07/1841 - Response to Information Request [As Published] · 132007.1841

STORMWATER MANAGEMENT PLAN 4

 

4.0 Site Stormwater Modelling

4.1 Methodology

The hydrology and hydraulics of the pre and post development scenarios were analysed using
the XP-STORM stormwater management model with storm patterns derived from Australian

Rainfall and Runoff publication and rainfall intensities derived for the Noosa area.

Due to the topography of the land and the layout of the site, it was determined that runoff from
the site will fall to the east, away from the road. Therefore the runoff will be directed to pits
located within the carpark and conveyed via an underground pipe network to the north-eastern
comer of the lot for discharge into OS4. The XP-STORM model was set up with a
conservative stormwater system design comprising of overland flow paths through carparks
and bio-retention areas collecting runoff before discharging into a swale along the eastern
boundary of the site. Details of the proposed bio-retention areas can be found in Part B of this
stormwater management plan. Roof water is to be collected in retention tanks to help attenuate

stormwater flows.

To accurately determine pre and post development flows, the Q10 and Q100 storms were
modelled. Storm durations of 10, 20, 25, 30 ,45, 60, 75, 90, 120 and 180 minutes were

investigated.

4.2 Selection of Modelling Parameters

XP-STORM modelling parameters were assessed from layout drawings, contours, QUDM
(Queensland Urban Drainage Manual) and considering the extent of proposed development

within the catchment.

4.2.1 Impervious Areas

In accordance with the current pre-developed situation, 0% of impervious ground area was
used in the pre-developed model. In the post developed model the percent of impervious
ground area was increased to 82% to represent the proposed development. This area was

measured from the site layout drawings.

 

BARLOW GREGG VDM M3048
DECEMBER 2007