Denbigh flood risk management scheme case study

Martin Wright Associates
Coastal & flood risk management engineers

Flood Risk Management and
Community Resilience

Denbigh Flood Risk Management Scheme

www.martinwrightassociates.com

INTRODUCTION

Mike Wellington


FLOODING IN THE UK

• Autumn 2000 was the wettest autumn in England and Wales for
over 270 years

• Parts of the UK were inundated by floodwater, sometimes on
several occasions

• The Government invited the President of the Institution of Civil
Engineers to establish a Commission to consider what approaches
to managing fluvial flood risk are appropriate to the 21st century


FLOODING IN THE UK

• In 2001 ICE published ‘Learning to Live with Rivers’

• This review supported the EA’s initiative in
raising awareness of fluvial flooding
concluding that ‘floods can only be
managed not prevented, and that
communities must learn to live with rivers

• Traditional approach in the UK focused on
Defences and managing the likelihood of
flooding


NEW APPROCHES TO FLOOD RISK MANAGEMENT

• Following widespread flooding in England in the Summer of 2007,
(Gloucester) Sir Michael Pitt undertook review of flood defences in
the England.

• Published in 2008 and made over 90 recommendations

• Both Welsh Assembly Government and DEFRA keen to adopt a
more holistic approach to how we deal with flood risk.

• In addition to the traditional methods used to prevent flooding -
such as building bigger and better defences now a greater focus on
ensuring that the community at risk is fully aware of the potential
consequences of a flood.


RECOMMENDATIONS OF THE PITT REVIEW (ENGLAND)
• increasing interest in alternative sustainable adaptation measures,
e.g. property resilience measures to enable a flexible approach to
adaptation

• the public need to be aware of a flooding risk before they can take
action to minimise it

• the EA should work to raise awareness in flood risk areas identifying
a range of mechanisms to warn the public, particularly the
vulnerable, in response to flooding to reduce the impact of floods
on individuals.

• levels of awareness should be raised through education and
publicity programmes


RECOMMENDATIONS OF THE PITT REVIEW (ENGLAND)
• the public should make up a flood kit

• raising awareness of risks
can build community
resilience to flooding
with a clear understanding
of risk


NEW APPROCHES TO FLOOD RISK MANAGEMENT

• Welsh Assembly Government’s Environmental Strategy Plan
recognised findings of Pitt and developed the New Approaches
Programme - A new approach to flood risk management in Wales

• The 'New Approaches' programme is aimed at facilitating this
change. The approach requires stronger partnership working, more
robust public engagement and a focus on consequence
management.


DENBIGH FLOOD RISK MANAGEMENT SCHEME

• In 2002, Denbighshire County Council carried out a Pre-Feasibility Study
of a culverted watercourse (known as Henllan Brook) that flows through
the town of Denbigh. The study focused on a specific length of the
watercourse in the Lenten Pool area of the town where flooding is
particularly prevalent and severe.

• Work on the Project Appraisal Report (PAR) commenced in January 2009
with an enhanced scope to include a detailed strategic investigation of
the entire length of the brook to ensure that any proposed
improvements in the Lenten Pool area would not create new problems
further downstream.



• In February 2009, the scope of the PAR was further extended as a result
of the Council’s successful bid to Welsh Assembly Government (WAG) to
be part of a Flood and Coastal Risk Management Programme that
attracted European Union Convergence Funding

• As a result of the above developments the content of the PAR was
expanded to meet the aims and objectives of the strategic WAG
programme - which in turn have been developed to be consistent with;

a) WAG’s ‘New Approaches Programme’
b) the recent Pitt Review and
c) the European Union Directive on the assessment and management of
flood risks


Henllan Brook www.martinwrightassociates.com

Historic Flooding in Denbigh www.martinwrightassociates.com

Flooding Lenten Pool – October 2001 www.martinwrightassociates.com

• Ordinary watercourse flowing through urban area
• Culverted on an ad-hoc basis over past 200 years
• Poor structural condition
• Limited maintenance regime
• Extensive commercial & residential development
• Regular and severe flooding
• 226 residential and 26 commercial properties at risk

Problem www.martinwrightassociates.com

Flood Paths and Properties at Risk www.martinwrightassociates.com


• No guidance from WAG or ‘toolbox’ regarding
implementation of ‘New Approaches’
• Rural community with large percentage of vulnerable adults
• Community did not fully recognise or understand flood risk
• Barriers to flood awareness raising that need to be overcome

Challenges www.martinwrightassociates.com

• Public apathy
• Denial of problem due to fears of property devaluation or
inability to get insurance
• Lack of Knowledge
• Forgetting to act as serious flooding had not happened
recently
• Lack of motivation
• Someone else’s problem

Barriers to awareness raising www.martinwrightassociates.com

Community Resilience www.martinwrightassociates.com

HOLISTIC SOLUTION ADOPTED
TRADITIONAL NEW APPROACH (FLOOD RISK MANAGEMENT)

1) Improve existing infrastructure 1) Improve existing infrastructure

2) Increase built environment resilience

3) Raise public awareness

4) Enhance community resilience

5) Improve flood warnings

6) Better land use management

7) Improve emergency response/recovery

8) Develop better asset management

9) Collaboration with key stakeholders

10) Protect/enhance the environment

Flood Alleviation to Flood Risk Management www.martinwrightassociates.com

REDUCING FLOOD RISK IN DENBIGH

TRADITIONAL

• 1,440m of new culverts ranging in size from 300mm to 2.1m x 1.0m

• Combination of open cut and tunnelling

• 635m of watercourse re-profiling and improvements

• Repair of existing culverts

• New screens

• New flood storage areas

Improving Existing Infrastructure www.martinwrightassociates.com

Proposed works www.martinwrightassociates.com

Phase One – A525 to Cysgodfa www.martinwrightassociates.com

Phase One –Cysgodfa Improved Inlet Structure www.martinwrightassociates.com

Phase 1A – Ruthin Road www.martinwrightassociates.com

Intake Structure at Clwyd Avenue www.martinwrightassociates.com

Phase 2 – Flow Attenuation www.martinwrightassociates.com

Phase 2 – Wet Ponds www.martinwrightassociates.com

Phase 2 – Attenuation Pond www.martinwrightassociates.com

Phase 2 – Lodge Farm www.martinwrightassociates.com

Phase 2 – Control structure www.martinwrightassociates.com

Phase 3 – Lenten Pool www.martinwrightassociates.com

Phase 3 – Lenten Pool (Tunnelling) www.martinwrightassociates.com

Phase 3 – Lenten Pool (Auger boring) www.martinwrightassociates.com

Phase 3 – Lenten Pool (Archaeology) www.martinwrightassociates.com

NEW APPROACH - ENGAGING THE LOCAL COMMUNITY

• Press Releases
• Scheme logo and signage
• Local advertising
• Public Exhibitions and displays
• Website and Social Media
• Flood Risk Workshops
• Weather centre
• Visualisations

RAISING PUBLIC AWARENESS www.martinwrightassociates.com

Press release www.martinwrightassociates.com

Scheme sign board www.martinwrightassociates.com

Scheme logo www.martinwrightassociates.com

Car Parking Advertisement www.martinwrightassociates.com

Exhibitions www.martinwrightassociates.com

www.denbighflood.co.uk - Home www.martinwrightassociates.com

www.denbighflood.co.uk - FAQ www.martinwrightassociates.com

facebook www.martinwrightassociates.com

Twitter@DFRMS www.martinwrightassociates.com

Text Alerts www.martinwrightassociates.com

Community Action www.martinwrightassociates.com

NEW APPROACH – EDUCATIONAL PRESENTATIONS

• School visits and Flood Risk Workshops
• Talks and interactive sessions
• Relating the scheme to the curriculum
• Questionnaires to take home to parents
• Competitions and prizes
• Weather centre
• Visualisations


How do you measure how effective it is?

Getting a baseline and monitoring
improvements using ACTIVOTE


Activote www.martinwrightassociates.com

Educational presentations www.martinwrightassociates.com

1. Options for solving flooding in Denbigh

2. What should be in a Personal Flood Plan?

3. What is in a flood kit?

Flood Risk Workshops www.martinwrightassociates.com

Personal flood plan www.martinwrightassociates.com

Flood kit www.martinwrightassociates.com

Weather station www.martinwrightassociates.com

Cost of Damages
( taken from the FHRC multi-coloured manual)

How do you measure how effective it is?
FLOOD RISK =
LIKELIHOOD OF CONSEQUENCES OF
FLOODING X
FLOODING
(Traditional (New Approaches)
Approach)
1% risk reduction?
Design Standard – 5% risk reduction?
1 in 100 % (plus 20% c/c) 10% risk reduction?
25% risk reduction?

Raising Public Awareness www.martinwrightassociates.com

www.denbighflood.co.uk

www.llifogydddinbych.co.uk

• Number of unique visitors: 1504

• Number of pages: 18,000

• Number of hits: 150,034

Scheme Website www.martinwrightassociates.com

Temporary
bridges
Phase 1 removed Phase 2
Starts on Road
Works in
site Closure
farmland
School Exhibition
Car park
visits start in library
adverts
go live


Phase 3 starts Construction
on site work complete
Excavation of
thrust pits
Tunnelling Flooding advice
works sent to
residents


Flood Risk Workshops

• 540 pupils actively involved

• By using the activote system it was possible to get instant feedback,
1 mark was awarded for the correct answer

• At the end of each session two sets of average scores were recorded

•A null hypothesis of:

“no difference in respondent’s awareness of flooding after
participating in a flood risk workshop” was used.

Educational and School visits www.martinwrightassociates.com

1.2
1.0
0.8

P(d)
0.6
0.4 P normal
0.2 P data
0.0
0.0 0.5 1.0 1.5 2.0 2.5
• Number of points = n = 16 d(i)
• Standard error of the sample = s = σd/√n = 0.570/4 = 0.143
• Number of degrees of freedom = DF = n-1 = 16-1 = 15
• Let D be the mean value of d(i) in the whole population; in order to find out the
probability that D<0
• t = (μd – D)/SE = (1.369 – 0)/0.143 = 9.605 with 15 degrees of freedom
• P(T) from this result is approximately equal to unity and therefore we can reject
the null hypothesis H0: μd <= 0; in fact, even t15,0.005 is only 2.947<< 9.605

• Concluding that the Flood Risk Workshop are highly effective at
raising awareness

Educational and School visits www.martinwrightassociates.com

PERSONAL FLOOD PLANS (MOST POPULAR ANSWERS)

1. Contact members of the family and friends to ensure that they are
safe

2. Contact details of the council, EA and Emergency Services

3. Have some sandbags ready in case of a flood

4. Make sure that you have insurance

5. Move valuables upstairs (or backup personal information or
sentimental photographs to the internet)

Flood Risk Workshop Feedback www.martinwrightassociates.com

PERSONAL FLOOD PLANS (LEAST POPULAR ANSWERS)

1. Flood barrier


FLOOD KITS (MOST POPULAR ANSWERS)

1. Food and water

2. Torch

3. First Aid Kit

4. Mobile phones

5. Life jacket

6. Camera

7. Radio


FLOOD KITS (LEAST POPULAR ANSWERS)

1. Lifeboat

2. Armbands

3. Umbrella


Flood Risk on School Curriculum www.martinwrightassociates.com

• A register of local events was compiled

• Events attended included:

Denbigh Show

Denbigh Plum Festival

Denbigh Heritage Festival

St David’s Day Festival

Denbigh Past, Present & Future

• 1600 members of the community engaged

Public Engagement Exhibitions www.martinwrightassociates.com

Displays were set up throughout the town at:

• Denbigh Library

• Foyer of Denbighshire County Council Office

• Morrison Supermarket

• Post Office and General Store

• Community Centre

• Public Houses

Public Engagements - Displays www.martinwrightassociates.com

• Denbigh Business Group

• Rotary Group

• Community Group

• Identified Scheme Champions

Public Engagement – Community Groups www.martinwrightassociates.com

• Facebook 121 regular visitors

• Twitter 19 followers

• Text Alert: 15 subscribers

Social Media www.martinwrightassociates.com

SCHEME LEGACY
How do you ensure public awareness and resilience is maintained?
How long lasting is a public awareness campaign?

Flood Risk Management Plan

1. Understanding the Existing Risk and Potential Consequences to the
Community

2. Measures to Manage Risk

3. Managing Future Risks – Action Plan

4. Technical Summary

FLOOD RISK MANAGEMENT PLAN www.martinwrightassociates.com

Prior to scheme www.martinwrightassociates.com

RECOMMENDATIONS

• Flood awareness & resilience included in the National Curriculum

• Funding for continuing awareness raising (post scheme) ring fenced

• Consideration given to reducing design standards from 1 in 100 yr (plus
20% for climate change) to a lesser standard for the construction of
new defences but use awareness and resilience measures to make up
shortfall

• Funding for design and development of schemes should be made
available to enable better forward planning

Flood Risk Management www.martinwrightassociates.com

RECOMMENDATIONS

• Flood risk management plans a mandatory operational tool linked to
the MARP, could be similar to CDM Health and Safety file

• Development of modern technology to reach wider community
including socially excluded and vulnerable members of society

• Use of social media is relatively inexpensive and should be developed
to become the standard

Flood Risk Management www.martinwrightassociates.com

Effect of ‘new’ legislation and responsibilities
• The Water Industry (Adoption of Private Sewers Regulations 2011)
• Flood & Water Management Act 2010 requires Local Authorities to:
 take the lead in managing the risk of all local floods
 investigate flood events and publish results
 develop, maintain and apply a local flood risk strategy
 establish and maintain a register of structures & features relevant
to flood risk
 designate structures that are relevant to flood risk
 build partnerships and ensure effective multi-agency working
 approve, adopt and maintain SuDS on new developments
 ensure flood resilience is incorporated into new buildings


Coastal & flood risk management engineers

QUESTIONS ?
For further information:


or assistance please do not hesitate to contact:

01244 677656
mike@martinwrightassociates.com

Mike Wellington

Thank You www.martinwrightassociates.com

Denbigh flood risk management scheme case study

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