Environment Canterbury monitors 172 sites (as at February 2008) throughout Canterbury from the Clarence River in the north to Danseys Pass in the south. The western-most sites are along the Southern Alps/Kā Tiritiri o te Moana.
There are 71 rainfall sites that are measuring intensities in 7.5 or 15 minute intervals depending on their proximity to the Southern Alps/Kā Tiritiri o te Moana. The earliest records available are from Ashley Gorge which dates back to 1949, and the Arthur's Pass site which commenced records in 1955.
The data from these sites can be used to assess storm intensities, provide the basis for flood warnings and provide daily, monthly or annual rainfall totals.
The 101 water level sites are recording a variety of river types. There are wide, braided, gravel-bed rivers, which have their headwaters in the Southern Alps/Kā Tiritiri o te Moana (e.g. the Waimakariri, Rakaia and Rangitata); narrower, braided, gravel-bed rivers fed from the foothills (e.g. the Pareora, Selwyn/Waikirikiri and Waipara); and small spring-fed streams. The earliest record of water level dates back to 1935 at Rakaia Gorge.
Flows are also measured at 81 sites, and this information is combined with the water level data to produce a continuous flow record. There is also historic water level and flow data for sites that are no longer operating.
Gauging data (a measurement of the stream’s width, depth and velocity) are also available for many small creeks and streams in the Canterbury area. It is dependent on each site as to how recently and frequently these have been gauged. Even if there are a large number of gaugings for a site, the flows won’t necessarily be indicative of the stream, as they are not measured continuously.