Wairau/ Awatere Resource Management Plan 17.4 Coastal Hazards 17.4.1 Issue Natural hazards can compromise human wellbeing and safety and cause damage to habitat, amenity values, property and infrastructure. Hazards can be aggravated by inappropriate land use management practices and activities. Climatic Change During the last decade there has been increasing evidence that a concentration of “greenhouse” gases in the earth’s atmosphere may be changing the world’s climate. In the coastal marine area most of the focus has been on the effect of sea-level rise, however for East Marlborough Coast the greatest impact may be due to an increased frequency or size of storm events. Historically sea-level rise has been minimal around New Zealand. Along the East Marlborough Coast the continual sediment movement and seismic activity has countered any sea-level rise with many of the gravel sections continuing to grow seawards. This is expected to occur if sea-level rise continues at approximately the same rate. This may not be the case though for the Wairau Lagoons. The stopbanks constructed around the Lagoons will limit the natural migration of the wetlands and inundation of the drier areas of the lagoon may occur. Provision could be made to allow for the natural migration of the estuaries and wetlands in the event of sea-level rise but this may be inappropriate for the Wairau Lagoons because of the developed nature of the area behind the stopbanks and the importance of the stopbanks for flood protection. Changes in the frequency and size of storm events may alter sediment movement and result in areas of increased erosion and/ or marine inundation. The possibility of this occurring has not been studied for the Marlborough area but, as many of the gravel beaches along the coast have the ability to rapidly replenish themselves after storm events, moderate storm events are not perceived to be a major issue. Catastrophic events could, though, result in the penetration and/ or destruction of the banks fronting the Wairau Lagoons and Lake Grassmere. This could result in the formation of large shallow embayments. Seismic Activity and Tectonic Movement The East Marlborough region, especially the Wairau Valley, is a very active seismic area and contains the Wairau, Awatere and Ward faults. Seismic activity can result in a number of different natural hazards including inundation by the sea, salt water intrusion into freshwater aquifers, and tsunamis. The 1848 earthquake was a particularly large earthquake resulting in subsidence of the sediment in the Wairau Lagoons by up to 1.5m, thus enlarging them considerably. South of White Bluffs the tectonic movement has been historically upwards with more rapid uplift south of Cape Campbell. This trend is expected to continue. However, sudden subsidence could result in marine inundation of Lake Grassmere. 17 - 8