240913_360CC to NC_Lot 5 Majestic Dr_OPW IR Response

Information Request Item 1, Part 1– Response: -
A desktop study was completed to determine the impact. The information used to
determine the situation was:
    1. The as-constructed survey of the original subdivision provided by Lands Surveying
       Dynamics; and
    2. Photo evidence of the batter for areas outside the property boundary and outside
       the survey extent. Photos were provided by Axis Surveys.

An approximation of the upstream catchment has been calculated to determine the flow
rate for a 1% AEP event.

As per the image below, the upstream catchment has been calculated to be approximately
1200m2.




Figure 1 – Catchment calculations based on the as-constructed survey provided by Land
Surveying Dynamics

The Time of Concentration has been calculated as 15mins using Figure 4.4 from QUDM for
the first 100m of flow and Friend’s equation for the subsequent flow. The resulting time of
concentration is approximately 15mins. Using the Mannings equation, the 1% AEP flow rate
has been calculated to be approximately 0.065m3/s.

The channel has a longitudinal grade of approximately 7.5%. The slope of the batter on the
development side has been calculated as a 1:3 batter.

The slope on the non-development side has been calculated as a 1:6 batter based on the
image below which was taken by Axis Survey.