FPM 1 in 100 (1%) AEP Floodway and Flood Fringe Area (DWER-014)

The Department of Water and Environmental Regulation produces floodplain mapping of rivers and major watercourses and provides floodplain development advice to ensure that proposed floodplain development has adequate flood protection and does not impact on the existing flood regime of the area.

This advice is related to major river flooding only. Other issues, such as stormwater drainage and environmental and ecological considerations are not addressed.

Both the floodway and flood fringe make up the 1 in 100 (1%) annual exceedance probability (AEP) floodplain, however there are areas where the floodplain exists, but the floodway and flood fringe does not. In such situations, a different floodplain management strategy applies (for example, the Swan River between the Narrows and Canning Bridges).

This dataset comprises two polygons - Flood fringe, and Floodway. The flood fringe is that part of the floodplain where development may be considered acceptable subject to certain building conditions that will provide adequate flood protection. The floodway is that part of the 1 in 100 (1%) AEP floodplain where development that is considered obstructive to major flows is not acceptable as it would increase flood levels upstream. No new buildings are acceptable in the floodway.

Note: To see the full scope of the floodplain mapping, 12 dataset layers are required to be loaded in the following order:

FLOODPLAIN DATASET LAYERS:
FPM Flood Level Points (m AHD) FPM Flood Level Contours (m AHD) FPM 1 in 100 (1%) AEP Floodway and Flood Fringe Line FPM Extent of Flooding FPM Levee Banks FPM Location of Cross Sections FPM 1 in 100 (1%) AEP Floodplain Development Control Area FPM Map Index FPM Bridges FPM Special Development Condition Area FPM 1 in 100 (1%) AEP Floodway and Flood Fringe Area FPM Floodplain Area

The dataset covers the following areas:

• Avon River – Toodyay, Northam, York and Beverley Townsites.

• Blackwood River – Augusta, Bridgetown, Nannup and Boyup Brook Townsites.

• Brunswick River - Greater Bunbury

• Coblinine River & Dorderyemunning Creek - Wagin Townsite.

• Collie River - Collie Townsite.

• Chapman River – Geraldton Townsite.

• Denmark River – Denmark Townsite.

• Gascoyne River - Carnarvon Townsite and the Lower Gascoyne.

• Gribble Creek - Kalgoorlie Townsite.

• Harding River - Roebourne Townsite.

• Irwin River - Dongara Townsite.

• Lower Collie River - Greater Bunbury.

• Preston River - Donnybrook Townsite.

• Serpentine River, Peel, Birrega & Oaklands Drains, Murray River and the Peel Inlet / Harvey Estuary - Peel Inlet / Harvey Estuary to Pinjarra and south to the Darling Scarp (Murray River) and Peel Inlet / Harvey Estuary to Wellard (Peel Main Drain), east to South Western Highway (Serpentine River) and north to Wungong Brook (Birrega Drain).

• Swan River, Canning River and Tributaries: Perth - Fremantle to Walyunga National Park (Swan River) and Canning Bridge to Brookton Highway (Canning River). Tributaries include Bennett Brook, Blackadder Creek, Ellen Brook, Helena River, Henley Brook, Jane Brook, St Leonards Creek, Susannah Brook (Swan River) and Southern River/ Wungong Brook (Canning River).

• Toby Inlet – Quindalup Townsite.

• Vasse-Wonnerup Estuaries, Broadwater and New River - Busselton Townsite.

For further information on flooding and floodplain management in Western Australia please refer to our Water Facts publications: Flooding in Western Australia (Water facts 13) and Floodplain Management (Water facts 14).

This information is available at the following addresses: https://www.wa.gov.au/system/files/2022-11/Water-facts-13-Flooding-in-Western-Australia.pdf https://www.wa.gov.au/system/files/2022-11/Water-facts-14-Floodplain-management.pdf

Glossary:

• Annual exceedance probability (AEP) - the likelihood of occurrence of a flood of a given size or larger in any one year; usually expressed as a percentage.

• 1 in 100 AEP flood - this means that there is a 1 in 100 (or 1%) chance of a flow of this size or larger occurring in any one year. This flood has a 50% chance of being experienced at least once in a person's lifetime. The 1 in 100 AEP flood has been generally adopted in Australia and overseas as the basis for floodplain management planning.

• Flood fringe - the area of the floodplain, outside of the floodway where development could be permitted provided it is compatible with flood hazard and building conditions provide an adequate level of flood protection. These areas are generally covered by still or very slowly moving waters during a 1 in 100 (1%) AEP flood.

• Floodplain - the portion of a river valley next to the river channel which is covered with water when the river overflows its banks during major river flows. The term also applies to land adjacent to estuaries which is subject to flooding.

• Floodway - the river channel and a portion of the floodplain where a significant flow or storage of water occurs during floods. If the floodway is even partially blocked, then the natural flooding regime of the area may be detrimentally impacted with flood levels being raised and affecting areas which may not have been previously affected. Development in floodways is to be avoided wherever possible.

• Australian Height Datum (AHD) - is a geodetic datum for altitude measurement in Australia. It was adopted in 1971 by the National Mapping Council as the datum to which all vertical control for mapping is to be referred. The datum is based on the mean sea level (1966-1968) being assigned the value 0.000m on the Australian Height Datum (AHD) at 30 tide gauges around the coast of the Australian continent.