ATTCH 3 - IR Response - Erosion, Coastal Processes and Stormwater (Dr Trevor Johnson)

Kenlynn Pty Ltd Report Number 620.12166-R01

Castaways Beach 3 November 2017
Stormwater Management Plan Version v0.1
Page 9

 

3 WATER QUALITY ANALYSIS
3.1 Overview

As discussed in Section 2.1, it is proposed to construct a basin(s) within each lot to receive the
stormwater runoff from that lot.

As demonstrated in Section 2.4, the basin(s) will be sufficient to capture the runoff from all events up
to and including the 1% AEP flood event

The performance of the basin(s) in treating the stormwater runoff from each lot was therefore analysed
using MUSIC.

3.2 MUSIC Model

A MUSIC model of a typical 1,000 m? allotment was setup, including the proposed bioretention basin
at the downstream end of the lot. The layout of the MUSIC model is shown in Image 2.

 

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Urban [Mixed]

 

 

 
 
   

 

Bioretention
Receiving Node

Image 2. MUSIC Model Layout

A mixed catchment approach was adopted, using six minute rainfall data from Cooroy station
(#40059) in the analysis, in accordance with MUSIC Modelling Guidelines (Version 1.0 — 2010).

The Urban node comprised an area of 0.1 ha, and a fraction impervious of 60%. Standard parameters
for the Rainfall-Runoff and Pollutant Concentrations were adopted, in accordance with the MUSIC
Modelling Guidelines.
The properties of the bioretention basin were as follows:

e High Flow Bypass = 0.082 m*/s

e Extended detention Depth = 0.3 m

e Surface Area = 100 m?

e Filter Area = 100 m?

e Unlined Filter Media Perimeter = 50 metres

SLR Consulting Australia Pty Ltd