University of Southampton Research Repository ePrints Soton Copyright © and Moral Rights for this thesis are retained by the author and/or other copyright owners. A copy can be downloaded for personal non-commercial research or study, without prior permission or charge. This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the copyright holder/s. The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the copyright holders. When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given e.g. AUTHOR (year of submission) "Full thesis title", University of Southampton, name of the University School or Department, PhD Thesis, pagination http://eprints.soton.ac.uk UNIVERSITY OF SOUTHAMPTON FACULTY OF ENGINEERING AND THE ENVIRONMENT School of Civil and Environmental Engineering PHYSICAL DRIVERS OF SALTMARSH CHANGE IN ENCLOSED MICROTIDAL ESTUARIES BY SARAH C. GARDINER Thesis submitted for the degree of Doctor of Philosophy January 2015 [ii] UNIVERSITY OF SOUTHAMPTON ABSTRACT FACULTY OF ENGINEERING AND THE ENVIRONMENT SCHOOL OF CIVIL AND ENVIRONMENTAL ENGINEERING Doctor of Philosophy PHYSICAL DRIVERS OF SALTMARSH CHANGE IN ENCLOSED ESTUARIES Sarah C. Gardiner Estuaries are among the most biologically productive ecosystems on the planet, per unit area, with intertidal habitats and particularly saltmarshes providing a variety or ecosystem services and supporting large numbers of both primary and secondary producers. These habitats are globally important and are found throughout tropical to temperate climates. Micro-tidal estuaries are found throughout the world and particularly sensitive to sea-level rise, as they are limited in their ability to adjust and are considered vulnerable to future changes .Hence, at a broad scale, understanding the drivers and mechanisms of saltmarsh change in micro-tidal systems is crucial in aiding decision making in future coastal management. This thesis explores the drivers and mechanisms of saltmarsh change through the development of a conceptual model, which is then tested using Poole Harbour, UK as a case study site. The potential drivers of saltmarsh change were investigated using a multidisciplinary approach, combining a GIS historic change analysis utilising aerial photography, charts and maps, a bathymetric analysis of the harbour morphology and a 2D hydrodynamic TELEMAC model. Spartina anglica rapidly colonised the Harbour at the end of the 19th Century increasing the saltmarsh area from approximately 120ha to over 900ha during the 1920’s, after which there was a decline in area that has continued to present day However, saltmarsh extent in 2005 was still approximately three times the extent prior to the colonisation of Spartina anglica. Poole Harbour is large and dendritic and spatially within the Harbour separate tributaries exhibit clearly distinct saltmarsh erosion and accretion trends. Accretion was seen to occur in relatively sheltered locations with short fetches, fronted by high mudflats, in areas that are flood dominant both in terms of hypsometry as well as tidal peak flow and slack duration. Erosion was seen to occur in relatively exposed areas where the marsh top and fringing mudflats are significantly lower and local sediments have a lower shear velocity than in accretionary regions. Saltmarsh erosion tends to occur in morphologically ebb dominant areas but not exclusively, suggesting multiple drivers are in operation. Poole Harbour is used in this study as an example of a wider global problem. At a broad scale, observations emphasise that saltmarsh changes occurring elsewhere in the UK, and [i] potentially elsewhere in the world, may be more complex than often portrayed. Highlighting the need for detailed case by case studies, that use all the data available over a sufficient time period. Multiple drivers of change control the net evolution of saltmarsh in Poole Harbour and this is likely to be a widespread conclusion for other estuaries globally. [ii] LIST OF CONTENTS LIST OF CONTENTS ..................................................................................................................................................... III LIST OF FIGURES ........................................................................................................................................................ VIII LIST OF TABLES ........................................................................................................................................................ XVII LIST OF ABBREVIATIONS ...................................................................................................................................... XIX DECLARATION OF AUTHORSHIP ............................................................................................................................ I ACKNOWLEDGMENTS ................................................................................................................................................ III 1 INTRODUCTION ..................................................................................................................................................... 1 1.1 RESEARCH AIMS ......................................................................................................................... 2 1.2 RESEARCH OBJECTIVES ................................................................................................................ 3 1.3 NOVELTY/ORIGINALITY OF RESEARCH ........................................................................................... 4 1.4 STRUCTURE OF THESIS ................................................................................................................ 4 2 LITERATURE REVIEW ........................................................................................................................................... 6 2.1 ESTUARIES ................................................................................................................................ 6 2.1.1 Estuarine Hydrodynamics ....................................................................................... 8 2.1.1.1 Tides...................................................................................................................................... 8 2.1.1.2 Waves .................................................................................................................................. 14 2.1.1.3 Estuarine mixing ................................................................................................................. 15 2.1.1.4 Extreme events ................................................................................................................... 16 2.1.2 Estuarine Morphology ........................................................................................... 17 [iii] 2.1.2.1 Sediments ........................................................................................................................... 17 2.1.2.2 Cross shore profile ............................................................................................................. 19 2.1.2.3 Hypsometry ......................................................................................................................... 20 2.1.3 Estuarine Habitats ................................................................................................. 22 2.1.3.1 Saltmarshes......................................................................................................................... 24 2.1.3.2 Saltmarsh change and conceptual model ......................................................................... 26 2.2 ESTUARINE MODELLING ........................................................................................................... 35 2.3 SUMMARY .............................................................................................................................. 36 3 SITE SELECTION ................................................................................................................................................... 38 3.1 POOLE HARBOUR: SITUATION AND CHARACTERISTICS .................................................................. 40 3.1.1 History and development ...................................................................................... 43 3.1.1.1 Human Development .......................................................................................................... 43 3.1.1.2 Geological Development .................................................................................................... 43 3.1.2 Hydraulic Characteristics ..................................................................................... 44 3.1.2.1 Waves .................................................................................................................................. 44 3.1.2.2 Tides.................................................................................................................................... 46 3.1.2.3 Sea-level Rise and Surges ................................................................................................... 48 3.1.3 Sediment Budget ................................................................................................... 48 3.1.3.1 Poole Bay ............................................................................................................................