Turbidity dynamics during spring storm events in an urban headwater river system: the Upper Tame, West Midlands, UK.

Over a 1-year period, field and satellite measurements of surface water turbidity were combined in order to study the dynamics of the turbidity maximum zone (TM) in a macrotidal estuary (the Gironde, France). Four fixed platforms equipped with turbidity sensors calibrated to give the suspended particulate matter (SPM) concentration provided continuous information in the upper estuary. Full resolution data recorded by the moderate resolution imaging spectroradiometer (MODIS) sensors onboard the Terra and Aqua satellite platforms provided information in the central and lower estuary twice a day (depending on cloud cover). Field data were used to validate a recently developed SPM quantification algorithm applied to the MODIS ‘surface reflectance’ product. The algorithm is based on a relationship between the SPM concentration and a reflectance ratio of MODIS bands 2 (near-infrared) and 1 (red). Based on 62 and 75 match-ups identified in 2005 with MODIS Terra and Aqua data, the relative uncertainty of the algorithm applied to these sensors was found to be 22 and 18%, respectively. Field measurements showed the tidal variations of turbidity in the upper estuary, while monthly-averaged MODIS satellite data complemented by field data allowed observing the monthly movements of the TM in the whole estuary. The trapping of fine sediments occurred in the upper estuary during the period of low river flow. This resulted in the formation of a highly concentrated TM during a 4-month period. With increasing river flow, the TM moved rapidly to the central estuary. A part of the TM detached, moved progressively in the lower estuary and was finally either massively exported to the ocean during peak floods or temporary trapped (settled) on intertidal mudflats. The massive export to the ocean was apparently the result of combined favorable environmental conditions: presence of fluid mud near the mouth, high river flow, high tides and limited wind speeds. The mean SPM concentration within surface waters of the whole estuary showed strong seasonal variations but remained almost unchanged on a 1-year-basis. These observations suggest that the masses of suspended sediments exported toward the ocean and supplied by the rivers were almost equivalent during the year investigated (2005). Results show the usefulness of information extracted from combined field and current ocean color satellite data in order to monitor the transport of suspended particles in coastal and estuarine waters.

Dynamics of the turbidity maximum zone in a macrotidal estuary (the Gironde, France): Observations from field and MODIS satellite data

The coexistence of ac and dc subgrids in a hybrid microgrid is likely given that modern distributed sources can either be ac or dc. Linking these subgrids is a power converter, whose topology should preferably be not too unconventional. This is to avoid unnecessary compromises to reliability, simplicity, and industry relevance of the converter. The desired operating features of the hybrid microgrid can then be added through this interlinking converter. To demonstrate, an appropriate control scheme is now developed for controlling the interlinking converter. The objective is to keep the hybrid microgrid in autonomous operation with active power proportionally shared among its distributed sources. Power sharing here should depend only on the source ratings and not their placements within the hybrid microgrid. The proposed scheme can also be extended to include energy storage within the interlinking converter, as already proven in simulation and experiment. These findings have not been previously discussed in the literature, where existing schemes are mostly for an ac or a dc microgrid, but not both in coexistence.

Autonomous Control of Interlinking Converters with Energy Storages in Hybrid AC-DC Microgrids

Distribution of organic matter in the Changjiang (Yangtze River) Estuary and their stable carbon and nitrogen isotopic ratios: Implications for source discrimination and sedimentary dynamics

Waves are fundamentally important to the physical and biological functioning of estuaries. Understanding and predicting contaminant transport, development of sedimentary structures, geomorphological response to changes in external forcings such as rising sea level, and response of estuarine ecosystems to contaminant stressors require understanding of the relative roles of wave- and current-driven sediment transport. We review wave-driven sediment resuspension and transport in estuaries, including generation of bed shear stress by waves, initiation of sediment motion by waves, and the ways waves modulate, add to, and interact with sediment transport driven by currents. A key characteristic of the wave-induced force on the seabed is extreme spatial and temporal variations; simple analytical models are revealing of the way such patterns develop. Statistical methods have been widely applied to predict wave resuspension of intertidal-flat bed sediments, and physically based predictors of resuspension developed from open-coast studies appear to also apply to short-period estuarine waves. There is ample experimental evidence to conclude that over the long term, waves erode and tidal currents accrete intertidal flats. Waves indirectly add to the formation of fluid mud by adding to the estuarine pool of fine sediment, and waves may fluidize subtidal seabeds, changing bed erodibility. Models have been used to explore the dynamic balance between sediment transport by waves and by currents and have revealed the key control of waves on estuarine morphology. Estuarine intertidal flats are excellent natural laboratories that offer opportunities for working on a number of fundamental problems in sediment transport.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2013RG000437

Review of wave‐driven sediment resuspension and transport in estuaries

A power transformer will yield a frequency response which is unique to its mechanical geometry and electrical properties. Changes in the frequency response of a transformer can be potential indicators of winding deformation as well as other structural and electrical problems. A diagnostic tool which leverages this knowledge in order to detect such changes is frequency-response analysis (FRA). To date, FRA has been used to identify changes in a transformer's frequency response but with limited insight into the underlying cause of the change. However, there is now a growing research interest in specifically identifying the structural change in a transformer directly from its FRA signature. The aim of this paper is to support FRA interpretation through the development of wideband three-phase transformer models which are based on three types of FRA tests. The resulting models can be used as a flexible test bed for parameter sensitivity analysis, leading to greater insight into the effects that geometric change can have on transformer FRA. This paper will demonstrate the applicability of this modeling approach by simultaneously fitting each model to the corresponding FRA data sets without a priori knowledge of the transformer's internal dimensions, and then quantitatively assessing the accuracy of key model parameters.

/pdf/modeling-power-transformers-to-support-the-interpretation-of-1tgwgxzzxz.pdf

Modeling Power Transformers to Support the Interpretation of Frequency-Response Analysis

Condition monitoring of an operating apparatus is essential for lifespan assessment and maintenance planning in a power system. Electrical insulation is a critical aspect to be monitored, since it is susceptible to failure under high electrical stress. To avoid unexpected breakdowns, the level of partial discharge (PD) activity should be continuously monitored because PD occurrence can accelerate the aging process of insulation in high voltage equipment and result in catastrophic failure if the associated defects are not treated at an early stage. For on-site PD detection, the ultra-high frequency (UHF) method was employed in the field and showed its effectiveness as a detection technique. The main advantage of the UHF method is its immunity to external electromagnetic interference with a high signal-to-noise ratio, which is necessary for on-site monitoring. Considering the detection process, sensors play a critical role in capturing signals from PD sources and transmitting them onto the measurement system. In this paper, UHF sensors applied in PD detection were comprehensively reviewed. In particular, for power transformers, the effects of the physical structure on UHF signals and practical applications of UHF sensors including PD localization techniques were discussed. The aim of this review was to present state-of-the-art UHF sensors in PD detection and facilitate future improvements in the UHF method.

Application of UHF Sensors in Power System Equipment for Partial Discharge Detection: A Review

In times of strongly increasing human uses of coastal zones estuaries deserve and do gain more attention in science and the public because of their extraordinary character in terms of their environmental setting as well as their economic potential Taking this into account the 50th Conference of the Estuarine Coastal Sciences Association was held in Venice, Italy, in June 2012 with the maxim ‘Today's science for tomorrow's management’ As a result of the Conference this special issue of Estuarine, Coastal and Shelf Science focusses on ‘Pressures, stresses, shocks and trends in estuarine ecosystems’ Here we identify the major hazards to estuarine ecosystems as belonging to three categories: human activities, climate change and extreme events; and we discuss the special issue contributions in this context Moreover, studies of indicators of environmental change and larger scale assessments of estuarine ecosystems are also highlighted There are examples providing scientific evidence for a ‘successful’ management in terms of ecosystem recovery However, for today's and future management it appears mandatory to use the term ‘successful’ in the sense of being beneficial for the ecosystem as well as for the stakeholders With this in mind, we discuss the future of, and challenges to, estuarine ecosystems in the light of the environmental change of the Anthropocene in a final section

Pressures, stresses, shocks and trends in estuarine ecosystems – An introduction and synthesis

Results from continuous monitoring of turbidity and water level at Burringham, on the tidal River Trent, UK, are presented for the period 18 May 1997 to 9 February 1998. These measurements, together with detailed readings of velocity and suspended sediment concentration over an individual tidal cycle near the opposite bank at Derrythorpe, help to describe the mechanisms and behaviour of the turbidity maximum (TM). It is demonstrated that there is a distinct pattern of fine sediment movement that reflects a predictable system response to changing hydraulic features. It is shown that the TM in this system is highly mobile, and its location depends on antecedent fresh water flow, and tidal range. Approximate representative flood and ebb tide suspended sediment concentrations of up to 13 g/l over this nine-month period have been derived from the data and plotted against fresh water flow and tidal range, in order to show the relationship between these parameters. Three semi-empirical polynomial regression models have been tested for goodness of fit against available data. It was found that a partitioning approach, whereby data are grouped into different categories depending on antecedent fresh water flow, yielded the lowest standard error for the period analysed. Analysis of detailed observations of suspended sediment concentration and velocity measured over an individual tidal cycle also help to elucidate the mechanism of tidal pumping within this system. These results also help to give an estimate of the relative magnitude of suspended sediment fluxes during typical low fresh water flow conditions. It is estimated that for low fresh water flow conditions, a typical spring tide can mobilise at least an order of magnitude more sediment than a neap tide.

Use of continuous turbidity sensor in the prediction of fine sediment transport in the turbidity maximum of the Trent Estuary, UK

There is a well-defined need to improve understanding of the dynamics of sediment erosion and deposition on intertidal channel banks, given their importance to channel stability, sediment budgets, depth maintenance, pollutant and nutrient transport, and ecological processes in estuarine systems. Conventional, manual methods for field monitoring of erosion and deposition, however, normally deliver information of low temporal resolution conditioned by infrequent field resurveys. To address this problem, this paper discusses a recently developed and improved automatic erosion and deposition monitoring technique, the Photo-Electronic Erosion Pin (PEEP) system, and its application to a tidal channel bank site at Burringham on the River Trent, U.K. The PEEP system allows the magnitude, frequency and timing of individual erosion and deposition events to be monitored much more precisely than with conventional manual methods. PEEP sensors also monitor light intensity and sediment temperature, variables which can influence bank stabilizing and destabilizing processes. Example results at both the event and spring-neap timescales are presented from a short PEEP system deployment between March and May 1997 at Burringham. These establish that discrete erosion events of >60 mm and 100 mm can occur in response to individual tidal cycles, events which are readily monitored automatically and quasicontinuously by the PEEP system. The capability of the PEEP approach to enhance temporal resolution of monitoring is demonstrated by the determination of the timing of the 100-mm bank erosion incident to an ‘ event window ’ of 2·75 h: this converts to mean bank erosion rate of 36 mm h−1over the period of inundation. In addition, the PEEP system defines the magnitude and date of two example deposition events of 47 and 92 mm on the lower bank during a sequence of rising spring tides. These represent mean deposition rates of 4·5 and 8·4 mm h−1respectively over the periods of inundation. The Burringham site is shown to be highly active, with regular and dynamic erosion and deposition cycles. Upper bank surface elevation oscillations, driven by this sediment cycling, were characterized by a strong 14-day cycle which clearly reflected the spring-neap cycling of tidal range. Sediment was deposited on the bank relatively quickly, but removed by erosion rather slowly, giving an asymmetric sediment cycling profile. Higher bank elevations were strongly correlated with high tidal ranges, and especially to water level peaks 2 days previously. Incorporation of a simple Wind Stress Index further improved the statistical explanation of tidal bank elevation, and suggested that high on-shore wind speeds were associated with increased bank erosion. Such vigorous sediment cycling means that many erosion-deposition sequences on tidal banks can be self-concealing and therefore may not be recorded by infrequent manual resurveys which will inevitably underestimate total activity. This reinforces the need for an automated method such as the PEEP system to determine these typically cyclic sequences of self-cancelling accretion and removal activity if site dynamism is to be correctly quantified. The ability of the PEEP approach to generate such detailed and high-resolution information on the temporal distribution of erosion and deposition events in tidal environments should significantly enhance future process and applied studies, especially of entrainment thresholds, sediment recycling, estuarine sediment supply and sediment fluxes, the operation of biomediation mechanisms, bank erodibility changes, storage and residence times of contaminants and site management options.

Steve Mitchell

Papers

Modeling Power Transformers to Support the Interpretation of Frequency-Response Analysis

Application of UHF Sensors in Power System Equipment for Partial Discharge Detection: A Review

Pressures, stresses, shocks and trends in estuarine ecosystems – An introduction and synthesis

Use of continuous turbidity sensor in the prediction of fine sediment transport in the turbidity maximum of the Trent Estuary, UK

Application of a Novel Automatic Erosion and Deposition Monitoring System at a Channel Bank Site on the Tidal River Trent, U.K.