Federation Villages Floodplain Risk Management Study and Plan
Table 25: Summary of Freeboard Asessment Boree Creek
Oaklands
Rand
Urana
MS/O
MS
O
O
MS
O
MS
O
0.06
0.1
0.01
0.01
0.1
0.02
0.15
0.01
0.0075 0.01 0.1 0.18
0.007 0.01 0.05 0.17
0.01 0.01 0.25 0.28
0.01 0.01 0.02 0.05
0.09 0.01 0.08 0.28
0.01 0.01 0.03 0.07
0.015 0.01 0.18 0.36
0.05 0.01 0.2 0.47
N
Uncertainties in Estimated Flood Levels Local Water Surge Wave Action Climate Change Total MS – Mainstream Flooding O – Overland Flooding
Morundah
H IB IT IO
Freeboard Element
IC
EX
Typically, the freeboard assessment would identify freeboard that would be appropriate for each flow mechanism. As shown above, the freeboard requirement across the study area is variable with mainstream requirements varying from 0.18 – 0.36m and overland requirements varying from 0.07 – 0.47mm. Following discussions with Council and the FRMC, the preferred approach is to apply a consistent freeboard across the study area and flow mechanisms. It is therefore concluded that a 0.3m freeboard is required to provide reasonable certainty that the flood risk in the 1% AEP is accounted for, for both overland flow and mainstream flooding. Flood Planning Levels
BL
6.4.1.3.
PU
The residential Flood Planning Level (FPL) is recommended to be based on the 1% AEP event plus freeboard. Justification for the selection of the 1% AEP event as the basis is provided in Section 6.4.1.1, and the assessment of applicable freeboard is as described in Section 6.4.1.2.
FO
R
Depending on the nature of the development and the level of flood risk, commercial FPLs can be varied based on either the design flood event selected or the choice of freeboard, acknowledging that businesses may be better placed to recover from flood related damages or implement flood protection/mitigation measures compared to residents. Section K4.4.1 of the Manual (Reference 5) states the following:
D
R
AF
T
“The greater flexibility of business in managing risk and recovering financially from flooding, means that FPLs for industrial and commercial development may be based upon a more frequent flood event. An acceptable level of risk may become a business decision for the owner or occupier. This allows for trade-offs between council’s responsibility to present and future owners and occupiers and the latter’s natural preference to accept the risk and potential damages as a business cost to lower initial set up costs.” (Reference 5). In some catchments, potential damages to commercial premises may be adequately avoided or limited by setting Flood Planning Levels based on a more frequent (i.e. ‘smaller’) design flood event. For simplicity however, adoption of the 1% AEP as the basis for commercial flood planning levels is recommended at this stage, subject to discussion with stakeholders, including the Floodplain Risk Management Committee and Council’s planning staff. As such, the FPL for commercial development is also recommended as 1% AEP + 0.3 m.
118048: R211211_FederationVillagesFRMSP.docx: 11 December 2021
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