Comparing the transitional behaviour of kaolinite and bentonite suspension flows

Past research has demonstrated the dramatic effects that variations in suspended clay can have on the properties of flow by producing a range of transitional flows between turbulent and laminar states, depending on clay concentration and fluid shear. Past studies have been restricted to kaolinite flows, a clay mineral that has relatively weak cohesive properties. This paper extends these studies to suspension flows of bentonite, a clay mineral that attains higher viscosities at far lower volumetric concentrations within a flow. The results show that the types of transitional flow behaviour recognized in past studies can also be found in bentonite suspension flows, but at lower suspended sediment concentrations, thus demonstrating an even more dramatic effect on flow properties, and potentially on sediment transport and resulting bed morphology, than kaolinite flows. The paper proposes new stability diagrams for the phase space of bentonite flows and compares these to past work on kaolinite suspension flows. These new data suggest that the transitional‐flow Reynolds number can be used to delineate the types of transitional flow across different clay types and assess modern and ancient clay‐suspension flows. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

Assessing market and non-market costs of freshwater flooding due to climate change in the community of Fredericton, Eastern Canada

There is a general consensus that climate change will increase the frequency and severity of freshwater flooding in many parts of the world. Communities prone to such flooding have struggled to understand the manner in which this will affect them (in both economic and social terms) and the appropriate way to adapt. In this study, we conduct a case-study investigation into the costs of freshwater flooding due to climate change along the Saint John River in Fredericton, NB, Canada. We develop a four-step framework that combines extreme event analysis, downscaled general circulation models, hydrologic analysis, and the contingent valuation method. Using this framework, together with primary data on a 2005 flooding event, we estimate market and non-market annual average flood damage under a number of climate and population scenarios. We find that non-market costs can represent up to 50% of total household costs of flooding events, and 23–42% of the total costs of flooding due to climate change, depending on the different climate and population scenarios considered. Incorporating such costs into flood adaptation planning may substantially increase support for active adaptation activities, especially in ‘worst case’ climate scenarios.     

Source and supply of sediment to a shoreline salient in a fringing reef environment

Reef-associated landforms are coupled to the health of the reef ecosystem which produces the sediment that forms and maintains these landforms. However, this connection can make reef-fronted coastlines sensitive to the impacts of climate change, given that any decline in ecosystem health (e.g. decreasing sediment supply) or changes to physical processes (e.g. sea level rise, increasing wave energy) could drive the sediment budgets of these systems into a net erosive state. Therefore, knowledge of both the sediment sources and transport mechanisms is required to predict the sensitivity of reef-associated landforms to future climate change. Here, we examine the benthic habitat composition, sediment characteristics (composition, texture, and age), and transport mechanisms and pathways to understand the interconnections between coastal morphology and the reef system at Tantabiddi, Ningaloo Reef, Western Australia. Benthic surveys and sediment composition analysis revealed that although live coral accounts for less than 5% of the benthic cover, coral is the dominant sediment constituent (34% on average). Sediment ages (²³⁸U/²³⁰Th) were mostly found to be thousands of years old, suggesting that the primary sediment source is relic reef material (e.g. Holocene reef framework). Sediment transport across the lagoon was quantified through measurements of ripple migration rates, which were found to be shoreward migrating and responsible for feeding the large shoreline salient in the lee of the reef. The derived sediment fluxes were comparable with previously measured rates of sediment production by bioerosion. These results suggest that sediment budgets of systems dependent on old (>10³ years) source materials may be more resilient to climate change as present-day reef health and community composition (i.e. sources of ‘new’ carbonate production) have limited influence on sediment supply. Therefore, the vulnerability of reef-associated landforms in these systems will be dictated by future changes to mechanisms of sediment generation (e.g. bioerosion) and/or physical processes. © 2018 John Wiley & Sons, Ltd.     

Transboundary impacts on regional ground water modeling in Texas

Recent legislation required regional grassroots water resources planning across the entire state of Texas. The Texas Water Development Board (TWDB), the state's primary water resource planning agency, divided the state into 16 planning regions. Each planning group developed plans to manage both ground water and surface water sources and to meet future demands of various combinations of domestic, agricultural, municipal, and industrial water consumers. This presentation describes the challenges in developing a ground water model for the Llano Estacado Regional Water Planning Group (LERWPG), whose region includes 21 counties in the Southern High Plains of Texas. While surface water is supplied to several cities in this region, the vast majority of the regional water use comes from the High Plains aquifer system, often locally referred to as the Ogallala Aquifer. Over 95% of the ground water demand is for irrigated agriculture. The LERWPG had to predict the impact of future TWDB-projected water demands, as provided by the TWDB, on the aquifer for the period 2000 to 2050. If detrimental impacts were noted, alternative management strategies must be proposed. While much effort was spent on evaluating the current status of the ground water reserves, an appropriate numerical model of the aquifer system was necessary to demonstrate future impacts of the predicted withdrawals as well as the effects of the alternative strategies. The modeling effort was completed in the summer of 2000. This presentation concentrates on the political, scientific, and nontechnical issues in this planning process that complicated the modeling effort. Uncertainties in data, most significantly in distribution and intensity of recharge and withdrawals, significantly impacted the calibration and predictive modeling efforts. Four predictive scenarios, including baseline projections, recurrence of the drought of record, precipitation enhancement, and reduced irrigation demand, were simulated to identify counties at risk of low final ground water storage volume or low levels of satisfied demand by 2050.     

Wind erosion of blanket peat during a short period of surface desiccation (North Pennines,Northern England)

Strong winds are a characteristic feature of UK upland areas. Despite this, understanding of aeolian processes in upland environments of the UK is limited. This paper presents direct measurements and observations of blanket peat erosion by wind action during a two week period of desiccation in the North Pennines, Northern England. A circular configuration of mass flux sediment samplers was used to collect peat eroded by wind action from 16 cardinal compass directions. Meteorological conditions (wind speed, wind direction, precipitation and temperature) were recorded by an automatic weather station set up adjacent to the site. Surface desiccation led to peat crust erosion and dust deflation. During short (≤1 hour) periods of precipitation, wind‐driven rainfall also caused erosion. Typically, dust flux rates were up to two orders of magnitude lower than recorded during periods of sustained wet weather. Measurements demonstrate the hitherto unreported rapid switch in process regime between wind‐driven rainfall and dry blow deflation in blanket peat environments. Dry blow processes of blanket peat erosion may become more important in UK upland areas if climate change promotes more frequent surface desiccation. Copyright © 2006 John Wiley & Sons, Ltd.     

Significance of geomorphological and subsurface drainage controls on failures of peat‐covered hillslopes triggered by extreme rainfall

On 19 September 2003, 40 landslides of 140–18 000 m³ volume occurred within 2·5 km² on the slopes of Dooncarton Mountain (Republic of Ireland) during a storm that may have exceeded 90 mm within 90 minutes. The landslides were investigated to determine the reasons for such a high density of slope failures. All of the landslides were surveyed within four months, and nine of them were investigated in detail. The six largest landslides, all peat failures, accounted for 57% of the more than 100 000 m³ of material displaced during the event. A consistent sequence of superficial materials was found on the failed hillslopes, including an extensive iron pan at the base of a buried soil horizon 0·3 m below the base of the peat. Morphologically, almost all of the landslides occurred on steep planar slopes or around sharp convexities, with the latter failures developing retrogressively upslope. The only significant relationship found from analysis of 371 subsurface pipes and 142 seepage cracks (defined here as contiguous fissures conducting concentrated subsurface flow) across all the failures was that the thinner the peat cover, the deeper the pipes and seepage cracks occurred below the base of peat. It is concluded that most of the landslides were probably caused by a combination of excess water pressures in the buried soil horizon and the thinner overburden of peat or peaty soil associated with the steeper slope segments. Pipes and seepage cracks formed on the iron pan probably existed prior to the failure event and may have contributed to the high water pressures as rainwater inputs exceeded their discharge capacities. One large peat slide was probably triggered by excess water pressures developed within and between artificial tine cuts. The properties of the blanket peat were generally of little consequence in the occurrence of the landslides, but relict desiccation cracks and other structural weaknesses through the peat mass were probably highly significant. Although several aspects of the peat failures correspond to previously published examples, the context of these failures in terms of the topography and upland catena is distinctive. Copyright © 2007 John Wiley & Sons, Ltd.     

Does geographic location impact the survival differential between screen- and interval-detected breast cancers?

Although mammography screening programs aim to diagnose breast cancer at an early stage, not all tumours are detected during the regular screening examination. This study examines the influence of various characteristics, including geographical residence, on the survival between screen- and interval-detected breast cancers among participants of a public population-based breast screening program in Queensland, Australia. The investigation was performed using the linked population-based datasets from BreastScreen Queensland and the Queensland Cancer Registry for the period of 1997–2008 for women aged 40–89 years at diagnosis. A Bayesian spatial relative survival modelling approach that accommodates rare outcomes in small geographic regions was adopted, with the use of Markov chain Monte Carlo computation, to evaluate the relative excess risk of breast cancer. In the multivariate Bayesian spatial model, higher relative excess risk of mortality was observed in interval-detected cancer (RER = 1.59, 95 % credible interval = [1.33, 1.89]) compared to screen-detected cancer. Higher cancer survival among the study cohort was also observed among younger women (40–59 years), those of non-Indigenous ethnicity, with localised (stage I) tumour stage as well as those not in the work force. There was no independent association with marital status. Moreover, there was no substantive evidence of either measured geographical or latent random spatial inequalities in survival among screening participants across Queensland, meaning the higher survival for screen-detected breast cancer patients compared to interval-detected women was consistent across the state. These results provide suggestive evidence supporting the effectiveness of the BreastScreen Queensland screening program in reaching socio-economically disadvantaged women as well as those living in rural and remote areas of the state, but also highlights the need for any interval cancer awareness programs to be geographically widespread.     

Annual to decadal morphodynamics of the foredune system at Greenwich Dunes,Prince Edward Island,Canada

The purpose of this study was to quantify relationships between season, sediment availability, sediment transport pathways, and beach/foredune morphology at Greenwich Dunes, PEI. This was done for periods ranging from a few days to multiple decades using erosion pins, bedframe measurements, annual surveys, and digital photogrammetry using historical aerial photographs. The relative significance of seasonal/annual processes versus response of the foredune system to broader geomorphic controls (e.g. relative sea level rise, storms, etc.) was also assessed. The data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at Greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area, resulting in ongoing differences in foredune morphology. They also demonstrate that models that incorporate wind climate alone, or even models that include other factors like beach moisture, would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology, especially the presence or absence of a dune ramp. Finally, the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope, over the crest, and onto the lee slope. Although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback, the overall decadal evolution of the foredune system at Greenwich is consistent with, and supports, the Davidson‐Arnott (2005) conceptual model of dune transgression under rising sea level. Copyright © 2012 John Wiley & Sons, Ltd.     

A large landslide event in a post‐glacial landscape: rethinking glacial legacy

Threlkeld Knotts (c. 500 m above sea level) in the English Lake District has hitherto been considered to be a glacially‐modified intrusion of microgranite. However, its surface features are incompatible with glacial modification; neither can these nor the subsurface structures revealed by ground‐penetrating radar (GPR) be explained by post‐glacial subaerial processes acting on a glacially‐modified microgranite intrusion. Here we re‐interpret Threlkeld Knotts as a very large post‐glacial landslide involving the microgranite, with an estimated volume of about 4 × 10⁷ m³. This interpretation is tested against published and recent information on the geology of the site, the glacial geomorphic history of the area and newly‐acquired GPR data. More than 60 large post‐Last Glacial Maximum (LGM) rock–slope failures have significantly modified the glaciated landscape of the Lake District; this is one of the largest. Recognition of this major landslide deposit in such a well‐studied environment highlights the need to continuously re‐examine landscapes in the light of increasing knowledge of geomorphic processes and with available technology in currently active or de‐glaciating environments. Copyright © 2012 John Wiley & Sons, Ltd.