Flood Study Report Wellington

This flood study identifies the nature and extent of the flooding problem in Wellington.\r\nEstimates of design discharges, velocities and levels for the 5%, 2% 1% and 0.002% AEP\r\nevents are provided.\r\n\r\nDesign discharges were calculated using flood frequency analysis. A complex flood frequency\r\nprocedure was necessary to account for the attenuation of floods by Burrendong Dam and the\r\ncoincidence of peaks on the Macquarie and Bell Rivers. It is very difficult to estimate the\r\naccuracy of the design discharges predicted by the flood frequency analysis. Several factors\r\nlimit the accuracy of the discharges obtained, including:\r\n\r\n* Uncertainty associated with gauging station rating curves and,\r\n* Relatively short length of records for hydrologic data.\r\n\r\nDesign flood levels and velocities were calculated using a computer based one-dimensional\r\nunsteady flow hydraulic model. Flood levels have been quoted to the nearest 0.1 m, the\r\naccepted limit of accuracy for hydraulic models. This aspect must be borne in mind when\r\nusing the results for development purposes.\r\n\r\nFlood mitigation options should be considered as part of a floodplain management study. The\r\nMIKE 11 hydraulic model developed as part of this study can be used to model flood\r\nmitigation options.\r\n\r\nThree rock weirs have recently been constructed in the Bell River to control the bed and bank\r\nerosion. Over a period the many years, the bed level of the Bell River may rise as sediment is\r\ndeposited upstream of these weirs. The effect this would have on flood levels should also be\r\nconsidered in the floodplain management study.\r\n\r\nUntil a floodplain management study and floodplain management plan can be completed,\r\ncouncil should formulate a interim flood policy. This interim plan should be based on the\r\nlevels and velocities contained in this report.