The Marlborough District Council is a unitary authority which combines the functions of both a District council and Regional Council. Its area includes the Wairau fault, a branch of the Alpine fault, which divides Marlborough into two distinct geographical areas approximately north and south of the Wairau River. North Marlborough is characterised by a wet climate while south Marlborough has a dry climate. Annual rainfall ranges from 600 mm in the south to 2,600 mm in the north. The Richmond Ranges, Bryant Ranges and the Marlborough Sounds dominate North Marlborough, much of which is covered in native forest with some exotic forestry. The Marlborough Sounds are an example of a drowned mountain valley known as a ria. The Marlborough Sounds coastline accounts for approximately 20% of New Zealand’s entire coastline.