Headwater Springs

Springs are surface water sources fed directly by groundwater – water that travels through gravels below ground. The Christchurch District Plan definition of a spring is “the point where groundwater, driven by artesian pressures, emerges to the surface and forms a pool, the head of a water body, or discharges within or into a water body on a permanent or intermittent basis“. Because springs are fed by groundwater, springs have a very constant temperature and flow rate in comparison to other surface waters such as rivers.

An aquifer is underground body of rock or sediment that holds water.  This water can be either confined, which means the water reservoir is covered with a layer of impermeable rock or clay, or unconfined which means there is a permeable layer of rock or soil between it and the surface.

The mechanism driving the discharge of most Christchurch springs. Click to enlarge

The Canterbury Plains have been built up over tens of thousands of years with hundreds of metres of gravels, silts and sands deposited by rivers. Rain and irrigation water falling onto the plains infiltrates through the soil into the little gaps between the gravels and sands to become groundwater which flows down the gradient of the plains towards the sea. The rivers also lose water to groundwater as they flow across their gravel beds.

Close to the coast around Christchurch, there are layers of finer silts, peats and sands at the surface from old beaches, estuaries, swamps and lagoons from when the sea level was higher. Groundwater finds it harder to flow within these sediments so at the edge of this ‘confining layer’ it is either pushed up to the surface as springs or continues to flow within the aquifer beneath.

We see this in the spring-fed streams of Christchurch, where the western parts of the streams at the edge of the confining layer have groundwater slowly seeping into the stream beds so that it can be hard to identify where the stream starts. In dry periods, the top of the groundwater, which we call the water table, is lower and the upper parts of the stream beds are often dry.

As the spring-fed streams flow eastwards, some of the groundwater which flowed under the confining layer can pop to the surface through local weaknesses in this layer. This water is under artesian pressure so when it comes to the surface as a spring it can sometimes be as quite spectacular bubbling sands.

Recharge from the Waimakariri River is a significant source of water to Christchurch spring-fed streams. The streams closest to the Waimakariri River, the Otukaikino and Pūharakekenui Styx Rivers, have water most chemically like the river. Streams more distant to the Waimakariri such as the Ōpāwaho Heathcote and Hiritini Halswell Rivers have more water sourced from rainfall recharge from the plains above. The groundwater feeding the springs can be sourced from large distances away, so the quality of the water is impacted by land use over large areas. Christchurch spring waters have been dated at between 2 and 14 years old.

ŌHRN began testing for nitrate leveks in one of the springs on Bunz Stream in 2024 as part of an ecological baseline study. Since that study, every three months we conduct the same test in the same spring to track changes over time. Find out about the results

ŌHRN began its exploration of springs in 2020 with a review of the NZ scientific literature on springs.  There was not much to read.  We then, with funding from Environment Canterbury, undertook an ecological baseline study of one exemplar headwater spring. We now continue that journey to monitor aspects of that spring, to discover more about it and to protect the headwater springs of the Ōpāwaho Heathcote River.  See the diagram of our journey below.  Click it to enlarge.