Infrastructure Strategy Wastewater However, the existing wastewater treatment plants will be seriously impacted by 700mm of sea level rise, which is predicted to occur by 2100. • The NZCPS is likely to influence the outcome of the 2017 consent applications for the Seddon and Havelock sewage treatment plants. The resource consent for the Rising water tables will affect the Council’s ability to continue irrigating land with Blenheim sewage treatment plant is due for renewal in 2023. Capital upgrades to • the plants are planned to meet the expected consent conditions. treated wastewater from the Blenheim wastewater plant (when the land is too wet and/or the water table is high.) Stormwater • More frequent and intense storms will increase the risk of sewer overflows in • Consolidation and updating of the stormwater resource consents is a primary urban areas via stormwater leaks into the sewer reticulation. objective of the Blenheim Stormwater Strategy. The NPSFM and NZCPS requirements will be reflected in the resource consent conditions. Stormwater Water Supply quality control measures are being installed on new sub-divisions and expenditure Increased frequency and duration of droughts will put strain on the water sources will be required to upgrade some existing discharges to freshwater and the coast. • particularly where aquifers are shared between public water supply and production Roads water. • The GPS may influence levels of service for Marlborough roads. • Increased droughts will place additional demands on water treatment and reticulation plant. 3. CLIMATE CHANGE Rivers and land drainage The current advice from the Ministry for Environment is outlined below. • Council may need to dig larger drainage channels, increase the height of existing Temperature: by 2040 temperatures are likely to be 0.7C – 1.0C warmer. Theo o and provide added bank protection to cope with increased rainfall intensity. number of days when the temperature exceeds 25C is increasing and the number ofo frosts are decreasing. By the end of the 21stcentury these very hot days could rise • As the sea level rises, pumped outfalls are also likely to be required to assist with from 6 days to 38 days per year and frosts could decrease from 19 to 7 days per year drainage of flat, low-lying land on the Lower Wairau plain where we can no longer respectively. rely on gravity to achieve discharges to the sea. Rainfall: The incidence of summer rainfall in Blenheim and extreme rainfall events are • More frequent high intensity rainfall events will place greater demands on the both likely to increase. However, there will be some regional variation. stormwater system. Urban drainage reticulation will be tested, detention areas will temporarily fill with storm water and overland flow paths will need to be utilised. Precipitation in the winter is likely to fall as rain rather than snow. This may increase Transport river flows during the winter with subsequent potential for flooding. Less snow melt could decrease river flows during spring, reducing the water available for abstraction. • Some road drainage will need to be upgraded. Sea level rise: Average sea level rose by 1.7mm per year over the last century. This • Bridges and culverts will need to be designed to cope with the increased flows. rate has increased over the last 20 years and is predicted to continue to rise. The effects are exacerbated by changing tide patterns and an increase in storm surges. • Slips are likely to become more frequent after heavy rain. Additional resources will be needed for road clearance and the securing of unstable hillsides. We will also Implications for our assets need to proactively regrade and secure steep roadsides. Wastewater • Marlborough’s wastewater treatment plants can continue to operate with a 300mm increase in sea level rise, as is predicted to occur over the next 30 years. 2018-2028 Long Term Plan Page 177