Case Studies

Western Port Green Wedge Integrated Water Management Strategy

Discipline

Integrated Water Planning

Client

City of Casey

Start Date:

December 2017

Completion Date:

August 2018

Project Overview & Outcome

Overview

Council was able to make an evidence based decision on whether or not to support further development and subdivision within the Western Port green wedge zone.

Outcome

The impacts on the overall water cycle, including flooding, potable, sewerage and groundwater were deemed to be too significant to allow further subdivision and development to occur.

Project Details

The Problem

The desire to reduce allowable minimum lot sizes to accommodate additional land subdivision emerged as a major concern for many Western Port Green Wedge residents.

The Response

The City of Casey initiated a planning review to determine if further development and subdivision should be allowed or
encouraged within the Western Port Green Wedge. In order to inform Council’s decision a number of specialist studies were commissioned, including an integrated water management strategy for the area.

The Details

The integrated water management strategy examined a number of potential subdivision and development scenarios. Each scenario was assessed against its impact in the following criteria:

Western Port as a Ramsar listed wetland
Surface water quality and flow regimes
Peak flood levels
Coastal inundation
Groundwater use
Potable water use and wastewater disposal
Acid sulphate soils

The Result

The integrated water management strategy quantified the impact of proposed development on each of the above criterion. To quantify the impacts a detailed whole of water cycle model and flood model were created. With the information provided in the report prepared by Engeny and the other expert studies, Council concluded that widespread increased levels of subdivision cannot be supported. The investigation also allowed Council to explain and justify its decision to the community.

Project Relevance

Assessment of future water supply demands and the impacts on potential water supply options.
Assessment of future water sensitive urban design treatment requirements associated with urban and rural subdivision.
Whole of water cycle modelling to assess existing conditions and also a range of proposed increases in development density.
Development of integrated water management servicing options for water supply, sewerage and stormwater treatment, determining fit for purpose water usages through the study area and aiming to minimise imported water in the form of potable water and runoff from upstream development.

Project Innovation

Assessment of the impacts of subdivision on a rural living context and determination of what threshold of subdivision is acceptable prior to impacts on existing waterways (this is a poorly researched field).

Flood mapping a 130 square kilometre area with Australian Rainfall and Runoff 2016 compliant methodologies shortly after the release of the new guideline and utilising newly released versions of flood modelling software (TUFLOW HPC).
Consideration of whole of water cycle impacts when assessing if development and subdivision should be allowed to occur in the green wedge area. This assessment also included coastal inundation, acid sulphate soils and groundwater use which are not often included in integrated water assessments despite their links to the water cycle.

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