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

The increases in impervious percentages were applied to the upgraded flood study’s hydrologic
model to determine the potential increase in runoff from each sub-catchment. This runoff was then
added to the hydraulic model to determine the impact on floodplain conditions downstream.
To assess the potential impact of increased impervious areas the model’s flood level results are
extracted and compared at selected locations. These locations are shown in Figure 4.

Hydrographs of water level results plotted against time have been prepared for each reference
location for two sample flood events for both existing and ultimate urbanisation conditions.

Selections of these hydrographs are presented in Figure 5 to Figure 8.

The extents of potential increases in flood levels due to unmitigated urbanisation are shown in
Figure 9 and Figure 10.




Lake McDonald Flooding Community Reference Group Report                                     Page 13