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Description: Hi James,This is an extract from the Wellington Floodplain Risk Management Study.F2. DATAData utilised for this Drainage Study included data provided by Wellington Council and datasourced independently by Evans & Peck. Further details are provided in the following section.F2.1 Design Rainfall DataDesign rainfall data for use in the hydrologic/hydraulic model was generated within the DRAINSmodel using intensity-frequency-duration (IFD) data for Wellington sourced from the Bureau ofMeteorology’s online IFD tool. Design rainfall patterns were generated within DRAINS for eventsfrom 5 to 100 years average recurrence interval (ARI) and for storm durations from 5 minutes to 9hours for Australian Rainfall and Runoff (AR&R) Rainfall Zone 2. An antecedent moisture conditionof 2 was used for each rainfall event generated from a scale of 1 to 4. This represents “rather dry”conditions with 0-12.5 mm of rain in the preceding 5 days before the storm.F2.2 SurveySurvey of the Apsley Drain channel was initially undertaken by Wellington Council in March 2012.A dxf file was provided showing the location and elevation of surveyed points along the trunkchannel and along road crests, along with some 0.2 m contours in suspected ponding areas, andground spot levels within properties in potentially susceptible areas. Information on culvert sizeswas subsequently provided.As Evans & Peck required channel cross sections in horizontal offset vs. elevation format, Evans &Peck calculated the required offsets for each channel cross section used. In addition, as the Councilchannel survey was limited to the channel only to the top of bank, the GIS and LiDAR elevationdata (refer Section 2.3 below) was used to extend each channel cross section into the floodplain.In October 2012, Wellington Council provided some additional survey detail and photographs of thepipes and culverts in the vicinity of the intersection of Maxwell and Thornton Streets, as well ascorrections to a number of culvert dimensions throughout the catchment.F2.3 GIS DataGIS data was provided to Evans & Peck by Wellington Council in two main packages. The firstpackage was provided in May 2011 and contained the majority of Council’s GIS layers. Thoselayers utilised for this Study included:§ Aerial photography;§ 2 m contours;§ Cadastre, road boundaries and street names;§ Stormwater pits and pipes;§ Main river flood extents and flood affected properties.The secondary package was provided in March 2012 and included a number of layers sourced fromthe NSW Land and Property Information:§ LiDAR ground surface elevation spot levels;§ 0.5 m contours.Using this data, Evans & Peck created GIS layers to represent key features of the modellingundertaken for the Drainage Study, in particular to identify sub-catchment boundaries (see FigureF1) and channel cross section extensions.F2.4 Historical Flood InformationAs described in Section F1.5, Wellington Council expressed concern regarding the perceivedpotential for property flooding at a number of locations within the catchment. However, no specificinformation was provided for historical flood dates, flood levels or properties inundated. This hasmeant that the hydrologic/hydraulic model was not able to be calibrated against any known floodconditions, and as such its accuracy cannot be determined. Section F4.5 discusses model resultsin the areas of concern and identifies properties with the potential for flooding.Lee GriffithSenior Strategic PlannerDubbo Regional CouncilP 02 6801 4000 F 02 6801 4259 E Lee.Griffith@dubbo.nsw.gov.au

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