A one-dimensional, implicit, finite-difference model is developed, calibrated and verified for three estuaries along the central Oregon coast. The model is used to generate controlled data for a large number of hypothetical estuaries. Two non-dimensional coefficients, K[subscript F], and. K[subscript I], are developed incorporating physical characteristics of the estuary which summarize the effects due to friction and inertia, respectively, These coefficients are used to explain the variability of tidal response throughout the complete range of hypothetical estuaries investigated. A predictive algorithm based on the derived relationships is presented and examples of its application to real estuaries is given. The results of this study can be used to predict modifications in tidal response due to proposed physical changes in an estuary, such as entrance dredging or filling of tidal flats. Field data of velocity, temperature and salinity for the Yaquina, Alsea and Siletz estuaries is included with the paper. / Graduation date: 1974

This thesis presents a cost-benefit analysis of tidal power generation with specific reference to the installation of a 300MW tidal farm in the Minas Passage, in Nova Scotia, in 2020, as a case study. Nova Scotia has set aggressive targets to increase the share of renewables in the province’s electricity generation mix and tidal energy is considered to be the ?sleeping giant? amongst renewable energy sources. After having estimated the many costs and benefits and having calculated the net present value of such a project, it is concluded here that the project should not proceed as its costs greatly surpass its benefits. However, it is recommended that further studies evaluating the costs and benefits at different levels of tidal penetration be conducted for the province.

Thesis (M.S.)--Naval Postgraduate School, 1993. / "December, 1993." Includes bibliographical references (p. 106-111).

Abstract The Tanshui river is the second largest of the rivers in Taiwan, including three major tributaries, Da-han stream, Shin-dian stream and Keelung river. The large fresh water outflow induced strong stratification of the estuary and coastal region. In this region of fresh water influence (ROFI), the flow is dominated by barotrophic tide, with modification of density induced baroclinic flow. This research tries to explore the variations of vertical structure of tidal current. The causing of the changes will be discussed based on hydrodynamic parameters. Data used include a year long bmADCP records and sea level elevations. The sampling period is Septemper 24 of 2003 to July 12 of 2004. The sampling site is 4km offshore of river mouth. Additional data are winds, precipitation, solar radiation (from CWB) and river discharge (from RMO). The results of analysis show that (1) strong flow during spring may induce large tidal ellipse, while the ellipticity degenerates during neap. (2) Tidal ellipticity increases when large freshwater discharge which induced strong stratification at the surface 1~ 2 meters. (3) Wind is a minor factor of ellipticity, even during strong wind over 10 m/s. (4) Influence of solar radiation and seasonal variation of tidal ellipticity is insignificant. In summary, the analysis indicates that the vertical structure of tidal current is modified by (1) spring- neap tide (2) freshwater discharge and (3) winds. Especially, during spring tide with large river outflow, the tidal ellipticity increase significantly due to frictional effect and vertical stratification.

It is necessary to subtracting the tidal height from the observed depth to derived real depth while conduct hydrographic survey. The tidal data can be collected by conventional tide gauge or by using real time kinematics (RTK) GPS survey in the near shore region. However, when setting up tidal instruments in the offshore areas, many restricts still remained due to many factors such as topography, weather, and sea state. On contrary, the RTK GPS survey method has the limitation on the radio transmitting range. Therefore, the tidal zone method integrates the tidal station data to calculate the offshore tide data which can solve these problems. Generally, the tidal zone is constructed by using real tidal station data around the narrow channel. But the tide data is not possible to integrate on both side of the Taiwan Strait due to the vertical datum is not identical due to current political separation. To overcome this problem, this study proposed tidal zone method based on the tidal height derived from a tide numerical model. The tidal zone method is consequently applied to improve the accuracy of the offshore hydrographic survey. After processing the tide data derived from the model output and performing harmonic analysis, this study utilized the analysis result to draw a co-tidal chart to demonstrate the tidal characteristics for the purpose of establishing the tidal zone of the Taiwan Strait. This study also accomplished correspondent tidal zones for all the tide stations of Taiwan west coast within 12 miles territorial waters. This study further proposed a virtual station method for offshore hydrographic survey tide correction which applied the analysis result of each numerical model grid point as a virtual tidal station to derive the offshore tide correction values with spatial continuous characteristics. This study selected three experiment areas based on the multi-beam echo sounder survey data acquired offshore Ma-Liuo tide station. The direct tide station correction, tidal zone correction, and virtual station correction methods are applied to the hydrographic survey data to evaluate the performance of the tidal zone and virtual station correction methods. According to the experiment results, the tidal zone and virtual station correction method improve 20 and 16 cm respectively over the direct tide station correction method in the offshore area with the distance 25 km to the Ma-Liuo tide station. It indicates that the feasibility of the tidal zone method and it can improve the hydrographic survey results significant while the tide characteristics are different. Tidal zone can provide the required information to decide a proper reference tide station according to the tidal characteristics for the hydrographic survey data post-processing.

The exchange flow through tidal inlets generates two-dimensional large coherent vortical structures (2DLCS), that are much broader than the water depth and exist because of the inherent instability of shallow shear flows. These vortical starting jets are critical to the mixing that occurs in the inlet area. Depending on the tidal period T, the width of the inlet W, and the maximum velocity in the inlet UMAX, the mixing will vary from poor exchange to efficient exchange. Here, we present laboratory and numerical experiments that study the formation of the 2DLCS at the mouth of the inlets. Experiments were conducted at large scale, in the shallow flat-bottomed water basin at the Institute of Hydromechanics of the University of Karlsruhe, Germany, which has the capability to generate a sinusoidal flow that simulates a series of tidal cycles. A set of idealized inlets were arranged in the tank, and by varying the tidal period and the maximum velocity, three different types of life-history were obtained (stationary dipole, dipole entrains, and dipole escapes). These types of life-history are defined by the mixing number depending if KW is equal, less or greater than a critical value. The experiments were visualized using color dye tracers. To quantify the shallow water velocity field, the Particle Image Velocimetry (PIV) technique was used. From the PIV data the vorticity field was obtained, and the regions where the vortex formed were identified. Then, a vortex time-evolution analysis was developed using iv physical parameters such as the position on the basin of the vortex, the equivalent diameter, and the maximum vorticity among others. The mixing number accurately predicts the behavior of the vortex for the first cycle on idealized inlets for the subsequent cycles; the structures behave differently than predicted by KW, because the blocking effect of the vortex /formed in the previous cycle. For characteristic times t*  tUWless than about 2, the dipole is attached to the inlet and forms rapidly. For later times, the dipole advects downstream, and slowly dissipates. Numerical experiments are also presented. Comparing the numerical data with the laboratory data, good agreement is reached, but important limitations are identified for the grid resolution and domain size.

This thesis discusses the importance of tidal turbine support structures through analytical and computational modelling. A head-driven analytical channel model was first developed to determine the sensitivity of the flow to the presence and type of support structures. It showed that there was a significant potential reduction in farm power output even when only considering approximate force coefficients for rotor and support structure. To confirm these findings, computational simulations were performed on a full-scale turbine to obtain more accurate force coefficients considering full rotor-support structure interactions. The flow interaction effects between the rotor and its support structure were studied using Computational Fluid Dynamics (CFD) for different support structure shapes for a range of tidal velocities including the power-capping zone. The integrated rotor force coefficients were higher in the presence of the cylindrical support structure than the elliptical support due to the higher opposing thrust from the cylinder in the channel redirecting the flow and increasing the flow velocity over the top half of the rotor. The presence of rotor caused a drop in the stream-wise forces on the support structure. The amplitude of the stream-wise sectional forces along the support structure height was lower in the case of an elliptical than a circular cylinder due to more streamlined shape of the ellipse. At device scale, the computational model was used to study the turbine performance in the power-capping zone by pitching the blades to feather. The influence of pitch-to- feather power-capping strategy was examined by studying the forces and angle of attack on the turbine blades, and the wake at three different blade pitch angles. Increasing blade pitch angle resulted in a significant drop in the average load on the blade. Also since the tidal channel flow has a shear in its velocity profile, the influence of shear on turbine performance was studied by comparing it to the same turbine in a uniform flow. The analytical channel flow model was used to investigate the characteristics of tidal stream energy extraction for large tidal farms deployed in tidal channels with specific focus on the limitations to realizable farm power due to turbine support structure drag and constraints on volume flow rate reduction. The force coefficients dataset from computational modelling was used to obtain a better estimate of the farm power output. Support structures were seen to contribute significantly to the overall resistive force in the channel and thus reduce the overall flow rates in the channel, leading to losses in realizable power. Over a wide range of channel characteristics, realistic levels of support structure drag lead to up to a 10% reduction in realizable power, and an associated reduction in the number of turbines that can be economically installed.

This thesis investigates sublittoral epibenthic assemblages, the ecological processes associated with distributions of benthic assemblages and potential ecological impacts arising from the de-ployment of tidal energy devices (TEDs) at a key tidal energy development site. An extensive field campaign was undertaken to collect fine-scale, in-situ data for local hydrodynamics, seabed structure and epibenthic assemblages. Data from a two-dimensional hydrodynamic model com- plemented in-situ flow data and provided an insight into possible changes to local tidal patterns after the deployment of a tidal array. The study revealed a highly complex tidal stream structure with maximal velocities reaching 4.2 ms1 during spring tide. The seabed was predominantly formed by scoured bedrock. Deployment of a tidal array was predicted to decrease tidal flow within and downstream of the array by up to 24 % for peak flows, whereas effects on the seabed were thought to be minor. Epibenthic assemblages were typical for tide-swept channels with a fringe of dense kelp forest along the shallow, sheltered waters of the channel, followed by a 'tran- sition zone' dominated by foliose red algae in the mid-depth ranges and animal turf assemblages in the deeper, very tide-swept waters. Multivariate analyses identified depth and bed-shear stress as being strongly associated with the distribution and composition of assemblages. In conjunction with presence-only data for epibenthic species, depth and bed-shear stress were used as predic- tor variables to develop site-specific habitat suitability models (HSMs) for a baseline and TED deployment case. Comparison of probability of occurrence values between the respective HSMs indicated a potential increase of suitable habitat for species inhabiting the deep, very tide-swept circalittoral following the deployment of TEDs, whilst assemblages along the fringes of the channel were mostly unaffected. This is the first attempt of using HSM as a tool for identification of potential changes in distributions of benthic species arising from the deployment of TEDs. The good overall performance of the models shows this tool may be valuable for for impact analysis of tidal energy development projects.

This research describes the position, strength and variability of the mixing front along the East Shetland coast and the geostrophic current associated with the front. Between 2004 and 2010, new current meter measurements have been made at two mooring sites on the East Shetland shelf. By combining the current meter datasets with other surface temperature and salinity observations, such as surface underway data from the ferry MV “Norröna” and existing hydrographic datasets, this research provides new insights into the seasonal variability of the currents on the east Shetland shelf. The results show that in this region of the northern North Sea the balance of heating-stirring results in a tidal mixing front close to a (log10( h/u3)) of 3.4. Along the steeply sloping shelf to the east of Shetland a mixing front is found in water around 100m depth and results in significant geostrophic currents of up to 20 cm/sec between June and August each year. Monthly volume transports associated with broad scale wind forcing are estimated to be between -0.27 and -0.51 Sv during the well mixed periods (December to March). During the summer months (June, July and August) wind driven transport reduced to an average of -0.27 Sv, at the same time the persistent southerly flow associated with the geostrophic transport contributes an equivalent transport (-0.24 Sv). Taking the east Shetland shelf as a whole (coast to 1.5°E) the maximum volume transport is estimated to occur in Autumn (September to October) when density driven currents remain significant and wind speeds begin to increase. In the narrow region close to the coast, however, monthly mean volume transport is observed to be highest during the summer months as a result of the strong jet-like currents that flow along the density front.

No description available.