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SHORTLISTING THE ALDE AND ORE ESTUARY OPTIONS
The process of shortlisting the options
In order to identify a short list of options from the long list of options, we have used the two modelling techniques outlined on the ‘Identifying the Long List’ page . These techniques have been used to identify how each option will affect the whole estuary under present conditions and scenarios of Sea Level Rise and Tidal Surges (like the 1953 flood event). This is done by considering how an option affects the following:
  • water speeds (velocity) and, where applicable, the extra amount of water that would enter and leave the estuary each tide (tidal prism);
  • erosion pressure; and
  • water levels.
Water speeds and erosion are linked in that an increase in water speeds in the estuary will generally result in an increase in erosion pressure on flood defences and intertidal habitats in front of the defences.

Using the results of these model exercises, we can see which options allow us to manage estuary
processes and which options do not. Only options that allow us to manage the estuary processes will be taken forward as ‘Shortlisted Options’ for the estuary.
This comprises options that allow us to minimise the effect of some or all of the existing conditions, such as reducing water speeds, in the Estuary. Options that do not allow us to manage the estuary
processes, for example by increasing erosion pressures, are unlikely to be considered further. The effects of each of these options on estuary processes is contained within the Consultation Document, click here.
Whilst we will not consider ‘do nothing’ options that have an adverse impact on the estuary processes, we will continue to look at options that include limited or no intervention.

THE SHORTLISTED OPTIONS FOR THE Alde and Ore ESTUARY
PROPOSED SHORTLIST OPTIONS

THE SHORTLISTED OPTIONS FOR THE Alde and Ore ESTUARY
The options proposed for shortlisting fall into two categories:
(1) Options that must be taken forward for more detailed technical, economic and environmental study, and (2) Options that are proposed to be taken forward on the basis of the model results.

(1) Options that must be taken forward
The following options must be taken forward for more detailed study. The reasons for this are set out below and in the consultation document - click here.

No Active Intervention – Defra requires us to consider this option as a baseline against which
other options must be compared.
Hold the Line – This option presents the existing situation and therefore provides a baseline against which other options can be compared. It was also stated as a preference during the previous rounds of consultation.
Breach at Slaughden management options – Slaughden Bend is influenced by both estuarine
and coastal processes therefore any decisions relating to this site need to take into account both
the results of the Estuarine and the Coastal strategies. As the long term sustainability of the
existing sea defences and shingle recycling at Slaughden is currently being investigated in the
Thorpeness to Hollesley Coastal Strategy, it is necessary to consider the impacts of the possible
Slaughden Breach management options on the Estuary in further detail.

(2) Options proposed for shortlisting
The results of the model exercises shows that the following options result in some benefits to estuary processes e.g. reduction in water levels, whilst also having some disbenefits e.g. by increasing water speeds. The issues associated with each of these options are set out below. The impact of each option on estuary processes is shown in Table 3.

Hold the Line + Bypass channel across the top corner of Sudbourne Marshes – this option has
been shown to reduce water speeds and erosion around Slaughden Bend (a key pressure point in the estuary) and the Upper Estuary, however it also results in an increase in water speeds and erosion in the Middle Estuary. It is proposed that this option is taken forward, and should be considered in combination with options that address the increases in water speeds and erosion in the Middle Estuary.

Barrier – this option would provide protection to areas upstream of the barrier location during storm or surge events. This option is therefore proposed as a shortlisted option.

Managed realignment options in the Middle Estuary:
  • Managed realignment at one or more sites in the Middle Estuary generally results in an increase in water speeds and erosion in the Middle and Lower Estuary however it does result in reduced water speeds and erosion in the Upper Estuary. Middle Estuary realignment also results in a noticeable reduction in water levels in the whole of the estuary. For this reason, it is proposed that managed realignment at one or more sites in the Middle Estuary is taken forward as a possible option, with the following taken into account.
  • Due to the large area of Sudbourne Marshes, managed realignment of the whole of this area would result in a noticeable increase in the amount of water entering and leaving the estuary, with associated increase in erosion pressure. Managed realignment of only part of Sudbourne Marshes is therefore proposed as a possible option.
  • Due to there being no natural boundary between Sudbourne Marshes, Town Marshes, Chantry Marshes and Gedgrave Marshes, it would be necessary to construct an artificial boundary around any proposed realignment site on any one of these marshes.
Managed realignment options in the Upper and Lower Estuary:
  • Managed realignment at any one or more sites in the Upper Estuary in isolation would generally result in a decrease in water speeds and erosion in the Upper Estuary and at the Estuary Mouth with an increase in erosion pressure in the Middle Estuary (between Orford and Slaughden). Conversely, managed realignment at one or more sites in the Lower Estuary in isolation reduces erosion pressure on the defences in the Middle Estuary whilst increasing erosion at the Estuary mouth. Therefore, it is conceivable that by undertaking a managed realignment at a site(s) in the Upper Estuary in combination with a site(s) in the Lower Estuary, the effects on estuary processes associated with each option in isolation can be balanced out.
  • The analysis of the impact of individual managed realignment sites in the Upper and Lower Estuary also indicated the following:
    • Gedgrave Marshes are very large: managed realignment at this site would result in a
      noticeable increase in the amount of water entering and leaving the estuary each tide, with an associated increase in erosion. Managed realignment of only part of Gedgrave Marshes is therefore proposed as a possible option.
    • The low level of the land at Aldeburgh Town Marshes means that flooding this area would result in a significant increase in the amount of water entering and leaving the estuary. This would result in increased water speeds and erosion on Slaughden Bend. These effects cannot be reduced by realigning only part of this site. It is therefore proposed that managed realignment at Aldeburgh Town Marshes is not considered further.
    • Managed realignment at sites in the Butley River (i.e. Chillesford Marsh and Stonebridge Marsh) results in a significant increase in water speeds and erosion within this river. Furthermore, these sites do not allow us to manage estuary processes elsewhere in the estuary. It is therefore proposed that managed realignment sites in the Butley River are not considered further.
For all other sites proposed in the Upper and Lower Estuary, the analysis did not show any effects on estuary processes that would prevent these sites from being shortlisted.

PROPOSED SHORTLIST OPTIONS
MANAGEMENT OPTIONS
Options that must be taken forward
 SHORTLIST OPTIONS
No Active Intervention Options Option 1: No Active Intervention throughout the whole Estuary
(Continued shingle recharge at Slaughden)
Option 2: No Active Intervention throughout the whole Estuary
(No shingle recharge at Slaughden)
Hold the Line options Option 3: Hold the Line throughout the whole Estuary
Option 4: Hold the Line + Bypass channel across the top corner of Sudbourne Marshes
Breach at Slaughden Management options Option 5: Breach at Slaughden + Hold the Line + Open Estuary Mouth
Option 6: Breach at Slaughden + Hold the Line + Closed Estuary Mouth
Option 7: Breach at Slaughden + Managed Realignment at site(s) in Upper Estuary + Hold the Line elsewhere
Option 8: Breach at Slaughden + Managed Realignment at site(s) in Middle Estuary + Hold the Line elsewhere
Option 9: Breach at Slaughden + Managed Realignment at site(s) in Lower Estuary + Hold the Line elsewhere
Options proposed for shortlisting
No Active Intervention/ Managed Realignment + Hold the Line options Option 10: Hold the Line + No Active Intervention / Managed Realignment at one or more site in the Upper estuary with one or more site in the Lower Estuary:
Upper estuary sites:
  • Blackheath Marshes
  • Iken Marshes
  • Hazelwood Marshes
  • Snape Marshes
Lower estuary sites:
  • Chantry Marshes (isolated from Gedgrave Marshes)
  • Gedgrave Marshes (partial only)
  • Boyton & Hollesley Marshes
Option 11: Hold the Line + No Active Intervention/ Managed Realignment at one or more site in the Middle Estuary:
  • Sudbourne Marshes (northern tip only)
  • Town Marshes (isolated from Sudbourne Marshes)
  • Lantern Marshes
  • Kings Marshes
Managed Realignment + Bypass Channel + Hold the Line options Option 12: Managed Realignment at Sudbourne Marshes + Bypass Channel across top corner of Sudbourne Marshes + Hold the Line elsewhere
Advance the Line Options Option 13: Barrier upstream of Orford or at Slaughden