Casterton & Sandford Riverine & Stormwater Flood Risk Investigation

Overview Glenelg Hopkins Catchment Management Authority is seeking proposals from suitably qualified and experienced tenderers to complete new climate ready flood risk mapping for Casterton and Sandford, accounting for riverine and stormwater flood risk. About Casterton and Sandford are located on Gunditjmara Country. Casterton, Glenelg Shire's second-largest town, has a population of approximately 1,700 and is situated on the Glenelg Highway (B160), about 50 km from the South Australian border. The CBD is located on the right bank of the Glenelg River within an incised valley that rises steeply to the east and west. During major floods, the river inundates the town centre from the north. Approximately 80 properties were estimated to be at risk of above-floor flooding in a 1% AEP event based on 2014 mapping. Casterton's flood risk has been relatively well understood since completion of the 2011 Flood Study (CARDNO, 2011), floor-level surveys, and the 2014 (Jan) Flood Warning and Intelligence Project. In addition to standard flood intelligence outputs, that project produced the Casterton Flood Visualisation Tool, an interactive flood emergency response tool that integrates mapping and flood impact information to support tactical decision-making before and during flood events. Sandford is a satellite hamlet of about 130 residents located about 4km southeast of Casterton and about 6km upstream of the confluence of the Wannon with the Glenelg. Purpose The 2014 flood mapping is likely to underestimate current flood extent and depth under Australian Rainfall and Runoff Version 4.2 (ARR V4.2) climate change guidance. As a result, updates to flood-related planning controls, the Municipal Flood Emergency Plan (MFEP) and Flood Class Levels are required. ARR V4.2 makes it clear that increasing rainfall intensity must now be factored into Casterton and Sandford's flood risk mapping. Objectives The key objectives of this project are for the successful tenderer to apply the latest modelling techniques and climate science to consolidate and comprehensively update the flood risk information from the three mapping and intelligence development projects referenced above, and to produce a new dataset that ensures land use and development controls, and emergency response plans, for Casterton and Sandford account for climate change and remain fit for purpose. Scope Key outputs from this project include: Revision of the multiple flood peak/backwater effects assessment completed for Casterton in 2014 Completion of an equivalent backwater effects analysis for Sandford, accounting for ARR V4.2 guidance Revision of Casterton's Flood Class Levels Revision of the Casterton Flood Visualisation Tool Enquiries Jane Blackburn (Contractual): Office: +61 (03) 55712526, j.blackburn@ghcma.vic.gov.au Graeme Jeffery (Technical): Office: +61 (03) 55712526, tenders@ghcma.vic.gov.au