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This section focuses on the City’s natural and physical environments. It is divided into two parts. The first briefly describes the City’s natural and physical resources while the second examines the effects of human activity on the environment and looks at residents’ perceptions of both the built environment and heritage features.
Christchurch City covers an area of 45,239.7 hectares. It is roughly circular in pattern with a radial network of roads. The City is bounded by the Port Hills to the south and the Pacific Ocean to the east. The northern boundary of the City is defined by the Waimakariri River.
Christchurch is situated within two distinct geological regions, the Port Hills and the Canterbury Plains. The Port Hills are part of a series of large eroded extinct volcanoes, the vents of which now form the harbours of Banks Peninsula.
The main rock type of the Port Hills is basalt, covered by a layer of loess (windblown dust) originating from the Southern Alps and Canterbury Plains. The Port Hills soils are yellow-grey or yellow-brown earth derived from basalt or loess and generally of low fertility. Most of the soils are susceptible to erosion, particularly soil creep and gully erosion.
The Canterbury Plains have been formed by outwash gravels deposited by rivers originating in the Southern Alps. The majority of the City is located on the shingle fans deposited by the Waimakariri River. Sand dunes and coastal sandflats border the plains to the north east. A low lying peaty area occurs between the coastal dunes and sandflats flats, and the plains.
There are a range of soil types found within the City. These include the fertile and versatile Waimakariri and Selwyn silt loams and sandy loam textures, soils which have natural drainage problems, and soils which are stoney to very stoney, poorly drained and susceptible to wind erosion.
The Alpine Fault lies approximately 100 km west of the City and the Porters Pass fault zone only 50 km to the west. Both of these faults are active and capable of generating major earthquakes.
There are very few remnants of native forest remaining within the City. Some pockets do exist on the Port Hills (largely in gullies) while Riccarton Bush is the last example of wetland podocarp forest in Christchurch.
Indigenous grassland (albeit modified), with scattered scrubland and trees are located in areas adjacent to the Waimakariri River and on the Port Hills. Other habitats include exotic forestry plantations, urban parks and gardens. The largest of these are the centrally located Hagley Park and Botanic Gardens.
Two micro-climates exist in the Christchurch area. The Port Hills, with a higher humidity and a greater seasonal variability of rainfall, and the plains, which are drier and have more evenly distributed rainfall. The Plains are affected by the dry, strong north westerly winds which dry out the soils, increasing their erosion potential and placing limits on forestry and agricultural productivity.
A summary of the City’s main climatic features are as follows:
Temperature
Mean daily maximum
Mean daily minimum
Mean annual maximum 320C
Mean annual minimum -40C
Sunshine
Annual average sunshine hours
Rainfall
Average rain days 1mm or more 87 per annum
Average annual rainfall 655 mm
Relative Humidity
Average relative humidity
Frost
Average days of screen frost (minimum air temps. less than 00C)
Winds
Average number of days with gusts reaching 63km/h or more
Average number of days with gusts reaching 96km/h or more