sand-mining along the Mangawhai- Pikiri coastline of New Zealand Flashcards
Mangawhai-Pakiri intro
- located in southern NZ, 5okm north Auckland
- sand essential mineral resource e.g. construction
- high quality sand resource occurs in nearshore zone - convenient for NZ’s metropolitan region: 1.5 mill pop (1/3 NZ), accounts for 35% GDP, 2015: 2.3 mill foreign visitors, outstanding coastal amenities, business, high-tech industry e.g.
Mangawhai-Pakiri - Offshore sand mining
-Nearshore dredging along the 20km coastline has operated for over 70 years. Although at Manhawhai it ended in 2005 it has carried on at Pikiri beach. Large proportion of this sand is replenishing Auckland tourist beaches and in the construction industry.
Mangawhai-Pakiri - Sediment Budget
- sand (non-renewable) deposited during Holocene
- few sizeable rivers in the area
- most sand thought to have been derived from offshore
- closed system: outputs of sand through nearshore mining not replaced by inputs from rivers and waves - extraction rates exceed inputs by river x5
- sand movement between major stores diminished
Mangawhai-Pakiri - Impact on coastal landforms
- rate of sand extraction unsuitable
- beaches startved of sediment: wider, flatter, less effective in absorbing waves
- higher energy waves erode beaches, dunes and spits vulnerable
- foredune ridges undercut by wave action, developing steep, sea-ward facing scarps
Mangawhai-Pakiri - Impact on coastal landforms
suggested increased rated of erosion likely in future: declining natural protection from extreme storms
- coastal retreat evident and attributed partly to sand extraction, and complicated by climate change
- long term retreat by end of century estimated at 35m,
- width of coastal zone susceptible to erosion varies from 48-111m (higher than any other Auckland beaches)
