Simulation of dam/levee-break hydrodynamics with a three-dimensional implicit unstructured-mesh finite element model

Dam failures usually cause huge economic and life losses , especially in urban areas where there is a high concentration of inhabitants and economic actors. In order to understand the physical mechanisms of the formation and development of dam-break flooding, lots of efforts have been put into different types of modelling techniques. However, most of existing models are 1D (one-dimensional) or 2D models based on the shallow water equations. In this paper, we present a 3D numerical modelling investigation of dam-break flow hydrodynamics in an open L-shape channel. A newly developed 3D unstructured mesh finite element model is used here. An absorption-like term is introduced to the Navier–Stokes equations in order to control the conditioning of the matrix equation in the numerical solution process and thus improve the stability. A wetting and drying algorithm is used here to allow the free surface height to be treated with a high level of implicitness and stability. The 3D model has been validated by comparing the results with the published experimental data. Good agreement has been achieved at six selected locations. This study shows that the 3D unstructured mesh model is capable of capturing the 3D hydraulic aspects and complicated local flows around structures in simulation of dam-break flows.     

Mechanism of the intermittent motion of two-phase debris flows

A typical two-phase debris flow exhibits a high and steep flow head consisting of rolling boulders and cobbles with intermittent or fluctuating velocity. The relative motion between the solid phase and the liquid phase is obvious. The motion of a two-phase debris flow depends not only on the rheological properties of the flow, but also on the energy transmission between the solid and liquid phases. Several models have been developed to study two-phase debris flows. An essential shortcoming of most of these models is the omission of the interaction between the two phases and identification of the different roles of the different materials in two-phase debris flows. The tracer particles were used for the velocity of solid phase and the velocity of liquid phase was calculated by the water velocity on the surface of the debris flow in the experiments. This paper analyzed the intermittent feature of two-phase debris flows based on videos of debris flows in the field and flume experiments. The experiments showed that the height of the head of the two-phase debris flow increased gradually in the initiation stage and reached equilibrium at a certain distance from the start of the debris flow. The height growth and the velocity of the flow head showed fluctuating characteristics. Model equations were established and the analyses proved that the average velocity of the two-phase debris flow head was proportional to the flood discharge and inversely proportional to the volume of the debris flow head.     

Froude scaling limitations in modeling of turbidity currents

The scaling problem associated with the modeling of turbidity currents has been recognized but is yet to be explored systematically. This paper presents an analysis of the dimensionless governing equations of turbidity currents to investigate the scale effect. Three types of flow conditions are considered: (i) conservative density current; (ii) purely depositional turbidity current; and (iii) mixed erosional/depositional turbidity current. Two controlling dimensionless numbers, the Froude number and the Reynolds number, appear in the non-dimensional governing equations. When densimetric Froude similarity is satisfied, the analysis shows that the results would be scale-invariant for conservative density current under the rough turbulent condition. In the case of purely depositional flows, truly scale-invariant results cannot be obtained, as the Reynolds-mediated scale effects appear in the bottom boundary conditions of the flow velocity and sediment fall velocity. However, the scale effect would be relatively modest. The Reynolds effect becomes more significant for erosional or mixed erosional/depositional turbidity currents as Reynolds-mediated scale effects also appear in the sediment entrainment relation. Numerical simulations have been conducted at three different scales by considering densimetric Froude scaling alone as well as combined densimetric Froude and Reynolds similarity. Simulation results confirm that although the scaling of densimetric Froude number alone can produce scale-invariable results for conservative density currents, variations occur in the case of turbidity currents. The results become scale invariant when densimetric Froude and Reynolds similarities are satisfied simultaneously.     

Bringing together raptor collections in Europe for contaminant research and monitoring in relation to chemicals regulations

Raptors are good sentinels of environmental contamination and there is good capability for raptor biomonitoring in Europe. Raptor biomonitoring can benefit from natural history museums (NHMs), environmental specimen banks (ESBs) and other collections (e.g. specialist raptor specimen collections). Europe’s NHMs, ESBs and other collections hold large numbers of raptor specimens and samples, covering long periods of time. These collections are potentially a valuable resource for contaminant studies over time and space. There are strong needs to monitor contaminants in the environment to support EU and national chemical management. However, data on raptor specimens in NHMs, ESBs and other collections are dispersed, few are digitised, and they are thus not easy to access. Specimen coverage is patchy in terms of species, space and time. Contaminant research with raptors would be facilitated by creating a framework to link relevant collections, digitising all collections, developing a searchable meta-database covering all existing collections, making them more visible and accessible for contaminant research. This would also help identify gaps in coverage and stimulate specimen collection to fill gaps in support of prioritised contaminant monitoring. Collections can further support raptor biomonitoring by making samples available for analysis on request.     

Using linear regression to measure bird abundance

This study investigated methods for identifying daily incidence rates for bird species. It focused on relationships between incidence rates, site and season. We used sightings of 23 common resident species routinely reported every month from January 2004 to December 2007 at seven wetland locations in the Thale Noi non-hunting area of southern Thailand. Our findings revealed that the log-linear model gives a quite satisfactory fit, so it appears a suitable type of model for bird abundance. On taking logarithms of the incidence rates though, the zero counts must be replaced by an appropriate constant. Our model suggests that Cattle Egret (Bubulcus ibis) was found at the Thale Noi non-hunting area with the highest incidence rate. In contrast, we found a low mean of model outputs for Lesser Whistling-Duck (Dendrocygna javanica) relative to the mean in the data, and this species was not observed on at least 25 % or 3 days per year. These data had a low number of zeros and a large number of various species. Therefore, we recognize a remark on “what is being counted” that it is important to reasonably explain the species abundance in terms of statistical and ecological approaches.     

Consumer attitudes on the use of plastic and cloth bags

This paper examines consumer attitudes and behavior on the use of plastic and cloth bags in Eski?ehir, Turkey. To this end, a structural equation model is proposed. Environmental consciousness regarding the use of plastic bags, social pressure, support for the banning of plastic bags, the intention to use cloth bags and behavior to reduce plastic bag use are employed as latent variables in the model. The intention to use cloth bags and the behavior to reduce the use of plastic bags are defined as endogenous latent variables in the structural model. In the conclusion of the study, it is identified that consumers who are environmentally conscious and feel under social pressure, tend to reduce the use of plastic bags and switch to using cloth bags.     

Economic potential for conversion to organic farming: a net present value analysis in the East Mau Catchment,Nakuru, Kenya

This paper discusses the economic potential in terms of income changes that may result from conversion to low-external-input agriculture (LEIA) organic farming in a Kenya’s catchment area. A spreadsheet model applying the gross margin and net present value analysis was developed to estimate economic returns to labour and land of alternative smallholder cropping systems in the East Mau Catchment. The income and costs over a 10-year horizon associated with current cropping practices of a typical farm household cultivating 1.12 hectares of maize–bean intercrop, Irish potato, carrots, tomatoes, cabbages and kales mix were characterized based on field work conducted in 2008–2010. An “average” smallholder LEIA organic farm was simulated based on the conventional one, and its income discounted. A comparison was then made of the two farm types. Results indicate annual net present value returns to cropped land average Ksh 21,878/ha ($ 267/ha) and Kshs 22,561/ha (€ 275/ha) in 2010 values for conventional and prototype LEIA organic farming systems, respectively. Net returns are particularly sensitive to crop yields and price and cost of fertilizers and seeds. Further efforts should be made to provide an economic analysis of other LEIA organic farming practices such as composting, double digging and agroforestry in terms of additional labour costs resultant. The model can be extended to build more scenarios on the role of price premiums. Additionally, further research should be done to exploit the socio-demographic factors affecting the adoption of low-external-input systems.     

When experts disagree: the need to rethink indicator selection for assessing sustainability of agriculture

Sustainability indicators are well recognized for their potential to assess and monitor sustainable development of agricultural systems. A large number of indicators are proposed in various sustainability assessment frameworks, which raises concerns regarding the validity of approaches, usefulness and trust in such frameworks. Selecting indicators requires transparent and well-defined procedures to ensure the relevance and validity of sustainability assessments. The objective of this study, therefore, was to determine whether experts agree on which criteria are most important in the selection of indicators and indicator sets for robust sustainability assessments. Two groups of experts (Temperate Agriculture Research Network and New Zealand Sustainability Dashboard) were asked to rank the relative importance of eleven criteria for selecting individual indicators and of nine criteria for balancing a collective set of indicators. Both ranking surveys reveal a startling lack of consensus amongst experts about how best to measure agricultural sustainability and call for a radical rethink about how complementary approaches to sustainability assessments are used alongside each other to ensure a plurality of views and maximum collaboration and trust amongst stakeholders. To improve the transparency, relevance and robustness of sustainable assessments, the context of the sustainability assessment, including prioritizations of selection criteria for indicator selection, must be accounted for. A collaborative design process will enhance the acceptance of diverse values and prioritizations embedded in sustainability assessments. The process by which indicators and sustainability frameworks are established may be a much more important determinant of their success than the final shape of the assessment tools. Such an emphasis on process would make assessments more transparent, transformative and enduring.     

Status differences in collective action and forest benefits: evidence from joint forest management in India

Does status matter in community-based forest management? If so, are the high-status households more benefited than the low-status households? What drives status differences, if any, in the appropriation of forest resources? To address these questions, we draw on a theory of status and resource use that defines one’s status as one’s relative position in a group on the basis of power, prestige, honor and deference. Following this perspective, we surveyed the heads of 341 forest-based rural households in India from 2009 to 2010. We find that collective actions themselves are status-driven and the high-status households are more interested and involved in status-maintaining collective actions such as decision-making and implementation, while the low-status households perform general tasks like forest patrol. Moreover, the high-status households derive benefits from local forest significantly more than the low-status households. Further, decomposition analysis shows that a household’s prestige and honor measured by its access to social resources, problem faced and useful contacts explain about 56 % of the status gap in forest benefits, while socioeconomic characteristics explain only 16 % of the gap. Thus, due emphasis on household status from a broader socioeconomic perspective is required to reduce inequality in participation and the distribution of forest benefits in co-management.