mangawhai- piriki beach case study Flashcards
what is this case study for?
economic development case study- UNINTENTIONAL IMPACTS to coastline
where is the Mangawhai- Pakiri coastline?
north island of New Zealand (east of Australia). the coastline is east of AUKLAND and is 20km stretch.
economic development:
why is sand a useful resource?
why is this a good location for sand mining?
high quality sand can be found in nearshore of east coast beach of northern peninsula; sand is in demand for construction industry and beach recharge for Auckland (TOURIST ATTRACTION); economic growth has increased demand and pressure to mine the area
only 50km from Auckland- New Zealand’s most dynamic, economic metropolitan region; third of county’s population live there= produces 35% of GDP; coast attracts millions of visitors and is growing rapidly
what extraction has occurred in this area?
how has this effected the sediment budget?
sand mining for over 70 years- ended at Mangawhai beach but continues at Pakiri (mainly nearshore extraction). 1994-2004: 165,000mcubed extracted a year; now 75,000mcubed a year.
extraction rates at Pakiri are five times the inputs.
Recently, MacCallum Brothers applied to continue sand mining but where refused on the inshore of Pakiri beach.
the sand was deposited during the Haloscene and so sediment is a non renewable resource along the coastline as it is a closed system (has no majors rivers fluvially transporting sediment so mainly offshore sediment is deposited) so the removal of sand is not replaced. (UNSUSTAINABLE)
sand dredging can cause bottom blanketing (when deposited, stirred up particles like clay and silt form a blanket on the bed which can smother organisms + the ecosystem can be disrupted as animals can be caught up in process.
what depositional landform does Mangawhai have?
and Pakiri?
a spit- which helps provide protection to the harbour behind it.
sand dunes
how have the beaches, sand dunes, and spits been affected by the sand mining?
beaches are starved of sediment- become wider+ flatter (changed profile shape)- less effective at absorbing wave energy so eroded more by destructive waves.
spits and dunes rely on constant sediment supply so are vulnerable- dunes become susceptible to wind erosion.
how has the harbour been effected by mining and storms?
increased erosion due to loss of sediment on beaches so increased coastal retreat.
spit that protects harbour has been breached before (1978- 28metre breach which altered tidal currents and led to the sedimentation of Mangawhai’s harbour. less sand on the beach will make this more likely in the future.
project to restore equilibrium: clear waterways to enable unobstructed water flow so marine habitats are sustained, as well as enhancing recreational activites like swimming; sand blown to estuary is recycled+ used to restore spit’s distal end to provide protection to estuary from open sea.
how are erosion rates expected to change overtime? what will be the impacts of this?
Auckland regional council studies: higher erosion rates likely with declining protection from extreme storm events. coastal retreat already evident- partially attributed to sand extraction and complicated by climate change+ rising sea levels.
long term retreat: 35metres by end of century (higher than any other 123 beaches in Auckland).
what are the opposing views about sand mining on this coastline?
FRIENDS OF PAKIRI BEACH: organisation protesting/ appealing against the sand mining; want to ‘protect and improve the Mangawhai- Pakiri coastline’. want to protect the ‘remarkable’ sand dunes which are at risk.
MACCALLUM BROTHERS: over half the city’s construction requirements come from Pakiri- construction market will suffer if denied permit to mine sand. claim the extraction is ‘sustainable and has minimal impact on the local environment’ and efficient as can be ‘delivered to centre of Auckland in bulk’ easily.
