North Solent SMP Appendix C Baseline Process Understanding Contents Page No C1 ASSESSMENT OF SHORELINE DYNAMICS...........................................1 C1.1 Introduction..........................................................................................1 C1.2 SMP Overview .....................................................................................2 C1.2.1 Geology.........................................................................................8 C1.2.2 Holocene evolution......................................................................11 C1.2.3 Wave climate...............................................................................14 C1.2.4 Tidal currents ..............................................................................23 C1.2.5 Sea level rise...............................................................................25 C1.2.6 Extreme water levels...................................................................27 C1.2.7 Inter-tidal habitats........................................................................38 C1.2.8 Vegetated Shingle and Sand Dune .............................................43 C1.2.9 Cliffs ............................................................................................43 C1.2.10 Beaches ....................................................................................44 C1.3 Large/Regional Scale ........................................................................48 C1.3.1 West Solent.................................................................................48 C1.3.2 Southampton Water ....................................................................49 C1.3.3 East Solent..................................................................................49 C1.4 Local scale.......................................................................................50 C1.4.1 Local scale – Hurst Spit to Calshot Spit ......................................51 C1.4.2 Local scale - Southampton Water (Calshot Spit to River Hamble, including the Lower Test, River Itchen and River Hamble) .....................67 C1.4.3 Local scale – River Hamble to Portsmouth Harbour entrance.....72 C1.4.4a Local Scale – Portsmouth Harbour entrance to West Wittering (Portsmouth, Langstone and Chichester Harbours)................................79 C1.4.4b Local scale – Portsmouth Harbour entrance to West Wittering (Portsmouth, Langstone and Chichester Harbours)................................90 C1.4.5 Local scale - West Wittering to Selsey Bill (including Pagham Harbour) .................................................................................................98 C1.5 References .....................................................................................108 i North Solent SMP Appendix C Baseline Process Understanding List of Tables Page No Table C1.1: Summary of Archaeological time periods.......................................11 Table C1.2: Solent region wave measurement sites..........................................16 Table C1.3: Occurrence of wave height exceedance .........................................19 Table C1.4: Extremes Analysis. Significant wave height return periods from modelled and measured data - Weibull predictions (where measured dataset is of sufficient duration to calculate wave height return period values) ............22 Table C1.5: Location of tidal diamonds ................................................................24 Table C1.6: Tidal streams relative to High Water Portsmouth...........................24 Table C1.7: Regional net sea level rise allowances (FCDPAG, 2006)...........26 Table C1.8: Determination of future sea and extreme water levels..................27 Table C1.9: Summary of extreme water levels zones for a return period 1:200 year event...................................................................................................................30 Table C1.10: Extreme Water Levels Lymington...................................................31 Table C1.11: Extreme Water Levels Calshot ......................................................32 Table C1.12: Extreme Water Levels Southampton ............................................32 Table C1.13: Extreme Water Levels Lee-on-the-Solent....................................33 Table C1.14: Extreme Water Levels Portsmouth ...............................................33 Table C1.15: Extreme Water Levels Langstone Harbour..................................34 Table C1.16: Extreme Water Levels Chichester Harbour .................................34 Table C1.17: Extreme Water Levels West Wittering..........................................35 Table C1.18: Extreme Water Levels Cakeham...................................................35 Table C1.19: Extreme Water Levels East Wittering...........................................36 Table C1.20: Extreme Water Levels Medmerry..................................................36 Table C1.21: Extreme Water Levels Selsey West Beach .................................37 Table C1.22: Potential factors in saltmarsh decline ...........................................41 Table C1.23: Comparison of HPI and LTEI as methods for predicting saltmarsh extinction. .................................................................................................42 ii North Solent SMP Appendix C Baseline Process Understanding List of Figures Page No Figure C1.1: Geomorphological forms across the North Solent, taken from the RESPONSE project (2006).................................................................................4 Figure C1.2: Coastal Biodiversity Action Plan habitats across the North Solent (SDCP, 2008) ..................................................................................................5 Figure C1.3: Existing shoreline defences across the North Solent....................6 Figure C1.4: Reclaimed areas across the North Solent since 1940 (SDCP, 2008) .............................................................................................................................7 Figure C1.5: Solid geology of the North Solent.....................................................8 Figure C1.6: Surface geology and nearshore sea bed sediments...................10 Figure C1.7: The Solent River, Early – to Mid Quaternary (SCOPAC Sediment Transport Study, 2004). .........................................................................11 Figure C1.8: East and Central Solent: sediment transport, stores and sinks (SCOPAC Sediment Transport Study, 2004) .......................................................13 Figure C1.9: Location of long-term wave instrumentation in Solent region. (Source: Channel Coastal Observatory) ...............................................................15 Figure C1.10: Percentage occurrence of wave height and direction...............17 Figure C1.11: Percentage occurrence of peak wave period (Tp) and direction ......................................................................................................................................18 Figure C1.12: Wave height exceedance at the measured and modelled sites ......................................................................................................................................20 Figure C1.13: Measured storm events from July 2003 to January 2008 ........21 Figure C1.14: Wave height return periods (years) at the measured and modelled sites............................................................................................................23 Figure C1.15: Comparison of current Defra sea level rise allowances with previous guidance of 6mm per annum for South East England region............26 Figure C1.16: Extreme Water Level zones in the North Solent SMP area.....28 Figure C1.17: Historical change in saltmarsh extent; West Solent (HPI) .......39 Figure C1.18: Historical change in saltmarsh extent; East Solent (HPI).........39 Figure C1.19: Change in cross-sectional area (Spring 2003/4 to Spring 2008) (CCO West Solent and East Solent Annual Reports, 2008) ..............................47 Figure C1.20: Sediment transport between Hurst Spit and Calshot Spit (SCOPAC Sediment Transport Study, 2004). ......................................................51 Figure C1.21: Evolution of Inchmery lobe feature ...............................................54 Figure C1.25: Sediment transport between Calshot Spit and the River Hamble (SCOPAC Sediment Transport Study, 2004). .......................................67 Figure C1.26: Sediment transport between the River Hamble and Portsmouth Harbour entrance (SCOPAC Sediment Transport Study, 2004).......................72 Figure C1.28: Sediment transport between Portsmouth Harbour and Chichester Harbour entrances (SCOPAC Sediment Transport Study, 2004).79 Figure C1.29: Sediment transport in Portsmouth, Langstone and Chichester Harbours (SCOPAC Sediment Transport Study, 2004)......................................91 Figure C1.30: Sediment transport between West Wittering to Selsey Bill (including Pagham Harbour) (SCOPAC Sediment Transport Study, 2004)....99 iii North Solent SMP Appendix C Baseline Process Understanding C1 ASSESSMENT OF SHORELINE DYNAMICS C1.1 Introduction Since the completion of the original Western Solent and Southampton Water, and East Solent Shoreline Management Plans (SMPs), there is now significant new information resulting from strategic studies, coastal monitoring and coastal defence schemes, aswell as changes in environmental designations and legislation. Furthermore, there