The Wolli Creek Piped Drainage and Overland Flow Analysis Draft Report of September 2001 identified that the East Hills Railway Line acted as a significant barrier to overland flows from the upstream catchments. In 2000/2001 the Rail Infrastructure Corporation (RIC) undertook duplication of the East Hills Railway Line (from a two track to a four track line). The works involved filling within the “pre duplication” cess to form a new track and construction of a concrete panel noise wall on both sides of the rail easement.

A detailed hydrologic/hydraulic assessment of these RIC works was undertaken in the Wolli Creek Investigation of the Impacts of the East Hills Rail Line Duplication on Overland Flows, Draft Report, May 2002. The DRAINS model set up for the previous September 2001 study, together with additional survey data was used to determine design flood levels. In summary, the modelling assumed that the railway line and the noise wall act together as retarding basins with low flow and high flow exits.

The May2002 report identified that these two works (filling and noise wall construction) significantly increased the flood levels and consequently the flood hazard within three areas, namely:

• the commuter car park near Kingsgrove Station,
• the community centre on Shaw Street, opposite West Drive at Kingsgrove,
• Powys Avenue at Bardwell Park.

Possible mitigation works were investigated and some reduction of the adverse effects of the duplication works could be achieved. However, it would be impossible to maintain the pre-duplication design flood levels, for the full range of design events, unless major changes were made to the noise wall.

As a consequence of the May 2002 report, RIC installed additional openings at the commuter car park near Kingsgrove Station and at Powys Avenue. This present 2007 report updates the outcomes from the May 2002 report at these three locations and in particular Council’s GIS property database of flood affectation downstream of Kingsgrove Avenue.