it can also have significant effects on stream hydrology. In this paired catchment study, we report the stream hydrological response to partial (62%) afforestation of a steep pastoral catchment in the western Waikato Region, North Island, New Zealand. We comprehensively analyse the hydrological regime changes over a 23-year period (including eight years before pine planting) with reference to a native-forested ‘control’ catchment. Our results show that afforestation has markedly affected stream hydrology. Seven years after planting, the total annual runoff was 380?mm lower than predicted for the catchment in pasture. Two phases of plantation thinning resulted in the difference between measured and predicted runoff reducing to only 129?mm. Peak flows reduced by ～50% while total stormflow reduced by ～30% – which we attribute to canopy interception attenuating and delaying water yield. The impact of plantation establishment on low flows is not so clear, although afforestation appears to have reduced low flows by ～25%. This study provides information on the hydrological impact of afforestation within a hitherto poorly-represented New Zealand environment (i.e. high rainfall, sedimentary lithology-based, North Island hill country).     

Whose field line is it anyway?

Gareth Chisham, Gary Abel and Steve Milan report on the October 2003 RAS "G" discussion meeting "Identifying the open–closed field line boundary in magnetospheric and ionospheric data sets".     

Phytoplankton biomass and nutrient distributions in the Amazon River plume: Environmental correlates

The distribution of phytoplankton biomass in the plume of the Amazon River over the Brazilian continental shelf is analyzed by the use of multiple regression. Previous attempts to assess how different parameters control phytoplankton biomass have used pairwise correlations. A multiple regression approach, however, allows the elucidation of collinearity between these parameters. This approach reveals that phytoplankton biomass may be predicted largely by the following three groups of collinear variables that resemble the factors of factor analysis: suspended-sediment concentration and transparency (which generally describe irradiance availability), salinity and temperature (which describe vertical stratification, a measure of water-column stability), and the ambient concentrations of nutrients (phosphate, nitrate, silicic acid, and nitrite). The effects of water clarity and nutrients have been previously described, but the importance of vertical stability has never been separated from the other two. Additional important single variables were oxygen, ammonia, and urea. The strength of the contribution of particular variables to a regression model depends on the season of the cruise and hence on the volume of riverine discharge.     

Tracking meteoric infiltration into a magmatic-hydrothermal system: A cathodoluminescence, oxygen isotope and trace element study of quartz from Mt. Leyshon, Australia

The oxygen isotope and trace element composition of hydrothermal quartz has been integrated with scanning electron microscope-cathodoluminescence (SEM-CL) images and fluid inclusion properties to track fluid sources and hydrothermal processes in the Mt. Leyshon Au deposit, Australia. Oxygen isotope and trace element data were collected on parallel traverses across the same quartz sections, using secondary isotope mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), respectively, with SEM-CL images obtained before analysis for petrographic context. Over the 280 to 650 °C quartz precipitation range suggested by fluid inclusion microthermometry, δ¹⁸O_quartz varies from 0.0 to 14.4‰, corresponding to a wide range of equilibrium δ¹⁸O_fluid values, from-6.1 to 10.2‰ (vs. V-SMOW). The δ¹⁸O_quartz signature varies systematically among distinct SEM-CL quartz generations (both within and between samples), and can be correlated with variations in temperature and fluid composition, but is independent of intra-generational oscillatory zoning. In contrast, Al and Li concentrations correlate broadly with CL intensity in oscillatory quartz, whereas their concentration is unpredictable in sealed fractures and overgrowths. Concentrations of B, Mg, Na, P, Cl, K, Ti, Mn, Fe, Ge, and Sn are independent of Al, Li, and oscillatory CL features, but Ti correlates with quartz precipitation temperature. Although no systematic correlation between δ¹⁸O_quartz and trace element concentrations was found, complementary patterns exist in narrow overgrowths of low δ¹⁸O_quartz ( 0‰) and high Al (> 10,000 ppma). These quartz zones likely formed during the incursion of ¹⁸O-depleted meteoric water into the magmatically-dominated Mt. Leyshon hydrothermal system. We interpret the highest Al concentrations as the result of high quartz precipitation rates, triggered by depressurisation of the hydrothermal cell. The decoupling of oxygen isotope and trace element patterns in quartz leads to the suggestion that (1) under most circumstances, temperature and fluid chemistry dominate δ¹⁸O_quartz, and (2) the trace element record, and in particular Al and Li, is influenced by the superimposed effects of quartz precipitation rate.     

Investigation of iron sulfide impact crater residues: A combined analysis by scanning and transmission electron microscopy

Abstract– Samples returned from comet 81P/Wild 2 by the Stardust mission provided an unequaled opportunity to compare previously available extraterrestrial samples against those from a known comet. Iron sulfides are a major constituent of cometary grains commonly identified within cometary interplanetary dust particles (IDPs) and Wild 2 samples. Chemical analyses indicate Wild 2 sulfides are fundamentally different from those in IDPs. However, as Wild 2 dust was collected via impact into capture media at approximately 6.1 km s^?1, it is unclear whether this is due to variation in preaccretional/parent body processes experienced by these materials or due to heating and alteration during collection. We investigated alteration in pyrrhotite and pentlandite impacted into Stardust flight spare Al foils under encounter conditions by comparing scanning and transmission electron microscope (SEM, TEM) analyses of preimpact and postimpact samples and calculating estimates of various impact parameters. SEM is the primary method of analysis during initial in situ examination of Stardust foils, and therefore, we also sought to evaluate the data obtained by SEM using insights provided by TEM. We find iron sulfides experience heating, melting, separation, and loss of S, and mixing with molten Al. These results are consistent with estimated peak pressures and temperatures experienced (approximately 85 GPa, approximately 2600 K) and relative melting temperatures. Unambiguous identification of preserved iron sulfides may be possible by TEM through the location of Al‐free regions. In most cases, the Ni:Fe ratio is preserved in both SEM and TEM analyses and may therefore also be used to predict original chemistry and estimate mineralogy.     

Geology and resource development of the Kelvin kimberlite pipe,Northwest Territories,Canada

The early Cambrian to late Neoproterozoic Kelvin kimberlite pipe is located in the southeast of the Archean Slave Craton in northern Canada, eight km northeast of the Gahcho Kué diamond mine. Kelvin was first discovered in 2000 by De Beers Canada. Subsequent exploration undertaken by Kennady Diamonds Inc. between 2012 and 2016 resulted in the discovery of significant thicknesses of volcaniclastic kimberlite that had not previously been observed. Through extensive delineation drilling Kelvin has been shown to present an atypical, steep-sided inclined L-shaped pipe-like morphology with an overall dip of 15 to 20°. With a surface expression of only 0.08 ha Kelvin dips towards the northwest before turning north. The body (which remains open at depth) has been constrained to a current overall strike length of 700 m with varying vertical thickness (70 to 200 m) and width (30 to 70 m). Detailed core logging, petrography and microdiamond analysis have shown that the pipe infill comprises several phases of sub-horizontally oriented kimberlite (KIMB1, KIMB2, KIMB3, KIMB4, KIMB7 and KIMB8) resulting from multiple emplacement events. The pipe infill is dominated by Kimberley-type pyroclastic kimberlite or “KPK”, historically referred to as tuffisitic kimberlite breccia or “TKB”, with less common hypabyssal kimberlite (HK) and minor units with textures transitional between these end-members. An extensive HK sheet complex surrounds the pipe. The emplacement of Kelvin is believed to have been initiated by intrusion of this early sheet system. The main pipe-forming event and formation of the dominant KPK pipe infill, KIMB3, was followed by late stage emplacement of additional minor KPK and a hypabyssal to transitional-textured phase along the upper contact of the pipe, cross-cutting the underlying KIMB3. Rb-Sr age dating of phlogopite from a late stage phase has established model ages of 531 ± 8 Ma and 546 ± 8 Ma. Texturally and mineralogically, the Kelvin kimberlite is similar to other KPK systems such as the Gahcho Kué kimberlites and many southern African kimberlites; however, the external morphology, specifically the sub-horizontal inclination of the pipe, is unique. The morphology of Kelvin and the other kimberlites in the Kelvin-Faraday cluster defines a new type of exploration target, one that is likely not unique to the Kennady North Project area. Extensive evaluation work by Kennady Diamonds Inc. has resulted in definition of a maiden Indicated Mineral Resource for Kelvin of 8.5 million tonnes (Mt) of kimberlite at an average grade of 1.6 carats per tonne (cpt) with an average diamond value of US$ 63 per carat (ct).