Stormwater Management Report · MCU19/0008

2. 1       L aw fu l p o in t o f d i sch arg e

Stormwater runoff from the existing site falls east as overland flow, discharging to Sunshine Beach.
Stormwater runoff from impervious areas of the development is proposed to be directed to an
underground tank located at the rear of the site. Runoff from the tank shall discharge via infiltration or
shall surcharge and discharge east to Sunshine Beach when at capacity as per existing conditions.
Stormwater runoff from pervious areas at the rear of the site shall similarly discharge east to Sunshine
Beach. It is noted that this discharge strategy was approved for recent development to the north at 24
Arakoon Crescent. Refer to Appendix B for further information.

2. 2       F l o od i ng

According to the NSC planning scheme flood hazard overlay mapping the development site is not
subject to flooding from any sources.

3      ST O RMWAT ER Q UANT IT Y MAN AG EMENT

The stormwater quantity analysis of the existing and developed site conditions has been undertaken
with reference to the requirements and procedure outlined by:

           Queensland Urban Drainage Manual (QUDM)
           Australian Rainfall and Runoff Volumes 1 & 2 (Aust R&R)
The following section of the report discusses the proposed development’s impact on peak stormwater
runoff and total runoff volume from the site and compares the existing site condition to ensure a no
worsening effect to downstream land.

3. 1       Catch men t Su mmary

Pre-Developed Site

The existing site consists of an existing house. Stormwater runoff initially falls east as overland flow
prior to concentrating and discharging to Sunshine Beach.
The existing site area is approximately 610m 2. The total impervious area was calculated to be
approximately 400m2 which equates to 65% fraction impervious (fi=0.65).
Post-Developed Site

The development involves the construction of a single dwelling and ground level features. Runoff from
impervious areas of the development is proposed to discharge via infiltration or overland to Sunshine
Beach when the tank surcharges. Runoff from pervious areas at the rear of the site shall similarly
discharge overland to Sunshine Beach as per existing conditions.

The catchment area remains unchanged at approximately 610m 2. The total impervious area was
calculated to be approximately 350m 2 which equates to 57% fraction impervious (fi=0.57).

3. 2       Sto rmw ater Det en ti o n & In fi l tra ti o n

Modelling indicates there is a reduction in peak flow and total volume off site as a result of the
development due to the reduction in impervious area. However, it is proposed to direct stormwater
runoff from developed areas of the site to a proposed infiltration tank which shall incorporate stormwater
detention to reduce the impact of runoff to the adjoining sand dunes to the east.
The Atlantis Flo-Tank Modular tank system was adopted as part of the stormwater design. An infiltration
rate of 0.6m/d was adopted based on soil conditions at the adjoining dwelling at 24 Arakoon Crescent.




4 April 2019                                 Stormwater Management Report                               5
S18-030                                           22 Arakoon Crescent,