Coasts KQ4-Mangawhai-Pakiri, New Zealand Flashcards
Give 2 uses of sand
- Concrete manufacturing
- Beach replenishment
Why is Sand so important to Auckland?
Auckland is located 50km south of Mangawhai-Pakiri, its New Zealand’s most dynamic metropolitan economic hub, accounting for a 3rd of the total population and over a 35% of total GDP, its growing rapidly, not only in finance and banking but also tourism, centred around its coastal amenities, 2019 saw over 2.93 million tourists (80th place).Sand is vital for beach nourishment and construction
How much sand was dredged between the years 1994 and 2004 as an estimate? Are the rates still the same>
Estimated 164,000 m^” year, although mining stopped at Mangawhai in 2005, it continued at Pakiri, with an estimate of 75,000 m^2 a year until 2020
Extraction rates at Pakiri exceed inputs by a factor of
5
Describe why sand is a non renewable resource at Mangawhai-Pakiri and what the overall effect of mining is due to this.
Deposited during the Holocene, past 9000 years, with few sizeable rivers in the area, it is thought to have been derived from offshore sources, coastal sediment budget here is thought to be closed. Thus outputs are not replaced by enough inputs from rivers or deposition by waves, thus the total sand supply is diminishing, as well as flows between the 2 major stores
How has the sand extraction resulted in erosion and increased vulnerability of land forms?
Extraction has led to more wide and flatter beach, so its less effective at absorbing waves, higher energy waves thus erode beaches and increase vulnerability of dunes and spits.
How have foredune ridges been effected?
They have been undercut by wave action, forming steep seaward facing scarps, loss of vegetation makes them more susceptible to wind erosion
In 1978, How did storms impact the coastline at Mangwhai and the local community and how was this restored?
28 meter breach after a storm, formed, at the base of Mangawhai, and a second breach altered tidal currents, which led to the sedimentation of the harbour, producing shallower water, threatening the waterfront community with flooding, dredging and groyne construction as helped to restore balance in some ways
Studies about the area by the Auckland regional council have shown what…
They have shown increased rates of erosion are likely with declining natural protection
How much is the estimated long-term retreat?
35 meters
How much are the estimated coastal erosion in width?
From 48 to 111 meters, this estimate is higher than a lot of the Auckland regions 123 other beaches
