15 May 2013

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Executive Summary

Introduction

This draft Stormwater Management Plan (SMP) covers the catchments of Brown Hill and Keswick Creeks, including Glen Osmond and Parklands Creeks, which are important drainage watercourses in metropolitan Adelaide.

The creeks have a relatively high flood risk, a low standard of flood protection and a long history of flooding issues. The combined Brown Hill and Keswick Creeks catchment is mainly contained within the local government areas of Adelaide, West Torrens, Mitcham, Burnside and Unley.

In 2008 the Stormwater Management Authority conditionally approved the 2006 Flood Management Master Plan as a stormwater management plan. However, due to subsequent community concerns, particularly in respect of proposed flood control dams in the upper reaches of Brown Hill Creek, the catchment councils and the Stormwater Management Authority agreed to prepare a revised stormwater management plan.

WorleyParsons was engaged by the Brown Hill Keswick Creek Stormwater Project in 2010 to prepare this draft SMP as an update to the 2006 Flood Management Master Plan (2006 Master Plan).

This SMP has been prepared in accordance with the Stormwater Management Planning Guidelines of the Stormwater Management Authority and with a range of objectives under the following headings:

  1. Protection from flooding
  2. Quality of runoff and effect on receiving waters
  3. Beneficial reuse of stormwater runoff
  4. Protection of watercourses and riparian ecosystems
  5. Effective planning outcomes
  6. Management of stormwater infrastructure

A key objective is to provide a standard of flood protection equivalent to the 100 year Average Recurrence Interval (ARI) event or better (subject to economic justification). Presently, the system is generally considered to have about a 10 year ARI level of protection.

Background

Development of the 2006 Master Plan was carried out in three stages.

The first stage was documented in the Flood Mitigation Study for Brown Hill and Keswick Creeks Stage 1 Technical Report (2005). Over 300 potential opportunities for mitigation works to reduce flooding were identified, including flood detention works, flow diversions and increasing channel and bridge capacities. Non-structural options were also considered and opportunities to include multipurpose benefits also were identified.

The second stage involved community consultation, which informed development of flood management measures, including a set of priority mitigation works. Final investigations involved hydraulic modelling to determine flood damages reduction provided by the works and development of the recommended flood management strategy. 

Floodplain modelling for the catchment was initially developed in 2003 and subsequently updated in 2006. Based on that modelling it is determined in the current investigation that damages for a 100 year ARI flood will cost about $187 Million and affect nearly 7,000 properties if no flood mitigation action is taken.

Development of this revised stormwater management plan will be a two stage process involving this SMP (the 2012 SMP) followed by a Final SMP.