ICE - Institution of Civil Engineers - Virtual Library

The European Union (EU) Water Framework Directive (WFD), which was transposed into law in most member states in 2003, introduces a new, integrated regime of protection, improvement and management to all water bodies. These include rivers and canals, coastal and estuarine waters and, in some countries, large marine areas. The WFD also aims to prevent further deterioration in water status and to reduce or phase out pollution from certain named ‘priority and priority hazardous substances’ (these are being identified as part of the process of agreeing a separate ‘daughter Directive’ to the WFD). Another key objective of the WFD is to ensure that water bodies reach ‘good status’ by the end of 2015. Reaching good status requires not only chemical but also new ecological targets to be met. Implementation of this ambitious Directive is continuing apace in both the UK and at EU level. Stakeholder participation is a key element of the provisions of the Directive and the navigation sector is ensuring that it gets involved in this process at all levels. This briefing note provides a short overview of these activities.

The two-dimensional finite-volume model ‘Hemat’ was refined to model the pathways, fate and decay factors of faecal indicator organisms for an integrated river and coastal basin water system. The numerical model was developed, calibrated and tested by modelling faecal indicator organism inputs from river sources. A comprehensive field data set was available including intensive offshore survey data collected during a two-week period; these were used as a time series for the verification of the hydrodynamic model. River discharges and water quality data were used as boundary and initial conditions for the model. The impact of alternative land-use management strategies on the water quality of the receiving estuarine and coastal waters was investigated by modelling a series of 14 scenarios. Generally, the model results show that the faecal indicator organism input from point sources of sewage effluent dominated during dry weather and base flow conditions. On the other hand, riverine sources (such as diffuse catchment sources) significantly dominated the concentrations in the bay both during and after rainfall events. Finally, it was found that a reduction in land used for animal husbandry can considerably reduce the critical peak concentration occurring after heavy rainfall events.

The present paper reviews the context of realignment in the UK from both a coastal process and policy context, and explains the approaches that can be adopted to implement realignment. A number of case studies are then presented covering both estuarine managed realignment schemes involving the removal of flood embankments; and natural barriers beaches where realignment is likely. The paper demonstrates that while realignment leads to more natural coasts, such approaches are not without their disadvantages. The breaching of coastal defences, be they natural or man-made, has environmental, social and economic implications. Although policies involving realignment might be the most sustainable solutions in theory, this does not mean that they will be immediately embraced by the public, when they have come to expect continued flood protection. It is suggested that the promulgation of policies involving realignment requires a number of elements including increasing public awareness of coastal change, floodproofing properties, providing temporary defence measures, restricting the development of new properties and considering governmental compensation for affected home owners.

The determination of design parameters for coastal structures has historically often involved the definition of maximum water levels, the highest significant wave height and the longest wave periods. The design then proceeds with these values using numerical models, direct design methods or physical model studies. Design studies have often been conducted with maximum water levels, using random seas with previously determined parameters, a chosen wave spectrum and a sufficiently large number of waves. Parametric analysis methods using multiple parameters have identified that different combinations of water level; wave condition; perhaps fluvial discharge; or sea bed condition; may all influence the response. Recent research into the most important responses of vertical structures (plunging wave impact, toe scouring, overtopping and overtopping-induced loading) indicates that these mechanisms are all linked to the occurrence of violent wave impacts. Wave breaking is a depth-limited phenomenon, with plunging breakers occurring only for a limited range of wave height to water depth ratios. For given storm wave heights, but tidally varying water levels, this wave-breaking regime will often only prevail for a limited amount of time, leading to the conclusion that the duration of maximum exposure, namely the length of time that a coastal structure is exposed to the most important wave-induced damage mechanisms, is a function of the combined probability of (at least) water level (tidal + storm surge) and wave height/storm profile characteristics. This may have significant consequences for the definition of critical design parameters and the parameter variations employed in model tests.

The safety of a deep water marine riser subjected to high axial and bending stresses was addressed with respect to potential fatigue failure. A three-dimensional non-linear dynamic analysis of a marine riser was carried out for response calculations. The response histories so obtained were employed for the study of the fatigue reliability analysis of the riser under random wave and random wave plus top vessel motion. A fatigue damage estimation of the riser was made using Miner–Palmgren's rule (S–N curve approach). A non-linear limit state function based on the above approach was derived in terms of random variables. The advanced first-order, second-moment method (Afosm) and Monte Carlo simulation technique were employed for reliability estimation. The design point important for probabilistic design is located on the failure surface. The influence of various random variables on overall probability of failure was studied through sensitivity analysis. The effect on riser fatigue reliability of uncertainties in various random variables is highlighted.