LISMORE FLOODPLAIN RISK MANAGEMENT PLAN 2014 GLOSSARY AND APPENDICES lismo - city council CONTENTS GLOSSARY 3 APPENDIX 1: BACKGROUND DOCUMENTS 6 APPENDIX 2: FLOOD BEHAVIOUR AND HISTORY OF FLOOD POLICY IN LISMORE 7 2. FLOOD HISTORY 7 2.1 PEAK FLOOD LEVELS 7 2.3 FLOOD POLICY IN LISMORE 10 2.3.1 HISTORY OF FLOOD POLICY 10 2.3.2 LISMORE LEVEE SCHEME 11 2.3.3 CURRENT LISMORE FLOOD POLICY 12 APPENDIX 3: DESIGN FLOOD EVENTS 13 3. FLOOD PROBABILITIES 13 3.1 AVERAGE RECURRENCE INTERVAL (ARI) 13 3.2 1 IN 10 ARI FLOOD 13 3.3 1 IN 20 ARI FLOOD 14 3.4 1 IN 100 ARI FLOOD 15 3.5 PROBABLE MAXIMUM FLOOD (PMF) 17 APPENDIX 4: DEVELOPMENT CONTROLS IN THE FLOOD RISK PRECINCTS 18 4.1 FLOODWAY PRECINCT 18 4.2 HIGH FLOOD RISK AND FLOOD ISOLATED (EVACUATION) 18 4.2.1 RESIDENTIAL 18 4.2.2 COMMERCIAL 19 4.2.3 INDUSTRIAL - SOUTH LISMORE (SOUTH OF HOLLINGSWORTH CREEK) 19 4.2.4 INDUSTRIAL - ALL OTHER AREAS 19 4.2.5 CONTROLS APPLYING TO ALL DEVELOPMENT 20 4.3 MEDIUM RISK PRECINCT (& CBD FLOOD LIABLE, SOUTH LISMORE FLOOD ISOLATED AND EAST LISMORE FLOOD LIABLE) 20 4.3.1 RESIDENTIAL 20 4.3.2 COMMERCIAL 20 4.3.3 INDUSTRIAL - SOUTH LISMORE (SOUTH OF HOLLINGSWORTH CREEK) 20 4.3.4 INDUSTRIAL - ALL OTHER AREAS 21 4.3.5 CONTROLS APPLYING TO ALL DEVELOPMENT 21 4.4 LOW FLOOD RISK PRECINCT 21 4.5 PREFERRED EXCAVATION AREAS 22 APPENDIX 5: CRITERIA & PRIORITIES FOR VOLUNTARY HOUSE PURCHASE 23 APPENDIX 6: CRITERIA & PRIORITIES FOR VOLUNTARY HOUSE RAISING 24 Lismore Floodplain Risk Management Plan 2014 ~ Glossary & Appendices 2 GLOSSARY Australian Height Datum (AHD) a common national surface level datum approximately corresponding to mean sea level. Annual exceedance probability (AEP) the chance of a flood of a given or larger size occurring in any one year, usually expressed as a percentage, for example, if a peak flood discharge of 500m3/s has an AEP of 5%, it means that there is a 5% chance (ie 1 in 20 chance) of a 500m3/s or larger events occurring in any one year (see ARI). Average Recurrence Interval (ARI) the long-term average number of years between the occurrence of a flood as big as, or larger than, the selected event. For example, floods with a discharge as great as, or greater than, the 20 year ARI flood event will occur on average once every 20 years. ARI is another way of expressing the likelihood of occurrence of a flood event. Catchment the land area draining through the main stream, as well as tributary streams, to a particular site. It always relates to an area above a specific location. Development is defined in Part 4 of the Environmental Planning and Assessment Act 1979 (EP&A Act). Infill development refers to the development of vacant blocks of land that are generally surrounded by developed properties. Conditions such as minimum floor levels may be imposed on infill development. New development refers to development of previously undeveloped land, for example, the urban subdivision of an area previously used for rural purposes. Redevelopment: refers to rebuilding in an area. For example, as urban areas age, it may become necessary to demolish and reconstruct buildings on a relatively large scale. Disaster plan (DISPLAN) a step by step sequence of previously agreed roles, responsibilities, functions, actions and management arrangements for the conduct of a single or series of connected emergency operations, with the object of ensuring the coordinated response by all agencies having responsibilities and functions in emergencies. Flood relatively high stream flow which overtops the natural or artificial banks in any part of a stream, river, estuary, lake or dam, and/or local overland flooding associated with major drainage before entering a watercourse, and/or coastal inundation resulting from super-elevated sea levels and/or waves overtopping coastline defences excluding tsunami. Lismore Floodplain Risk Management Plan 2014 ~ Glossary & Appendices 3 Flood compatible materials materials used in building construction that can withstand inundation without suffering any form of damage and which can be readily cleaned when floodwaters subside. Flood liable land is synonymous with flood prone land (ie) land susceptible to flooding by the probable maximum flood (PMF) event. Note that the term flood liable land now covers the whole of the floodplain, not just that part below the flood planning level (FPL). (See flood planning area). Floodplain area of land that is subject to inundation by floods up to and including the probable maximum flood event, that is, flood prone land. Flood planning area the area of land below the FPL and thus subject to flood related development controls. The concept of flood planning area generally supersedes the ‘flood liable land’ concept in the 1986 Manual. Flood planning levels (FPLs) are the combinations of flood levels (derived from significant historical flood events or floods of specific AEPs) and freeboards selected for floodplain risk management purposes, as determined in management studies and incorporated in management plans. Flood storage areas those parts of the floodplain that are important for the temporary storage of floodwaters during the passage of a flood. The extent and behaviour of flood storage areas may change with flood severity, and loss of flood storage can increase the severity of flood impacts by reducing natural flood attenuation. Hence, it is necessary to investigate a range of flood sizes before defining flood storage areas. Freeboard a factor of safety typically used in relation to the setting of floor levels, levee crest levels etc. It is usually expressed as the difference in height between the adopted flood planning level and the flood used to determine the flood planning level. Freeboard provides a factor of safety to compensate for uncertainties in the estimation of flood levels across the floodplain, such as wave action, localised hydraulic behaviour and impacts that are specific event related, such as levee and embankment settlement, and other effects such as “greenhouse” and climate change. Probable maximum flood (PMF) the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation. Generally, it is not physically or economically possible to provide complete protection against this event. The PMF defines the extent of flood prone land, that is, the floodplain. Lismore Floodplain Risk Management Plan 2014 ~ Glossary & Appendices 4 Reduced Level (RL) refers to the height of a point above the Datum Surface. RL refers to reducing (or equating) levels (elevations) to a common datum, which is either a real or imaginary location with a nominated elevation of zero. The most common convenient datum was mean sea level. On small surveys that require the collection of elevation data the datum can be assumed and for practical purposes it simply needs to be far enough below the survey area to avoid negative numbers, thus the starting point of a survey might be nominated to be RL 100.00 Risk chance of something happening that will have an impact. It is measured in terms of consequences and likelihood. In the context of the manual it is the likelihood of consequences arising from the interaction of floods, communities and the environment. Lismore Floodplain Risk Management Plan 2014 ~ Glossary & Appendices 5 APPENDIX 1: BACKGROUND DOCUMENTS The following documents were referred to in the preparation of the Lismore Floodplain Risk Management Plan 2013: Lismore Floodplain Management Plan 2002, Lismore City Council Lismore Floodplain Management Plan, Issue No. 1, Patterson Britton & Partners, November 2000 Floodplain Development Manual, New South Wales Government, 2005 Various Flood Modelling reports prepared by Worley Parsons 2007-2010 Lismore Local Environmental Plan 2000, Lismore City Council, 2000 Lismore Development Control, Chapter 8 - Flood Prone Lands, Lismore City Council Draft Lismore Local Environmental Plan 2010, Lismore City Council Lismore Local Environmental Study 2010, Lismore City Council Peer Review – Lismore Floodplain Risk Management Plan 2011, GeoLINK 2011 Lismore Floodplain Risk Management Plan 2014 ~ Glossary & Appendices 6 APPENDIX 2: FLOOD BEHAVIOUR AND HISTORY OF FLOOD POLICY IN LISMORE 2. FLOOD HISTORY A number of factors are responsible for flooding in Lismore. Its latitude and proximity to the coast make it liable to the effects of extreme weather mechanisms, viz tropical cyclones from January to April, and east coast lows from April to July. The catchment above Lismore is fan-shaped and the valleys and streams are steep providing a relatively quick transfer of rainfall to runoff. The whole of the runoff from the 1,400km2 catchment squeezes through a narrow section of floodplain at Lismore, which is located at the confluence of Wilsons River and Leycester Creek. The floodplain lies at approximately 9.5m AHD with significantly lower levels near Lismore Park in Central Lismore. At the confluence, the Leycester Creek floodplain is approximately 2 to 2.5m higher than the upper Wilsons River floodplain. This causes the upper section of the Wilsons River to act as a natural detention basin. During the very early rising stages of a flood it is not uncommon for floodwaters from Leycester Creek to back up into the Wilsons River, and once the storage is filled the flow reverses and discharges into the lower, southerly section of the Wilsons River. 2.1 PEAK FLOOD LEVELS The graph below shows the history of flood events and peak flood levels in Lismore since 1870 as measured at the Police Station and, from 1955, the rowing club gauge. The rowing club is located at the end of Magellan Street some 500 metres downstream from the junction of Leycester Creek and Wilsons River. Prior to the construction of the CBD flood levee wall in 2005, peak flood levels above 9.0m AHD exceeded the general level of the river banks and caused significant inundation of residential and commercial areas.