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Flood Management

Posted by Pete on 28 March 2012
Filed under: General

Local government in NSW has the primary responsibility for controlling the development of flood-prone land, through the application of policy developed by the NSW Government, through the Office of Environment and Heritage (OEH) and in collaboration with the State Emergency Service (SES).

In this context, floodplain management involves a flood study, which defines the technical details of the nature and extent of flooding in a particular location, a floodplain risk management study, which evaluates management options that address flood risk and flood management issues, and a floodplain management plan, which essentially outlines strategies to manage flood risk and flood management issues.

The Bungendore Floodplain Risk Management Committee, one of Council’s s.355 committees, was established to assist Council in the development of planning guidelines for flood prone areas within Bungendore.

The primary responsibility of the committee is to oversee the preparation of a Floodplain Risk Assessment Study and Plan for Bungendore. Central to this effort is the development of a computer model that simulates water flows through Turallo, Halfway and Millpost Creeks. The model helps to identify flood prone land, as identified in the Bungendore Flood Map (click on the map to view it in greater detail) that is part of the current DCP, and can simulate the impact of a range of flood mitigation measures on these flows.

Bungendore Flood Map

As a result of the modelling undertaken to date, flood mitigation measures being considered for Bungendore include:

  • Clearing vegetation within the floodway area, to improve flow through the creek system;
  • Raising the current levee bank along Turallo Creek, to increase the water level that can be handled by the creek system;
  • Extending the Turallo Creek levee bank to the east of the railway line, to improve the function of the levee system;
  • Constructing diversion banks and channels adjacent to Halfway Creek, upstream of the village area, to divert floodwater flows into Millpost Creek and away from the village area.

The Captains Flat Floodplain Risk Management Committee was recently established to develop a similar model and flood mitigation plan for the Captains Flat area.

4 Comments

  1. Comment from Liz
    10 July 2012 @ 18:43

    Great flood map. What does ‘floodplain land’ mean though? Is it the maximum extent of inundation?

    • Reply from Pete
      11 July 2012 @ 00:26

      Floodplain Land is land that is susceptible to inundation by a probable maximum flood (PMF) event, being the largest flood that could conceivably occur at a location based on current knowledge.

      On the recommendation of the NSW Department of Planning and Infrastructure, there will be a slight change to the way in which ‘flood prone’ land is defined in the new Palerang Local Environmental Plan. Rather than using the PMF level to define the flood planning area, it will simply be defined as the level of a 1:100 ARI (Average Recurrent Interval) flood event (the same as the 1% Annual Exceedance Probability level currently used) plus 0.5 metres freeboard. In Bungendore, the new 1:100 ARI + 0.5m level is not as high as the current PMF level, so the flood planning area under the new PLEP will be correspondingly smaller.

  2. Comment from Lyn Peel
    17 May 2013 @ 18:07

    Presumably we can expect to see greater flooding as a result of climate change and the increasing number of adverse weather events. This will have a flow on effect on insurance premiums. Do you really believe that the mitigation being done will really change much?

    I’d like to buy a property right in this flood zone area but am reluctant to buy now and find in 10 years that it is worthless as a result of constant flooding.

    Thanks
    Lyn

    • Reply from Pete
      17 May 2013 @ 19:00

      Remember that the proposed improvements are only flood mitigation measures—they will only reduce the impact of flooding, not eliminate the flooding altogether.

      All we can do when we model events is to predict what might happen, based largely on historical data. The nature of flooding may well change with changes in the prevailing climate, and if we see any significant deviation from our model in the future, we will refine it and reassess our mitigation strategy.

      The pattern of flooding, however, as predicted by the model, is largely governed by geographical factors. As such, the actual pattern is unlikely to change dramatically. It is more the frequency of particular events that is likely to change. In this respect, the model will remain as reliable as it is—the model itself predicts the impact of a rain event, not the frequency of particular events.

      Deciding whether or not to purchase a particular property is a decision that must be made by the individual. The information provided through flood modelling is available to assist in making such decisions. The relevant council planning regulations, such as those governing mandatory floor levels, are also designed to help minimise property damage in the event of a flood.

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