Sewer model development under minimum data requirements

Planning, design and operation of urban drainage systems is often based on hydraulic sewer modelling. Sewer models are also increasingly used to quantify pollution loads discharged to aquatic ecosystems (e.g. via combined sewer overflows), which ultimately allows an estimation of the ecological impact emanating from urban drainage systems. The establishment of such network models, however, requires detailed and accurate information about the sewer network structure and the connected surface area. This infrastructure data is often unavailable, confidential or available in ‘paper’ format only. The present paper outlines a novel approach to develop a hydraulic sewer model constrained by a minimum amount of data. The approach combines the application of a surface flow accumulation algorithm to a selectively manipulated Digital Elevation Model (DEM) with a routine for hydraulic network dimensioning to generate a close-to-reality sewer network ready to be implemented in a hydraulic modelling platform. The method is tested for three real-life catchments of which characteristics vary in scale, topography, state of development and network complexity. For all cases the generated network is implemented on the EPA-SWMM platform to allow hydrodynamic simulations. Model performance is assessed by (1) evaluating the spatial match of existing and generated network layout, (2) comparing the estimated hydraulic dimension with real-life infrastructure data and (3) benchmarking simulated runoff with measured data for a defined validation period. The analysis shows that the presented method is capable of reproducing the original network layout, network length and corresponding discharge rates based on little, freely available information. Further research potential is identified to improve the hydraulic dimensioning and the application to complex systems that include control structures. The presented approach is useful to estimate the scope of drainage networks including layout and design (e.g. for preliminary planning in emerging areas) to screen existing networks and to identify critical spots where more precise information is required.     

Commodity conservation: The restructuring of community conservation in South Africa and the Philippines

The world over, neoliberal modes of conservation are hybridising with, or even replacing, other forms of conservation. Under the banner of ‘win–win’ policies, planners actively work to commoditize natural resources and the social relations that determine the use and conservation of these resources. While these general processes seem to hold sway globally, it is crucial not to lose sight of the context specific ways in which neo-liberalism influences conservation practice and local outcomes. The paper examines how neo-liberalism’s global pervasiveness becomes manifest across different levels and scales in South Africa and the Philippines. The conclusion suggests that as a result of these neoliberal pressures, emphasis is shifting from local constructions of ‘nature’ by communities to what the environment should mean for communities in terms of commodified resources and growing capitalist markets.     

Collisional records in LL-chondrites

Abstract One-third of all the LL-chondrites have exposure ages of ～15 Ma and were exposed to cosmic rays following a collisional break-up. The probability that the 15-Ma peak represents a random signal is calculated to be less than 2%. Considerably lower probabilities are obtained if only LL5s or subgroups of high ⁴⁰Ar retention are used. Furthermore, we show that the peak shape agrees with statistical constraints obtained from multiple analyses of samples from the St. Severin LL6-chondrite. The frequency in and out of the 15-Ma peak varies significantly for different petrographic LL-types. The radiogenic ⁴⁰Ar retention systematics (most LL-chondrites retained ⁴⁰Ar_rad) shows that no substantial heat pulse resulted in the 15-Ma collisional event. Interestingly, smaller exposure age clusters at ～28 Ma and ～40 Ma match up well with clusters in the histogram of L-chondrites. The distribution of LL-exposure ages is not consistent with that expected for a quasi-continuous injection of LL material into a resonance zone of the asteroid belt. The near absence of exposure ages shorter than 8 Ma either indicates a lack of recent collisional events or considerably longer transfer times than inferred from dynamical considerations.     

Volcanic particle aggregation in explosive eruption columns. Part II: Numerical experiments

The goal of this paper is to determine the parameters that control the aggregation efficiency and the growth rate of volcanic particles within the eruption column. Numerical experiments are performed with the plume model ATHAM (Active Tracer High resolution Atmospheric Model). In this study we employ the parameterizations described in a companion paper (this issue). The presence of hydrometeors promotes the aggregation of ash particles, which strongly increases their fall velocities and thus their environmental impact. The tephra mass is about two orders of magnitude greater than that of hydrometeors during typical Plinian eruptions without interaction of external water. Ice is highly dominant in comparison to liquid water (> 99% by mass). This is caused by the fast column rise (> 100 m s^− 1 on average) to very cold altitudes. Most particles occur in the form of frozen aggregates with low ice content.The collection efficiency is governed by the availability of hydrometeors acting as adhesives at the particles’ surface in our study, and wet ash particles have a higher sticking capacity than icy ones. Therefore, aggregation is fastest during the eruption within the column when limited regions of liquid water exist and when particle concentrations are very high (of the order of 10⁵ cm^− 3). Increased humidity in the background atmosphere generally leads to enhanced ice formation, but shows only a weak influence on the aggregation process. First sensitivity studies showed, however, a significant increase of the liquid water fraction when considering salinity effects. The availability of water or ice at the particles' surfaces is also governed by the surface properties, the porosity and permeability of ash, which are not well established to date. Particle growth is significantly enhanced for greater differences in the sizes and fall velocities among particles, as gravitational capture becomes more efficient. Our experiments indicate a major influence of the erupted particle size distribution. First sensitivity studies show that electrostatic forces result in a significant enhancement of aggregated particles.The present exploratory study provides new insights into the sensitivity of the ash aggregation process to a number of key parameters. Our results indicate the need of further constraining particle composition, size, porosity, permeability, and surface properties at low temperatures by in situ observations in the laboratory and in the field. In addition further research on electrostatic aggregation would be desirable.     

Accuracy of soil heat flux plate measurements in coarse substrates – Field measurements versus a laboratory test

Summary The in-situ performance of heat flux plates within coarse porous substrates might be limited due to poor contact between plate and substrate. We tested this behaviour with a simple laboratory set-up. Two test substrates were placed above a reference material of known thermal conductivity between a warm and a cold plate to establish a vertical heat flux. The temperature gradients and the response of a soil heat flux plate were measured. By means of the Fourier law of heat conduction the thermal conductivity of each test substrate was calculated, thus incorporating all heat transfer within the volume and representing the “effective” conductivity. The laboratory method had an accuracy of up to ±7% (±13% for a smaller set-up). In comparison, heat flux plate-derived heat fluxes showed errors of up to 26%. Use of heat flux plates in coarse substrates is not recommended without additional measurements.     

Darss Sill as a biological border in the fossil record of the Baltic Sea: evidence from diatoms

Biostratigraphical and palaeoecological analyses of cores along a transect from Femer Belt to the Arkona Basin reveal that North Sea waters began to enter the western Baltic Sea between 8600 and 8400 calibrated years BP. Studies of diatoms indicate that Mecklenburg Bay was characterised by slightly brackish-water conditions between 8400 and 8000 cal. years BP. At around 8000 cal. years BP increasing salinity is indicated by a strong dominance of the diatoms Paralia sulcata and Dimeregramma minor. Some centuries later another diatom assemblage appeared and became dominant in Mecklenburg Bay. This assemblage includes Hyalinella lateripunctata and Pravifusus hyalinus species typical of shallow water areas along the Atlantic coast today. At this time the first marine molluscs made their appearance. The oldest shell of a marine mollusc found in our material is dated to 7600 cal. years BP. The associated assemblage that includes adult specimens of the gastropod Aporrhais pespelicani indicates higher salinities than today.During the Littorina Sea stage a marine diatom flora with P. sulcata, Catenula adhaerens and D. minor crossed the Darss Sill and became widely distributed in the Arkona Basin, Pomeranian Bay and the Baltic Sea proper. In contrast, taxa indicative of the Hyalinella lateripunctata/P. hyalinus assemblage are only found west of the Darss Sill in Femer Belt and Mecklenburg Bay. Apparently, the Darss Sill threshold has been acting as an important salinity border from around 7800 cal. years BP until today.     

Diel Activity Patterns and Foraging Dynamics of the Sea Urchin Tripneustes ventricosus in a Tropical Seagrass Community and a Reef Environment (Virgin Islands)

Abstract. Feeding and movement activity patterns and the foraging behavior of the sea urchin Tripneustes ventricosus were investigated in a Thalassia testudinum seagrass bed and on a patch reef at St. Croix, U.S. Virgin Islands.
Most of T. ventricosus in the seagrass bed fed during both the day and night. Consumption of seagrass blades amounted to 1.4 g dw · individual^-1· d^-1 (mean sea urchin size 12.1 cm ambitus diameter). The population consumed approximately 3.6% of the daily seagrass production.
The movement of T. ventricosus was diel with high nocturnal activity levels and rates of locomotion, and little activity during daylight hours. Foraging activity was reduced under turbulent conditions. Movement rates were not governed by food availability. T. ventricosus travelled 3.7 m · d^-1 on the patch reef. Individuals in the seagrass bed moved 8.8 m · d^-1, most of which was accomplished during the night. The area traversed contained more than one hundred times the amount of food consumed daily. It is assumed that this behavior requires high energy expenditures for locomotion, thus yielding a low net energy profit from feeding.
The high rate of movement in seagrass beds may represent an innate behavioral adaptation to predation by night-active helmet conchs ( Cassis spp.). Fitness optimization by T. ventricosus may have been achieved by minimizing the predation risk during night hours. In an evolutionary context, survival by means of an increased energy expenditure for locomotion may compensate for the lower net energy gain from foraging.     

Stable carbon isotopes of graphite from Bogala Mine,Sri Lanka

The ratios of the carbon isotopes ¹³C and ¹²C of twenty-four graphite samples from Bogala Mine, Sri Lanka have been determined. The graphites are isotopically very similar (mean value $\text{?7.76? °}{}^{13}\text{C}{}_{\mathrm{PDB}}$; range $\text{<2?}$). Three models for the biogenic or abiogenic origin of the graphite deposit are discussed.