and Koromiko on numerous occasions with many smaller coastal settlements and rural areas being equally affected. • Millions of dollars of damage can occur during a single event ie; Wairau River Flood July 1983. In severe cases businesses may not be able to recover financially. Built • Major storms can cause simultaneous flooding across the entire region and thus the impact can be widespread. Some floods may also take many months to completely rectify any damage. Potentially, the most threatening flood issue facing the region at present is a large flood (ie; >1:100 years) occurring in the Wairau River catchment. This would impact severely on the multitude of vineyards grown on the flood plain. Natural: • Alterations to river channels including bank erosion, channel scour or build-up and channel diversion. Sediment-debris deposition, and dispersal of chemicals, effluents (dairy farm ponds, septic tank discharge sites, water entering town sewage networks) and rubbish (from tips) across floodplains. • Damage from the 2016 Kaikoura earthquake has also impacted river levels and floodbanks, changing the profile of flood risk until repairs were undertaken. It is likely that future earthquakes will have similar impacts. How do we • Most of the major rivers have flood protection works. The most substantial works manage this risk? in the region protect the Wairau Plains, Lower Wairau Diversion, Renwick and Blenheim townships and consists of three networks. 1. Wairau River Protection Works: 1:100 year stopbank protection designed for 5,500 m³s-1 flood – allowing for 900 mm freeboard. 2. Ōpaoa/Taylor River: Protection works consist of an engineered dam and a 1:100 year stopbank network through the Blenheim Township. Designed flow 170 m³s-1 with 400 500 mm freeboard. 3. Omaka/Fairhall/Upper Ōpaoa/Roses Overflow: Protection works consist of 1:100 year stopbank protection to Hawkesbury Bridge (Omaka) and New Renwick Road (Fairhall). • Telemetered river level recorders and high altitude rain gauges operate in most of the major catchments, providing an early flood warning system. The maximum warning time offered is around 3½ hours, depending on the catchment. Most of the focus has been on the Wairau River, because of the population base and value of the land. What more • Impact assessments of a flood greater than 1:100 years. should we be doing? What is the future • With climate change expected to bring more extreme weather patterns it is likely risk? that the frequency of severe rain storms will increase. Marlborough Civil Defence Emergency Management Plan, 2017-2022 Page 97