EXECUTIVE SUMMARY

This Flood Risk Management Study and Plan (FRMS&P) focuses on the overland flow flooding issues within the Griffith urban area. The Study has been commissioned by Griffith City Council (Council) to assess and make recommendations for maintenance or reduction of flood risk within the Griffith CBD. This FRMS&P follows on from the Griffith CBD Catchment Overland Flow Flood Study prepared by WMAwater and adopted by Council in March 2012.

A floor level survey has been undertaken and used in producing a tangible flood damages assessment. The flood damages assessment was used to highlight key areas which should be prioritised in terms of providing flood relief and to assess the potential benefit of any relief works. Of the 216 properties surveyed (70 residential and 146 commercial), a total of 19 residential and 99 commercial or industrial properties are likely to be flooded above floor level in the 1% AEP event. For the same event, of the properties surveyed, 69 residential and 125 commercial or industrial properties are affected by over ground flooding. The estimated annual average damages per flood affected residential property up to the PMF event is $2,440 with 72 of the surveyed lots flood affected and 64 of these with building inundation above floor level. For commercial/industrial properties annual average damages per flood affected property up to the PMF event is $5,880 with 142 of the surveyed lots subject to flood affectation and 138 of these liable to above floor flooding.

The Flood Study identified a number of key areas where flooding was an issue. Yambil Street, Burrell Place, Cutler Avenue, Noorla Street and Lenehan Road were all highlighted as flooding hot-spots. For the purpose of this FRMS&P the total study area was divided into a number of sub-areas based on their flooding characteristics, previously identified hot-spot areas and type of land use. Six sub-areas were identified and referred to as; the CBD area; Industrial Zone; Crossing Street area; Junction of Wakaden and Ulong Streets; Hyandra Street area; and, Noorla Street Residential area.

As part of this FRMS&P the hydraulic model was used to assess where improvements made to the drainage system could effectively reduce flood depths and potential flood damages to properties. Drainage modification options investigated included a combination of upgraded pipe networks, installation of retention basins and open channel improvements. Each of the options was considered in terms of the impact of flood levels and tangible flood damages for each of the previously identified flooding hot-spots and the sub-areas.

All options were assessed using the 1% AEP flood event (100-year ARI). A number of options would provide benefits to different areas reducing flood levels and flood associated damages and further discussion with Council will be undertaken to identify the high priority areas or options.

The Flood Liable Lands Policy, Floor Heights Policy and OSD Policy have all been reviewed. Recommendations have been made, especially in relation to identifying the Flood Planning Area.

(FPA) and setting the Flood Planning Level (FPL) and building floor levels. This matter will require further discussion with Council engineers and planners to finalise an appropriate FPA, FPL and building floor level requirements.

The draft Plan has been endorsed by Council and the Floodplain Management Committee and was held on public exhibition for community feedback before this final Flood Risk Management Plan was issued.