Table 12: Blockage of Saltwater Creek Structures

7.6.1 Saltwater Creek Structures

For structures over Saltwater Creek, the ARR2016 guidelines consider blockage due to various sources and allowing for the factors listed below:

• Debris Type and Dimensions - Whether floating, non-floating or urban debris and typical sources and sizes; • Debris Availability – The volume of debris available in the source area; • Debris Mobility – The ease with which available debris can be moved into the stream; • Debris Transportability – The ease with which the mobilised debris is transported once it enters the stream; and • Structure Interaction – The resulting interaction between the transported debris and the bridge or culvert structure.

A blockage assessment was undertaken in accordance with ARR2016 guidelines. Each of the structures crossing the Saltwater Creek channel were assessed and blockages were derived (see Table 12).

Table 12: Blockage of Saltwater Creek Structures Event AEP Blockage % AEP > 5% 0% AEP 5% - AEP 0.5% 0% AEP < 0.5% 15%

7.6.2 Drainage Network

Book 9 of ARR2016 addresses estimation of runoff in urban areas and provides detail on the blockage of pit inlets. A blockage factor of 50% is advised for sag pits and a blockage factor between 0% and 20% is specified for on-grade pits depending on the specific catchment characteristics. The Community Consultation (see Section 4.1) responses consistently identified that the blockage of kerb inlets was exacerbating flooding. Therefore, a blockage factor of 20% has been adopted for ongrade pits and 20% for sag pits in the catchment.

For the PMF event, all structures were blocked completely.