Wairau/ Awatere Resource Management Plan Policy 1.3 Recognise prospecting and small-scale exploration as activities with limited environmental impact for any area not having particular ecological significance. The Council believes that provided appropriate measures are undertaken during the process of establishing extractive industries, these can be successfully accommodated within the Plan area. 24.4 Issue The effectiveness of river channels and their ecology is affected by the build up (aggradation) of gravel and sediment by natural processes; or also affected by excessive depletion, often by commercial extraction, of this valuable resource. The control of gravel and sediment extraction from a river has environmental, river control and commercial consequences. Rivers are dynamic natural processes carrying sediments eroded from their catchments out to the sea. Sometimes the sediment transport carrying capacity of the river is greater than the supply rate, which then can lead to erosion of its riverbanks and riverbed and possibly changes to ground water recharge. This effect can be accentuated by excessive gravel extraction from the river. Where a river reach is in balance with no net deposition it is said to be in regime. The natural geology of the catchment, tectonic activity, whether the sea is readily removing sediments from the river mouth, and changes in flow regime are the major factors affecting whether a river is aggrading, eroding or in regime. Catchment vegetation is another, usually secondary, factor. For the main Wairau floodplain the coastline is prograding and this is a major factor in gravel building up in the Wairau River channel downstream of Jeffries Road. The aggradation of gravel in this reach is also probably affected by the change in flow regime with the blocking off of the Opawa channel at Conders Bend in 1914. Sediment deposition is occurring for the Lower Wairau since the change in flow regime with the Wairau Diversion construction in 1964 and its continual enlargement. Conversely the Awatere River is entrenched below a historical floodplain for most of its length by a combination of the sea removing its transported sediment and geological factors. The upper reaches of the Wairau River and its tributaries are more dynamic with waves of gravel and sediment moving through due to storm activity. These upper catchment river reaches appear to have a cyclic aggradation/ erosion pattern with no clear indications of channel aggradation. The same can be said for the Clarence and Waima (Ure) River systems. Gravel and sand is a valuable commercial commodity. In the Wairau/ Awatere area the amount of gravel and sand required by industry can at present be adequately supplied from the riverbeds. The manner in which gravel and sediment is extracted can also be seriously detrimental to environmental and ecological factors associated with the riverbed. 24 - 2