RFI - P0478-26-001_45_Maple_Street_Cooroy_SWMP

3            Existing Site
3.1          Site Overview

The site, located at 45 Maple Street and 9 Myall Street, Cooroy, is bounded by commercial suites and health care
services to the north, Maple Street to the west, Myall Street to the east, and residential dwellings to the south. The
site has two existing access driveways, one from Maple Street and one from Myall Street. Surrounding properties
are zoned Community Facilities and medium density residential.

Topography generally falls to the east with survey ground levels ranging from approximately RL 122.5 m AHD in
the west to approximately RL 114.8 m AHD in the east. Drainage across the site primarily occurs as sheet flow
towards the east, discharging into the adjacent properties and Myall Street.

No dedicated stormwater infrastructure is currently provided within the site. It is understood that there is an
upstream catchment of approximately 637 m2 associated with Lot 3 on RP99323 that directly flows into the site.




Figure 3-1: Subject Site Location




3.2          Flow Calculation Using the Rational Method

The Rational Method was initially applied as a verification tool to cross-check outputs from the DRAINS
hydrological model, which was subsequently developed to assess both pre- and post-development flows.

The time of concentration (Tc) of 14 minutes was determined using figure 4.4 – Overland sheet flow times (refer
to Figure 3-3) in accordance with Table 4.6.6 of QUDM. This approach provides a reliable estimate of the travel
time for runoff from the hydraulically most distant point in the catchment to the outlet.

A maximum flow path length of 92.4m was adopted, based on QLD Globe (refer to Figure 3-2).

To refine the analysis, the following factors were incorporated to ensure accuracy and representativeness of the
stormwater design:

 45 MAPLE STREET, COOROY
                                         24 June 2026                                                 P a g e |6
 Stormwater Management Plan
 Client Reference: P0478-26-001
 Prepared for Myall Rise PTY LTD