Infrastructure Strategy more scarce there are likely to be further requests to plant private land within key use herbicide in and near waterways expires in February 2019. In preparation for the Wairau floodways (especially the Opawa, Wairau and Taylor River floodways), and new resource consent application, significant monitoring work has been carried out requests for inclusion of these areas within the 1 in 100 year standard of the Wairau between 2015 and 2018 to both meet existing consent monitoring requirements and floodplain. Where ‘compatibility’ cannot be agreed there is a land purchase budget assist with the renewal application. The draft Marlborough Environment Plan includes each year for acquisition of private land. The budget has not increased. for the restricted use of herbicides for aquatic weed control as a ‘permitted activity.’ Viticulture is progressing westwards up the Wairau Valley. Land above the Waihopai Council expects some opposition from the community to the use of herbicides in and confluence has a lower standard of flood protection. A rate review within the term of near waterways. These considerations need to be weighed up alongside the impact of the Infrastructure Strategy may see further requests for an increased level of service in impaired drainage levels. If the Council were to move away from the use of herbicides the upper Wairau Valley. The strategy assumes that the current level of service this would result in a significant increase in operational costs. The strategy assumes remains materially unchanged and the rate review will align the funding and service the proposal will be adopted. levels. Most adjacent vineyard owners above the Waihopai confluence have now recognised Impacts of flood gates on fish migration that it is in their interest to leave an adequate fairway to provide for flood capacity and A total of 249 gravity outlets have been installed under river stopbanks. Simple to undertake edge protection works, which are typically some combination of rock and floodgates (or flap valves) are constructed on the outlet of these culverts to prevent willow planting to provide a good buffer between the active channel and productive water flowing back from the river. These floodgates, while essential for preventing the vineyards. Accordingly, since the floods of 2011 and 2012 Council has assisted some backflow of floodwater, adversely affect movement of whitebait and other fish into the property owners with the design and construction of new works, with the works to be drainage network. owned by the landowner. 1.3 Climate change Vineyard developments also appear to be causing increased runoff on the gently Managing the impact of coastal storm waves and sea level rise sloping, moderately impermeable land of the southern valleys to the south of New Renwick road and State Highway 63 to the west of Renwick. This will need to be on drainage managed with larger culvert sizes and increased maintenance of the drainage The lower Wairau Floodplain includes several thousand hectares which are less than channels. 2 metres above sea level. 1.2 Environmental expectations Sea level rise will impact on coastal erosion and drainage of this low-lying farm land. Weed control Average sea levels are predicted to rise by 0.3 m by 2050, which will impact on drainage gravity outfalls and require more pumping, alter general water table levels The blocking of drainage and stormwater channels by thick aquatic and terrestrial and may increase saline intrusion in the very low-lying areas. Sea level rise is also weeds is a major maintenance issue. Weed growth can reduce the hydraulic likely to lead to an increase in wave lap type erosion in the lower reaches of the performance of the channels by a factor of 10 reducing the drainage efficiency and Wairau and Opawa Rivers. increasing the flood risk to nearby properties. Regular annual removal using herbicide or by excavation is essential. The marine storm wave forces are a very important factor. In the past they have formed a sand bar, typically extending a kilometre to the north. The bar is formed by a The spread and extent of weed is increasing and new weeds regularly arrive in combination of marine forces, tidal flows into the Vernon Lagoons and river flows from the Marlborough. Conversely there is an increasing expectation from the public of more lower Wairau and to a lesser extent the lower Opawa. A training groyne at the mouth of weed removal and there is generally increasing environmental (resource consent) the Wairau River has helped to maintain an open channel to the sea and scour any sand constraints on the manner in which aquatic weed removal is carried out. accumulation. There is some evidence of increased accretion at the mouth of the Lower Opawa. The situation continues to be monitored and may require additional dredging. If The use of the herbicides is a key tool for maintaining both the drainage network and a required, dredging will be a significant maintenance cost. number of key streams infested with aquatic weed. The current resource consent to 2018-2028 Long Term Plan Page 208