Infrastructure Strategy Potential impacts of climate change on flood flows Option to address it Implications of the options (financial and non- Climate change will also alter the frequency and severity of flood events. Current financial) advice to Council is that by 2050 a given 100 year or 1% AEP flood will increase in climate change. Uncertainty as to level of flood protection and risks. size by 10 – 15%. That means the current 5500 cubic metres per second (cumecs) Damage to property and crops. Wairau flood could increase to over 6000 cumecs. However, flood flows are likely to be variable — in some catchments they may actually decrease, while increasing in other Possible reputational damage. areas. The various scenarios will be investigated through a detailed technical review to commence in 2019. The potential effects on levels of service and options will be Lower levels of flood protection – Kent Street tributary, Picton presented to the Council for consideration (see options below) Option to address it Implications of the options (financial and non- financial) 2 Options and implication Preferred Option Benefits 2.1 Levels of service and increasing demand for flood Status Quo No significant upgrade work protection Undertake minor Cost savings if culvert construction and reinstatement Level of flood protection for the Wairau floodplains improvements to culverts can be coordinated with port refurbishment. Option to address it Implications of the options (financial and non- to improve flow but accept Helps manage rate increases. financial) additional flood hazard as culverts can achieve only Costs PREFERRED OPTION Benefits around 60%-70% of 100 year flood flow. Properties exposed to increased flood risk. Maintain and upgrade the Recognises agreements reached through the Wairau Additional cost to new development of increased floor floodways passing across Rivers Floodway Management Plan in 1994. Defer the culvert upgrade the main Wairau until works can be levels due to lower level of flood protection floodplain to provide a Certainty that building and land use planning can coordinated with Kiwi capacity for flood sizes of proceed to an agreed standard. Rail/Port Marlborough up to a 1 in 100 year Costs upgrades to port return period for the Wairau river and other Financial costs of ongoing upgrades outline budget to major floodplain rivers of 2028 of $10.5M. the Lower Wairau, Wairau Environmental impacts of river control works. Upgrade culverts at Benefits Diversion, Opawa, Taylor, earliest convenience Omaka, Riverlands Co-op Improved flood protection for properties in Waitohi and others. Stream catchment. Maintain the existing level Benefits Costs of protection, but do not Avoids the need for flood protection upgrade works. Cost to undertake works and restore port facilities increase the level of estimated to be in excess of $10M. protection to meet a 1 in Costs 100 year return period if the magnitude of floods Community consultation and consent required. increases as a result of 2018-2028 Long Term Plan Page 209