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).