USC FloodStudyUpdate Report - Flipbook - Page 5
dedicated drainage reserves in the urban areas. Within the major creeks, flow is typically
contained within the channel. There are some areas, however, where floodwater breaks out of
the channel into flood runners (minor creek anabranches) or low-lying flood storage areas.
In the 20% AEP event, water begins to inundate the South Creek floodplain, particularly in the
lower reaches. This is extended further in the 10% and 5% AEP events as floodplain storage
areas fill. In the 2% and 1% AEP events, the overbank areas become much more connected
and convey water more effectively. This continues into the 0.5% and 0.2% AEP events with flow
paths becoming wider and conveying a greater flow. One of the most notable changes across
these events is the increase in flood storage upstream of Bringelly Road. In the 0.2% AEP
event, Bringelly Road starts to overtop at the crossing of South Creek.
In the PMF event, wide flow paths are activated that are typically 1 m to 2 m deep along the
major creeks. Flooding also becomes hazardous in some of the urban areas.
Using the above information, properties subject to potential flood affectation and flood-related
development controls have been identified, and Council will include this information on the
relevant Section 10.7 planning certificates. Mapping of design flood behaviour is provided in
Appendix C, with planning maps that are relevant for development controls as follows:
Hydraulic categorisation (floodways, flood storage and flood fringe) for 1% AEP in
Figure C28;
Flood Planning Area (FPA) in Figure C35; and
Flood Risk Precincts (FRP) in Figure C36.
Flood damages were also estimated as part of this study. In the 50% AEP event, flood damage
in the upper South Creek catchment is primarily attributed to external damages (landscaping,
fencing, sheds, etc.). In the 20% AEP event, there are two properties estimated to have above
floor flooding. This increases to 10 properties in the 1% AEP event. In the PMF event, there are
estimated to be 232 properties flooded above floor, with 435 affected by flooding altogether.
The average annual damages from flooding are estimated to be approximately $466,600. The
flood damages for the 50% AEP event are estimated to be almost $400,000 (or $13,000 per
property). This steadily increases with each AEP event, with the estimated flood damages being
$1.8 M in the 1% AEP event and $2.5 M in the 0.2% AEP event. In the PMF event, the damages
reach almost $21 M.