5255NSCResponse

ill

Callaghan & Toth

 

2.2.2 Overland Flow Network

The existing 1% AEP overland extents has been determined by survey and site inspection (the
boundaries are shown on Plan 2103-02).

There are currently no formal overland flow paths from Key Court to the canal.

There are two sag points in Key Court, one in front of No. 17 and one in front of No.18.

It is assumed that 1% AEP in excess of pipe flows would currently flow through properties
adjacent sags into the canal.

2.2.3 Reference Flood Records

The defined flood level on council flood certificate is RL 2.4 for 1% AEP 2100 with a minimum
floor level of RL 2.7. This flood level has been used to calculate areas when compensating
filling has been applied to the soil proposed to be used from the overland flow easement
excavation.

This level was not used for the overland flow path as it is above natural ground levels at the
road frontage and so the whole area will be ponded water when this event occurs.

We have instead designed the overland flow path to work with a local 1% AEP flow up until
RL1.55 at the property canal boundary and so a river flood up to the canal boundary level
considered the maximum height to which the overland flow path can be expected to function.

2.3 Proposed Improvements

The proposed improvements consist of shaping a trapezoidal swale 1% AEP overland flow path
along the proposed easement.

2.3.1 Proposed Overland Flow Path

Proposed overland flow path will be created by lowering the natural ground along the proposed
easement by a maximum of 250mm at the front boundary which will taper to Om just past the
new house location- refer to Plans 2103-03 & 04.

This overland flow path is required to be 250mm deep at the road frontage so as to take 1%
AEP flows before the flood waters flow through adjoining properties.

The overland flow path dimensions proposed is calculated to take the excess flow above which
the 300° pipe and the 300mmx600mm box culvert are able to take in a 1% AEP (Refer to
Appendix A).

2.3.2 Compensation Allotment Filling

The volume of earth required for removal for the overland flow path of 12 cubic meters will be
added to the front yard between the new building and the front boundary which will not have
any impact on the flood levels as required in Information Request Item 3.

 

2103 19 Key Ct SWMP February 2021