The given co-ordinates will take you to Palmerston North's Hokowhitu Lagoon, a meander cut-off of the Manawatu River.
Meanders
Rivers, particularly in their middle and lower reaches, as they flow over more gently sloping ground, begin to curve back and forth across the landscape forming meanders. These are caused by both erosional and depositional processes. Sediment is eroded from the outer curve of each meander bend and deposited on an inner curve further downstream. This causes individual meanders to grow larger and larger over time.
Meandering river channels are asymmetrical. The deepest part of the channel is on the outside of the bend and, because water flows faster in deeper sections and on the outside of the bend the river travels towards the bank, undercutting occurs. Material is eroded from that bank. In the shallow areas on the inside of the bend the water flows more slowly and can't therefore carry so much sediment, thus material is deposited along this side.
River bluffs and cliffs can eventually occur on the outer bank, while a point bar (a gently sloping 'beach' of sand,gravel,pebbles) forms on the inner bank.
The term meander comes from the ancient Greek name for the Maeander/Meander River (in SW Turkey now) which was celebrated in ancient times for its convoluted course. Its name came to be descriptive of such rivers. The associated river god is also called Meander.
Oxbow lakes
When a meander grows so big and loopy that two bends of the river join an oxbow lake is formed. This happens when a breach allows a chute channel to connect these two close parts of the bend. The point where the bends intersect is called a meander cut-off. The main river continues to flow now straight on along the new channel while the loop is gradually cut off. As the flow of water reduces here sediment builds up. This can eventually completely fill the oxbow lake and it can disappear. If a water supply is maintained, eg; from a side stream the lake will remain.
The Hokowhitu Lagoon is an example of unreliable water levels in an oxbow. To maintain the level for recreational purposes the City Council installed an artesian bore in 2008. Then in 2014 the lagoon drained due to an earthquake and it took many months to get it back to a good level.
Palmerston North's Oxbow Lakes
When Europeans began settling in PN there were five oxbow lakes in existence. Maori had used them for food gathering ( especially eels) and the surrounding bush for birds and berries. However, as settlement continued, four of the lakes/lagoons were drained. Only the Hokowhitu Lagoon remains today.
The five local oxbow lakes:
1. Te Ngutu Lagoon - corner of Churchill Ave, College & Albert Sts
2. Ruahine or Hokowhitu Lagoon - also known as Centennial Lagoon
3. Awatapu Lagoon - cnr Botanical & Park Rds
4. Un-named lagoon - cnr College St & Kent Cres
5. Awapuni Lagoon - between Awapuni Racecourse & Pioneer Highway & Maxwell's Line
Additional note: Currently, another oxbow, or series of them, that was outside the city previously is now joining the urban landscape as housing development expands along Napier Rd between Sutton Place and James Line.
There is a series of oxbows along the base of the old river terrace on what was previously industrial or mainly rural land. They were known to the Maori as Whakapokapoka Lagoon. The City Council will take over management of the whole lagoon protecting biodiversity, managing water run-off, developing recreational areas like walkways and so on.
Information from the Manawatu Standard, 18.11.19. https://www.stuff.co.nz/manawatu-standard/news/117447574/oxbow-creates-water-feature-for-proposed-new-neighbourhood
References used (all online):
www.alevelgeography.com/meanders/
www.onegeology/earthprocesses
"Notes on the History of the Hokowhitu Lagoon" by Ian Matheson - online: manawatuheritage.pncc.govt.nz
"Atene Skyline Vista",GC3Y54H, an Earthcache by edvern - a great example of a meander cut-off of the Whanganui River.
Activities/Questions:
Qn 1. Using the given co-ordinates go out onto the footbridge across the Hokowhitu Lagoon. Look up and down the lagoon. What do you observe about its general shape along its length?
NB. Optional Activity: If you are interested in some further details on this lagoon, look at the information boards - one at the eastern end of the footbridge, the other at WP2 (S 40 22.232 E 175 37.777).
Qn 2. Variable water levels are common in oxbows. (a) To maintain this lagoon for recreational purposes what was installed in 2008? (b) What happened in 2014 that caused the lagoon to drain?
Qn 3. What are the two main processes that form meanders, and describe briefly how each contributes to this formation?
Qn 4. What causes meanders to become oxbow lakes?
Qn 5. Hokowhitu Lagoon is the only oxbow lake still remaining in PN. Name one other and where it was located?
NB. Optional Activity: For an interesting aerial view you might like to try bringing up the google map (satellite view) from the cache page and follow along the Manawatu River from PN to the sea. It gives a great overview of the river's many meanders, including places where the loops look likely to become future cut-offs. You can also see evidence of many old oxbows - most just shapes on the land, some still containing water
Please send your completed answers to the cache owner and wait for approval to log the cache.