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Brooklands Lagoon is an important link in a chain of wetlands that runs along the central Canterbury coast. More than 90% of natural wetlands have been drained or destroyed in New Zealand. This lagoon is one of the few remaining natural wetlands.
Formation of the Estuary
In geological time, estuaries are short lived, part of a landscape which is constantly changing. In terms of our human life spans, the processes by which estuaries evolve often appear to be slow and difficult to distinguish.
Sediments washed down the Canterbury rivers from the Southern Alps after the last ice age slowly advanced the coastline eastward. As recent as 500 years ago an estuary formed at the mouth of the Waimakariri River mouth as sand carried to the coast by the Waimakariri and Ashley Rivers built up along the shore. A series of dunes formed in rows along the coast as the coastline crept outwards. The sand (now 20m deep) also created a spit, enclosing an estuary where fresh water from the Waimakariri and Styx Rivers mixed with sea water in the semi-enclosed basin. The sand spit protected the enclosure from strong shore currents and breaking waves.
European settlement began about 1840 on the Canterbury Plains and land has progressively been cleared and drained for farming, roading and townships destroying much of the coastal wetland area. In recent times changes to the estuary have sometimes been sudden and dramatic such as when the Waimakariri River scoured the area surrounding it during a flood in 1867 and during 1920s and 1940s when the position of the main channel at the mouth of the estuary changed almost daily. The present form of this estuary known as Brookland Lagoon has had considerable human help.
Until the 1940s, the Waimakariri River opened two-thirds of the way along the spit just north of where Spencer Park is today. In 1930 engineers dug a cutting through the sand hills creating a direct course for the Waimakariri River to the sea to lessen the risk of flooding. When the cut was opened in 1931 the river continued to flow through the lagoon. It wasn’t until the river flooded in 1940 that the mouth shifted 3km north to Kairaki. Even then the river did not use the cutting, and the remains lie buried deep in the sand some distance south of the present day mouth.
Brooklands Lagoon today.
Both the Waimakariri (Water of the mountains) and Styx (Otukaikino) Rivers enter the lagoon at its mouth. Although the lagoon changes with the tides, only storms or very high spring tides significantly mix the fresh river water with salt sea water. The southern half of the lagoon has a particularly low salinity almost all the time.
The lagoon provides a breeding habitat, wintering site and a feeding stop for birds migrating between the North and South Islands. The lagoon covers 270 hectares, is 4.5km long and 0.8km at its widest point. The lagoon is comprised of three areas:
The Southern Lagoon
The southern lagoon is a wildlife refuge where the high tide only covers the mudflats between two and four hours a day. Extensive areas of saltmarsh, consisting of rushes, sedges and salt tolerant grasses, surround shallow ponds. This vegetation provides protection for insects and coastal skinks. The salt concentration in the water is usually very low offering suitable conditions for invertebrates such as tunneling mud crabs, mudflat snails and rag worms. An observation platform, at the southern end of the lagoon, provides a place for observing birdlife, including Canadian geese, shoveler, grey teal and white-faced heron.
The Mid-Lagoon
The mid-lagoon area is a mixture of reed beds and open mudflats which, at low tide, form the main feeding ground for birds such as godwits, South Island pied oystercatcher (torea), caspian tern (taranui) and the banded dotterel (tuturiwhatu).
The Northern Lagoon
The main channel forms the northern lagoon. Shellfish, such as pipi and cockles, can be found in sandy patches close to the lagoon mouth. Eels (tuna), brown trout and yellow-eyed mullet, which can tolerate the higher concentration of salt water, feed around the mouth of the Styx River. The Styx River mouth is an important location for whitebaiting and an inanga spawning area. Shy and reclusive birds, such as the Australasian Bittern and Marsh Crake, live in the raupo wetland that forms a dense and impassable mat at the mouth of the Styx River. Unfortunately they are rarely seen due to their excellent camouflage colouring.
Spit Flora
The vegetation on Brooklands Spit is an example of a natural dune-land plant community. Cottonwood, flax, manuka, sand convolvulus and a couple of huge akeake and ngaio trees (with canopies nearly 10m across) can be found on the spit.
The Future
The lagoon is slowly silting up as sand and mud is carried into the lagoon when the Waimakariri floods or sand is blown into the lagoon off the sand dunes. As the lagoon becomes shallower, clumps of rushes trap the sediment and spread outward, reducing the amount of open water. Salt-tolerant plants become established, initially on the edges of the lagoon and later on the built-up islands formed by the rushes. Pollution from nutrients and effluent are contaminating the
lagoon. Nitrates, phosphates and animal faeces are being washed into the lagoon from the Styx and Waimakariri Rivers. Pine trees that were planted to stabilise the sand dunes are spreading into the lagoon, smothering native salt marsh species. Under these influences the lagoon may disappear in time, leaving little evidence of its existence.
Recreation Walks
Brooklands Lagoon Walk takes you along the western edge of the lagoon. At the southern end of the lagoon, wildlife observation platforms are located with views across the ponds and saltmarsh. At the Earth cache coordinates you will find a bird hide beside the walkway with excellent views over looking the Lagoon. At the height of the season more than 3000 birds may be at the lagoon, a feeding and resting place for 74 species of birds. Continuation of this walk will take you to Brooklands settlement. This return walk takes 3–4 hours.
The Waimakariri Walk will lead you through sand dunes to the east of the lagoon to the mouth of the Waimakariri River. At several locations along the walk you can wander down to the beach and back to the lagoon. The sand dunes are very susceptible to erosion and many areas have been planted to stabilise the area. It is important for walkers to keep to the tracks to avoid damaging the plants that protect the sand dunes. The Waimakariri River mouth is an important whitebaiting area and is popular for salmon fishing. This return walk takes 3–4 hours.
References: Owen, S J (Ed.). (1992). The estuary: where our rivers meet the sea and. Christchurch City Council Parks Unit
To log this cache visit the given coordinates at the bird hide on the Brooklands Lagoon walkway. Notice boards at S43° 25.758 E172° 42.419 and S43° 25.766 E172° 42.307 are good places to find useful information and maps of the area. Parking is available near these locations at the start of the walkway.
At the earth cache site consider the answers to the questions below and email the answers to the owner:
1. Note the time and date of your visit. Was the tide in, out or somewhere between?
2. Briefly explain in your own words:
What you think has happened to the former opening to the sea after the Waimakariri River mouth diverted to its present location in the 1940s. What action was taken by humans and what maintenance is required today.
3. Name a similar estuary in this coastal region which has two rivers flowing into it.
4. Either
(a) Take a photo of your GPS showing the coordinates and showing where you think the former opening to the sea might have been in the background overlooking the lagoon. Your photo can be downloaded with your log.
(b) Take a WP reading with your GPS resting on the Bird Hide window sill. Note the elevation and estimate the compass bearing to the former opening to the sea.
Logging your find online include only answer number 1. Downloading a photo if you have one is optional (see geocaching guidelines).
Additional Hints
(Decrypt)
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