A hydraulic assessment of flood levels in South Creek was conducted to
determine the impact of filling within the ADI site floodplain. An existing
Department of Land & Water Conservation hydraulic model was used to
conduct this assessment. Prior to the Hydraulic modelling analysis, meetings
were held with DLWC and Penrith City Council to obtain their requirements
and discuss the appropriate modelling procedures acceptable to the
concerned authorities. Subsequent meetings were also held with DLWC
during the study to resolve and agree on emerging issues.
The results of the hydraulic modelling indicate that the impact of the
proposed filling (Lend Lease Master Plan) on flood levels in South Creek is
almost totally contained within the ADI site. The maximum predicted increase
in flood levels on the ADI site is 140 mm for the 1%AEP storm event. At the
downstream boundary of the site, a negligible increase of 20 mm is expected,
20 mm is considered to be well within the expected accuracy limits of the
hydraulic model. At the upstream boundary, a maximum increase of 40 mm
is expected reducing to less than 20 mm at a distance 900m upstream of the
boundary. This increase in flood levels does not affect the residential areas of
Cambridge Park which are raised well above peak flood levels. Similarly,
properties at Link Road, Dunheved are also not affected by this small rise in
flood levels. The Dunheved Golf club house is also positioned well above the
peak flood levels.
Additional investigations at the upstream end of the ADI site which included
the removal of a significant flow restriction at the old munition railway bridge
indicated a decrease of 0.5 m in the 1% AEP flood levels at the upstream
boundary of the ADI site. This means a change from a an increase of 40 mm
in flood levels to a decrease of 500 mm at the upstream boundary of the site.
The hydraulic analysis also indicates that the impact of filling on flood levels in
Ropes Creek at the St Marys STP is negligible (less than 10 mm).