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Exploring the energy potential of the oceans is a promising alternative to produce clean energy with a reduced environmental impact. Brazil has a significant tidal potential, particularly in the coastal region of the north, which covers the states of Amapá, Pará and Maranhão. The Boqueirão Channel, located in São Marcos Bay in Maranhão, is recognized for its wide tidal variability and strong tidal currents, which shows it has a significant tidal potential. This article examines the energetic characterization of this estuary in terms of tidal currents. Based on measurements taken in situ using an Acoustic Doppler Current Profiler and a Conductivity, Temperature and Depth sensor, the area is modeled in Delft3D software, with velocity results adjusted and validated to allow accurate representation of tidal currents. The theoretical potential of an area of 1.5 km 2 , considering a hydrokinetic turbine with diffuser, was estimated at 85.75 GWh. The results obtained are compared with those in the literature. Taking into account the available area and the physical constraints of the channel, it is possible to estimate a Levelized Cost of Energy - LCOE of 0.185 $ kWh − 1 for the projected hydrokinetic farm. • Hydrodynamic modeling of the site using measured data is reported. • The viability of the estuary is demonstrated. • The importance of sites with intermediate tidal currents is highlighted. • Hydrokinetic diffuser-augmented turbines are competitive alternative to improve in a tidal farm efficiency. [ABSTRACT FROM AUTHOR]

The measurement and computation of discharge measurement in tidal streams using a fast and minimally intrusive method is developed. The discharge of tidal streams is highly unsteady because of influences from ocean tides and upstream river flow. Measurement of the discharge at a stream with such complex currents is limited by the efficiency and cost of conventional measurement instruments and methods. Thus, it is necessary to introduce new measurement approaches and instruments for measuring the discharge of tidal streams. This study installs high-precision Argonaut-SW under a sounding weight to be hung from a vertical line using a single-drum winch. The Argonaut SW is modified to be a mobile device to measure the velocity distribution and water depth from the surface. This study also uses the observed data to establish an efficient discharge measurement method suitable for tidal streams, which utilizes the relationship between mean and maximum velocities for rapidly estimating discharge in the future. This method is applied on the tidal reach of the Keelung River. The results show that the discharge measurement method established by this study can not only greatly improve the accuracy of discharge measurement but also significantly reduce the time, labor, and cost required for measuring discharge in tidal streams. [ABSTRACT FROM AUTHOR]

Discharge measurement in a tidal stream is always a difficult task. Owing to the complex flow conditions, discharge measurement in tidal streams has to be finished quickly, and must be highly efficient in order to yield an accurate measurement of real-time discharge. Measuring the discharge of tidal streams is done in three steps: (1) establishing the stage and cross-sectional area relation, (2) estimating the index velocity by using a velocity distribution equation based on the probability concept, (3) establishing the relationship between the index and mean velocities. Then the cross-sectional area and mean velocity can be estimated by the gage height and index velocity, respectively. The discharge of tidal streams is computed as the product of the cross-sectional area and mean velocity. The velocity distribution of the Taipei Bridge and Guan-du Bridge in the Tanshui River were established and analyzed to demonstrate the use of discharge measurement by index velocity for estimating the discharge of this tidal stream. The results reveal no large difference between the discharges measured by the conventional methods and the index velocity. This pilot study proposed a cost-effectiveness and efficient method. It is an easy, quick, and accurate model for measuring the real-time discharge of a tidal stream. It makes automatic, real-time, and continuous monitoring of the discharge in a tidal stream become possible. [ABSTRACT FROM AUTHOR]

Abstract: Global energy demand continues to grow and tidal and wave energy generation devices can provide a significant source of renewable energy. Technological developments in offshore engineering and the rising cost of traditional energy means that offshore energy resources will be economic in the next few years. While there is now a growing body of data on the ecological impacts of offshore wind farms, the scientific basis on which to make informed decisions about the environmental effects of other offshore energy developments is lacking. Tidal barrages have the potential to cause significant ecological impacts particularly on bird feeding areas when they are constructed at coastal estuaries or bays. Offshore tidal stream energy and wave energy collectors offer the scope for developments at varying scales. They also have the potential to alter habitats. A diversity of designs exist, including floating, mid-water column and seabed mounted devices, with a variety of moving-part configurations resulting in a unique complex of potential environmental effects for each device type, which are discussed to the extent possible. [Copyright &y& Elsevier]

Deep recent surveys have considerably improved our picture of the outer Galactic halo by unveiling a complex level of substructuring in the form of streams, stellar clouds and debris systems. Here I discuss some of the recent findings and present their general properties. [ABSTRACT FROM PUBLISHER]

Abstract: Marsh restoration projects require quantitative and qualitative tools to monitor restoration. Restoring hydroperiod supports marsh plain vegetation development and is critical to successful restoration. We can determine if a favorable hydroperiod has been restored by measuring tidal amplitude in the marsh channels and on the marsh plain. In large systems, it is not practical to measure water elevations at many locations. Stream order analyses (hydrogeomorphic analysis) of tidal channels are recognized techniques for evaluating hydraulic performance of mature fluvial systems. We adapted the stream order analysis technique to examine the changes in tidal channel morphology within marsh restoration projects. Order analysis assigns an increasing number (order) to each new branching of a stream channel. The numbering system normally begins with the smallest channels (first) and increases in number, as the channels become larger and more complex. This technique, often-termed “top-down” ordering, has been used to compare stream complexity in different size drainage areas and has been used to aid in designing stream restoration projects. In rapidly changing systems we found that reversing the order of the channel ordering (bottom up) preserves the channel morphological characteristics and better characterized rapidly changing systems, such as within marsh restoration projects. [Copyright &y& Elsevier]

The efficient method presented herein is based on the regularity of water flow in an open channel, which is maintained by nature at a constant ratio of mean to maximum velocities at a channel section. This ratio is a function of a parameter of a probability distribution that is equivalent to velocity distribution in the physical space. The maximum velocity can be determined quickly by measuring only a few velocities from a single vertical axis. As well as the ratio, the location of the sampling vertical axis on which the maximum velocity occurs tends to remain invariant with time. The mean velocity in a section can be rapidly determined by estimating the product of the maximum velocity multiplied by the ratio. The cross-sectional area of an open channel can be determined by the relation between gage height and area. Thus, the discharge in an open channel may be estimated as the product of mean velocity multiplied by the cross-sectional area. This efficient method can be used with any current meter to reduce the time and cost of discharge measurement in open channel flows under tidal effect. The available data of the Tanshui River downstream reach of which is in an estuarine area is used to illustrate the accuracy and reliability of the method. The results show that the simple but reliable method is capable of estimating discharge in tidal streams. [Copyright &y& Elsevier]

Eight Atlantic herring (Clupea harengus L.) implanted with ultrasonic transmitters were tracked to determine their movements during the pre-spawning period in the tidally energetic, upper St Lawrence estuary. Herring released near the south shore travelled upriver near the shore while herring released near an island where significant spawning occurs remained in the vicinity of that island. Herring near the shore moved upriver regardless of the tidal phase while herring close to the island swam actively against tidal currents during both phases of the tide. Herring near the coast may have been migrating to an alternate spawning site further upriver while herring near the island remained in close proximity to the island's spawning site as a result of their behaviour. Herring travelling near the coast seemed to take advantage of tidal currents by swimming with tidal streams when the tide flowed in the migratory direction (flood tide) and by swimming against them when the tide flowed counter to it (ebb tide). These fish gained more ground during the flood tide than they lost during the ebb. A circular statistical analysis of movements-through-water showed that fish were oriented against the flow during the ebb phase. Selective tidal stream transport was not observed since there was no evidence of vertical migrations associated with tides. [ABSTRACT FROM PUBLISHER]

A quantitative model has been developed which predicts geographical movements of demersal fish on the European continental shelf by combining tidal stream vectors calculated from Admiralty tidal data with known patterns of fish behaviour. The model interpolates the speed and direction of the tidal current at any specified position and allows for the cyclical change of current speed between neap and spring tides. Fish behaviour is specified in terms of swimming speed and direction, as well as times of vertical migration and the duration of the intervening period in midwater. Times of vertical migration to and from the bottom can be specified theoretically in relation to regular tidal events (slackwater, high or low tide, etc.), or practically using actual observations made by sonar or data storage (archival) tags. Simulated tracks can be used singly to predict the behaviour of individual fish in relation to biological problems, or collectively to predict the distribution of whole populations in relation to management problems. These predictions can be formulated so that they can be tested experimentally. The model is being used to reconstruct the ground tracks of fish fitted with data storage (archival) tags and also to predict the theoretical movements of individuals and populations. It has been validated by reconstructing the ground tracks of fish tracked in the open sea using sector scanning sonar and transponding acoustic tags. Potential applications include estimating transfer coefficients for use in spatial assessment models, assessing the exchange of fish between fishable areas and areas closed to fishing for conservation reasons, and providing a theoretical framework for analysing returns from conventional fish tagging experiments. [ABSTRACT FROM PUBLISHER]