In 2014, Council commissioned Cardno Pty Ltd to undertake a Floodplain Risk Management Study and Plan (FRMSP) for the urban areas within Hornsby LGA. The study defines existing flood behaviour and associated hazards of the study area and assesses potential flood mitigation options to reduce flood damages and risk.

Finalisation of the FRMSP was put on hold during the council amalgamation process in 2016 and in 2020 the FRMSP was updated using the latest Australian rainfall, runoff and topographical data.

Identification of flood prone properties is based on the criteria that the property may be inundated by overland flow of over 150mm during a 100 year Average Recurrence Interval (ARI) storm event.

The latest modelling identified 3,872 urban properties (9% of properties in the Shire) that may be affected by overland flow/flooding.

You can search for your property on the interactive Flood Map on the right hand side of this page to see if your property is identified as flood prone land (technically known as a Flood Planning Lot).

The draft Floodplain Risk Management Study and Plan (FRMSP) provides the basis for future management of Hornsby Shire’s urban and riverine catchments that are liable to flooding.

The draft FRMSP includes:

• an assessment of previous flood investigations
• results of community consultation program undertaken as part of the study
• flood behaviour including hazard categorisation and the impacts of climate change on existing flood behaviour
• environmental, social and other planning issues related to the study
• Risk management measures and recommended flood management options.

View the Floodplain Risk Management Study and Plan.

To view the appendices, click the documents in the Document Library or the links for the larger appendices.

Hornsby Shire Council LGA covers approximately 499.6 km2. The draft FRMSP focusses on the 38 urban catchments within the LGA which have a stormwater drainage system. The majority of these developed urban areas are concentrated towards the south of the Shire or are located along the Pacific Highway. The urban portion of these subcatchments contain the majority of the Shire’s population and developed land and therefore is the main focus of this study.

The dominant form of flooding in these areas is overland flow. It may result from obstruction of overland flow paths due to development, the conversion of natural creeks systems into piped systems, and other similar effects.

Rural catchment areas are not included in this FRMSP. The rural areas of shire will be subject of a separate study which will form an addendum to this report.

Make a submission by:

• completing the form below
• emailing hsc@hornsby.nsw.gov.au
• writing to the General Manager, Hornsby Shire Council, PO Box 37, Hornsby 1630.