Modelling sediment transport as a moving wave — The transfer and deposition of mining waste

The movement of slugs of bedload from a discrete input point down a river has proved difficult to model using conventional finite-difference formulations of equations of motion. A model is proposed which makes explicit allowance for the mean sediment velocity and, through a dispersion coefficient, the distribution of sediment velocity about the mean. A second comparative model uses the normal mass conservation or sediment transport continuity approach. The models have been tested over a 43-month period using data from seven monitored cross-sections of the Kawerong River on Bougainville Island, Papua New Guinea, a system which receives waste from a large copper mine. The dispersion model performs considerably better than the mass-conservation model.     

Sustainability of transhumance grazing systems under socio-economic threats in Langtang,Nepal

The decline or loss of traditional social- ecological systems may induce adverse effects to the societies and ecosystems. Transhumance, the recurring and seasonal movement of grazing livestock, is increasingly constrained by a numbers of factors including policy, land use and soeio-economic changes in Nepal. To explore how these changes have affected the transhumance, this study investigated transhumance at the Langtang valley in central Nepal. The specific objectives of this study were to determine the herd size and composition, spatial-temporal patterns and to identify the major drivers of the system and the system changes. Data were collected from field study comprising semi-structured interviews with the herders, focus group discussions, key informants survey, and observations of rangeland and livestock management systems. The study revealed that the transhumanee system in the Langtang is influenced by two types of drivers. In one hand, traditional practices are contributing to the sustainability of the system. On the other hand, the grazing patterns and adaptive responses are strongly influenced by changes in government policies, socioeconomic and cultural transformation, livestock productivity, markets, rangeland conditions and climate change. The findings of this study help with the development and implementation of transhumance management policy for the sustainability.     

Insights From a Multi-Method Recharge Estimation Comparison Study

Although most recharge estimation studies apply multiple methods to identify the possible range in recharge values, many do not distinguish clearly enough between inherent uncertainty of the methods and other factors affecting the results. We investigated the additional value that can be gained from multi-method recharge studies through insights into hydrogeological understanding, in addition to characterizing uncertainty. Nine separate groundwater recharge estimation methods, with a total of 17 variations, were applied at a shallow aquifer in northwest Ethiopia in the context of the potential for shallow groundwater resource development. These gave a wide range of recharge values from 45 to 814 mm/a. Critical assessment indicated that the results depended on what the recharge represents (actual, potential, minimum recharge or change in aquifer storage), and spatial and temporal scales, as well as uncertainties from application of each method. Important insights into the hydrogeological system were gained from this detailed analysis, which also confirmed that the range of values for actual recharge was reduced to around 280-430 mm/a. This study demonstrates that even when assumptions behind methods are violated, as they often are to some degree especially when data are limited, valuable insights into the hydrogeological system can be gained from application of multiple methods.     

The contribution of faint blue galaxies to the submillimetre counts and background

Observations in the submillimetre (submm) waveband have recently revealed a new population of luminous sources. These are proposed to lie at high redshift and to be optically faint because of their high intrinsic dust obscuration. The presence of dust has been previously invoked in optical galaxy count models which use the Bruzual & Charlot evolution models with an exponential τ =9 Gyr star formation rate (SFR) for spirals, and these fit the count data well from U to K . We now show that by using either a 1/ λ or Calzetti absorption law for the dust and re-distributing the evolved spiral galaxy ultraviolet (UV) radiation into the far-infrared (FIR), these models can account for all of the 'faint' ( 1 mJy) 850-μm galaxy counts, but fail to fit 'bright' ( 2 mJy) sources, indicating that another explanation for the submm counts may apply at brighter fluxes, e.g., quasi-stellar objects (QSOs) or ultraluminous infrared galaxies (ULIRGs). We find that the main contribution to the faint, submm number counts is in the redshift range 0.5< z <3, peaking at z ≈1.8. The above model, using either dust law, can also explain a significant proportion of the extragalactic background at 850 μm, as well as producing a reasonable fit to the bright 60-μm IRAS counts.     

Community resilience,globalization, and transitional pathways of decision-making

This article investigates the impacts of globalization processes on community resilience. It argues that theoretical concepts such as transition theory can provide a lens through which resilience pathways at community level can be better understood, and proposes a framework focused on a social resilience approach for understanding community resilience as the conceptual space at the intersection between economic, social and environmental capital. It argues that certain types of communities are losing resilience through increased embeddedness into globalized pathways of decision-making, while other communities may be gaining resilience, although not one system is either totally resilient or totally vulnerable. Striking the right ‘balance’ between communities and their scalar interactions with the global level is key for maximization of community resilience: while too much isolation of a community may be bad in light of over-dependency on local resources, skills and people, ‘over-globalization’, with possible loss of autonomy and identity, may be equally fraught with problems. In particular, relocalized communities have, so far, not shown much tangible success, as almost all members of the relocalization process at community level are simultaneously embedded within the global capitalist system through their dependencies on global economic processes.     

Estimating sediment transport in a braided gravel channel — The Kawerong River, Bougainville, Papua New Guinea

It is difficult to estimate sediment transport in braided rivers because of the complex hydraulics of rapidly changing multi-channel systems. This paper describes an algorithm for generating sets of braided-river hydraulic parameters for use with sediment transport equations. The algorithm uses random number-based simulation techniques and empirically determined probability distributions of individual hydraulic variables from the White River (U.S.A.) and the Kawerong River. A test of the suitability of the algorithm for the estimation of sediment transport was carried out over a period of two years using the Meyer-Peter and Muller equation on eight reaches of the Kawerong River in which sediment transport is known. The test produced a mean absolute error of 16.3% suggesting that the algorithm may have some potential in braided-river modelling.     

Wood as a driver of past landscape change along river corridors

The role of wood as a driver of landform development appears to have been overlooked in the interpretation of palaeo‐landscape change along river corridors. Deforested river corridors and wood‐free rivers characterize ‘modern’, managed landscapes, but along natural river corridors both driftwood dynamics and tree reproductive strategies can have a dramatic impact on the style and rate of channel and floodplain development. Therefore, we believe that interpretations of the post‐glacial history of river valleys across the northern temperate climatic zone could be usefully reassessed, incorporating the roles of riparian trees. Copyright © 2008 John Wiley & Sons, Ltd.