Dodder Catchment Flood Risk Assessment & Management

European Background

European Flooding

1998 - 2002 2003 – 2007

Fatalities 700 345

Major Floods 100 120

Displaced people 500,000 -

Insured economic Losses

€25 Billion €12 Billion

Figures from Emergency Disasters Database (EM-DAT)

2002 August (1:100 to 1:500 year event) Czech Republic, Slovakia, Italy, Spain, Germany, Romania, Bulgaria, Croatia,

Hungary, and Ukraine Vltava, Elbe and Danube rivers reached record highs

2005 August (>1:200 year event) Romania, Germany, Austria, Moldovia, Switzerland, Poland

Slovenia, Serbia Danube Rhine

Catchment Flood Risk Management Plan (CFRMP)

Inception Report Hydrology Report Hydraulics Report Preliminary Options Report Urban Drainage Accommodation

Report Draft Final Report

Maintenance Report Sediment transport model

Final Report Strategic Environmental Assessment (SEA) Appropriate Assessment (AA)

Objectives

Dodder Catchment

121 sq. kilometres (47 sq. miles)

Three LA’s DCC, SDCC and DLRCC

Main Channel 19km d/s two reservoirs

Tallaght Stream 5 km Owendoher 10 km Whitechurch 8 km Little Dargle 8 km Dundrum Slang 8 km Tidal Region 2 km Very steep with a history

of flooding (gradient 1:115)

Data Collection

Hydrometric Data Survey data, property

registers Environmental areas Geotechnical surveys Defence Asset Data Flooding History Previous studies Individual Risk Receptors

(IRR), hospitals, fire stations etc.

Survey of catchment & estuary

Cross-sectional survey

Bridge & culvert survey

Weir Survey

Defence Asset Survey

Silt surveys

Large inlet surveys

Light Detection And Ranging (LiDaR)

Hydrological Analysis

Review of historic Floods

Analysis of Hydrometric & Meteorological

data

Estimation of design floods

Sensitivity tests for uncertainty

Climate change

Catchment changes

Hydraulic Analysis

Build and verify hydraulic Model

Model runs for 2,5,10,25,50,100,200

&1000 years flows.

Sensitivity testing of model

Freeboard

Mapping & defining floodplains

Development of historical flood maps Developing flood extent (risk) maps for

10, 100 (200 tidal) and 1,000 year modelled events (10%, 1% and 0.1% AEP)

Development of flood hazard maps (properties, risk receptors & major infrastructure under threat)

Defence failure scenario’s, protected areas

Risk analysis for Global Warming Scenario

Example flood depth mapping in the Dodder Catchment

Example flood hazard mapping in the Dodder Catchment

Review of land usage &

Proposed Development

Existing developed land

Development Plans for each LA

Draft Development Plans

Local Plans Area Plans Other Plans (drainage,

etc.)

Development of Flood Risk Scenario’s & Options Do nothing Tidal Barrage Improvement to channel

conveyance Relocation of properties * Flood Warning system* Culverting* Diversion of watercourses Catchment wide SuDS* Proactive Maintenance Reactive Maintenance Overland Floodways Public Awareness Campaign Rehabilitation of existing

defences Deculverting/ replacing

bridges Individual property

protection Upstream Storage Walls and Embankments

Core Criteria Objective

Economic (±30%)

a Ensure flood risk management expenditure is risk based Benefit Cost Ratio, 10.0=+30%, 1.0=0%, 0.1=-30%.

Social (±30%)

a Human Life. Minimise health and safety risk of flood risk management options

b Protect key infrastructure c Protect existing, and where possible create new waterside access

and recreational and community facilities

d Maintain, and where possible increase, existing waterside access for fishing

Environmental & Heritage(±30%)

a Safeguard and promote sustainable land use in keeping with WFD

b Support the achievement of good ecological status/good ecological potential (GES/GEP) under the WFD. Particularly morphology as a supporting element to ecological status

c Protect the flora and fauna of the catchment and, where possible, enhance biodiversity, Remove Alien Species

d Protect, and where possible enhance, fisheries within the catchment

e Protect, and where possible enhance, landscape character and visual amenity

f Protect and where possible enhance known features of cultural heritage importance and their settings

Technical (±10%)

a Ensure flood risk management options are operationally viable and to minimise maintenance required.

b Ensure flood risk management options are technically and logistically viable

c Ensure flood risk managed effectively into the future Other a No increase in flood risk to other areas

Multi Criteria Analysis

• Overall scenario must score positive to become viable option• Benefit Cost Ratio ≥ 1

Dodder SEA (Draft)

Strategic Environmental Assessment of Dodder CFRAMS.

SI 436/2004 Planning & Development (SEA) Regulations 2004, Revoke Art.6 of 2003 Regs.

Fall out of EU Regs 2001/42/EC.

MammalsSix species of bat were found during the preparation of the Dodder Habitats Management Plan. These are;

• Pipistrelle (Pipistrellus pipistrellus)- most frequently recorded,

• Soprano pipistrelle (Pipistrellus pygmeaus), • Leisler’s bat (Nyctalus leisleri), • Daubenton’s (Myotis daubentonii), • Brown Long-eared bat (Plecotus auritus), and• Whiskered/Brandt’s bats (Myotis

nysticanus/brandti).

Cormorant 1 Goosander 1 Sand Martin 3

Wigeon 1 Coot 1, 2 Swallow 3

Teal 1 Black-headed Gull 1 Spotted Flycatcher 1,3

Pochard 1 Common Tern 1 Redpoll 1

Tufted Duck 2 Kingfisher 1, 3

Amber List Species of Medium Conservation Concern in Ireland recorded in the River Dodder Conservation Area (adapted from Newton et al.,

1999).

Assessment Unit Dodder AU, DS Donnybrook APSR

Water bodies Dodder

Preferred flood risk management option Hard Defences

Flood risk (1% AEP event)The flood extent maps show that 1467 residential and commercial properties are at risk from flooding from the River Dodder during a 1% AEP event. The hydraulic model shows that the flood risk is from a combination of out of bank flooding and overland flow.

Receiving Environment

Properties Utility Assets(No)

Transport Routes

(length km)

Agricultural Land (hectares)

Social Amenity (No)

Residential(No)

Commercial(No)

1362 105 0 13.13 0 0

Other features and receptors

4 CSOs 11 listed monuments including water mills, bridges, religious sites, houses and enclosures Land cover – discontinuous urban fabric, industrial and commercial units Fishery habitat is good for all salmonid life stages throughout most of the Dodder system No designated protected areas in the vicinity Important areas of green space which are of significant ecological and natural heritage importance WFD ecological status is poor WFD objective is to restore to at least good status by 2021 (extension due to highly impacted sites)

This option consists of hard defences along the left and right bank of the River Dodder. The map shows an indicative line of the location and extent of the flood defences that would protect the APSR during a 1% AEP event. The preferred option would involve the construction of 1,683m of flood walls and 351m of flood embankments averaging 1.2m above ground level.

Multi Criteria Analysis (MCA) Results

Benefit Cost Ratio (BCR) MCA scores

CFRAMP reviews

Sent to EU with plan, SEA & AA statements.

Every 6 years subsequently

Major alteration(s) occurs in catchment

Further Information OPW

Suir

Lee

Fingal, East Meath

Dodder

Dodder Construction

Thank you

Any Questions?