Time to talk knowledge

As part of the secondary school qualification repackaging, the Ministry of Education has requested the geography education community define what constitutes their “critical body of knowledge.” In this article, I discuss three knowledge‐oriented themes focused on: (a) recent assessment trends in geography; (b) the predictive value of NCEA Level 3 geography with 100‐level success and (c) the nature of knowledge as expressed by the New Zealand Curriculum and assessment. Taken together, these themes suggest a need for a serious conversation about knowledge in school geography, as a pre‐cursor to the re‐design of the geography standards matrix.     

Representation of Uncertainty and Integration of PGIS-based Grazing Intensity Maps Using Evidential Belief Functions

In a project to classify livestock grazing intensity using participatory geographic information systems (PGIS), we encountered the problem of how to synthesize PGIS-based maps of livestock grazing intensity that were prepared separately by local experts. We investigated the utility of evidential belief functions (EBFs) and Dempster's rule of combination to represent classification uncertainty and integrate the PGIS-based grazing intensity maps. These maps were used as individual sets of evidence in the application of EBFs to evaluate the proposition that " This area or pixel belongs to the high, medium, or low grazing intensity class because the local expert(s) says (say) so ". The class-area-weighted averages of EBFs based on each of the PGIS-based maps show that the lowest degree of classification uncertainty is associated with maps in which "vegetation species" was used as the mapping criterion. This criterion, together with local landscape attributes of livestock use may be considered as an appropriate standard measure for grazing intensity. The maps of integrated EBFs of grazing intensity show that classification uncertainty is high when the local experts apply at least two mapping criteria together. This study demonstrates the usefulness of EBFs to represent classification uncertainty and the possibility to use the EBF values in identifying and using criteria for PGIS-based mapping of livestock grazing intensity.     

Equilibrium erosion of soft rock shores with a shallow or absent beach under increased sea level rise

A process-based numerical model was used to explore the response of soft rock shores with low volume beaches to variable rates of sea level rise. Equilibrium recession rates were simulated for ranges of wave height and period, tidal amplitude, rock strength, beach volume and rate of sea level rise. Equilibrium shore profiles were found to be steeper with higher rates of sea level rise. Beaches were represented as protective surfaces yet were found to cause no significant reduction in equilibrium recession rate when their volumes were below a critical threshold. Reduced equilibrium recession rates were found with beaches that extended sufficiently far below low tide level. The model results imply that, given several constraints, a very simple relationship exists between increased rates of sea level rise and the response of eroding composite soft rock/low volume beach shores.     

Sediment resuspension events induced by the wake wash of deep-draft vessels

Hydrodynamics and sediment resuspension events, induced at the shoreline by a deep-draft vessel passing nearby, are described. Measurements (pressure, currents and turbidity) were obtained at 4 Hz, on a lower beach ~50 m from a channel where large car ferries operate in Wootton Creek, Isle of Wight. The study focuses on a representative 8-min 32-s-long record, during which two large vessels passed the channel section. At the shore, the passage of each vessel induced a long-period water-level drawdown, followed by a water-level oscillation (seiche) of similar period, and the short-period waves of the wake. Both drawdowns were the main constituents of the prevailing wave pattern. The second drawdown was the largest in amplitude, in response to a higher speed of the ferry, and the influence of the seiche which had been activated during the preceding event. Two successive peaks of turbidity were observed shortly after this drawdown. Analyses of current velocity and direction indicate that the sediments resuspended originated from the shallower upper beach. Anthropogenically induced erosion of the foreshore is predicted at Wootton Creek.     

Natural aggregates in the performance and durability of concrete: chemical characteristics

This article continues from the earlier feature in Geology Today (2011, v.27, n.4) and looks at the influence of chemical reactivity within concrete due to the presence of unsound aggregates or deleterious material incorporated in the aggregate used in the concrete mix. Some of the more disruptive problems from chemical unsoundness come from the presence of chlorides, which cause rusting in reinforced concrete or, sulphate attack from ground waters. Both of these reactions are relatively common in Britain. Alkali–silica reactions with aggregates and cement is not too prevalent in Britain but can be very prevalent and disruptive elsewhere in the world.     

Field Comparison of Micropurging vs. Traditional Ground Water Sampling

Micropurge sampling of ground water wells has been suggested as a possible replacement to traditional purge and sample methods. To compare methods, duplicate ground water samples were collected at two field sites using iraditional and micropurge methods. Samples were analyzed for selected organic and inorganic constituents, and the results were compared statistically. Analysis of the data using the nonparametric sign test indicates that within a 95 percent confidence interval, there was no significant difference between the two methods for the site contaminants and the majority of analytes. These analytical results were supported by visual observations with the colloidal borescope, which demonstrated impacts on the flow system in the well when using traditional sampling methods. Under selected circumstances, the results suggest replacing traditional sampling with micropurging based on reliability, cost, and waste minimization.     

River stabilisation due to changing climate and vegetation during the late Quaternary in western Tasmania, Australia

The Stanley River in western Tasmania, Australia, contains sub-fossil rainforest logs within the channel and floodplain. Of the more than 85 radiocarbon dates obtained, all but 3 date from 17 ka to the present and permit an interpretation of fluvial and related environmental changes over this period. Particular attention is focused on the interactive relationship between the river and its riparian rainforest. Following the Last Glacial Maximum, the Stanley River was a laterally active gravel-load system reworking most of its valley floor in the upstream reaches. With ameliorating conditions at the end of the Pleistocene, climate became less seasonal and flow regimes less energetic. Huon pines already present in the catchment, re-asserted themselves in the form of dense tree cover along the river banks and floodplains with basal floodplain deposition shifting from gravels to coarse sands and granules. By about 3.5 ka, a further change in climate reduced stream discharges substantially. As a result the channel reduced in size, transported finer sediment, became laterally stable, and the floodplain accreted with overbank deposits of sand and silt. Huon pines falling into the channel formed obstructions of woody debris, some surviving for 2 ka. These have reduced stream power and boundary shear stress, further contributing to channel stability. Generational sequences of Huon pines on the river banks, some extending back 1–2 ka, are additional evidence of this stability. Since the Pleistocene, changing climate and the re-establishment of dense riparian rainforest appear to have stabilised the river channels and floodplains of western Tasmania.