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Two commercial Navier-Stokes solvers are applied to wave-wave and wave-structure interaction problems leading to the final application of simulating a single float of the wave energy converter (WEC) Manchester Bobber in extreme waves and a fixed section of the Pelamis in regular waves. First the two software packages CFX and STAR CCM+ are validated against measured results from physical tank tests concerning the interaction of 3 non-linear focused wave groups of different steepness (Ning et al. 2007). The agreement for all of these cases is very good and could even be improved from first order to second order wave setup at the wavemaker. However, in preliminary regular wave tests, the damping of the waves is identified to be an issue, which is the reason for focusing the waves and placing the structures in the following experiments approximately one wavelength behind the wavemaker. The interaction of fixed vertical and horizontal cylinders in regular waves are simulated concerning the forces on the structures (Kriebel 1998, Dixon et al. 1979). For the horizontal cylinder non-linear force oscillations of double the wave frequency could be modelled in good agreement with physical tank data, where linearised models failed. For the vertical cylinder the problem of the secondary load cycle due to a backward-breaking wave behind the cylinder is of special interest (Stansberg 1997, Chaplin et al. 1997). Here, the horizontal forces on a slender cylinder with a diameter approximately equal to the wave height are simulated successfully. Furthermore, the highly non-linear wave run-up in front of the cylinder is resolved well in the numerical approach. The next set of simulations includes rigid body motion. Here, the forced oscillations of a cone shaped body near the still water surface is simulated. These results are compared with test data published by Drake et al. (2008). For these cases the non-linearity of the experiments is discussed by comparing the sum and differences of the force and surface elevation time histories for a set of simulations with opposite excursion of the cone. The hydrodynamic forces on the cone surface are resolved in very good agreement. The solution of the surface elevation close to the cone surface is also resolved reasonably well. After having validated the codes for fixed wave-structure interaction problems and forced motion, the CFD methods are finally applied to problems relevant to the survivability of WECs. First a single float in waves is modelled. This challenging case combines the extreme wave setup with a floating body problem in one and two degrees of freedom including the interaction of the float inertia with the inertia of a separate mass attached to it. The vertical translations of the float are compared with physical tank tests by Stallard et al. (2008). This case clearly demonstrates the capabilities and challenges in using CFD to simulate WECs. When representing the pulley and counterweight system by a simplified external body force rather than the full setup, the calculated translations of the float agreed better with the measured results from the physical tank test. Furthermore the codes are used to simulate a single fixed section of the Pelamis device in regular waves. The surface elevations close to the device are discussed and the forces acting on different strips on the structure are presented.

(n order to reduce the impact of flooding and water quality degradation in urban areas sustainable urban drainage systems (SUDS) are increasingly being implemented throughout the UK. The thesis is concerned with one such type of system, namely retention ponds. With an absence of continuous long-term monitoring data to demonstrate how well these ponds perform in practice, a mathematical model was developed to investigate their flow attenuation and water quality enhancement characteristics. Simulations obtained with the model aimed to quantify how well ponds, designed using current UK guidance, are likely to perform now and under climate change scenarios. Furthermore, the model was used to study the effect of innovations in pond design. Initial modelling concerned ideal, generic ponds, with the knowledge gained being used to guide a case study on Linbum Pond in Scotland. Results show that the volume of temporary storage and the design of the outlet device are both of critical importance in meeting both flow attenuation and water quality enhancement targets. Furthermore, results also indicate the importance of dilution in achieving water quality targets. Simulations show that not only should a large permanent pool be provided but that water quality performance improves significantly when ~his volume is provided using larger surface areas as opposed to by deeper permanent pools. The assimilation of the knowledge gained in the study has enabled a set of improvements to current retention pond design to be proposed.

A study has been undertaken to supplement design methods and develop innovative approaches for the effective management of rivers and floodplains to reduce flood risk. The focus has been on enhancing the understanding and representation of the hydrodynamic processes of a variety of flow conditions and the associated hydraulic interaction with selected obstruction types, such as mangroves and vehicles for the representative river basins of the Merbok and Klang, on the West Coast of Peninsular Malaysia, and the Valency, near Boscastle, in the UK. For the study of the hydrodynamic processes of natural floodplains, a numerical model has been refined to investigate the effects of mangroves on tsunamis, with the inclusion of modelling idealised test cases. A similar model has then been applied to a mangrove fringed floodplain for the Merbok river basin. In recognising the importance of mangroves as natural defences against flooding disasters, a novel innovative and environmentally friendly approach, namely the Artificial Mangrove Shelter (AMS), has been first initiated and modelled, for the sustainable restoration and rehabilitation of mangroves along floodplains. In studying the hydrodynamic processes of urban floodplains, a series of experimental investigations has been undertaken on stationary scaled model vehicles in laboratory flumes, to study the effects of vehicles on flood flow propagation and, the influence of the flood flows on the stability of the vehicles. In order to develop a useful innovative approach to evaluate the degree of hydraulic stability for vehicles, a novel three colour zone envelope curve has been first introduced and developed, herein known as the Traffic Light of Hydraulic Stability (TLHS), to identify the likelihood of vehicle movement. The study was then extended to investigate the consequential hydraulic impact of flooded vehicles on blocked bridges, through a physical modelling study in a laboratory flume, with the purpose being to replicate a typical section of prototype floodplain conditions for the Boscastle and Klang. In this study, eventually natural and urban environments along the rivers and floodplains have consideration the hydrodynamic processes and interaction between hydraulic obstructions and flood flows, with novel and practical approaches being developed for effective management of rivers and floodplains.

Using the qualitative case study research design, this thesis examines marine policy and marine environmental management system with regard to fisheries, waste disposal and pollution, as well as marine environmental protection and conservation. Management tools have been used to evaluate government’s organisation and legislation, human resources, policy development, technical management, implementation and enforcement. The model of a marine policy and environmental management is established in the findings. Further, this research is an applied study, with outcomes of practical value in dealing with the issues concerned.

Libya is a country of desert and the arid climate makes it in extreme lack of surface water. Groundwater then becomes a very important resource to meet the economical and agricultural demand in the northern coastal areas. Groundwater has been over-exploited and some problems occurred such as saline deterioration and aquifer deterioration since 1960s. To better understand these problems for a proper management solution, this project was setup for groundwater investigations aiming better management strategy in Wadi Baye as a case study based upon the governmental water management requirement. Based on systematic literature review and data collection on geology, hydrogeology and other related environmental aspects, the groundwater systems were studied in terms of recharge and discharge, boundary and recharge and hydraulic characteristics using field based, hydrochemical/isotopic analysis and numerical modelling approaches. A series of techniques were employed to study the spatial and temporal variations of the groundwater flow field and hydrochemistry in the shallow and deep aquifer systems. The isotope signature was also used to understand the hydrochemical evolution of groundwater in Wadi Baye. It is found that the shallow groundwater is mainly influenced by the palaeo-saline hydro-environment, the deep groundwater geochemistry is impacted by mixture with the modern water around 50 km off the coastal line. A 3D groundwater numerical model was built using ModFlow based on proper calculation and calibration of the major hydraulic parameters. Calculation of groundwater budgets shows that total annual averaged recharge is 167K m3/d in Wadi Baye; the exploitable resources for shallow and deep aquifers are 33.7K and 15.6K m3/d respectively. Groundwater exploitation potential indicates that both shallow and deep groundwater systems are under over-exploitation. Sensitivity analysis of hydraulic conductivity, specific yield (storitivity) and precipitation recharge shows that hydraulic conductivity poses the greatest impact to the model in Wadi Baye. Three groundwater utilisation plans were proposed for further prediction in the future 10 years using the calibrated groundwater model. Modelling scenarios show that shallow and deep groundwater field will draw down under existing and increasing abstraction plans; drawdown in shallow groundwater will be greatly reduced if abstraction reduces to exploitable level and the overall flow field can remain stable or recover. However water level around the concentrated abstraction area will still drop down due to the localised negative balance by pumping. The best management strategy was proposed based on the modelling scenarios, to achieve a sustainable water management for the Wadi Baye area.

During the last few years the interest on the behaviour of both gravel and mixed beaches has increased because of the interest in soft coastal engineering measures for combating erosion. In contrast to gravel beaches, little research has been devoted to the sediment transport of beaches containing a mixture of both sand and gravel sediment (Mason and Coates, 2001). Thus, because of the limited understanding surrounding these beaches, mixed sand and gravel coastlines have a lot of research potential for both coastal resource management and scientific reasons. In recognition of this, a series of 3-dimensional physical model tests has been undertaken in order to examine the behaviour of gravel and mixed beaches more closely. The 3-D physical model tests were carried out in the 3-D wave basin located at Franzius-Institute (Marienwerder) of University of Hannover, at a nominal scale of 1:1. During the study, measurements of beach profiles and of cross-shore and long-shore current data were taken, generated by oblique wave attack, along gravel and mixed beaches with a uniform slope and a trench. New formulae for predicting wave breaking depth index, breaking depth and height, undertow velocity, long-shore current velocity and step and berm elevation have been proposed. A new parametric profile model has been developed in order to predict the beach profile changes of gravel and mixed beaches with a uniform slope and a trench due to sediment transport. The results of the new parametric profile model and of the refined parametric model SHINGLE have been validated against field and experimental data. The results of this validation were encouraging for the refined model, showing better accuracy than the SHINGLE model and showing that it has the potential to be a valuable tool in the design and management of gravel and mixed beaches.

A study has been undertaken to investigate and improve the representation and modelling of a range of various hydrodynamic, biochemical and sediment transport processes relating to the transport of enteric bacteria organisms in estuarine waters. In this study a relatively simple turbulence model was first further investigated to predict the complex three-dimensional flow structure in a flume with vegetation. The main purpose of this part of the study was to try and acquire accurate velocity profiles of complex flows without the need for a more advanced two-equation turbulence model, requiring values for a number of unknown coefficients and extra computing cost. The results showed that the simple two layer mixing length model was capable of giving more accurate complex velocity profile predictions, with the advantage of requiring limited coefficient data. Formulations developed through earlier studies for dynamic decay rates were then refined and included in the numerical model. The model predictions were tested against field data, with good agreement being obtained. Further refinements to the representation of the transport of bacteria through the flow field were included in the model by the novel addition of the interaction of bacteria with the sediments by partitioning the total bacteria into their free-living and attached phases using a dynamic partitioning ratio. This ratio was related to the suspended sediment concentrations. The novel method used in this study was to include the re-suspension and deposition of the absorbed bacteria with the sediments and this approach has been tested against analytical solutions for steady uniform flow conditions, and published field and experimental data. The model was then applied to the Severn Estuary. After calibration against available data sets the model was then run for different scenarios to investigate the effects of different hydro-environmental conditions on the bacteria distributions in the Severn Estuary. The model was finally used to investigate the impact of the proposed Cardiff-Weston tidal barrage on the hydrodynamic, the sediment transport and bacterial processes within the Severn Estuary. The results showed that the barrage would reduce the currents, as well as significantly reducing the suspended sediment concentrations and bacteria concentration levels in the estuary.

Hydro-environmental models have provided robust tools for efficient planning of water resources, flood risk and water quality, as well as increasingly being used for new challenges such as marine renewable energy, and have increasingly attracted growing interest. The new challenges ahead for use of hydro-environmental modelling tools has led to an increasing interest in considering the water system as a whole, and with a larger system framework, with this being achieved by expanding the modelling domain further than the area of the interest to capture the whole hydrodynamic and water quality and/or sediment transport processes. This study has focused on the enhancement of hydro-environmental modelling tools through improving the link between 1-D and 2-D models for the purpose of modelling river, estuarine and coastal water basins. The study has considered traditional boundaries, as well as the development and implementation of less conventional boundary conditions such as momentum absorbing boundaries which were used in simulating the marine renewable energy schemes. A GIS based 2-D hydro-environmental numerical model, namely DIVAST GIS, has been developed in this study and has been dynamically linked to a 1-D model using various linking methods, such as water levels discharges and overlapping methods. The model was augmented with a user-friendly GUI (Graphical User Interface), which was developed using OpenMI standards and thereby facilitate the opportunity to link with other models. The models were applied to two practical and site specific studies. Firstly, the linked models were refined in an application to undertake a hydro-environmental impact assessment study for two different marine renewable energy schemes proposed to extract energy from the Severn Estuary and Bristol Channel. These schemes included the Severn Barrage and an array of tidal stream turbines. The 1-D and 2-D models were linked using the overlapping method and validated against field and laboratory data. Faecal bacteria indicator levels were modelled by considering the interactions between the bacteria and the sediments and a dynamic decay rate, based on turbidity and solar intensity, was deployed for enhanced accuracy in modelling the bacterial fluxes. The linked model showed promising potential in modelling the hydro- environmental impact of marine renewable energy devices and structures. Secondly, the linked models were refined to predict breach failure and flood risk predictions of an artificial breach and flood inundation in the Greenwich Embayment, London. Comparisons were made implementing 1-D/2-D linked models using two different 2-D numerical schemes, namely the ADI and TVD schemes, and using three different 1- D/2-D linking methods, namely water levels discharges and discharges with momentum conservation. The results showed that the predicted flood inundation extent was different when using the two different schemes, as to be expected, and with the results also showing that the link method with the momentum transfer not making a significant difference to the model predictions for this study. Moreover, it was found that the flood inundation and extent predicted using the ADI and TVD methods were similar when the 1-D and 2-D models were linked through the discharge method, while the results were significantly different when the water level method was used to link the models. Consequently, it is recommended that the discharge link method should be used for linking 1-D and 2-D models in applications as for flood defence breaches as reported herein.

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