2014-11-17 General Committee Agenda

GENERAL COMMITTEE MEETING AGENDA   17 NOVEMBER 2014




                                        Page 13 of 49

GENERAL COMMITTEE MEETING AGENDA                                                                 17 NOVEMBER 2014

                 (i) installing a traffic calming (traffic slowing) system on the road at each end of the floodway
                     (1st preference)
                (ii) adopting a wire cable traffic barrier (2nd preference)
                (iii) widening the road embankment (3rd preference simply because of the expected culvert
                     design complications and loss of trees associated with this option).
                «   Consider the safety benefits of a flat (no undulations) road surface along the length of the
                   floodway.
                ¢   Consider the incorporation of debris capture poles upstream of the main channel culvert.
                e   Consider any possible design variations that could reduce the length of the long 3/2100 pipe
                    culvert, such as releasing it into a constructed open channel.
                e   Though not directly related to the road design, | have taken a casual glance at the proposed
                    Erosion and Sediment Contro! Plan prepared by SMEC Urban (plan 334006E-EW-111B)
                    and | believe it to be grossly inadequate. The plan refers to an outdated reference
                    document, and does not appear to present adequate information fo manage soil erosion and
                    sediment runoff during the construction phase.
                Recommendations with regards the need for safety screens on the inlet of the proposed
                3/2100 long culvert
                | have not had time to review the need for safety screens to be placed on the long 3/2100 pipe
                culvert in accordance with chapter 12 of QUDM (2013), but from a brief review it would appear
                that the need for such screens may be exist some time in the future. Consequently, it would be
                highly beneficial if a design option could be found that would reduce the length of these culverts.
                The issue of ‘no worsening’
                It is my opinion that the use of terms such as ‘no worsening’ or ‘no worse off are inappropriate
                when applied to the potential flood outcomes associated with road upgrades that seek to reduce
                the flood potential of a road by raising the road.
                If these terms are used in the setting of development conditions, then there is the potential that
                the terms would be considered unlawful because they fail the overriding ‘fare and reasonable’
                test, which must be applied to all laws, and all development conditions.
                The problem is, that if taken literally, then there can be no hydraulic solution that could possibly
                achieve ‘no worsening’ outcomes for all residents both upstream and downstream of the road,
                during in ail possible flood events. Therefore, if there is no possible solution that achieves all
                the required outcomes, then the condition, if applied literally, could be considered unreasonable
                and therefore unlawful.
                The proposed Garnet Street upgrade is a classic case. If you design the culvert for a specified
                debris blockage of 20% such that upstream flood levels are equivalent to the existing conditions,
                then the following possible ‘real world’ outcomes exist:
                e   If the actual debris blockage during a particular flood is less than 20%, then upstream flood
                    levels will be lower than the ‘existing case’ and therefore there will be less flood storage and
                    less flood attenuation. Consequently the peak discharge passing the road will increase and
                    therefore downstream properties will be ‘worse off.
                 e  If the actual debris blockage during a particular flood is greater than 20%, then upstream
                    flood levels will be higher and therefore upstream residents will potentially be ‘worse off,
                    while downstream properties will be better off.
                 In my opinion, there is no feasible design option that can achieve a ‘no worse off’
                 outcome for everyone in all possible ‘real’ storms.
                 Printed: 06 November 2014        CREEKS: CORRIDORS OF OPPORTUNITY                  Page 5:

                                                                                                          Page 13 of 49