Dundee Coastal Study Stage 2

Dundee Coastal Study Stage 2

Draft Plan - Options Report

May 2011

Dundee City Council

260186 BNI SNI 002 *

PiMS

09 April 2011


Draft Plan - Options Report

May 2011

Dundee City Council

Mott MacDonald, Caledonian Exchange, 3rd Floor, 19a Canning Street, Edinburgh EH3 8EG, United Kingdom

T +44(0) 131 221 2300 F +44(0) 131 221 2399, W www.mottmac.com

Dundee City Council Tayside House, 28 Crichton Street Dundee DD1 3RB


Mott MacDonald, Caledonian Exchange, 3rd Floor, 19a Canning Street, Edinburgh EH3 8EG, United Kingdom

T +44(0) 131 221 2300 F +44(0) 131 221 2399, W www.mottmac.com

Revision Date Originator Checker Approver Description

A 21.04.2011 L. Mair D. Dray P. Phipps First Issue

B 05.05.2011 L. Mair P.Phipps For Consultation

Issue and revision record

This document has been prepared for the titled project or

named part thereof and should not be relied upon or used

for any other project without an independent check being

carried out as to its suitability and prior written authority of

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Mott MacDonald accepts no responsibility or liability for this

document to any party other than the person by whom it was

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To the extent that this report is based on information supplied

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Mott MacDonald in preparing this report.

260186/BNI/SNI/002/* 09 April 2011 PiMS


Chapter Title Page

Executive Summary 1

1. Introduction 2

1.1 Background _______________________________________________________________________ 2

2. Options 3

2.1 Guidelines ________________________________________________________________________ 3

2.2 Method ___________________________________________________________________________ 3

3. Dundee Coast Management Sections 4

4. Dundee Coastal Study Options 5

Appendices

Appendix A. Management Section Sketch Plan

Figures

Figure 1.1: Dundee City Frontage

Tables

Table 3.1: Management Sections

Table 4.1: Options

Content



Dundee City Council (DCC) is responsible for 16.5km

of coastal frontage and has discretionary powers to

build flood defences for non-agricultural land under the

Flood Prevention (Scotland) Act 1961. Dundee City

Council has commissioned Mott MacDonald to produce

preferred outline management solutions for different

frontage sections, to submit to the Dundee City Council

City Development Committee and also obtain approval

from the Scottish Government for progression of the

schemes.

This report provides a record of the proposed short-

listed options to take forward to more detailed

consideration.

Executive Summary



1.1 Background

Dundee City Council (DCC) is responsible for 16.5km of coastal

frontage and has discretionary powers to build flood defences for non-

agricultural land under the Flood Prevention (Scotland) Act 1961. The

frontage extends from Invergowrie Bay in the west to the Dighty Burn in

the east, and includes environments ranging from shingle foreshores,

industrial areas, reclaimed land and sandy recreation beaches

Figure 1.1: Dundee City Frontage

Dundee City Council is currently investigating potential flood defence

options as part of the Dundee Coastal Study Stage 2. The purpose of

the Stage 2 Study is to produce a preferred outline management

solution to present to the Scottish Government in order to obtain

approval for progression of the scheme.

As part of the process to develop preferred outline management

solutions, a short list of preferred options was developed through a

Multi Criteria Analysis (MCA) Workshop. The MCA options workshop

for the Dundee Coastal Study Stage 2 was held in Dundee City Council

Offices in Dundee and was attended by members of the Dundee City

Council and Mott MacDonald.

The preferred options that were identified during this workshop are

presented in this Draft Plan – Options Report.

1. Introduction



2.1 Guidelines

Under Scottish Government1 and Defra FCDPAG

2 guidelines when

undertaking the project appraisal process all possible strategies for

coastal management should be considered. The options include

strategies ranging from minimum interference ‘do nothing’ and ‘maintain

existing’ through to high interference hard engineering structures.

All options have been initially reviewed but only those considered

appropriate for the particular site conditions, protection needs and

standards of service were to taken forward to full benefit cost analysis.

2.2 Method

A multi criteria approach was adopted to support semi-quantitatively the

suitability and cost of different options against the assets benefiting

from defence. The asset criteria such as property, infrastructure,

environment and tourism etc. were weighted in relation to their

importance within the section of the frontage under consideration.

The broad relative cost of a coastal management option was also

considered against the assets to be protected. Such a method helps to

filter out unsuitable options and provide an auditable trail for future

reference in the decision making process.

This approach is recommended in the Scottish Government’s Flood

Prevention Schemes: Guidance for Local Authorities guidelines, Defra

FCDPAG guidelines and was updated using recent guidance from the

Joint Defra/EA Flood and Coastal Erosion Risk Management R&D

Programme3.

_________________________

1 Flood Prevention Schemes: Guidance for Local Authorities (2005). CHAPTER 5

Economic Appraisal. Most recent files are available from the Scottish Government website: http://www.scotland.gov.uk/Publications/2005/10/0794935/49364

2 Project appraisal guidance: procedural guidance for operating authorities. Most recent

files are available from the Defra website: http://www.defra.gov.uk/Environ/Fcd/pubs/pagn/default.htm

3 Risk and Policy Analysts Ltd. (2004) Evaluating a multi-criteria analysis (MCA)

methodology for application to flood management and coastal defence appraisals Guidance for the MCA-based element of the current approach to appraisal. Outcome of the Joint Defra/EA Flood and Coastal Erosion Risk Management R&D Programme. R&D Technical Report FD2013/TR

2. Options



Owing to the length of the frontage (approx. 16.5km),

compartmentalised flood cells, the variety of environments, existing

defences, and assets, the frontage was divided up into 9 management

sections.

The management sections have been presented below in Table 3.1.

Table 3.1: Management Sections

Section Length Area Existing Defence Issue

1 1,050m Landfill site Shallow gradient vegetated embankment with light rock armour and rubble protection

Erosion

2 1,565m Airport Steep armoured embankment with rock armour, rubble, concrete block, and brickwork protection.

Flooding & Erosion

3 3,185m Riverside Drive Sloped open faced masonry revetment with wave wall

Flooding

4 3,585m City Centre and Port of Dundee

Vertical pointed masonry wall Flooding

5 720m Industrial Area Sloping rock filled gabion baskets, concrete and rock rubble embankment

6 1,470m Coastal Walkway Concrete walkway backed by a masonry retaining wall

7 460m Yacht Club Shallow sloping shingle and grassed bank

Flooding & Erosion

8 2,290m Broughty Ferry Sloping masonry block/concrete wall revetment above shingle beach

Flooding

9 2,570m Beach and Dunes Dunes, sandy beaches with groynes and rubble/boulder upper banks

Flooding & Erosion

A sketch plan (MMD-260186-C-SK-000-XX-0025) detailing the

management sections has been provided as an appendix (A) to this

document.

3. Dundee Coast Management Sections



The shortlist of proposed options are presented below in Table 4.1 with

respect to the 9 management sections.

Table 4.1: Options

Management Section

Long-list of management solutions

The options to be taken forward to the short-list have been shown in bold

Comments

Section 1:

Landfill Site

� Do nothing

� Do minimum/ maintain/tidy

� Rock armour revetment

� Reno mattress

� Concrete mattress

� Open stone asphalt

� Structural wall (concrete, gabion basket

etc)

� Beach recharge

The do nothing and beach recharge solutions were not deemed suitable as they did not satisfy the environmental and public health objectives for this section.

Owing to the potential contaminated land issues, this section requires a solution which will act as a barrier to protect the potentially contaminated material. The structural wall solution was deemed unsuitable as this section requires a natural looking and sustainable solution to fit with the environmental regeneration which is planned for this section of the frontage.

A structural wall would also be isolated with no “hard” structure to tie into at each end, therefore would not satisfy the strategic objective. The reno mattress, concrete mattress and open stone asphalt solution are all similar variations of generic erosion protection solutions, and therefore the suitability of each will be assessed with respect to specific site conditions.

Section 2:

Airport

� Do nothing

� Do minimum/maintain

� Earth Bund with erosion protection

� Secondary earth bund set back from

the frontage (suitability dependent on

the aviation regulations)

� Coastal protection structure

� Wave wall

� Secondary flood defence around buildings

The do nothing, do minimum/maintain and coastal protection structure solutions were deemed unsuitable as they did not satisfy the technical objective of protecting at-risk assets (i.e. the airport) from flooding as they did not involve an increase in defence height. The secondary flood defence around buildings solution was also deemed unsuitable as it assumed that the runway could be closed from time to time during flood events. This would have also impeded access to the runway from the terminal and service buildings.

Section 3:

Riverside Drive

� Do nothing

� Do minimum/maintain/monitor

� Improve (fill in gaps etc)

� Raise current level of defence

� Raise land at defence and wall level

� Secondary bund around playing field

� Replace wall

� Temporary demountable flood barriers

It has been identified that an increase in the defence level is required to fulfil the technical objective of defending the frontage and assets from flooding over the 100 year study life. Owing that do nothing, do minimum/maintain/ monitor and improve do not involve an increase in the defence level, these are considered unsuitable solutions. The secondary bund around the playing field was deemed unsuitable as it could not be implemented along the full Riverside Drive frontage section. There was discussion of dividing Section 3 in two parts to allow for this and will be assessed in due course. The replace wall solution was deemed unsuitable due to its upfront capital cost with no added benefit.

4. Dundee Coastal Study Options



Management Section



Comments

Section 4:

City Centre and Port of Dundee

� Do nothing


� Flood wall

� Land raising

� Demountable flood barrier

� Reconstruct wall (pile etc)

� Individual flood protection for buildings

� Rock armour revetment w/ crest structure

For this frontage section, only 2 solutions fulfilled the objectives. Do nothing and do minimum/maintain were discounted as they do not involve increasing the existing defence level. There is the potential for this section to be further divided into the “operating port” and “non-operating port” frontages. This could then mean that the do minimum solution could be considered for the “operating port” area. Land raising was not considered feasible due the large area involved. The reconstruct wall option was considered not feasible owing to the upfront capital cost and considering the high residual life of the existing wall. Individual flood protection around buildings was deemed unsuitable as it did not protect infrastructure or the public’s safety. The rock armour revetment was deemed unsuitable because of the still functioning Port of Dundee facility.

Section 5:

Industrial Area

� Do nothing


Due to the existing relatively high defence levels and the minimal landward assets, it was decided that the most suitable solution for these areas would be do nothing and do minimum.

Section 6:

Coastal Walk

� Do nothing

� Monitor/maintain

This section has been recently upgraded and defence level is sufficient to defend the frontage, critical infrastructure and assets from flooding and coastal erosion. Therefore the only 2 solutions considered are the do nothing and the monitor/maintain options.

Section 7:

Yacht club

� Do nothing


� Recharge

� Sediment retention structures

� Edge structure

� Land raising (on frontage or at rail line)

� Fill in gaps in landward flood wall

There is currently no erosion protection in place along this frontage. If left unprotected, there is potential for the coastal footpath to be lost and put pressure on the railway line. It is for this reason that the do nothing solution was deemed unsuitable. The land raising solution was also deemed unsuitable due to the minimal property requiring protection. Although a short list of 5 options has been highlighted, a combination of solutions must be implemented to fulfil the objectives. For example, Do minimum and maintain should be coupled with fill in gaps, as the do nothing does not afford any flood protection. Likewise, sediment retention structures and recharge.

Section 8:

Broughty Ferry

� Do nothing


� Flood wall

� Shingle recharge

� Beach management

� Temporary demountable flood barriers

� Mechanical street barriers

The key requirement for a management solution along this section of the frontage is to provide flood defence for the properties in Broughty Ferry. To achieve this requirement, a solution must involve an increase in the current defence level. Therefore, the do nothing, do minimum/maintain, shingle recharge and beach management solutions were all deemed unsuitable.



Management Section



Comments

Section 9:

Beach and Dunes

� Do nothing


� Manage dunes

� Sediment retention structure (e.g.

groynes) & recharge

� Offshore breakwaters

� Hard rock revetment structures

Both beach erosion and dune degradation affect this section of the frontage, therefore the do nothing solution did not fulfil the objectives. If compromised the dune systems would afford no benefit with respect to flood defence. The offshore breakwater solution was deemed unsuitable as it would not increase the flood deference level and would prove costly. Hard revetment structures were considered out of keeping with the environmental and amenity objectives and were therefore discounted as solutions. Hard revetment rock structures are currently in use at the far eastern extents of the frontage, and appear to be fulfilling their coastal protection requirements. Therefore, it may be sensible to divide this management section further.

Source: MCA Workshop Spreadsheets




Appendices

3 260186/BNI/SNI/002/* 09 April 2011 PiMS


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