Small-scale heterogeneity and soil-moisture variability in the unsaturated zone

The distribution of water within a soil profile can only be partly explained by the time distribution and rate of surface-water input. Observed differences in soil moisture within the unsaturated zone result from the interaction of surface-water inputs with spatially inhomogeneous soil characteristics. Water which initially percolates vertically is differentially impeded as a result of subtle textural changes in the soil, and is then preferentially retained in such zones of transition, causing large differences in soil-water content to occur. The scale of this vertical variability is of tenths of metres, whilst lateral variability of soil moisture reflects textural changes over a few metres. The observed influence of small-scale heterogeneity on soil-water content suggests that the conventional assumptions of isotropicity and homogeneity of the textural and hydraulic properties of porous media used in drainage basin and hillslope hydrological models need scrutiny, even for single stratigraphic units.     

Thermal regime at the Upper Stillwater dam site, Uinta mountains, Utah: Implications for terrain, microclimate and structural corrections in heat flow studies

A detailed study of the subsurface thermal regime at the Upper Stillwater dam site, Uinta Mountains, northeast Utah, has been made. Temperature measurements were made in 36 drillholes located within a 1 km² area and ranging in depth from 20 to 97 m. Holes less than about 40 m deep were used only to obtain information about spatial variations in mean annual surface temperature. Several holes in or near talus slopes at the sides of the canyons have temperature minima approaching 0°C between 10 and 20 m indicating the presence of year-round ice at the base of the talus. Another set of holes show transient thermal effects of surface warming resulting from clearing of a construction site 3.5 years prior to our measurements. Most of the remaining holes show conductive behavior and have gradients ranging from 13° to 17°C km⁻¹. Measurements made on 44 core samples yield a thermal conductivity of 5.6 (std. dev. 0.35) W m⁻¹ K⁻¹ for the Precambrian quartzite present. Surface heat flow estimates for these holes range from 70 to 100 mW m⁻². However, the local disturbance of the thermal field by topography and microclimate is considerable. A finite difference method used to model these effects yielded a locally corrected Upper Stillwater heat flow of about 75 mW m⁻². A final correction to account for the effects of refraction of heat from the low conductivity sedimentary rocks in the Uinta Basin into the high conductivity quartzite at the dam site, produced a regionally corrected Upper Stillwater heat flow between 60 and 65 mW m⁻². This value is consistent with the observed heat flow of 60 mW m⁻² in the Green River Basin to the north and the Uinta Basin to the south.     

The stratospheric quasi-biennial oscillation observed in the semidiurnal ground pressure data

Ground pressure observations made at Macao (22^○N, 113^○E) from 1953 to 1991 are analyzed and compared with the stratospheric quasi-biennial oscillation (QBO) data obtained during the same interval. The periods of the two phenomena and their time evolution are found to be close to each other. Furthermore, the time series of the stratospheric winds and the S2(p) QBO signature are highly correlated, thus confirming earlier analysis. On this basis, pressure measurements obtained at Batavia (now Djakarta: 6^○S, 107^○E) from 1870 to 1944 are used to trace back the QBO phenomenon before the advent of systematic stratospheric balloon measurements. The inferred period, which varies between 25 and 32 months, suggests that the QBO has been present in the atmosphere at least since 1870.     

Elemental fingerprints of isotopic contamination of hebridean Palaeocene mantle-derived magmas by archaean sial

One of the major puzzles presented by the geochemistry of the Palaeocene plateau lavas of Skye and Mull (N.W. Scotland) is that, although a very strong case can be made that the magmas are variably isotopically contaminated by Archaean Lewisian continental crust, little evidence has been gleaned to date from their major- and trace-element compositions to illuminate this hypothetical process. The combined results of published Sr-, Nd- and Pb-isotope studies of these lavas allow the basalts and hawaiites to be divided into three broad groups: essentially uncontaminated; contaminated with granulite-facies Archaean crust; contaminated with amphibolite-facies Archaean crust. Members of each group show distinctive chondrite-normalised incompatible-element patterns. The processes which gave rise to isotopic contamination of these lavas also affected the abundances and ratios of Ba, Rb, Th, K, Sr and light REE in the magmas, whilst having negligible effects on their abundances and ratios of Nb, Ta, P, Zr, Hf, Ti, Y and middle-heavy REE. Because such a wide range of elements were affected by the contamination process, it is postulated that the contaminant was a silicate melt of one or more distinctive crustal rock types, rather than an aqueous or similar fluid causing selective elemental movements from wall rocks into the magmas. As previous experimental and isotopic studies have shown that the Skye and Mull basic magmas were not constrained by cotectic equilibria at the time when they interacted with sial, the compositions of the contaminated lavas have been modelled in terms of simple magma-crust mixtures. Very close approximations to both the abundances and ratios of incompatible elements in the two groups of contaminated basalts may be obtained by adding 15% to 20% of Lewisian leucogneisses to uncontaminated Palaeocene basalt. Nevertheless, major-element constraints suggest that the maximum amount of granitic contaminant which has been added to these magmas lies between 5% and 10%. These estimates may be reconciled by postulating that the contaminants were large-fraction cotectic partial melts of Lewisian leucogneisses, leaving plagioclase residua. A corollary of this hypothesis is that it is necessary to postulate that the magma chambers where the sialic contamination occurred were, in fact, dykes or (more probably) sills. The very large surface-to-volume ratios of such magmas bodies would permit the systematic stripping, by partial melting, of the most-easily-fusible leucogneisses and pegmatites from the Lewisian crust, whilst failing to melt its major rock types. A present-day analogue to this situation may be the extensive sill-like magma bodies detected by geophysical methods within the continental crust beneath the Rio Grande Rift, southwestern U.S.A.     

Lead analysis of sediment cores from seven Connecticut lakes

Lead analyses were performed on sediment cores from seven Connecticut lakes by dilute acid leaching. The absolute concentrations of lead varied from core to core, but the lead profiles were similar in all of the cores, and each depicted a point where the concentration of lead sharply increased above background levels. The background lead concentrations observed in the bottom portions of the cores ranged from 12-54 g Pb/g sediment with a mean of 30 g Pb/g, and increased to a mean maximum of 310 g Pb/g. In six of the lakes significant increases above background levels were not noted until between 1924 and 1952, suggesting that, at least for Connecticut lakes, the point in a lake sediment core where the concentration of lead began to increase was after ca. 1924, and on average about 1930. Lead concentrations declined in the surface sediments of only three of the lakes, mostly since the 1980's, and presumably in response to the phasing out of leaded gasoline. However, significant declines in lead concentrations were not observed in the remaining cores, possibly due to increased motor vehicle use within the airshed of the lakes and/or changes in the export of lead to the lakes from their watersheds.     

Influence of initial density of cohesionless soil on evolution of passive earth pressure

This paper focuses on the influence of the initial void ratio on the evolution of the passive earth pressure and the formation of shear zones in a dry sand body behind a retaining wall. For the numerical simulation a rigid and very rough retaining wall undergoing a horizontal translation against the backfill is considered. The essential mechanical properties of cohesionless granular soil are described with a micro-polar hypoplastic model which takes into account stresses and couple stresses, pressure dependent limit void ratios and the mean grain size as a characteristic length. Numerical investigations are carried out with an initially medium dense and initially loose sand using a homogeneous and random distribution of the initial void ratio. The geometry of calculated shear zones is discussed and compared with a corresponding laboratory model test.     

A design study of an energy-dissipating cladding system

A design study has been conducted to explore the use of structural cladding panels with energy-dissipating cladding-to-frame connections for seismic-resistant design. The study identifies several issues involved in the modelling and analysis of frames with energy-dissipating cladding-to-frame connections, establishes concepts for design, and provides a preliminary assessment of the force and deformation demands that are likely to be placed on panels and connections. Non-linear dynamic analyses indicate that the clad frames perform well, based on observations about maximum interstorey drifts, maximum plastic hinge rotations in the frames, and maximum ductility demands on the cladding-to-frame connections.     

Recultivation and renewal of a balanced landscape in the lignite mining area of the Rhineland

The lignite mining area of the Rhineland provides an excellent example for planned recultivation of large open-works. In order to properly carry out recultivation measures, it is necessary to conduct basic research on the ecological factors which compose a balanced landscape. The problems involved in reconstructing a landscape, which has been pitted by large-scale open-cut mines, are discussed from the aspects of: planning and construction of a new landscape-relief, proposed agricultural and forestry use, nature preserves and resort areas. The aim of recultivation, from the ecological point of view, is to renew the natural biological potential and to reform the landscape, so as to provide the healthiest environment for Man.