Bed shear stress in the southern North Sea as an important driver for suspended sediment dynamics

This paper addresses the spatial and temporal patterns of drivers for sediment dynamics in coastal areas. The basic assumption is that local processes are dominating. The focus is put on the bed shear stress in the southern part of North Sea giving the basic control for deposition–sedimentation and resuspension–erosion. The wave-induced bed shear stress is formulated using a model based on the concept that the turbulent kinetic energy associated with surface waves is a function of orbital velocity, the latter depending on the wave height and period, as well as on the water depth. Parameters of surface waves are taken from simulations with the wave spectrum model WAM (wave model). Bed shear stress associated with currents is simulated with a 3D primitive equation model, Hamburg Shelf Ocean Model. Significant wave height, bed shear stress due to waves and currents, is subjected to empirical orthogonal functions (EOF) analysis. It has been found that the EOF-1 of significant wave height represents the decrease of significant wave height over the shallows and, due to fetch limitation, along the coastlines. Higher order modes are seesaw-like and, in combination, display a basin-scale rotational pattern centred approximately in the middle of the basin. Similar types of variability is also observed in the second and third EOF of bed shear stress. Surface concentrations of suspended matter derived from MERIS satellite data are analysed and compared against statistical characteristics of bed shear stress. The results show convincingly that the horizontal distribution of sediment can, to a larger extent, be explained by the local shear stress. However, availability of resuspendable sediments on the bottom is quite important in some areas like the Dogger Bank.     

Temporal and spatial circulation patterns in the East Frisian Wadden Sea

This work deals with the analysis of simulations carried out with a primitive equation numerical model for the region of the East Frisian Wadden Sea. The model, with 200-m resolution, is forced by wind, air–sea heat, and water fluxes and river runoff and is nested in a German Bight 1-km-resolution numerical model, the latter providing tidal forcing for the fine resolution model. The analysis of numerical simulations is focused both on responses due to moderate conditions, as well as to extreme events, such as the storm surge Britta, for which the model demonstrates very good skills. The question addressed in this paper is how well the model output can be compressed with the help of empirical orthogonal function analysis. It is demonstrated that, for the short-time periods of the order of a spring–neap cycle, only a few modes are necessary to almost fully represent the circulation. This is just an illustration that the circulation in this region is subject to the dominating tidal forcing, creating clear and relatively simple response patterns. However, for longer periods of about several months, wind forcing is also very important, and correspondingly, the circulation patterns become much more complex. Possible applications of the results in hindcasting and forecasting of hydrodynamics and sediment dynamics in the coastal zone are considered.     

Issues and Options in the Delineation of Well Capture Zones under Uncertainty

The delineation of wellhead protection areas (WHPAs) under uncertainty is still a challenge for heterogeneous porous media. For granular media, one option is to combine particle tracking (PT) with the Monte Carlo approach (PT‐MC) to account for geologic uncertainties. Fractured porous media, however, require certain restrictive assumptions under this approach. An alternative for all types of media is the capture probability (CP) approach, which is based on the solution of the standard advection‐dispersion equation in a backward mode, making use of the analogy between forward and backward transport processes. Within this context, we review the current controversy about the correct form of the conceptual model for transport, finding that the advection‐diffusion model, which represents the diffusive interchange between streamtubes with differing velocities, is more physically realistic than the conventional advection‐dispersion model. For mildly to moderately heterogeneous materials, stochastic theories and simulation experiments show that this process converges at the field scale to an effective advection‐dispersion process that can be simulated with conventional transport models using appropriate macrodispersivity values. For highly heterogeneous materials, stochastic theories do not yet exist but there is no reason why the process should not converge naturally as well. Macrodispersivities appear to be formation‐specific. The advection‐dispersion model can be used for capture zone delineation in heterogeneous granular media. For fractured porous systems, hybrid equivalent porous medium and discrete fracture network or CP‐based approaches may have potential. In general, capture zones delineated by PT without MC will always be too small and should not be used as a basis for land‐use decisions.     

Interactions between barotropic tides and mesoscale processes in deep ocean and shelf regions

Ocean Dynamics - The interactions between barotropic tides and mesoscale processes were studied using the results of a numerical model in which tidal forcing was turned on and off. The research...     

Role of Stranded Gas from Central Asia and Russia in Meeting Europe’s Future Import Demand for Gas

Stranded gas is natural gas in discovered fields that is currently not commercially producible for either physical or economic reasons. This study examines stranded gas from Russia and Central Asia and the role it can play in addressing Europe’s growing demand for imported natural gas requiring additional volumes of gas in excess of 130 trillion cubic feet. We find sufficient volumes of stranded gas in fields in the Central Asian state of Turkmenistan in the Amu-Darya Basin and in Russian fields in the West Siberian Basin. The analysis focused on the estimated cost of extraction and delivery to a single market location for various concentrations of gas in stranded gas fields in Central Asia and Russia. At import prices of 10 per million British thermal units (MMBTU), there are sufficient gas resources in stranded fields that can be commercially developed and delivered to the European market. If, however, imported gas prices fall below10 per million British thermal units (MMBTU), there are sufficient gas resources in stranded fields that can be commercially developed and delivered to the European market. If, however, imported gas prices fall below 7 per MMBTU, most of the stranded gas evaluated from West Siberia will not be commercial. The costs of delivering gas from the largest stranded gas fields in Turkmenistan and Azerbaijan were calculated to be greater than 30% below the costs of delivering gas from the largest stranded gas fields in Russia, which are located in the Yamal Peninsula. Central Asian gas producers, particularly those east of the Caspian Sea, have limited market options due to the near monopoly position that Gazprom holds in transporting pipeline gas from east of Europe. This study examines several additional options to supply gas to Europe by reviewing expected delivered costs from North African and Atlantic basin suppliers.     

Icing of wires in mountain areas of Georgia

The peculiarities of wire icing in mountain areas of Georgia are investigated using the observational data of 14 meteorological stations of Georgia. Determined are the maximum frequency and the maximum mass of glaze-ice deposits, as well as the frequency of deposits of different mass and thickness. Considered are the effects of orography and meteorological conditions on the wire icing processes.     

Soil aggregation estimates in CZO-Fuchsenbigl

The study presents results on the informativity and spatial variation of soil aggregation characteristics in one of the Critical Zone Observatories (CZO) in Europe – Fuchsenbigl, Austria. Water stable aggregates of different size were measured, and strong relationships between soil aggregation estimates were found. The horizontal variation of water stable aggregates at particular depths can be explained by certain vertical heterogeneity of the soil profiles in space. The water stable aggregates in 1–3 mm size dry aggregates in the upper layer vary from 44% to 76% under native vegetation, drop to 1% under intensive cultivation, and comprise 19% in land not tilled for 5 years. The results allow linking the characteristics of soil structure with other biotic and chemical properties for better estimation of the driving forces for soil aggregate formation.     

Quantitative assessment of vegetation cover and soil degradation factors within terrain units for planning,monitoring and assessment of renaturation along oil and gas pipelines

This paper evaluates the renaturation activities applying the quantification of vegetation cover (VC), the site suitability analysis (SSA) based on the predefined criteria (slope steepness category (SSC), soil erodibility factor (K) and VC) and soil erosion model (SEM) results within the terrain units (TUs) along pipeline rights-of-way (RoW). Quantification of VC percentage is performed to assess the overall restored VC from 2005 to 2007. The results of the quantitative analysis in 2007 show that the total area of restored VC is 10.7 km², and 8.9 km² still needs to be restored to comply with the environmental acceptance criteria. As a result of SSA, TUs were prioritized by erosion vulnerability and this allowed to better understand the landscape behaviour in regards to erosion processes. SEM provided more detailed predictions of erosion classes falling into TUs. SEM identified 40% of erosion sites occurred from 2005 to 2010.