FLOODPLAIN MAPPING

This report describes the determination of the boundary of the land liable to flooding (on a 1: 25,000 scale topographical map), on the Coomalie Creek floodplain lying within the administrative area of the Coomalie Community Oovernment Council. The 1 in 100 Annual Exceedence Probability (AEP) flood discharge of Coomalie Creek at the Stuart Highway Crossing 08170066 was determined by frequency analysis of annual flood maxima at 08170066. Frequency analysis was shown to produce a more accurate estimate of the 1 in 100 AEP flood discharge at 08170066 than a rainfall runoff model The 1 in 100 AEP flood level at Coomalie Creek/Stuart Highway crossing was then determined from the extended rating curve. The I in 100 AEP flood discharge of Coomalie Creek was also estimated at a surveyed river section 7 kilometres upstream of 08170066, using the RORE model with a regional value for the RORE parameter. The I in 100 AEP flood level at this section was then determined from Manning's formula The boundary of the land liable to flooding, east of Batchelor on the Coomalie Creek floodplain, and immediatly downstream of the Coomalie Creek/Stuart Highway crossing was found by assuming an uniform flood slope. This slope was computed from the estimated I i