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| POTENTIAL
IMPLICATIONS OF SHORTLISTED OPTIONS The images below are provided to help you in formulating feedback for all the shortlisted options. The images of No Active Intervention throughout the whole Estuary (Option 1) and Hold the Line throughout the whole Estuary (Option 3) represent the two ends of the range of options being considered. In addition, images have been provided of an example of the implications of a breach at Slaughden (Option 5) and managed realignment (Options 10 and 11). These images present a 'birds eye' view of the Alde and Ore Estuary, showing where the high tide and low tide will extend under these options on a day-to-day basis, based on tide levels today. The area covered by the low tide (the blue areas) shows the land that will be underwater at all times. The area covered by high tide (the brown areas) shows the land that will be periodically under water i.e. the intertidal area. These images do not show the extent of flooding that would occur under an extreme event; we will investigate this during the next stage of the study, once we have confirmed which options should be taken forward for detailed assessment. OPTION 1: NO ACTIVE INTERVENTION THROUGHOUT THE ESTUARY '(MAINTENANCE OF SLAUGHDEN SEA DEFENCES) Under this option, all land below the the Mean Low Water Spring line would be permanently flooded. This will include all the marshes currently located behind the existing flood defences, with the exception of Snape Marshes, Blackheath Marsh, Hazelwood Marshes, Lantern Marshes and Hollesley Marshes which would be flooded intermittently. Water speeds and erosion in the Lower and Middle Estuary would increase whilst water speeds and erosion in the Upper Estuary would decrease. Water levels throughout the Estuary would be reduced and the amount of intertidal habitat in the estuary may increase.
OPTION 2: NO ACTIVE INTERVENTION THROUGHOUT THE ESTUARY (NO MAINTENANCE OF SLAUGHDEN SEA DEFENCES) This option would involve ceasing all maintenance, repair and renewal work on the defences throughout the Alde and Ore Estuary and the sea defences at Slaughden. This option would also involve a breach at Slaughden. Under this option, all land below the Mean Low Water Spring line, including marshes located behind the existing flood defences would experience intermittent flooding with the exception of Sudbourne Marshes, Chillesford Marsh and Stonebridge Marsh which would be flooded permanently. Water speeds and erosion in the Lower and Estuary would decrease whilst water speeds and erosion in the Middle and Upper Estuary and Butley Creek would increase. There would be a noticeable decrease in water levels in the Upper Estuary and a marginal decrease in the Lower and Middle Estuary. There would be a significant increase in the amount of intertidal habitat in the estuary.
OPTION 3: HOLD THE LINE THROUGHOUT THE ESTUARY (NO BREACH AT SLAUGHDEN BEND) This option would involve maintaining the existing flood defences on their current alignment throughout the estuary. This option also assumes that the sea defences along the coastal frontage at Slaughden are maintained. The change that this option would have on the low and high tides is shown in Figure 3. The low and high tide levels under this option are similar to the current low and high tide levels in the Estuary. Under this option, the assets behind the defences would continue to be protected. As sea levels rise, this option would result in an increase in water levels, water speeds and erosion pressure on the defences. The intertidal habitats in front of the defences would also experience increased erosion. To account for the increased pressure on the defences and rise in water levels, the existing defences would need to be raised and strengthened to provide the same standard of protection as today.
OPTION 5: BREACH AT SLAUGHDEN + HOLD THE LINE + OPEN ESTUARY MOUTH This option would involve deliberately breaching (putting in a channel across) Slaughden at a position to be determined in the future to give the estuary a second mouth. The remaining defences within the estuary would be maintained on their current alignment throughout the estuary. Figure 4 shows the area over which high spring tide water levels would extend under this option. A breach at Slaughden with the existing Estuary Mouth remaining open could result in a decrease in water speeds and erosion in the Middle and Lower Estuary. This would reduce pressure on these defences, increasing their lifespan. In the Upper Estuary, flows would be dominated by the new breach and this area would experience an increase in water speeds and erosion pressure.
OPTIONS 10 & 11: NO ACTIVE INTERVENTION/ MANAGED REALIGNMENT AT ONE OR MORE SITES IN THE UPPER, MIDDLE AND / OR LOWER ESTUARY These options would involve either naturally allowing the defences to deteriorate or deliberately breaching the defences in a controlled manner. This would result in a loss of the land use at the managed realignment site, with a gain in intertidal habitats at these sites. Figure 5 provides an example of managed realignment at a site in the Upper Estuary, showing the area over which high spring tide water levels would extend under this option. Managed realignment at shortlisted sites in the estuary could have a combination of effects, such as reducing water speeds, erosion and water levels. This will reduce pressure on key areas such as Slaughden Bend and the remaining defences within the Estuary, increasing their lifespan. The overall impact in Estuary processes will depend on the location and number of managed realignment sites.
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