Amended Stormwater Plan

SC5551 - 28 Elkhorn Dr, Tewantin                                                                     10



4.0 Stormwater Quantity Management
4.1      Background
The proposed sub-division and associated increase in impervious areas has the potential to create or
exacerbate drainage problems to downstream areas and/or drainage infrastructure. The purpose of this
section of the SWMP is to determine the general requirements for bulk stormwater management for the
proposed development. The design shall ensure that rainfall event discharges are conveyed from the site
in a manner that complies with Council’s stormwater planning guidelines and does not result in a worsened
drainage situation to downstream infrastructure, without causing a nuisance or annoyance to
residents/property owners.


Under existing conditions the subject site has a catchment crest beginning approximately 88m east off the
south-western corner, to approximately 36m east off the north-western corner. The western portion of the
catchment sheet flows over the west boundary into the neighbouring lot. The eastern portion of the
catchment sheet flows east into Noosa River Esplanade. Refer to Figure 4.1 on the following page.


4.2      Site Drainage Constraints and Opportunities
4.2.1    Drainage Constraints
No lawful point of discharge exists to the downstream western or eastern properties. Earthworks to the
western boundary to achieve grade out to the new road must be minimised to avoid large height retaining
walls.


4.2.2    Drainage Opportunities
It is proposed to discharge all roof areas to a lawful point of discharge (the new road kerb and channel),
and the new road will provide a formal underground drainage downstream to an existing connection in
Elkhorn Drive. Ground areas of Lots 1-5 will sheet flow over the western boundary, and ground areas of
Lots 6-11 will sheet flow into the new road. The drainage system from Elkhorn Drive to Noosa River
Esplanade will be upgraded to cater for the proposed development. This proposal will ensure a situation of
non-worsening discharge to the downstream boundary conditions.