This thesis documents the work undertaken to investigate and improve the theoretical and practical requirements for two-dimensional hydrodynamic modelling of coastal and estuarine areas, in particular to the inter-related aspects of: - wetting and drying of relatively large intertidal areas, and - the influences of waves on both current generation and variations in mean water level. The work outlined in this thesis began as a result of a perceived lack of understanding and confidence in the application of finite element models to coastal and estuarine situations. In response to this observation an investigation into the modelling parameters, particularly those that affect model performance during the simulation of wetting and drying, was undertaken. This initial investigation into the effect of these parameters upon model performance forms the first component of this study. Testing was performed to provide a quantitative assessment of the effect of these parameters upon model performance. The initial tests were simple examples designed to investigate the behaviour of a single specific parameter. Subsequent tests were more complex and assessed the combinations of various parameter selections. Once the model was shown to accurately simulate the movement of waters in a coastal and estuarine environment, wave forces were incorporated. The aim of the second component of the study was to modify the hydrodynamic model to predict the net current and water levels attributable to the influences of waves. Tests examined the effects of the application of wave induced forces in a range of applications, including the simple case of a uniform beach, comparisons to a physical model, and an example from a real coastline. The final outcome of this study is the development of a modelling tool that can accurately represent the forces of tides, winds and waves upon water movement in a shallow coastal and/or estuarine region. Furthermore, the qualitative and quantitative assessments of parameters that affect the performance of the model provide greater confidence in model results and better understanding of the applicability and limits of the modelling technique. Principal outcomes of the study are: - an improved understanding of the parameters which influence the behaviour of hydrodynamic models; - a better understanding of the applicability and limits of the modelling technique; and - an enhanced software system based on an existing modelling software system which is applicable to studies that require simulation of the combined forces of tides, winds and waves.

Avec pour cas d’étude les Programmes de mesures de la Directive-cadre « stratégie pour le milieu marin », cette thèse étudie les usages attendus et effectifs des évaluations économiques, et plus largement du langage économique, dans l’élaboration des politiques publiques d’environnement. En France, les Programmes de mesures ont été élaborés via des réunions rassemblant des membres des administrations centrales et déconcentrées ainsi que des parties prenantes, aussi bien au niveau national qu’à l’échelle des sous-régions marines. Une étude des incidences socio-économiques et environnementales des mesures nouvelles, présentée comme une analyse coût-efficacité, a été conduite par des bureaux d’études. Des observations directes ont été menées au cours de 27 de ces réunions.Une analyse de contenu des discours ainsi collectés montre un faible recours au langage économique (i.e. interventions et arguments économiques). Toutefois, la proportion de langage économique dans l’ensemble des discours augmente après la présentation des résultats de l’étude d’incidences. L’absence d’objectifs bien définis et majoritairement acceptés par les parties prenantes émergeant du processus d’élaboration des Programmes de mesures explique en partie la difficulté qu’a eue l’étude d’incidence à remplir son rôle d’outil d’aide à la décision. L’élaboration des Programmes de mesures a alors été analysée comme un processus de coordination entre agents, nécessitant l’émergence de représentations communes des problèmes d’environnement marin, dans un contexte de forte incertitude. Une analyse textuelle menée sur 25 extraits d’entretiens auprès de participants au processus d’élaboration des Programmes de mesures fait apparaître la coexistence de quatre représentations du Bon état écologique. / With a focus on the programmes of measures of the European marine Strategy Framework Directive, this work explores the expected and effective uses of economic valuation, and more widely of economic language, in support of the implementation of environmental public policy. In France, the programmes of measures were elaborated via meetings gathering central and decentralised administration members as well as stakeholders, both at national and sub-marine regions scales. A socio-economic and environmental impact assessment of new measures, presented as a cost-effectivness analysis, has been conducted by external consultants. Direct observations were conducted during 27 of those meetings. A content analysis of collected speeches shows that economic language (i.e. economic interventions and arguments) is hardly ever used. However the share of economic language within speeches increases once the impact assessment of new measures has been introduced. The lack of well defined and widely accepted objectives arising from the programmes of measures elaboration process partly explain why impact assessment struggled to find its place as a tool for supporting decision-making. The Programme of measures elaboration has then been analysed as a coordination process, requiring emergence of shared representations of marine environment issues, in a highly unpredictable context. The textual analysis of 25 interviews extracts, conducted with participants to the programme of measures elaboration process, highlights the coexistence of four representations of the Good environmental status.