NERC Environmental Risk to Infrastructure Innovation Programme (ERIIP) Coastal Landfill and Shoreline Management: Implications for Coastal Adaptation Infrastructure Case Study: Pennington Prepared by: R.P. Beaven, A.S. Kebede, R.J. Nicholls, I.D. Haigh, J. Watts, A. Stringfellow This report was produced by the University of Southampton Waste Management Research Group and Energy and Climate Change Group as part of a study for the “Coastal landfill and shoreline management: implications for coastal adaptation infrastructure” project. This was funded by the Natural Environment Research Council (NERC: NE/N012909/1) as part of the Environmental Risks to Infrastructure Innovation Programme. Suggested citation: R.P. Beaven, R.J. Nicholls, I.D. Haigh, A.S. Kebede, J. Watts, A. Stringfellow, 2018. Coastal Landfill and Shoreline Management: Implications for Coastal Adaptation Infrastructure — Pennington Marshes Case Study. Report for Natural Environment Research Council. 37pp. Cover photograph, courtesy of Anne Stringfellow, University of Southampton. View of Pennington seawall (2018). 2 Table of Contents: Abbreviations .................................................................................................................................... 5 1. Introduction .............................................................................................................................. 6 2. Background ............................................................................................................................... 6 2.1 Study Site .............................................................................................................................................. 6 2.2 Shoreline management plans ............................................................................................................... 7 3. Method ................................................................................................................................... 11 3.1 Literature and site survey ................................................................................................................... 11 3.2 Coastal erosion survey ........................................................................................................................ 11 4. Landfill assessment .................................................................................................................. 12 4.1 Local setting ........................................................................................................................................ 12 4.2 Pennington landfill sites ...................................................................................................................... 13 4.3 Pennington Marshes landfill site history and characteristics.............................................................. 18 4.3.1 Waste, leachate and landfill gas analysis ....................................................................................... 20 4.3.2 Landfill engineering: lining or capping ............................................................................................ 21 5. Coastal flooding and erosion at Pennington .............................................................................. 21 5.1 Erosion and Implications of sea level rise ........................................................................................... 22 6. Coastal defence performance ................................................................................................... 22 6.1 Potential for overflow, overtopping and breaching ............................................................................ 22 6.2 Potential areas of inundation .............................................................................................................. 28 6.2.1 Inundation across the current tidal flood plain ............................................................................... 28 6.2.2 Extreme water level events ............................................................................................................. 30 6.2.3 Potential leachate generation in response to extreme water level events ..................................... 31 7. Management options ............................................................................................................... 32 7.1 Maintain the Hold the Line SMP ......................................................................................................... 32 7.2 No Active Intervention SMP ................................................................................................................ 33 7.3 Managed realignment SMP ................................................................................................................. 33 7.4 Removal of the landfill ........................................................................................................................ 35 8. Comments and Recommendations ........................................................................................... 36 9. Acknowledgements ................................................................................................................. 36 10. References .............................................................................................................................. 37 3 List of tables Table 1: Shoreline management plan (SMP2) policies for the various units in the study area. ............. 8 Table 2: Data description and usage for the Pennington study site. .................................................... 12 Table 3: Key summary of the history and characteristics of the landfill sites in the Pennington study area. ...................................................................................................................................................... 16 Table 4: Structural failure probabilities of the Pennington sea wall under different return periods and medium sea-level rise scenarios. .......................................................................................................... 27 Table 5: Sea level rise projections for low, medium, high and extreme high (H++) scenarios at Pennington by 2050 and 2100. ............................................................................................................. 28 Table 6: Estimated height and width requirements, and indicative costs, for the Pennington sea wall under four sea level rise projections and a Hold the line SMP. ............................................................ 32 Table 7: Comparison of estimated costs for existing hold the line management and a realigned sea defence ................................................................................................................................................. 35 List of Figures Figure 1: Geographic location of the study region and the historic and authorised landfill sites. Map scale: 1:25,000. ............................................................................................................................................................. 9 Figure 2: Map showing distributions of the various land use and coastal wetland habitats and the different nature conservation/designated sites at Pennington (Source: EA datasets). Map scale: 1:25,000. ...................................................................................................................................................................... 10 Figure 3: Pennington sea wall embankment, looking east, with the wetland (Butts Lagoon) on the left and the Solent on the right (23 July, 2017). ................................................................................................. 13 Figure 4: (a) Historic landfills, and (b) authorised landfills at the Pennington study site ...................... 14 Figure 5: Efford landfill site, looking north (23 July, 2017). ............................................................................. 15 Figure 6: Pennington Marshes landfill (a) from the northwest corner of the site (b) from the southeast corner of the site (23 July, 2017). ......................................................................................................... 15 Figure 7: Marshes south of Pennington Marshes Landfill, looking across Butts Lagoon to the Solent (23 July, 2017). ............................................................................................................................................................ 18 Figure 8: Map showing ground elevations of the landfill sites and surrounding area, plus the crest heights of the seawall (Kebede, 2009). ............................................................................................................... 19 Figure 9: (a) 1973 map of Pennington site showing area identified as Pennington Marshes refuse tip (b) Pennington site showing potential landfill site areas. Maps sourced from DigiMap. ...................... 20 Figure 10: Map of Lymington Seawall highlighting the sub-sections of comparable elevation (m aOD) as defined by Kebede (2009). ................................................................................................................... 23 Figure 11: Freeboard depth, showing the impact of tidal variation. ........................................................... 23 Figure 12: Pennington sea wall crest elevation along its length showing different section heights. 1- in-200 year return period extreme water level in the current day (2015) and future (2050, 2100) under