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

STORMWATER MANAGEMENT PLAN 7

 

6.0 Post-Development Flows

6.1 Rationale

The peak flows for the design storms for the post development conditions were derived using

the XP-STORM model set up in accordance with the proposed development layout.

In accordance with the pre development scenario the post developed site was modelled with
the discharge point being the north-eastern environmental drainage area. However no
structures will actually be located within this environmental area. The XP-STORM model was
set up with a preliminary stormwater system design comprising of open bio-retention areas
collecting runoff from carparks and hardstand areas before discharging into a swale along the

eastern boundary.

As a result of the increase in impervious ground areas and defined flow paths, detention of
stormwater will be required to ensure that the development does not increase existing flow
rates at the point of discharge. This storage volume will be achieved by roofwater harvesting
tanks or equivalent with a combined volume of 192kL. These tanks will be located under car

parking areas and will be detailed further in a future operational works application.

An XP-STORM node layout plan for the post-development scenario is included in Appendix
Cc.

6.2 Results

Table 6.1 indicates the greatest peak flows for the post development model.

Table 6.1: Post development peak flows
ARI Design Storm (min) Peak Flow (m’/s)

10 25 0.714
100 25 1.002

 

 

 

 

 

 

 

 

As shown in the above table the post-developed flows compare very well to that of pre-
developed. This is due to the stormwater mitigation included in the development in the form of

harvesting tanks. XP-STORM pre development model output is included in Appendix C.

 

BARLOW GREGG VOM M3048
DECEMBER 2007