Cardno Amended flood report July 2018

Response
Additional hydrologic and hydraulic modelling has been undertaken in the technical memo to provide
a solution to this issue. All design events up to the defined flood event (39% to 1% AEP) have been
modelled to meet requirement O22 of the Natural Hazards Overlay Code.

Section 5 provides a summary of the hydraulic results from the modelling. The results indicated that
the proposed development does not cause any negative impacts both internal and external to the
site. Maximum flood depths, water surface elevations, velocities, affluxes and hazards have been
provide in the figures attached (Attachment B).

The modelling determined that for all design events, no negative impacts were caused by the
proposed development either on or offsite. Access to the proposed buildings as per the drawings
shown in Attachment A remains flood free with no impacts on human safety identified.


2 Site Description
A site description can be found in the original flood study, (Flood Study Noosa Care – Carramar
WE17064 24 July 2017).

3 Hydrology Model
The original flood study (Flood Study Noosa Care – Carramar WE17064 24 July 2017) setup a
hydrology model with a full range of rainfall event durations for the 10% and 1% AEP events. The
same hydrology model and methodology were adopted to capture the peak events for the new 39%,
10%, 5% and 2% AEP events.

3.1   RORB Parameters
An initial and continuing loss approach was adopted to represent the expected losses from the
design storm events. An initial loss of 15.0 mm and a continuing loss of 2.5 mm/hr were adopted.
The parameters adopted for this study are provided in Table 3-1, which has been validated using
the Rational Method.

The AR&R 2016 Intensity Frequency Duration (IFD) data was used to define the rainfall intensities
for use in the hydrology model. To account for the impact of climate change the rainfall intensities
were increased by 20 percent.

3.2   RORB Validation
As there was no stream flow gauge within the catchment, there was no opportunity to
calibrate the rainfall and runoff model (RORB) using known flow hydrographs and rainfall.
Validation of the RORB model was undertaken using the Rational Method at the outlet point
of the catchment. The Bransby-Williams method was used to calculate the time of
concentration.

Table 3-1 below shows the Rational Method parameters adopted, with validation
results presented in Table 3-2. The C10 values adopted are in line with the parameters
previous flood study.
Table 3-1 Rational Method Parameters
 Ration Method Parameters        Total Catchment
 Catchment Area (ha)                   503
 Fraction Impervious                  0.24
 Runoff Coefficient (C10)             0.76
 Time of Concentration (min)          77.5