Info
The Project
Computer controlled video monitoring of the Ashburton River Mouth gives viewers a running display of coastal conditions, a view of the lagoon, and an indication of river flow.
Environment Canterbury uses the information to help communities make better decisions about the long-term management of the region's rivers and coasts.
Previous data collection has been limited to occasional and irregular visual observations. The video camera system offers the council the first real opportunity to obtain reliable long-term data on river mouth dynamics and processes.
Environment Canterbury
Environment Canterbury is responsible for preserving the natural values of the region's coastal environment.
Environment Canterbury covers a land area of 4,222,000 hectares from Kekerengu in the north to the Waitaki River in the south. The Main Divide forms the western boundary and the region extends 12 nautical miles into the Pacific Ocean.
The main role of Environment Canterbury is to promote the sustainable management of natural and physical resources, primarily under the Resource Management Act 1991.
Environment Canterbury plans for and manages wide-ranging activities. Its work is split into 12 significant activity areas: the coastal environment, harbours, air quality, civil defence, energy, management of hazardous substances and waste, land, natural hazards, pests, public passenger transport, regional land transport, and water quality and quantity.
The Site
Environment Canterbury has stationed its Cam-Era station at the mouth of the Ashburton River, a braided waterway typical of most in the Canterbury region.
All rivers run to the sea – but the union of fresh and salt water is not always harmonious.
The Ashburton River meets the coast approximately halfway along the Canterbury Bight, a 135-kilometre stretch between Banks Peninsula in the north and Timaru in the south.
The river's mouth is similar to all those along the bight, with the main channel flowing into a long, narrow coastal lagoon. Tangata Whenua call these lagoons hapua, uniquely distinguishing them from other types of lagoons and estuaries.
Hapua are mostly fresh water, and run parallel to the coast, trapped by a long narrow barrier beach. They are not permanent, taking shape when the river mouth is pushed north by waves transporting sand and gravel. They go through a distinctive sequence of creation and destruction.
When river flows are low, coastal processes dominate, pushing sand northward and shifting the river mouth with it, but when rivers are in flood, the impounding spit is prone to breaching directly opposite the main channel of the river. Previous research suggests this sequence can happen up to once a year on the Ashburton.
The average annual flow in the Ashburton River is only about 17 cumecs (cubic metres per second) at the mouth, with flows often dropping to below six cumecs, particularly from February to April. High flows are common from October to January when spring snow melts in the Southern Alps.
During periods of low flow (usually less than four cumecs), extreme displacement of the river mouth can lead to prolonged periods of mouth closure.
River mouth closure has many associated problems and can upset fish spawning cycles, lead to a decline in water quality and increase the risk of flooding and cliff erosion.
Mouth closure is a natural process, but the duration and extent can be affected by human activities. Understanding river mouth dynamics is essential to the sustainable management of Canterbury rivers.
