Implementation of Mitigation Works to Date

To date, there have been a number of flood mitigation measures from the Towradgi Creek Floodplain Risk Management Plan (June 2003) which have been implemented. These are summarised below.

Towradgi Creek Planning Matrix

A planning matrix for the Towradgi Creek catchment has been adopted by Council and forms part of DCP 2009 (Chapter E13 – Floodplain Management). The matrix considers the range of land uses, and the potential risk to flooding, within the floodplain up to the level of the probable maximum flood. Using this approach, a matrix of development controls, based on the flood exposure and the land use, has been developed that balances the risk of exposure across the floodplain.

If you are developing in this area, you will need to refer to DCP 2009 to ensure that Council’s requirements with respect to floodplain management are understood and met.

Railway Street, Corrimal - Culvert Amplification Works

This project involves the design of culvert amplification works in the piped section of North Corrimal Creek between the eastern (downstream) side of the Northern Distributor and No.29 Railway Street. The proposed works aim to reduce the incidence of flooding in the local area via the amplification of the existing Railway Street culvert system and associated outlet works.

The proposed works principally comprise removal of the existing twin 1,800mm diameter pipes and replacement with culverts of the same size to those beneath the Northern Distributor (3 x 3,000mm wide x 1,800m high).  The length of the proposed drainage system is approximately 95m.

The design of the works, including the resolution of conflicts with existing services and the preparation of a Traffic Management Plan aimed at minimising the disruption to traffic during construction, has been completed.

During the design process, a detailed estimate of the construction cost was prepared. As this cost significantly exceeded the benefits to be derived from the project, implementation of the works was terminated as it was not considered viable.  However, Council is pursuing the investigation of alternate flood mitigation options in order to provide flood benefits to the local community. This includes potential improvements to the downstream section of north Corrimal creek.

Railway Street, Corrimal - Improvements to North Corrimal Creek

Council is currently investigating potential flood mitigation works to improve the hydraulic performance of the section of North Corrimal Creek downstream (to the south) of Railway Street, Corrimal, in order to reduce flooding in the local area. A number of concept options aimed at improving the performance of the creek have been investigated, and a recommendation made for a preferred option to proceed to detail design. 

Railway Street, Corrimal - Debris Control Structure

This involves the installation of a debris control structure and channel works along North Corrimal Creek, immediately upstream (on the western side) of the Northern Distributor culverts near Railway Street.   The aim is to reduce the frequency with which the existing Northern Distributor culverts block with debris.

The proposed works comprise:

• The installation of vertical posts, across the base of the creek, to act as a debris trap.
• Reshaping and rock-lining of the culvert inlet area.
• An off-line elevated storage area to collect floating debris which would otherwise be carried downstream by surcharging floodwaters.
• Improvement of an existing track to provide access down to the base of the creek to allow debris to be removed; landscaping works to revegetate the area.

Design and construction of these works have been completed.

Colgong Crescent, Towradgi – Footbridge

The proposed works involve the demolition of the existing footbridge over Towradgi Creek and replacement with a new footbridge at a higher elevation to achieve flood mitigation benefits for the area.  The objective of the elevated footbridge, which provides a pedestrian link between Colgong Crescent and Linga Street, is to allow more floodwaters to flow through and reduce the amount of debris trapped beneath the footbridge.

The footbridge also includes vertical screens added to both sides of the structure for the purpose of providing privacy to the adjacent residential development.

Design and construction of these works have been completed.

Bellambi Street, Justine Ave and Cheryl Place, Tarrawanna - Flood Mitigation Works

The aim of the project is to mitigate the impacts of flooding in the area by providing well defined overflow paths in combination with measures to reduce the potential for the existing underground culvert system to block with debris.

In order to achieve this, the proposed works include:

• Improvement of the existing culvert in Justine Avenue to increase its capacity to accept water and to reduce the potential for debris blockages.
• Cutting of an opening in the rear wall of 2 Bellambi Street to allow flow through the wall then onto the yard and Bellambi Street. This will reduce the diversion of flow from the rear of the property southwards towards existing development, thereby reducing potential damage during floods.
• Construction of a low earth mound at Cheryl Place to deflect floodwaters away from nearby houses.

Design and construction of these works have been completed.

Lemrac Avenue, Corrimal - Flood Mitigation Works

The objective of the project is to mitigate the effects of floodwaters conveyed by the existing channel (part of North Corrimal Creek) between No 8 and 10 Lemrac Avenue and along Lemrac Avenue south of the intersection with Willow Grove.

The proposed works include:

• Provision of flood proof walls on the boundaries of a number of properties to reduce the frequency of ingress of surcharging floodwaters onto the properties, divert floodwaters downstream towards the open creek that runs between No 1 and 5 Lemrac Avenue, whilst also limiting the potential damage caused by waterborne debris.
• Installation of a debris trap upstream of the rear boundary of No 8 Lemrac Avenue and reshaping of the confluence of North Corrimal Creek and an unnamed watercourse immediately upstream. This aims to improve the alignment of creek flows, minimise the amount of debris transported downstream to the existing culvert under Lemrac Avenue and thereby reduce its potential for blockage.
• Installation of a trash rack at the inlet of the Lemrac Avenue culvert to further reduce its potential to block with debris.

Design and construction of these works have been completed.

Underwood Street, Corrimal - Flood Mitigation Works

These works, which aim to mitigate the flood problems associated with the Corrimal retail area, involve the implementation of a scheme of flood mitigation measures along North Corrimal Creek between Underwood St and downstream of the Princes Hwy.

The outcome of investigations undertaken indicate that the existing underground drainage system needs to be upgraded in order to implement the mitigation measures.

Separate investigations will be undertaken to determine the feasibility of upgrading the existing drainage system.

Voluntary Purchase

Under the Floodplain Risk Management Plan, nine properties are earmarked for voluntary purchase. To date, three properties along Pioneer Road, Towradgi have been purchased and demolished by Council.