Agenda Item No: Report
Report Title: River Ouse to Seaford Head Coastal Defence Strategy : to
consider flood risk management options
Report To: Cabinet Date: 19 July 2005
Lead Councillor: Cllr Neil Commin
Ward(s) Affected: Newhaven (Valley, Denton & Meeching); Seaford (Central,
South and East); Ouse Valley & Ringmer, Kingston, all Lewes
Report By: Director of Planning and Environmental Services
Contact Officer(s): Lindsay Frost, Director of Planning & Environmental Services
Purpose of Report: to consider comments on options to manage flood risk on the
tidal River Ouse between the A27 and Newhaven and the coastal frontage between
Newhaven and Seaford, for onward submission to The Environment Agency.
1 Cabinet endorse the comments set out in Section 2, and paragraphs 3.1 and
4.2, of this report as a response to the current consultation by the Environment
Agency on options for flood risk management.
2 The flood risk management options emerging from this work be taken into
account in the preparation of the Lewes District Local Development Framework.
Reasons for Recommendations: To assist in the development of a strategy for
sustainable flood risk management in the area.
1.1 The District Council is working with the Environment Agency (advised by
consultants Black & Veatch), the County Council and other partners to
produce a long-term Strategy to manage flood risk on the tidal Ouse between
the A27 and Newhaven, and along the coastal frontage from Newhaven to
Seaford Head. The Strategy looks ahead a hundred years, and has to
address the challenges arising from climate change, which will raise sea levels
and increase flood risk.
1.2 Previous consideration by Cabinet in June 2003 and June 2004 has led to
agreement to participate in the strategy (Minute 22, 4 June 2003 refers) and
comments on a draft inception report to guide preparatory work on the
strategy (Minute 18, 7 June 2004 refers).
1.3 Work on the strategy has made considerable progress over the last year,
leading to the identification of broad options for managing flood risk, which are
now the subject consultation with key stakeholders. A copy of the consultation
material, which summarises the options on which views are now sought, is
attached as Appendix A. (Colour copies have been sent separately to all
Cabinet members). Cabinet is asked to comment on the options and indicate
any preferred options to be taken forward into further work leading to a draft
strategy. Such a draft strategy would be the subject of wider public
consultation over next winter.
1.4 The Environment Agency are also consulting concurrently with a range of
other stakeholders (see page 4 of attached comments form). Any views
received from Town & Parish Councils will be reported verbally to the Cabinet
1.5 The current work is also very relevant to the forthcoming Local Development
Framework for Lewes District and needs to be taken into account as future
planning policies are developed.
2 Comments on Options put forward by the Environment Agency
(a) General Flood Risk Management Options
2.1 Option 1 (No active intervention or "Do Nothing") is not favoured because of
its adverse effect on flood risk to local communities and important local
transport infrastructure. Parts of Newhaven and Seaford, farmland on Lewes
Brooks, the A26 road and the Lewes/Newhaven/Seaford railway would be
subject to regular flooding. These harmful impacts would far outweigh the
environmental benefit in terms of creation of new intertidal habitat and the cost
savings from carrying out no flood defence expenditure.
2.2 Option 2 ("Do Minimum") is not favoured, as it is a short term option only, to
undertake minor repairs to existing flood defences. Eventually, the defences
would fail, leading to similar adverse consequences to Option 1 for local
communities and infrastructure in the longer term.
2.3 Option 3 (Hold the Line) is the favoured option, maintaining the current
defences and upgrading them where necessary to protect against sea level
rise. This general approach may not be applied universally, with some degree
of retreat of existing defences worthy of consideration, particularly in the Ouse
Valley (see Options 4 – 9 below).
(b) River Ouse Flood Risk Management Options
2.4 Options 4, 5 and 6 all involve managed realignment of the west bank of the
River Ouse, by abandoning the existing tidal flood bank along the west of the
river and then either setting it back to an alignment through Lower Rise
(Option 4), or Upper Rise (Option 5) by construction of new shorter tidal flood
banks, or by allowing the whole of the Brooks to be flooded up to the high
ground on the valley side (Option 6). Therefore, these options represent a
progressive retreat of the currently defended flood plain back eventually up to
the valley side. All these options increase tidal river flows through Newhaven
and measures to mitigate the impact of these increased flows will be
necessary. Implementation of any of these options would require agreement
with landowners for construction of new tidal banks and acquisition of land to
create new inter-tidal habitats.
2.5 Moving from Option 4 to Option 5 to Option 6 gives progressive benefits in
terms of reducing flood risk in Lewes and creation of new inter-tidal habitat,
but progressive disbenefits in terms of loss of agricultural land, existing nature
conservation interest and rights of way, diversion of power lines and other
construction costs. Option 6 is the cheapest option as it involves no
construction of new flood banks. ~These options represent a very difficult
trade-off between different interests, which is hard to assess without a
comprehensive analysis of costs and benefits. Cabinet is recommended to
reserve its position pending receipt of full analysis, but at this stage it is
recommended that all these options remain under consideration.
2.6 Both Options 7 and 8 involve managed realignment of the east bank of the
river, to leave the areas up to the power lines (7) and the valley side (8)
undefended. The same point about agreement/acquisition of land applies, as
above. Option 8 has some significant disbenefits including regular flooding of
the A26 and the railway; re-routing of power lines; loss of agricultural land and
rights of way. On the plus side, there would be some reduction to flood risk in
Lewes and creation of new inter-tidal habitat. Mitigation measures would be
needed in Newhaven. Overall, the disbenefits of this option appear to clearly
outweigh the benefits, so it is not favoured.
2.7 Option 7 is preferred as it continues to protect essential transport
infrastructure in the area, through construction of new set back defences,
albeit at higher cost.
2.8 Option 9 allows occasional use of Lewes Brooks as a flood storage reservoir
during peak flows on the Ouse, through construction of weirs through the
existing tidal river embankments. This would assist in reducing flood risk in
Lewes and help address the odd position experienced in October 2000 where
800 properties in Lewes were under water, but large tracts of farmland on the
flood plain south of the town were dry. This option is favoured for further
investigation, on the understanding that appropriate compensation
arrangements are agreed with landowners for use of the land during flood
2.9 All of the options 4 – 9 inclusive may affect future plans being developed for
an off-road Ouse Valley Cycleway between Lewes and Newhaven, by the
County Council and its partners. It is recommended that the Environment
Agency liaise closely with ESCC on this issue.
(c) Newhaven Mitigation Measures
2.10 Measures A and B involve construction of a tidal barrage, with (A) or without
(B) lockgates, either at Newhaven or at Piddinghoe, to control the volume of
tidal water passing through Newhaven during each tidal cycle and also control
flow velocities. As an alternative to the barrage options, the river banks
through Newhaven could be straightened to reduce the scouring impact of
increased water volume velocity along the river channel. (Measure C).
2.11 Measure C appears to have least impact, but is still an expensive option. Of
the two barrage options, Measure A is preferred as it maintains navigation on
the river, albeit at higher cost. Accordingly, Measure A and C are preferred to
go forward for further consideration.
2.12 The possibility of a tidal barrage on the river north of Newhaven would offer
the opportunity to revisit past proposals for a new relief road around the north
of the town, reducing traffic on the Town Centre Ring Road and relieving
congestion problems associated with the Swing Bridge. If this option goes
further, it would be a matter for the Environment Agency and ESCC to assess.
(d) Coastal Frontage Flood Risk Options
2.13 Options 10, 11 and 12 are all "hold the line" options to protect Seaford from
sea flooding. Option 10 involves continuation of the current beach recycling
programme and Options 11 and 12 offer alternative means of defence by
construction of either rock offshore breakwaters (11), or timber or rock groynes
(12) respectively. All these are medium cost options which would maintain the
present standard of defence.
2.14 In principle, it is recommended that all these options are acceptable, although
both Options 11 and 12 will have some adverse impact on the appearance of
the beach compared with the current situation. They would, however, avoid
the need for annual beach recycling. More detailed information is required
before a clear preference can be identified.
2.15 Option 13 involves managed realignment of the coastline adjacent to Tide
Mills and setting back of the coast defences to an alignment in front of the
railway line. Such a proposal was suggested in the draft Shoreline
Management Plan, recently published for public consultation. This would
increase the possibility of sea flooding on land in front of the railway line, but
this is a lower financial cost option than Options 10, 11 and 12. Again, this
option is recommended for further consideration including more detailed
assessment of local environmental impact.
3 Financial Appraisal
3.1 There are no financial implications arising directly from the report. However,
Cabinet should note that the District Council owns a large number of
properties on the tidal flood plain in Newhaven and Seaford, including
residential flats, industrial estates, offices, parks and open spaces. These
could be adversely affected if Options 1 or 2 were selected.
3.2 Cabinet has already agreed to make a total financial contribution of £5,000
over two years (£2,500 each in 2004/05 and 2005/06) towards the costs of the
strategy. The total costs of the strategy are in the region of £350,000 borne by
the Environment Agency with grant aid from DEFRA.
3.3 Other costs will involve staff time, and provision of data to the EA's appointed
consultants, which can be covered by existing budgets.
4. Environmental Implications
4.1 I have completed the Environmental Implications Questionnaire and there are
significant environmental effects as a result of the report's recommendations.
These are outlined in this report and in Appendix A. The overall aim of the
strategy is to delivery sustainable flood risk management.
4.2 The study area includes three known private water supplies, located either
within the flood plain or immediately adjacent to it. These are Iford Village,
Iford Manor and Newhaven Port & Properties supply (located at Denton).
Options which impact upon the aquifer sources of these supplies (Options 1,
2, 5, 6 and 8) will need to consider provision of alternative water supplies for
the village of Iford and the port of Newhaven.
5 Risk assessment
5.1 I have completed a risk assessment in accordance with the Council’s Risk
Management methodology and have identified the following risks and
Risk Mitigating factors
Rising sea levels and increased Support for Options which “hold the line”
flood risk by upgrading existing flood and coast
defences where necessary.
Flood risk to LDC property Support for Options which “hold the line”
by upgrading existing flood and coast
defences where necessary
Saline intrusion into established Raise issue with Environment Agency
water supplies in Iford and and seek protection of existing water
Newhaven system and/or provision of new water
5. Background Papers
Selsey Bill to Beachy Head Shoreline Management Plan, Gifford
Associates for South Downs Coastal Group, June 1997
Revised Selsey Bill to Beachy Head SMP, Consultation draft, Halcrow for
South Downs Coastal Group, January 2005
Report to LDC Cabinet, 4 June 2003 or "Proposed Ouse to Cuckmere
Group Defence Strategy"
Report to LDC Cabinet, 7 June 2004 on "Proposed Ouse to Cuckmere
Coast Defence Strategy : Inception Report"
A - Consultation Leaflet, June 2005
Director of Planning & Environmental Services
28 June 2005