Swmp

4.0 STORMWATER QUANTITY MANAGEMENT

 The existing property is developed with commercial structures being a driveway, large
 commercial building with 2 tenancies and associated hardstand surfaces, as shown in
 Figure 4.1. The existing fraction impervious value is approximately fi=0.79.




                                Figure 4.1 Existing Site Structures



The developed fraction impervious value was determined from the proposed architectural
layout, and found to be fi=0.73. It is anticipated the peak flow rates between the existing
and developed cases will be comparable. The proposed stormwater flow regime ensures
no-worsening of flows, while providing the site with a Lawful Point of Discharge to a newly
constructed kerb inlet pit in Noosa Drive.


The 1-Year ARI (63 % AEP), 10-Year ARI (10 % AEP), 100-Year ARI (1 % AEP) were
calculated using the Rational Method, where the time of concentration was 5 minutes
(standard inlet time) for both the existing and proposed developed case, in accordance with
QUDM (2016). Table 4.1 below presents the results of the Rational Method calculation
comparing the existing and proposed developed case peak flows.