Infrastructure Strategy This sets the standard for all of the Wairau floodplain. Flood protection and drainage Lower levels of flood protection costs are met by the benefiting ratepayers through a progressive targeted rate Significant rivers flow through the urban areas of Picton and Waikawa. While most (between 10% and 100%) dependent on the level of service provided to the area. All areas are protected from a 1:50 year flood event, this is not yet in place for the Kent but two of the floodways are up to the desired level of service. Works are underway to upgrade the lower Wairau and Riverlands Co-op floodways to complete the capacity Street tributary of the Waitohi River. The culverts where the river flows under Kiwi upgrades. Methods for increasing flood capacity include constructing stopbanks and Rail and the Interisland Ferry parking area are not able to meet the 50 year ARI for deepening the river channel through gravel extraction. Waitohi floodwaters and has resulted in flooding of upstream property. However, further upgrading of the culverts under the KiwiRail shunting yard and the final stage Stormwater flows in Blenheim and Picton and the effects of new under the Interislander car parking yard would be prohibitively expensive due to the disruption to the port activities and the reinstatement of rail and road infrastructure. urban development Port Marlborough and Kiwi Rail have some medium term plans for a major overhaul of The Building Act 2004 requires the floors of new buildings to be protected in a 1 in 50 the shunting yard and port facilities. The upgrade of the culverts has been deferred. . year return period flood event. The main challenge related to urban areas is to ensure that the system of drains, natural watercourses, pumping stations, and floodgates can The Council also provides emergency assistance to a large number of small river adequately cope with the stormwater runoff that occurs in a 1 in 50 year return period catchments that have not initiated flood protection schemes. These including the Rai flood. Valley, Wakamarina River, Pelorus River, minor streams in Havelock, Momorangi and Ngakuta Bays, Okiwi Bay and a number of other sites in the outer sounds. Flood This level of protection from stormwater flows is being achieved for many, but not all of hazard maps have been prepared for many of the catchments in rural areas. They are the dozen watercourses in Blenheim and Picton. provided to guide building and land use decisions for residents in areas where there are no flood protection works. Residential, industrial and commercial development is resulting in more impermeable (hard) surfaces, which reduces absorption of rain by land and increases the amount of Wairau land drainage areas and land use changes rainfall runoff into the small rivers, streams and drains via stormwater pipes. This is The Wairau drainage area covers 8,000 hectares of low lying floodplain, which is occurring in all urban areas, especially Blenheim, Picton, and Renwick. The Riverlands drained by 200 km of minor watercourses and 18 pumping stations. This land is to the industrial area is also expanding rapidly, and includes the rezoning of rural land to east of Blenheim and O’Dwyers Road. The Council is committed to avoiding more than industrial zoning. 2-3 days of ponding occurring in paddocks in these drainage areas. The proposed rezoning of the lower terrace (south of Gibson’s Creek) of Renwick from The drainage system consists of a mix of deliberately excavated drains and natural rural to large-lot residential was delayed until the flood risks were better understood. watercourses with floodgated culverts into the major rivers, and a series of pumping The proposed outcome is to allow some additional development but with some stations. upgrade works combined with building restrictions in high hazard areas. The Council recognised that Caseys Creek required a major outfall channel upgrade to enable The current drainage network was last formally reviewed in 2015. This review development of the rezoned Blenheim North areas provided for by Plan Change areas recognised there has been significant intensification of land use and subdivision, a 64, 65 and 67. For this reason, hydrologic and hydraulic reviews of the Caseys Creek trend towards viticulture and an expectation of a generally high level of service since catchment and Opawa River outfall were carried out in 2015. the Wairau Scheme was established in 1960. The additional stormwater discharge in the upper Murphy’s Creek catchment due to An extra 15.3km was included in the managed network of drains following the 2015 urban growth has been resolved through a collaborative decision making process. The review. This provides a drainage outfall to all rural land parcels greater than 1 hectare decision reflects residents’ concerns that additional stormwater would degrade the within the Lower Wairau Drainage Scheme area. quality of a spring-fed creek. The consultative process resulted in a satisfactory outcome for all the major stakeholders and will set a standard for future developments. Similar planning processes are likely to be required for remaining catchments. 60% of the land within the Lower Wairau designated floodway is owned by the Council while 40% remains private ownership. Private land owners are required to use the land in ways that are compatible with floodway management As viticulture land becomes 2018-2028 Long Term Plan Page 207