Wairau/ Awatere Resource Management Plan flood flows safely. There is no ‘do nothing’ option, and the economics of undertaking river control works on the main Wairau floodplain are a secondary issue. On the Wairau floodplain, works need to be built to control at least to a standard of a 1 in 50 year return period event to achieve the specified standard of the Building Act. Most urban areas of New Zealand have higher standards, a 100 year return period event being a common standard. Furthermore, some of the works, cannot sensibly be designed to a lower standard than a 1 in 100 year period event. The inter-related nature of the floodways and the floodplain areas at risk means that it is appropriate to have the same standard for all main floodplain rivers, except for some isolated pockets of identifiable flood prone land. Most of the Wairau floodplain is protected from floods in the major rivers up to 1 in a 100 year return period event. Exceptions to this are: • Within the stopbanked floodways of the rivers; • Riparian margins of non-stopbanked tributaries; • Areas where river control works do not yet protect land to the intended standard; and • Areas of ponded/gently flowing floodwaters where it is not economically feasible to construct flood protection works. These areas on the Wairau floodplain are depicted by a flood hazard overlay. The degree of hazard within this hazard overlay is site specific and varies from location to location. A flood hazard overlay is not drawn for areas outside the Wairau floodplain because of a lack of information on the flood hazard. Urban and industrial areas can have particularly high flood losses and any further expansion of such areas should be planned so as to avoid the flood breakout paths of extraordinary floods. Flood losses can also be reduced by timely warnings and emergency actions. Local stormwater also causes significant nuisance on the lower plains, which has been worsened by high stopbanks on the major rivers inhibiting drainage. Outside the main Wairau floodplain the benefit of carrying out structural protective works is lower and the costs of full protection often outweigh the benefits. 17.3.3 Methods of Implementation Council Maintain and improve river control works on the major rivers as Activities detailed in a suitable comprehensive integrated engineering plan. Maintain and improve a network of constructed channels and structures to deal with local stormwater (and drainage) as detailed in a suitable comprehensive engineering plan. Encourage retirement of eroding mountain lands. Prepare a flood response manual regarding emergency procedures during flood occurrences in association with Emergency Response. 17 - 6