Determination of Horizontal Aquifer Anisotropy with Three Wells

Existing methods for the determination of horizontal aquifer anisotropy by means of pumping tests require a minimum of four wells, one for water withdrawal and three for drawdown observations. This paper shows how the same methods can be used to determine anisotropy with as few as three wells, if at least two of them can be pumped in sequence. A field example is included. A method of analyzing data from more wells than the above minimum, by least squares, is also described.     

A State-Of-The-Art Approach to Hydrologic Data Management

High-accuracy electronic data acquisition equipment, a solid-state memory, computer interface and software have been developed to provide a complete system for measuring and recording water level changes.
A small, stand-alone hydrologic instrument (SE1000) provides the automation and accuracy of solid-state electronics in pump tests, slug tests, and long- and short-term ground water monitoring. The unit is powered by a high-performance battery pack with a minimum life of four years. This instrument can be buried at the monitoring site for protection from vandals, animals and temperature extremes. Ten pre-programmed 949-point data schedules are standard. One schedule is logarithmic with an initial data interval of 0.2 seconds. Nine linear schedules provide data intervals ranging from 15 minutes to 1.5 days and corresponding test durations ranging from 10 days to 46 months. The stored data can be recovered directly via the LCD display or transferred to a computer. Software provides automatic data reduction with hard copy tables and plots.
This instrument has been used successfully in various locations in the United States.     

Characteristics of diamondiferous Plio-Pleistocene littoral deposits within the palaeo-Orange River mouth, Namibia

The Orange River, the principal conduit transporting diamonds from hinterland sources to the Namibian coast in post-Cretaceous times, is characterised by an extreme wave dominated delta that has given rise to a progression of coarse rudaceous littoral deposits preserved onshore for > 150 km north of the mouth. Under the long-lived, prevailing vigorous wave, wind and northward longshore drift regimes, the Orange River outfall has been reworked into, amongst others, a series of economically viable, diamondiferous Plio-Pleistocene onshore gravel beach deposits. These placers comprise spits and barrier beaches in the proximal reach within the palaeo-Orange River mouth that, after ca. 5 km northwards, merge into extensive but narrow linear beaches that, in turn after ca. 70 km, give way to pocket beaches. Gravel and diamond size decreases northwards away from the ancestral Orange River mouth. The linear and pocket beach types have considerably higher diamond content but lower average diamond stone size than the two proximal units that are characterised by low diamond grade but comparatively large average diamond size. Given the risk of delineating low grade alluvial diamond deposits accurately, we present here sedimentological reconstructions of the subtidal, intertidal and supra-tidal facies that constitute the spit and barrier beach sequences, based largely on face mapping of exploration trenches and open-cast, mine cuts, as well as the results of large tonnage, sampling campaigns. Diamond distribution is also linked convincingly to basic littoral processes that were operational within the palaeo-Orange River mouth during the complex transgression that gave rise to the + 30 m package in Plio-Pleistocene times. In both the spit and barrier beach settings, the intertidal deposits prove to be the most promising targets whereas the subtidal sediments are the least economic. The constant raking associated with coarse, cobble–boulder-sized gravel foreshore deposits in an energetic micro-tidal wave regime increased the average diamond stone size in the intertidal deposits to 1 to 2 carats per stone (cts/stn), but the lack of fixed trapsites (no competent footwall within the palaeo-Orange River mouth at that level) prohibited the accumulation of substantially enriched diamondiferous gravels. Consequently, grades of only 1.5 to 6 carats per 100 tons (cpht) are realised. The highest grades (2 to 6 cpht) are found in the landward-facing, intertidal beach deposits on the spits where gentle reworking in that sheltered environment had somewhat enriched and preserved the diamond content. Significantly, the low average stone size of ca. 0.5 cts/stn in this lower energy setting probably reflects that of the general diamond population available at that time. In contrast, the sand-rich subtidal deposits in the spit sequence return the lowest grades (0.1 to 0.5 cpht), similar to those in the slightly younger, subtidal transgressive boulder lags of the barrier beaches. However, the stone size in the spit subtidal sediments is also low (0.1 to 0.5 cts/stn) due to the highly mobile, fine-grained character of those deposits, whereas that in the subtidal transgressive lag is large (2 to 3 cts/stn) as a result of the local, semi-permanent turbulence associated with the boulder-sized clasts in these gravel sheets. Diamond distribution is therefore also influenced by littoral facies and associated beach types, in addition to the spatial and temporal parameters that have already been documented for the onshore marine placers of the southern Namibian coast.     

‘Public intellectuals’, geography, its representations and its publics

Recent years have seen academic geographers engaged in a series of debates over the current state of the discipline, its ‘relevance’ to others in the social sciences, to policy-makers, and to those studying geography at school age. This short critical review builds upon an issue raised in this journal [Thrift, N., 2002. The future of geography. Geoforum 33, 291–298], namely the role of geographers as public intellectuals. After reviewing the different ways in which the notion of public intellectuals has been understood, the paper turns to geography’s representations and to its publics. The paper concludes by arguing for an appreciation of the full range of ways in which geographers call forth publics through a range of representational strategies. It suggests that regardless of how geographers perform publicly and intellectually, two things are perhaps worth remembering: it is in the interest of geographers to name what they do as geography and to name themselves as geographers.     

Power spectrum analysis of the light curve of RR Tauri

Power spectrum analysis is applied to the light curve of RR Tauri. Periodicities are found at 80, 200 and 533 days with some variation in the peak positions and power for different decades. Factors involved in the classification of the variable are discussed.Receipt delayed by postal strike in Great Britain.     

Evidence for a 55-50 ka (early Wisconsin) glaciation of the Cordilleran ice sheet, Yukon Territory, Canada

Cosmogenic ¹⁰Be ages on boulders of 54-51 ka (n = 4) on a penultimate Cordilleran ice sheet (CIS) drift confirm that Marine Oxygen Isotope Stage (MIS) 4 (early Wisconsin) glaciation was extensive in parts of Yukon Territory, the first confirmed evidence in the Canadian Cordillera. We name the glaciation inferred from the mapped and dated drift the Gladstone. These results are in apparent contrast to the MIS 6 (Illinoian) age of the penultimate Reid glaciation to the east in central Yukon but are equivalent to exposure ages on MIS 4 drift in Alaska. Contrasting penultimate ice extents in Yukon requires that different source areas of the northern CIS in Yukon responded differently to climatic forcing during glaciations. The variation in glacier extent for different source areas likely relates to variation in precipitation during glaciation, as the northern CIS was a precipitation-limited system. Causes for a variation in precipitation remain unclear but likely involve the style of precipitation delivery over the St. Elias Mountains possibly related to variations in the Aleutian low.