2018-05-14 GC Agenda Attachment 1 to Item 6 Lake MacDonald Dr Community Reference Group Investigations Report

6.1      Discussion of results
The results show there is a small increase in flood levels immediately downstream of some of the
urban areas. However, these small increases are attenuated as flood waters expand across the
floodplain and pass through the significant waterway crossing of the north coast rail line. The rail
line includes a high embankment which guides upstream flood waters towards the bridge opening
immediately upstream of Elm Street. The constriction of the bridge acts as a hydraulic control
allowing controlled rates of flood waters to pass through the bridge opening. This controlling affect
removes any evidence of the small increase in flood levels simulated upstream of the crossing.
This analysis demonstrates that if the planning scheme did not contain provisions to manage
additional stormwater runoff then a small increase in design flood levels could be observed in
areas upstream of the north coast rail line; however, these increases do not translate to areas
downstream of the rail line.

On the basis of the simulation results and with consideration of the provisions of the Planning
Scheme this analysis concludes that planned increases in urbanisation within the Cooroy township
urban footprint will not increase peak flood levels in the vicinity of Highland Drive, Lake
MacDonald.




Lake McDonald Flooding Community Reference Group Report                                       Page 19