Annual Report 2009/2010 - Hawkesbury City Council - NSW ...

Council continually seeks to improve methods to provide an effective response and excellence in
customer service to the general public through training of Council staff on new and upcoming
legislative requirements and development of improved internal procedures when dealing with non
complying developments
Water Quality
Flood Plain Management
Introduction
Hawkesbury City Council is responsible for local planning and land management in Hawkesbury River
floodplain and surrounding areas between the suburbs of Yarramundi and Wisemans Ferry.
The unique characteristics of the Hawkesbury-Nepean flooding has been described as exhibiting a
combination of the worst characteristics of riverine flooding (depth and extent), and the worst
characteristics of flash flooding (rapid rise of floodwaters and limited warning time).
Measures of Performance
Measure
1. Responding to requirements of
Floodplain Development Manual: the
management of flood liable land, New
South Wales Government, April 2005.
How is the Hawkesbury performing?
Implementing the Floodplain Risk
Management Process
In particular:
• Establishing a Floodplain Risk Management Committee
• Collecting flood related data
• Preparing a Flood Study
• Preparing a Floodplain Risk Management Study
• Preparing a Floodplain Risk Management Plan
• Implementing the Floodplain Risk Management Plan
Current status and trends
For significant flood events, the inflow from the Hawkesbury River and its tributaries exceeds the outflow
through Sackville gorge causing the valley to fill. Flooding can be of great depth by comparison with other
NSW coastal rivers and the difference in depths between major and extreme flood is greater than that
which occurs elsewhere. Depths of over the floor Hawkesbury – Nepean River flooding for houses with
floors at the current flood planning level (FPL) adopted by Council (i.e. 1 in 100 year flood level without
any freeboard allowance) are approximately:
• 2 metres for the 1867 flood of record (i.e. about a 1 in 200 year flood event); and
• 9 metres for a Probable Maximum Flood event.
Many existing dwellings have floor levels, which are well below the current FPL. These dwellings would
experience significantly deeper and more hazardous depths of flood inundation.
Isolation of towns essentially arises due to the historic settlement of the valley and the fact that the urban
2009/2010 Annual Report Page 83