1 Identifying Properties at Risk of Flooding Duncan McLuckie Principal Flood Specialist NSW Office of Environment and Heritage Department of Premier and Cabinet

Question Advice From Manual Fit for Purpose Planning Context Potential Data Sources Hierarchy of Information Sources Simplistic Approaches and Limitations Outline

How can we reasonably identify those properties that are likely to be subject to flood risk outside of formal flood study areas? Key Question?

Keep Flood Storage Maintain Floodways Land Capability Land Set Aside for Basins

Isolation From Flood Free Land Low Flood Island High Flood Island Bridges cut in 5% AEP Flood Ready Evacuation

Fill, Floor Level, ER, Detention Fill, Floor Level, ER, Velocity, Detention Specific Considerations for Planning Control Fill & Floor Level, Layout, Detention

FDM Section C9 Strategic planning incorporate relevant management plan outcomes and complementary measures should be implemented. Can consider full range of relevant issues. Controlling Development during the Management Process Is important. Need to:  Use current knowledge  improve knowledge  Think strategically considering the full range of risk, as info available  Use policies to control development based upon available information and update as knowledge improves

FDM Section C9 Controls Based on Historical Flood Information  Incomplete picture of risk => Range? Scale? Frequency?  Limits on Knowledge of Exposure to Hazard? Variation in Hazard? Inability to identify cumulative impacts  Controls based upon location and/or development scale  Additions and extensions considered on merits  Backwater areas and small scale and infill development. General controls floor levels etc.  Areas where significant flows expected and larger scale developments. Condition to assess flood impacts and derive development controls.

What are we using the data for? Can it lead to detailed development controls? Can it deal with cumulative Impacts? Can it support Emergency Response Planning? Does the approach suit the degree of potential exposure? Is the coverage sufficient? Does it consider potential flood controls? Is it simply to identify the need for further investigation or an area of interest? Is it fit for this purpose? Does it involve sufficient rigour? Is it reliable? Is it up to date? Are the limitations documented? Fit for Purpose

Planning Certificates Council need to answer whether the land in question is subject to a flood related development control Electronic Housing Code Requires identification of properties that may require flood related development controls s117 Direction and Model Flood Clause => Feed into statutory planning Can apply to mapped and unmapped areas => Understand a flood risk to a property may exist => Support consideration of effective controls to manage flood risk/impacts in a study Planning Context

Studies Strategic Studies => Concentrate on Areas of Greatest Exposure to Risk or with Greatest Growth Potential Studies into Specific Problems/Works – Localised, Infrastructure Projects, not always full range Developer Studies – Localised General or broad scale studies – e.g. Valley Studies There will, most likely, be gaps in studies or in the degree of information in studies to meet needs Potential Sources

Historic Data Council Records/Files/Black Spot Registers Post Event Data Collection Reports Local Histories Newpapers Agency Records Other Sources Potential Sources

Hierarchy of flood information for use in flood risk management as follows: a.Risk/Hazard Maps derived from info about Flood behaviour and likelihood (Management study and some flood studies) b.Map showing the extent of floods of a range of likelihoods (Flood Studies) c.Map based on historic flood levels with AEP estimated by flood frequency analysis (Simple investigation not considering flood range) d.a historic flood map without flood frequency analysis (historic Info) e.the QRA Interim Floodplain Assessment Overlay (composite complementary data) as a way to determine where further flood studies are required As a trigger for development assessment (preferably where refined locally) Queensland Commission of Inquiry (2011)

Generally limited in ability to satisfy needs Trigger for need for consideration of flood in development assessments. Not able to provide detailed controls. Derived Information Approaches based upon reasonable engineering judgement and simplistic methodologies Sophistication possible depends upon the available information and budget Simplistic Approaches

Simplistic modelling Using 2D models Preliminary Assessments Give general understanding of flooding Could help focus where efforts needed in more detailed investigations eg data collection Help to prioritise detailed investigations Can lead you astray Need to Check against historic info for reasonableness Other reasonableness tests -> structures, ground truthing Highlight limitations and ensure these are attached to the data. What is the Data fit for ? Simplistic Approaches

Local Overland Flooding – Major Drainage Councils have flexibility => depths/flowpaths/scale Alignment of original watercourses Determination of flowpaths – Prediction of Flowpaths Hot spots  Understand controls  Simple calculations to inform judgements  Distance from centre of bank => derive area of interest  Reasonableness test => ground truthing  Document approach =>can be revisited as better information Highlight limitations and ensure these are attached to the data. What is the Data Fit For? Simplistic Approaches

Riverine Flooding Simplistic approaches Determine controls and Simplistic Modelling of control points Bank full assessments – 2 to 5 year Check against historical data Interpolate in between as best as possible Do reasonableness test Extend existing info with extreme flood estimate Highlight limitations and ensure these are attached to the data. What is the Data fit for? Simplistic Approaches

Vegetation Mapping eg black box – infrequently flooded – flood fringes Soil Mapping Changes in Catchment conditions => vegetation, development – impacts on floods? Changes in Floodplain => topographic change, development impacts, infrastructure crossings, changing flood behaviour Not reflected in these methodologies Highlight limitations and ensure these are attached to the data. What is the Data fit for? Complementary Information

What are we using the data for? Can it lead to detailed development controls? Can it deal with cumulative Impacts? Can it support Emergency Response Planning? Does the approach suit the degree of potential exposure? Is the coverage sufficient? Does it consider potential flood controls? Is it simply to identify the need for further investigation or an area of interest? Is it fit for this purpose? Does it involve sufficient rigour? Is it reliable? Is it up to date? Are the limitations documented? Fit for Purpose