FLOODPLAIN MANAGEMENT

> Port Macquarie-Hastings Interim Flood Policy

• How does flooding occur?
• Flood Study Processes
• How is a flood measured?
• Where can I obtain flood information?
• Flood Management Studies and Plans

(above) Corner of Bell Street and The Boulevard, Dunbogan, April 1963

How does flooding occur?

Flooding occurs when there is too much water coming from the contributing catchment area into a downstream location that is unable to move this water efficiently away. Simply, there is more water coming in than going out.

Flooding can be looked at in two ways.

The first is as a result of an inefficient stormwater network (localised flooding) and the second is because of a water body (lake, dam, river) being supercharged with incoming water (mainstream flooding).

While Council endeavours to minimise the effects of localised flooding through adequate sizing of pipes/channels and overland flow paths, Council cannot guarantee that every property will be dry 100 percent of the time - ie: during extreme storm events.

If your property is experiencing localised flooding, first contact your local branch of the State Emergency Services for immediate assistance and then contact Council to enable us to investigate the problem and undertake remedial works where possible.

Flood Study Process

Port Macquarie-Hastings Council has conducted flood studies for all mainstream flooding areas (lakes and rivers) in accordance with the Floodplain Development Manual.

This manual dictates a three-step process whereby a flood study is conducted for the catchment to ascertain the height water will rise in a specific rain event.

From this rain event a contour corresponding to the flood height is mapped. The second step in this process is a study investigating all of the mitigation options for the area and ascertains how effective they will be.

The third step is the development of a management plan that reviews all of the options and recommends the most feasible options.

Port Macquarie-Hastings Council is concerned with the implications of mainstream flooding and mitigation measures that are both feasible and cost effective.

Through the flood study process, measures considered for minimising over floor flooding include levee banks, voluntary house raising, setting minimum floor levels, planning controls and the maintenance of a flood level warning system.

Wauchope Rail Bridge, 1968 flood

 How is a flood measured?

Flood heights are measured in relation to a common datum-AHD, Australian Height Datum. The datum to which all flood heights are measured is mean sea level. Mean Sea Level is 0m AHD.

Floods are modelled for certain rainfall events and are listed in statistical terms.

The common flood frequencies measured are 1:20yr, 1:50yr and 1:100yr and PMF (Probable Maximum Flood). This should be interpreted as follows:

A storm with a given intensity has a 1:20, 1:50 or 1:100 chance of occurring in any one year. Or relating that to a yearly percentage, 1:100 is a 1 percent chance, 1:50 is a 2 percent chance and 1:20 is a 5 percent chance.

Where can I obtain flood information?

Maps showing flood-affected areas are available for purchase by contacting Council's environmental engineer.

The majority of flood studies, management studies and management plans are available for download and are also available for viewing at Council's office.

Written information relating to flooding can be purchased from Council by applying for the Section 149 Certificate.

Section 149 Certificate

Section 149 of the Environmental Planning and Assessment (EP&A) Act 1979 requires that local councils, upon application, must issue a Planning Certificate providing information on the planning controls relating to any piece of land within the Council area. This information includes the hazard of flooding.

Flood Management Studies, Plans and Policies

Council has prepared a number of Floodplain Management Studies, plans and policies that are available upon request to the public:

• Lake Cathie/Lake Innes Flood Study 1984
• Camden Haven Flood Study 1989
• Camden Haven Floodplain Risk Management Plan 2004
• Hastings River Flood Study 2006
• Interim Port Macquarie Local Government Area Flood Policy 2007
• Wrights Creek Flood Study 2008

Flood Education Information

The following pamphlets provide important information for residents living on the lower floodplains of the Camden Haven River.

 Dunbogan: FloodSafe.pdf (143KB)

 Laurieton: FloodSafe.pdf (137KB) 

For more information, contact Council on (02) 6581 8111.