cpd foundation seminar: designing flood resilience€¦ · 03/07/2019 · designing flood...

CPD

Foundation

Seminar:

Designing

Flood

Resilience

June 2019

1

Peter Brett Associates – now part of StantecWe are development and infrastructure consultants

• A leading consultancy of

engineers, planners,

scientists, and economists.

• Creating and delivering

commercial and social

value for our clients and the

communities in which we

work.

750Staff

£62mTurnover 2017/18

Located across

the UK and Europe

Offices16

2

Chris

Downs

Director of

Water

Elisabetta

Torricelli

Senior Associate

in Hydro Team

Presenters

Introduction

Designing for Flood Resilience

This seminar will look at:

• Common flood risks - including flood risk areas

• Desktop research - what you should be looking for

• Insurance, value and development potential

• Considerations for surveyors in flood risk areas

• Planning for flood risks and building resilience

3

Common

flood risks

Common flood risks Flood Risk

4

Potential Sources of Flooding:

• River Flooding (Fluvial)

• Surface Water Flooding (Pluvial)

• Coastal Flooding (Tidal)

• Foul Drainage Flooding

• Groundwater Flooding

• Reservoir/Canal Breach

5

Common flood risks

Flooding Principles

Caused when flow in rivers exceeds channel capacity

Floodplain Development:

Inappropriate Appropriate

6

Common flood risks Sources of Flooding - Fluvial Flooding

Simple Rules for Floodplain Development

• Not at risk of flooding

• Not cause increased flooding elsewhere

History of Floodplain Development

7


Floodplain Roles

Conveyance

• Upstream Impacts

Storage

• Downstream Impacts

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Caused when water does not penetrate into the ground due to:

• the surface being impermeable (not porous)

• when the ground is already saturated

• drains are not functional or overwhelmed

9

Common flood risks Sources of Flooding - Pluvial Flooding

Common drainage infrastructure issues:

• 1:2yr or 1:5yr historical design standard

• 1:10yr capacity with surcharge

• Gully blockage in autumn

Pluvial flooding an increasing problem –

More intense local storms…

due to climate change?

10

Common flood risks Sources of Flooding - Pluvial Flooding

Occurs where the natural level of the water in the ground (water table) has risen above the surface of the ground.

• Permeable underlying rock acts as a reservoir

• Prolonged rainfall

• Rising groundwater levels until water appears on the ground surface

• Usual discharge points such as semi-permanent springs that connect to drains and watercourses cannot stop the aquifer filling up much higher than normal.

• Aquifer overflows via new springs with no natural watercourse outlet causing flooding.

• Development (i.e. landfill) obstructing groundwater flow routes

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Common flood risks Sources of Flooding - Groundwater Flooding

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Common flood risks Sources of Flooding - Groundwater Flooding

Desktop

research

River Flooding

• EA flood level data and mapping, BGS records, Canal & River Trust, insurance

records, local inspection of watercourse and blockage potential, hydraulic modelling

Surface Water Flooding

• EA mapping, Local authority (LLFA & Highway Authorities) and water company

records, Internal Drainage Boards insurance records, local enquiries and local

inspection of low spots

Coastal Flooding

• EA records, insurance records, local enquiries and local inspection

Groundwater Flooding

• BGS and local authority records, local enquiries

Foul Drainage

• Local authority and water company records, local enquiries

Artificial Flooding Sources

• EA and local authority records, local enquiries and local inspection

13

Desktop researchSources of Flooding Data

• NPPF (2018) & accompanying Planning Practice Guidance (2014) sets out national policy in development and flood risk for England

• Aims to ensure planning process avoids inappropriate development in areas at risk of flooding and direct development away from areas of highest risk

• In exceptional circumstances where new development is necessary in flood risk areas, policy aims to ensure it is safe, without increasing flood risk elsewhere, and where possible, reducing flood risk overall.

Flood Zones refer - probability of river & sea flooding, ignoring the presence of defences (Table 1 of PPG)

Annual Exceedance Probability (AEP):

• A flood with a 1% AEP (i.e. 1 in 100 year event) has a 1 in a 100 chance of being exceeded in any year.

• Can be sometimes misinterpreted as indicating - associated magnitude is only exceeded at regular intervals, or time until the next event of this magnitude.

• AEP correctly acknowledges that floods can and do occur at any time.

Flood Zones are shown on EA’s web site Flood Map for Planning (Rivers & Sea)

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Desktop researchNational Planning Policy – NPPF & PPG

https://flood-map-for-planning.service.gov.uk/

• Zone 1 – Low Probability – Land having < 1 in 1,000 annual probability of river or sea flooding (Shown as ‘clear’ on the Flood Map – all land outside FZ2s 2 & 3)

• Zone 2 – Medium Probability – Land having between a 1 in 100 and 1 in 1,000 annual probability of river flooding (Land shown in light blue on the Flood Map)

• Zone 3a – High Probability – Land having > 1 in 100 annual probability of river flooding (Land shown in dark blue on the Flood Map)

• Zone 3b – Functional Floodplain – Zone comprises land where water has to flow or be stored in times of flood. LPA should identify in their SFRAs areas of functional floodplain and its boundaries accordingly, in agreement with the EA (Not separately distinguished from Zone 3a on Flood Map). Often the 1 in 20 year annual probability floodplain.

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When is a FRA required?

• Developments located in FZ2 or FZ3 including minor development and change of

use

• Development > 1 hectare (ha) in FZ1

• Development < 1 ha in FZ1, including a change of use in development type to a

more vulnerable class (for example from commercial to residential), where they

could be affected by sources of flooding other than rivers and the sea (for example

surface water drains, reservoirs)

• Development in an area within FZ1 which has critical drainage problems as notified

by the EA

FRA not required for sites < 1ha in FZ1. Still need to consider if site could be affected

by other sources of flooding, for example surface water

For all sites in all flood zones a viable surface water drainage strategy must also be

demonstrated.

16


EA Flood Map for Planning

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Example EA Flood Level Data

EA fluvial flood maps do not tell the whole story:• Not all watercourses modelled

• Accuracy may not be suitable – may require additional hydraulic modelling

• Projected impacts of climate change not included

• May not reflect the benefit afforded by all defences

• Areas Benefitting from Defences are not immune to flooding - breach and overtopping risk remains

In some cases, hydraulic modelling may be required to define flood risk:

• Age of EA hydraulic modelling – hydrology out of date, channel been modified, land raising/development within catchment floodplain not represented

• EA Flood Mapping based on coarse high level modelling – JFLOW mapping

• Culverts not represented - floodplain not realistic representation

• Site specific topographical survey of the site enables floodplain to be mapped more accurately than EA Flood Map

• If results differ from EA Flood Map:• Agree with EA that site is at a different risk of flooding than shown on EA Flood Mapping and therefore different mitigation

measures required.

• Option to formally undertake a Flood Map Challenge.

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Table 3 – Flood Risk Vulnerability & Flood Zone

‘Compatibility’

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• Where development is ‘Appropriate’

– still a requirement to provide

suitable flood mitigation.

• Does not reflect need to

avoid/manage flood risk from

sources other then rivers and sea.

• Sequential Test required?

• Exception Test required?

According to projections:

• Increase in sea level

• Increase in rainfall intensity

• Increase in river flow

Environment Agency Climate Change guidance for use in FRA’s (2016)

• Provides contingency allowances for potential increases in river flow, rainfall intensity and sea level change attributed to climate change.

• Appropriate allowance to be used based upon geographical region within the UK, proposed design life of the development, the vulnerability of the proposed land use and the Flood Zone the site is located in.

• Based on UKCP09 projections

UKCP18 – updated climate projections

• Further guidance on application of UKCP18 to development planning likely to be published in 2019.

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Desktop researchClimate Change

Insurance

PBA has pro actively supported the design

development of our proposals at South

Thamesmead, providing solutions to

constraints and working collaboratively with

stakeholders

to establish a route forward.

John Brooker

Insurance Value and development potential

• Previously - Statement of Principles (SoP) - Government &

insurance companies - provide flood insurance coverage to

domestic properties at significant risk of flooding.

• Flood Re- replaced SoP in April 16 - a levy and pool system

covering the UK.

• Flood Re – a not-for-profit scheme - run & financed by insurers -

cap domestic flood insurance prices – aim to keep premiums

affordable for households in high-risk areas.

• Significant risk of flooding - no worse than a 1.3% or 1 in 75 annual

chance – estimated covers most at risk 2%, or 250,000 homes -

though others suggest it would mean 370,000 homes.

• 3 bed house average repair cost for flood damage - £30k –

further £15k to flood proof – e.g. NRVs, tiling floors & raising power

points (RICS 2014).

21





stakeholders


John Brooker

• Association of British Insurers - £1.1b a year of flood damage

prevented by the UK’s current network of river barriers & defences.

• ABI – modelling work shows UK inland flooding - on average, cost

almost 3 X more on an annual basis without the defences – i.e.

£1.8b rather than £0.7b across UK.

• In England - Government currently spends £0.6b each year on

building & maintaining flood defences – EA recommended that

annual this should be £1b.


22

• Mortgage lenders in the UK generally require mortgage holders to

purchase buildings insurance that includes cover for flooding.

• Value of a property at risk from flood is less than one that is not -

in part, due to obtaining building insurance cover for the property.

• Building insurance therefore important in determining whether a

property is mortgageable - owners and prospective purchasers

need to verify this cover is provided & maintainable by determining

the property’s flood risk.

• Reduction in value may range from negligible to severe, depending

on the particular circumstances of the property’s location, situation,

type of construction, and flood defences, both to the geographic

area and to the property in particular.

• The impact on value can be reduced by ensuring better flood

defences are in place and by increasing the flood resilience of the

property and its contents.


23

Considerations

for surveyors





stakeholders


John Brooker

Considerations for surveyors in flood risk

areas

• Once location of a new development has been determined -

consideration of the development’s layout is the next important

stage – master planning.

• A site-specific flood risk assessment for individual development –

apply sequential approach - site may have lower risk areas –

locate flood sensitive development here.

• Assessment should be carried out on behalf of the developer -

should be proportionate to the flood risk - should take account of

other assessments that have been produced.

• Needs to consider not just the development’s risk of flooding - also

impact the development will have on flood risk off-site.

24

Considerations for surveyors in flood risk

areas

• What is the risk to the property from flooding?

• River ● Surface Water

• Coastal ● Foul Drainage

• Groundwater ● Reservoir/Canals

• Assess level of risk

• Currently – EA & LLFA data – site specific FRAs & F/P

modelling

• Future – Climate change – EA & site specific modelling

• How will flood risk affect the value and insurability of the property

• What can be done to deal with any flood risk to the property

25

Planning for

flood risks and

building

resilience





stakeholders


John Brooker

Planning for flood risks and building resilience Background

• 6 of 7 most wettest years - occurred since 2000.

• While the most recent severe flood was 2016 – over 20,000

properties flooded – 2007 was most recent largest scale flood.

• 2007 flood - over 55,000 properties flooded across England &

Wales - 13 people lost their lives - devastating impact – 62% of

households had to move out of homes – 12% waited 6 months or

longer to return - emotional impact & well-being effects.

• Led to the Pitt Review – several ongoing themes

• Unlearned lesson: not sandbags in your doorway - close-fitting

flood board.

• Stop smothering gardens with hard surfaces - creating run-off.

• New developments should allow water from roofs & streets to

seep into ground - rather than run to sewers - SuDS

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Planning for flood risks and building resilience Planning

• Avoiding development on the floodplain –

• difficult many our towns / cities built close to river on floodplain

– e.g. London local to Thames defended FZ3

• A good flood risk assessment -

• Consider local position – readily available info – using to

inform development plans

• Site specific - sequential approach applied – e.g. place

buildings in low risk part of site

27





stakeholders


John Brooker

Planning for flood risks and building resilience Flood Risk

28





stakeholders


John Brooker

Planning for flood risks and building

resilience – Flood Risk

• Buyers of a newly-built property - reasonable expectation -

property will not be prone to flooding –

• In the uncommon case - property is built on the floodplain - flood

risk should be mitigated as far as possible. Properly applied,

current government policy on development and flood risk – NPPF

– supports this expectation.

• Approx. ¼ of properties flooded in 2007 – had been built in

previous 25 years.

• Pitt Review – pushed for the national approach we now have -

presumption against building on the floodplain – where possible

move new development to lower flood risk areas.

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stakeholders


John Brooker


resilience - Resilience

• Resistance and resilience measures - help to minimise damage to

property from flood water - greatly reduce the length of time for

recovery of a building.

• Resistance measures –

• normal retrofitted to existing buildings - need to consider

impact on building

• aimed at keeping water out of buildings – or at least

minimising amount entering

• Resilience measures - aimed at minimising the damage caused

when a building is flooded - allowing recovery to take place as

quickly as possible

• Resilience – easier to design – elements can be retrofitted – flood

damage repairs should be resilient.

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stakeholders


John Brooker


resilience - Resilience

Ref: Improving the Flood Performance of New Buildings - Flood Resilient Construction - UK Gov

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stakeholders


John Brooker

Planning for flood risks and building resilience Resistance & Resilience

Ref: Know Your Flood Risk

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stakeholders


John Brooker

Planning for flood risks and building resilience Resilience

• Water compatible internal walls –

• Silicon-mineral/ Magnesium Oxide board

• Technitherm cavity wall insulation

• Also provides fireproof/thermal insulation - Medium cost

• Water compatible flooring

• Tiled flooring, rather than fitted carpets/laminate

• Concrete floor to replace timber

• Also provides fireproof/thermal insulation - Medium to high

cost

• Water compatible kitchen and bathroom fittings

• Steel kitchen units

• ‘Sealwise’ - Waterproof Construction Board

• Originally for hospital/industrial use - Medium-high to High

cost

33





stakeholders


John Brooker

Planning for flood risks and building resilience Resilience

• Raised electrics / meters

• Local electricians

• A practical limit to how high electrics/kitchen appliances

can be raised

• Medium to high cost

• Plinths for kitchen white goods; wallmounted boiler

• Local builders/electricians/gas-qualified engineers

• Medium cost

34





stakeholders


John Brooker

Planning for flood risks and building resilienceRESISTANCE

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Planning for flood risks and building resilienceSustainable Drainage

What are SuDS? • Reproduction of the natural processes

of infiltration, evaporation and evapotranspiration

• Encourages management of water as close to its source as possible

• Soft and hard solutions

3 Key Points





stakeholders


John Brooker

Design Flood Resilience 3 Key Point

• New development should be moved to low flood risk areas –

both locally and at a site level.

• Where this not possible, a combination of resilience

construction techniques and resistance measures should be

used to mitigate the risk as well as considering SuDS for

surface water drainage.

• On existing properties, retro fitting of resistance measure

needs the building fabric to be carefully assessed.

37

@PeterBrettLLP

peterbrett.com

Thank you for listening

Any Questions?

https://twitter.com/PeterBrettLLP

https://www.linkedin.com/company/peter-brett-associates

cpd foundation seminar: designing flood resilience€¦ · 03/07/2019 · designing flood...

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