Narromine Flood Study - Final Report

The activities comprising the present investigation included:

1. Review of flooding patterns in the area presently covered by the model and preparation of a brief for additional cross sectional survey which would also cover areas earmarked by Council for possible future development. These areas are shown on Figure 1.1.
2. Adjust the MIKE 11 model to incorporate the overbank flow paths discussed previously, extend the model into the potential development areas and confirm that the potential downstream control on flood levels in the town (i.e. the banks of the irrigation canal between the Mitchell Highway and Warren Road), were correctly incorporated in the model.
3. In view of the modifications to the hydraulic model, it was necessary to tune it to reproduce flooding patterns observed during the February 1955 flood of record, prior to using it for design flood estimation. Recorded peak flood levels were available for the February 1955 flood.

Section 2 discusses the amendments to the hydraulic model which were made to simulate the overtopping of the river bank and water filling the southern floodplain, as well as the refinements made to the model to simulate flooding on the southern side of the Main Western Railway. As mentioned, in view of the substantial changes to the model, it was considered advisable to test its ability to reproduce February 1955 flooding patterns. This task required some adjustments to the “2006 Floodplain Model” to replicate the “February 1955 Floodplain”.

Section 3 describes the results of hydraulic modelling of the design flood events and presents information on the distribution of flows and peak water surface levels in Narromine. Results are presented as peak flood depths and elevations, peak water surface profiles and plans showing indicative extents of inundation and provisional flood hazard based on the depth and velocity criteria presented in the Floodplain Development Manual, 2005.

Section 4 contains a list of references.

Supplementary details are given in the Appendices. Appendix A contains tabulations of flood level, discharge and velocity data for each of the design storm events modelled and sketches of culverts are presented in Appendix B.