Lithgow Floodplain Management
Lithgow Flood Study Review
What was the objective of the Flood Study Review for Lithgow?
The study objective was to review and update the hydrologic and hydraulic modelling for the Farmers Creek catchment to define the nature of both Main Stream Flooding and Major Overland Flow in the urbanised parts of Lithgow for floods up to the Probable Maximum Flood. A requirement to provide similar information in future growth areas led to the development of new hydrologic and hydraulic models for the adjacent catchment of Marrangaroo Creek.
The information presented in the report will form the basis for the preparation of the future Floodplain Risk Management Study and Plan for Lithgow. The Floodplain Risk Management Study and Plan will assess the economic impact of flooding on existing urban development, review options for flood mitigation and prepare a plan of works and measures for managing the present and future flood risk in Lithgow.
Where does Main Stream Flooding occur in Lithgow?
Main Stream Flooding in Lithgow occurs when flow surcharges the channels of Farmers Creek and Marrangaroo Creek, as well as their major tributaries. These flows may be several metres deep in the channels and relatively fast moving. Main Stream Flooding also occurs when flow surcharges the major pipelines that have been laid along the routes of natural channels as the catchments have urbanised.
Where does Major Overland Flow occur in Lithgow?
Major Overland Flow results from runoff which travels as either sheet or concentrated flow over grassed and paved surfaces in individual allotments, or along roads en-route to the trunk drainage system, or surcharges the minor pipes in the catchment headwaters and the lateral sub-catchments bordering the trunk drainage systems. Major Overland Flow is limited to areas affected by depths of flow greater than 100 millimetres.
What is the Probable Maximum Flood?
The Probable Maximum Flood is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation coupled with the worst flood producing catchment conditions. The Probable Maximum Flood defines the extent of flood prone land (i.e. the floodplain). The extent, nature and potential consequences of flooding associated with events up to and including the Probable Maximum Flood should be addressed in a floodplain risk management study.
What has been defined as flood prone land in Lithgow?
Flood prone land in Lithgow has been defined as land which is inundated to depths greater than 100 millimetres during a Probable Maximum Flood event. It comprises areas that are affected by both Main Stream Flooding and Major Overland Flow.
My property was never classified as ‘flood prone” or “flood liable” before. Now it is. Why?
The Lithgow Flood Study Review has a wider and more comprehensive scope of investigation than previous flood reports. This study includes Farmers Creek catchment and the catchment of Marrangaroo Creek to define the nature of both Main Stream Flooding and Major Overland Flow in the urbanised parts of Lithgow and future growth areas for floods up to the Probable Maximum Flood.
This is why more properties, some of which are a long distance from any natural channel, are now identified as being flood prone.
What if I disagree with the flood mapping for my area?
Council has used up-to-date modelling techniques, as well as expert assistance from consultants and the NSW State Government, to determine mapping and analysis of risk. Council believes our flood level estimates are as accurate as possible at this point in time.
If you believe that are not correct for your property, you can seek professional advice relating to your property and request Council to review.
How do I find out what the flood level is for my property?
If your property has been included in the Lithgow Flood Study Review Report, Council’s duty planners can assist you to identify the 1% AEP flood level, the interim flood planning level and area, the flood hazard and hydraulic category and other relevant data from the computer modelling data that supports the report.