RFI - Attachment H - Stormwater Management Plan_Issue C_

15 May 2019



5         STORMWATER
5.1       Flooding

Based on Noosa Shire Council flood mapping, the site is not subject to flooding from any sources.

5.2       Site Based Stormwater Management Plan

The aim of the Stormwater Management Plan outlined below is to:

          Prevent or minimise adverse social or environmental impacts from stormwater runoff
           originating from the proposed development.
          Achieve acceptable levels of stormwater runoff quality and quantity.

The Stormwater Management Plan aims to identify Stormwater Quantity and Quality Best
Management Practice for the site and demonstrate that water quantity and quality impacts will be
minimised in receiving waters.

The Stormwater Management Plan outlines the site in two sections, the operational phase and the
construction phase. The operational phase addresses treatment of contaminated runoff from the
developed site by mechanical methods before discharging into receiving waters whilst the construction
phase of the Stormwater Management Plan addresses erosion and sediment control to prevent
contamination of water sources by stormwater runoff during construction of the site.

5.3       Operational Phase

5.3.1 Proposed Site Drainage

Stormwater runoff from the proposed development will be collected and conveyed via new stormwater
pit and pipe network to a combined detention/treatment tank located at the South Eastern corner of the
new building. Overflow and treated water from the tank will discharge by way of new piped connection
to the stormwater infrastructure constructed as part of the masterplan ROL development.

The new building and carparks will be constructed over a basement car park. The stormwater from the
roof and the on-grade carpark will be directed to the new detention and treatment tank, suspended
from the basement roof slab.

Runoff from the landscaped areas at the front of the site will collected by a new pit and pipe system for
discharge to the new detention and treatment tank.

The basement will not be subject to direct rainfall runoff as the basement entries are covered by roof
areas and ramps.

It is proposed to construct a sump and pump for the basement subsurface drainage and any stormwater
that may track in off cars parked within the basement. This system will not be required to cater for
direct rainfall or stormwater runoff. Current geotechnical testing notes that no groundwater was
present to a depth of 4m below surface level, however it is noted that groundwater is subject to seasonal
fluctuations.

Due to the levels of the basement it is envisaged that the basement subsoil drainage may require
treatment to neutralise the acidic prior to discharge from the site to the sensitive downstream receivers.
Levels of treatment will be determined in accordance with the site specific acid sulfate soils
management plan to ensure levels of acidity are consistent with the downstream environment. It is


Excellence with Economy in Engineering                                                                       9
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