Att 4 - SWMP · MCU21/0117

                    2. 4. F L O O D C O N S I D E R A T I O N S

            The Noosa Shire Council Intramaps Flood Hazard Overlays show that the proposed
            development site is not likely to be subject to flooding or inundation up to and including
            that during an extreme (500 year) flood event.



            3. STORMWATER QUANTITY
                    3. 1. D I S C H A R G E T O P E A R L S T R E E T

            As the existing site and upstream catchments currently drain overland into private and state-
            owned property to the north and the proposal seeks to discharge the run-off to the legal
            point of discharge in Pearl Street, a comparison of the pre-development discharges to post-
            development discharges for the site’s drainage catchments is not appropriate. To
            demonstrate that the discharges will not cause nuisance to upstream or downstream
            properties, the proposed drainage line to be constructed in Pearl Street has been modelled
            using the 1% AEP storm event, allowing a 20% increase to rainfall intensity to account for
            climate change impacts (2090 climate change factor for RCP8.5 scenario).

            Based on contours of the locality, the typical surface run-off will drain northeast towards the
            existing drainage channel north of Lot 0 SP 260162. The existing catchment is
            predominately comprised of the road and verge strips draining to the table drain. The area
            considered to contribute to the street drainage system is shown in Figure 2.6 – Proposed
            Catchments Plan as the external catchments. Due to existing run-off from the table drain
            upstream of the site now being captured in the new stormwater line, the total run-off in the
            table drain is reduced from the existing conditions, providing a potential improvement to
            any localised flooding or surface flow issues.

            To ensure sufficient capacity exists in the stormwater network, the upstream catchment
            draining into the existing stormwater infrastructure has been estimated based on the Noosa
            Council contour and stormwater infrastructure maps, with an estimated catchment area of
            6.7Ha as shown below in Figure 3.1 – Existing stormwater network catchment. This volume
            was modelled as a constant inflow rate upstream of the proposed connection point to
            simulate the full catchment draining through the piped network at the time of the design
            storm.




                                                                                                               Page 7 of 26
P +61 7 5211 1003              A 37 Mary St, Noosaville Qld 4566        E [email protected]   recorconsulting.com