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Flood study

Wallarah Creek Catchment Flood Study

Catchment Description

The Wallarah Creek catchment is located on the Central Coast of New South Wales and occupies an area of 33 km2.

The catchment is drained by two major watercourses (Spring Creek and Wallarah Creek) as well as a number of unnamed tributaries which carry runoff in an easterly direction into Budgewoi Lake. Although the catchment is largely undeveloped, a number of urban settlements are scattered across the area including Blue Haven, Wallarah and Bushells Ridge as well as part sections of Doyalson, San Remo, Charmhaven and Woongarrah. The urban sections of the catchment are typically drained by a stormwater system which conveys runoff below ground and into one of the receiving watercourses. The watercourses ultimately drain into Budgewoi Lake which forms the eastern boundary of the catchment.

Purpose of Study

During periods of heavy rainfall across the Wallarah Creek catchment, there is potential for water to overtop the banks of the various creeks and waterways and inundate adjoining properties. There is also potential for the capacity of the stormwater system to be exceeded leading to overland flooding. Flooding has been experienced across the catchment on a number of occasions in the past including 2007 as well as more recently in 2015.

Several flooding investigations have previously been completed in an effort to better understand flood behaviour across different sections of the Wallarah Creek catchment. However, a comprehensive flood study of the entire catchment that considers both mainstream and overland flooding has not been prepared.

In recognition of this limitation, Wyong Shire Council resolved to prepare a Flood Study for the Wallarah Creek catchment. The Flood Study provides a technical assessment of flood behaviour and is the first step in the preparation of a Floodplain Risk Management Plan that will outline how the risk of flooding can be managed across the catchment.

This report forms the Flood Study for the Wallarah Creek catchment. It documents flood behaviour across the catchment for a range of design floods for existing topographic and development conditions. This includes information on flood discharges, levels, depths and flow velocities for a range of design floods. It also provides estimates of the variation in flood hazard and hydraulic categories across the catchment and provides an assessment of the potential impacts of climate change on existing flood behaviour.

Additional Information

Field Value
Title Wallarah Creek Catchment Flood Study
Publication Date 30 April 2016
Themes Land and Resource Management
Spatial Extent
Map data © OpenStreetMap contributors
Council/LGA Central Coast Council
Author/ Prepared by Catchment Simulation Solutions
Publish date 12 September 2017
Update date 16 May 2018
River Basin 211 - Macquarie Tuggerah
Place Name Blue Haven
Approval State Approved
Submitted for approval 10 May 2018
Submitted by SES System Administrator
Approved 12 June 2018
Approved by dstazic
Data Comment

The ‘Wallarah Creek Flood Investigation’ was prepared by Gutteridge Haskins & Davey for Wyong Shire Council. The study was completed in three separate stages:

  • Stage 1 (December 1992) involved defining flood behaviour along Wallarah and Spring Creeks under current (i.e., 1992) conditions as well as ‘fully developed’ catchment conditions. This included the development of a RORB hydrologic model and a MIKE-11 hydraulic model to define flood behaviour;
  • Stage 2 (June 1993) looked at options for mitigating the predicted increases in peak catchment flows and flood levels associated with full development of the catchment (as defined in the Stage 1 report). The report determined that a detention basin located on Spring Creek (upstream of the Doyalson Link Road) afforded the most benefits in terms of reducing flood impacts across residential areas adjoining Spring and Wallarah Creeks.

  • Stage 3 (May 1993) involved defining the potential impacts associated with failure of the detention basin on Spring Creek recommended as part of the Stage 2 investigations. It utilised the DAMBRK software to undertake the detention basin failure simulations.

Identifier 43a75ec8-0610-4d4e-aee3-024d602ea590