sand mining along the mangawhai - pakiri coastline Flashcards
how far is the Pakiri and Mangawai beach from Auckland
83.5km
why is sand in demand for industry
due to it being an essential mineral resource, in the modern economy and has use in construction, such as concrete, glass and beach nourishment
how does this beaches location make it attractive for sand mining
it is of high quality sand, and is located within 100km Of Auckland, a main city in new Zealand
give an overview of past and current sand mining
- nearshore dredging on the coastline for 70 years
- 1994 - 2004 160,000m3 a year where extracted
- current rates = 75,000m3 a year (until 2020)
ratio of inputs (of sediment) to outputs
1:5
what impact is it having on coastal landforms (the mining
- beaches, are starved of sediment and thus have become wider and flatter
- more erosion, occurs, thus making dunes and spits vunerable
- foredune ridges, are undercut by wave action, developing steep, seaward facing scarps
what happened in 1978
- storms, caused a 28 meter breach at the base of the Mangawai spit and a second surge altered coastal currents, leading to sedimentation in the Mangawai harbour
what is happening in Mangawai harbour
sedimentation with shallow water, is presenting a flood risk to the waterfront community of Mangawai
what statistics for coastal retreat in the future are there
- long term retreat, is expected to be 35 meters, and the width of the erosion zone is to be between 48 and 111 meters
- this estimate, is higher than 123 of Auckland’s regions beaches)
what are humans doing to modify the landscape
- dredging and groyne construction, to help restore some equilibrium
- taking sediment, away from the Mangawai beaches, leading to more exposed erosion risks
what impacts on the costal system has this had/ is having on the landforms and coastal system
- long term retreat estimated at 35 meters
- erosion of sand dunes, and spits, due to less sediment thus more venerable to erosion
- pine tress, have increased erosion risk.
