08/1128 - Information Response to Biodiversity Items & Ecological Impact Items - Place Designs [As Published] · 132008.1128

BCROG RF Response to Council 20081126 Page 18 of 28

item 43.

Provide ecologist comment of the impact of on site detention of water (i.e. volumes within
rainwater tanks) to downstream uses.

Downstream Uses

The downstream use of the site is currently vacant open space conservation and Noosa National Park to the
west. To the north is existing drainage reserve receiving stormwater from the conventional piped
stormwater system.

Site Detention of Water

Information provided by the Consultant Engineer (Cardno) for items 25 & 26 was reviewed. It identifies
that, the rainwater tanks required by the Queensland Development Code and the Noosa Planning Scheme
Policy 6, will have a storage capacity 442 IW’ of stormwater. The management of stormwater through bio-
retention devices design in accordance with the Water Sensitive Urban Design Guidelines specifically
designed for SEQ (Healthy Waterway Partnership) climatic and environmental conditions provided is
considered to provide best environmental management practice.

The bio-retention devices are designed to reduce peak flows through detention capacity, and return more
water to groundwater through infiltration than provided in conventional urban design. Water that
infiltrates the soil will eventually discharge to the wet heath areas within the adjoining Noosa National Park.
It is considered that the sandy subsoil of the coastal dune system will facilitate infiltration and allow water
to transfer via groundwater to the lower wet heath areas over a longer time frame potentially reducing
affect of drought.

Sensitivity of Ecosystems and Significant Species

As outlined in the response to Item 42, the acid frogs are dependent on the pH level being maintained in
breeding waters within the Open Heath areas of the Noosa National Park. These are species most sensitive
changes in hydrology.

{t is concluded that the wet heath areas are adapted to the variable climatic conditions of drought and
torrential rain, such that any minor differences in discharge level as a result of rainwater tanks and bio-
retention basins will not be significant subject to water quality meeting the modelled pollutant reductions
are achieved

Item 44

Council requests an ecologist comment regarding the impact of the concentration of flows
from the site to the designated discharge areas.

Concentration of Flows

The Consulting Engineer has provided comment on the design of the proposed level spreaders to be
constructed for approximately 40m length parallel with the 20m buffer on the western basin and inside the
property boundary for 15m on the northern basin.

The prevention of scour and increased turbidity and suspended solid entering water ways or the wet heath
areas is the most likely impact if flow concentration have not been allowed for or the installation to the
designed spreader is not effected on the ground. Quality control in the construction of the discharge
spreader will reduce the risk, long with ongoing maintenance of these devices. Attention to this detail at