The West Coast Region of New Zealand
The West Coast Region (Te Kaunihera Whakakotahi o Te Tai Poutini) extends over a distance of 600 km from Kahurangi Point in the north to Awarua Point in the south – greater than the distance between Auckland and Wellington. The region is bounded in the east by the Southern Alps and in the west by the Tasman Sea and has a land area of 23,000 square kilometres.
The Coast has a diverse geography and can be described as a region of rainfall and rivers. The Alpine Fault runs the entire length of the region and with its unique geology and dramatic uplift, the resulting product is a very dynamic regional landscape. Some three quarters of the region is in indigenous forests. The region is home to a number of national parks including having parts of its region within the South-West New Zealand World Heritage Area; a recognition that places this part of New Zealand among the worlds premier and enviable natural landscapes.
The West Coast is well endowed with a number of natural resources such as pounamu, sphagnum moss, coal, gold, timber, pastoral, fisheries including whitebait along with the largest area of indigenous forest and a largely unmodified environment in the country. The economy is largely underpinned by resource based industries. However, other industries such as tourism have now grown into an important component of the regional economy.
The West Coast has fewer extremes of climate than the east coast regions. Greymouth’s sunshine hours of 1980, and Hokitika’s of 1964 are ahead of Auckland’s 1825. But we also receive a generous and reliable rainfall. Near the Main Divide it exceeds 8000 mm annually – declining to a more manageable 2000 mm at the coast. At high altitudes there are snowfalls all year round. In the region’s southern parts this contributes to glaciers that reach to within a few hundred metres above sea level.
Surface winds do not reflect the prevailing westerly flow at higher altitudes. More sheltered locations provide a variety of different microclimates, with warm moist north-westerlies common.
Weather systems crossing the region produce marked changes in wind direction and air mass characteristics. The approach of fronts produces a warm moist airflow of tropical origin. The passage of a front is usually followed by a cold dry airflow of polar origin. In both cases the air travels considerable distances over the open sea, the nearest land mass being over 1600 km distant. As a consequence, the air is very clean and pure.
A low pressure area to the east of the South Island may promote an easterly airflow over the region. On these occasions, particularly in winter, strong easterly winds may descend down major river valleys. In more sheltered inland locations, cold air may be trapped in valleys forming temperature inversions.
Winters are often sun-filled, with few frosty mornings, even in south-westland, while springtime is traditionally wetter. Northern areas such as Karamea border on sub-tropical.
Land and soil
The West Coast has been described as a region of mountains, rainfall and rivers. These features combined with the processes of uplift and erosion have resulted in a landscape of unique character, two thirds of which is mountainous.
The Alpine Fault runs most of the length of the region. East of the fault are deeply dissected mountain ranges. To the west, rivers and streams are steeply graded – the distance from source to sea usually less than 50 kilometres. Towards the coast alluvial and beach deposits occupy a 10-15 km wide strip which extends inland along river systems. Plains areas are, with some exceptions, generally localised and composed of outwash silts and gravels. They are subject to frequent flooding.
With most of the region being mountainous or hilly and forested, soils are generally leached podsolised yellow brown earths or gley podsols which are shallow in depth and low in fertility. The combination of steep slopes, high rainfall and seismic activity commonly result in high erosion rates.
At high altitudes the crests of the ranges are frequently bare.
In the valley floors the soils are recent gley or organic soils. On higher terraces these are the poorly drained and badly leached pakihi soils.
On lower lying sites closer to valley floors, the soils are more freely drained and have a higher natural fertility. These soils are more productive and form an essential element in the region’s agricultural economy.