Chapter 14 - Land Disturbance 14.0 Land Disturbance 14.1 Introduction Much of the Wairau/ Awatere Plan area is hilly and mountainous. Large areas of the hill and mountain country is extremely eroded or vulnerable to the effects of land disturbance activities. Land clearance and earthworks such as burning, crushing, logging and tracking can increase the volumes of sediments and nutrients entering the waterways and increase the amount of debris in streams. If poorly managed these processes can make land even more erosion prone. The Marlborough District has previously had land disturbance controls in place. Firstly under the Soil and Rivers Control Act of 1941 (and subsequent amendments), and more recently a Land Disturbance Regional Plan introduced and made operative by the Marlborough District Council in April 1995. The fundamentals of that Land Disturbance Plan have been incorporated into this Plan and form the basis of the land disturbance objectives, policies, methods and rules contained herein. 14.2 Issue The potential for land disturbance activities to reduce land production potential, damage the natural and cultural values of the land, or increase likelihood of erosion, flooding or deposition in water. 14.2.1 Effects of Sediments Soil that has been exposed by vegetation clearance is more exposed to rain, wind and frost. If at the same time, it has been loosened by cultivation or excavation it is more easily eroded by the elements. Eroded soil usually moves downhill (the exception is soil eroded by wind) and eventually enters a river or the sea. There the finer soil will settle, a process called sedimentation. Sedimentation can cause damage to marine and freshwater ecosystems, and may reduce the quality of the water for instream values and uses such as drinking or irrigation. Larger soil particles including gravel and cobbles, can similarly be eroded and deposited in downstream river channels thus reducing the waterway area and leading to flood overflows. 14.2.2 Effects on Natural and Cultural Values of the Land (Including Landscape) Buried archaeological, cultural and historical artefacts are at risk of destruction from land disturbance. For example, excavation and cultivation may disturb waahi tapu or obliterate pa sites. Land disturbance can also change the landscape. Excavation and vegetation clearance change landforms and may take years to revegetate. Indigenous forest and grasslands can be destroyed by burning or clearance. 14.2.3 Effects on Natural Hazards Excavation can destabilise hill slopes. Excavation makes cuts into hill faces which may then collapse. In high rainfall environments, cultivation and removing vegetation may increase the risk from erosion. Sedimentation can also block waterways and flood channels, thereby increasing the risk of flooding during periods of high flow. 14 - 1