Garnet Street RFI_20150513_ITC (Part 1)

Road Barriers                           Road barrier in the form of guard rail has been
                                        proposed for the southern side of Garnet Street for
                                        the full length of the upgrade works.

Pipe Size                               Pipe sizes consist of DN 2700mm, DN 2100mm and
                                        2400mm x 1200mm RCBC and pose a minimal risk of
                                        entrapment.
Travel Time                             For the DN 2700mm pipe arrangement, a length of
                                        14.64m and pipe velocity of 1.38m/s (Hydrology and
                                        Water Flood Report) have been used to calculate a
                                        travel time of 10.6 seconds.
                                        For the 2400mm x 1200mm RCBC arrangement, a
                                        length of 15.00m and pipe velocity of 0.93m/s
                                        (provided by Hydrology and Water) has been used
                                        to calculate a travel time of 16.1 seconds. Whilst
                                        this time is greater than an expected pipe full travel
                                        time of 10 seconds, this set of culverts is elevated
                                        above the base of Cooroy Creek and operates as a
                                        secondary system during flooding.
                                        For the skewed orientation of the DN2100 pipe
                                        arrangement, a length of 69.34m and pipe velocity
                                        of 1.83m/s (provided by Hydrology and Water) have
                                        been used to calculate a travel time of 37.9 seconds.
                                        Whilst this time is greater than an expected pipe full
                                        travel time of 10 seconds, this set of culverts is
                                        elevated above the base of Cooroy Creek and
                                        operates as a secondary system during flooding.
Cooroy Creek – flow and accessibility   Cooroy Creek has a history of conveying significant
                                        flows from a large western catchment and regularly
                                        flows full to the extent of overtopping Garnet
                                        Street.
                                        The culvert amplification works provide a balanced
                                        solution whereby Garnet Street meets the safe
                                        trafficable  requirements     without    adversely
                                        impacting on flood levels upstream and
                                        downstream.
                                        While the inundation levels across Garnet Street will
                                        be reduced by the amplification works, the greater
                                        Cooroy Creek will continue to flow at high levels at
                                        regular intervals. On this basis, hazards and risk
                                        associated with the culverts must be considered in
                                        the context of the Cooroy Creek flow characteristics.
                                        Furthermore, construction of inlet screens on the
                                        culverts and potential blockage as a result of debris
                                        collection may result in the balanced flow/flood
                                        storage model being compromised and adverse
                                        changes to flood levels in the greater area.