This report sets out the findings of an investigation which was undertaken to refine the design of the elements comprising the Combined Trunk Drainage Upgrade Scheme ( the Scheme) which was recommended in The Town of Young Floodplain Risk Management Plan (the Plan). The benefits that the construction of the Scheme would provide in terms of reducing the extent and depth of flooding for a storm with an Annual Exceedance Probability (AEP) of 1 per cent are shown on Figure 3.19, which has been taken from the report titled “The Town of Young Floodplain Risk Management Study and Plan” (Lyall & Associates, 2015) (refer Appendix A of this report for a copy). The key components of the Scheme as defined in the Plan are as follows:
- Basins B1, B2 and B5 in the upper reaches of Railway Drain, as well as Drainage Lines U3 and D3 in its middle and lower reaches;
- Basins B3a, B3b, B3c and B3d in the upper reaches of Chance Gully, as well as Drainage Line D2 in its lower reaches; and
- Drainage Lines U1 and D4 in the middle and lower reaches of Golf Course Drain.
Following an initial review of the Scheme by the Consultant, Hilltops Council (Council) and the Office of Environment and Heritage (OEH), it was decided to omit stormwater drainage line U3 from the Scheme due to the required depth of excavation where it crosses the existing rail corridor. Drainage Line D3 was also shifted west from Zouch Street to Lynch Street to allow flow in the existing trunk drainage line which is located in the rail corridor to be intercepted and diverted south to Burrangong Creek.