2014-11-17 General Committee Agenda

GENERAL COMMITTEE MEETING AGENDA   17 NOVEMBER 2014




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GENERAL COMMITTEE MEETING AGENDA                                                                 17 NOVEMBER 2014

                views of a hydraulic consultant working for a developer.
                A local government such as Noosa Council must consider a wide range of often conflicting
                interests and expert opinions when determining their maintenance schedule and their strategy
                for the management of waterways. The opinions expressed with the ‘Hydrology & Water’ report
                may be appropriate purely from a flood management perspective, but may not be appropriate
                when all issues are considered, including available funds.
                On this matter, it is my opinion that:
                e   Clearing natural wood debris from creeks can reduce the risk of debris blockages, but also
                    increases flow velocities within creeks, which increases the risk of channel erosion, which
                    increases the risk of more woody debris becoming available.
                e   Thus, there is the risk that clearing woody debris simply increases the risk of more woody
                    debris becoming available.
                e   Rather that taking the environmentally destructive option of removing woody debris from
                    creeks, the best option is to incorporate design features into road culverts that reduce the
                    risk of this debris adversely impacting upon flood levels.
                e   In most cases it is my recommendation that ‘natural’ woody debris should remain within
                    creeks, and only removed when it collects against structures such as debris traps and
                    culverts.
                Culvert design options for the management of debris at the culvert
                Design options for the management of debris blockages at road culverts include:
                e   Use of debris deflector walls (usually used in association with box culverts).
                e   Use of debris collection poles (able to be used adjacent both pipe and box culverts).
                 In this case | would consider the use of treated timber debris collection poles the likely best
                treatment option.

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                     Figure 3 — Debris deflection walls         Figure 4 — This is not a good example of
                                                                         debris collection poles
                 Recommendations with regards to the overall design of the Garnet Street upgrade
                 With regards to the overall design of the road upgrade | offer the following recommendations:
                 e  Adopt the debris blockage conditions as outlined in Table 1.
                 e  Consider all design options that would avoid the use of solid traffic barriers along the
                    floodway, such as:

                 Printed: 06 November 2014        CREEKS: CORRIDORS OF OPPORTUNITY                   Page 4.

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