Prevention of Wellbore Clogging by Intermittent Abstraction

Wellfield “Tull en ’t Waal” (water utility Vitens Midden Nederland) suffers extensively from wellbore (or mechanical) clogging. To prevent this type of clogging, wells have been operated intermittently since August 2005 using a carrousel well operation schedule. Since the introduction of this schedule, wellbore clogging has become minimal.     

Assessing Soil Remobilisation in Catchments using a 137Cs-sediment Hillslope Model

Soil redistribution studies are important, especially in water supply catchments, because the rate at which denudation is occurring has implications for offsite water quality. However, the extent to which soil is redistributed within the landscape can be difficult to determine. This challenge can be overcome using fallout caesium-137 (¹³⁷Cs). This paper describes the rates of soil loss and remobilisation in two sub-catchments within the Sydney Basin region, namely Kembla and Kentish Creeks, which drain to the Cordeaux reservoir. The total inventories of ¹³⁷Cs in catchment soils were determined, a ¹³⁷Cs-regression equation and a theoretical diffusion and migration model were used to established relationships between ¹³⁷Cs inventories and the rates of soil loss. These relationships revealed relatively low occurrence of soil loss in Kentish Creek, but two slopes in the Kembla Creek sub-catchment had losses that appear to be moderate. However, there was no clear evidence to suggest whether slopes in upper and lower reaches of catchments had specific patterns of soil remobilisation. Qualitative categorisation of the slope elements using a ¹³⁷Cs-sediment hillslope model can be a useful sentinel for land users and decision makers even if absolute rates of soil loss or gain are not certain. The findings suggest that sediments mobilised in the study sub-catchments are not likely to impact significantly on the water quality in the Cordeaux reservoir.     

Late Cenozoic uplift of the Amanos Mountains and incision of the Middle Ceyhan river gorge, southern Turkey; Ar–Ar dating of the Düziçi basalt

Using the Ar–Ar technique, we have obtained the first numerical dates for the Pleistocene volcanism along the valley of the River Ceyhan in the Düziçi area of southern Turkey, in the western foothills of the Amanos Mountains. Our six dates indicate a single abrupt episode of volcanism at  270 ka. We have identified a staircase of 7 fluvial terraces, at altitudes of up to  230 m above the present level of the Ceyhan. Using the disposition of the basalt as an age constraint, we assign these terraces to cold-climate stages between marine oxygen isotope stages 16 and 2, indicating rates of fluvial incision, equated to surface uplift, that increase upstream through the western foothills of this mountain range at between 0.25 and 0.4 mm a^− 1. Extrapolation of these uplift rates into the axis of the range suggests that the entire  2300 m of present-day relief has developed since the Mid-Pliocene, a view that we confirm using numerical modelling. Since  3.7 Ma the Amanos Mountains have formed a transpressive stepover along the northern part of the Dead Sea Fault Zone, where crustal shortening is required by the geometry. Using a physics-based technique, we have modelled the overall isostatic response to the combination of processes occurring, including crustal thickening caused by the shortening, erosion caused by orographic precipitation, and the resulting outward flow of mobile lower-crustal material, in order to predict the resulting history of surface uplift. This modelling suggests that the effective viscosity of the lower crust in this region is in the range  1–2 × 10¹⁹ Pa s, consistent with a Moho temperature of  590 ± 10 °C, the latter value being in agreement with heat flow data. This modelling shows that the nature of the active crustal deformation is now understood, to first order at least, in this key locality within the boundary zone between the African and Arabian plates, the structure and geomorphology of which have been fundamentally misunderstood in the past.     

Developing effective environmental indicators--does a new dog need old tricks?

Environmental indicators are being increasingly used to emphasise the relevance of monitoring. However, indicators must also be effective. In particular, they must be able to answer management questions, be accessible to the target audience and be sufficiently precise. Here, we use a time series of mercury levels in plaice from Liverpool Bay to illustrate how specific management questions can be formulated, answered, and the precision of these answers assessed. We also show how a programme design can incorporate a series of management questions that are likely to arise over time in response to observed changes in a time series.     

Landscape-Scale Analysis of Interactions between Insect Defoliation and Forest Fire in Central Canada

Analysis of Ontario's historical records from 1941–1996 showed that spruce budworm, Choristoneura fumiferana (Clem.) caused whole tree mortality within 389×10³ km². This amounted to 9.2% of the annually cumulative area with moderate-severe defoliation. Large (>2 km²) fires were reported in approximately 65,000 km² and overlapped only 2.8% of the area of reported spruce budworm (SBW) caused tree mortality. Within the 417×10³ km² defoliated by SBW at least once in 1941–1996, the maximum total area recorded as defoliated in any year was over 20 times the maximal area burnt. In the 19,950 km² experiencing both wildfire and SBW defoliation, analysis of the spectra of time lags between the two disturbance types indicated that fires occurred 3–9 years after a SBW outbreak disproportionately often. This window of opportunity for wildfire varies geographically: it starts later after SBW outbreak and lasts longer in western than in eastern Ontario. In addition, 7.5% of the areas containing SBW killed trees were burnt in western compared to 4.8% in eastern Ontario. These geographical differences may result at least partly from slower decomposition of dead fuels in the drier climates of the western SBW belt compared to the eastern SBW belt. The implications for climatic change are discussed.     

Too‐low magnetic inclinations in central Asia: an indication of a long‐term Tertiary non‐dipole field?

Observed Tertiary palaeolatitudes in central Asia are more southerly (by about 1600 km on average) than those predicted from the Eurasian reference palaeopoles. Subsequent northward displacements of the central Asian terranes are unlikely to have been this large. In this study we analyse to what extent non-dipole fields, especially octupole fields, can explain this phenomenon. A global (zonal) octupole field manifests itself in two ways. (1) Because the reference APWP is based mostly on results from the UK and North America, its palaeopoles will be far-sided as seen from the North Atlantic, but near-sided as seen from eastern Asia, giving predicted palaeolatitudes that are too high. (2) An octupole field contribution produces observed palaeolatitudes, as calculated with the dipole formula for central Asia, that are too low. Both effects therefore increase the palaeolatitude anomalies in Asia. We find that an octupole/dipole field ratio (G3) of 0.06 or greater will reduce the palaeolatitude discrepancies significantly and is of the same magnitude as the G3 estimate of a recent analysis of Early Tertiary European and North American data.