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MURIWAI COASTAL ENVIRONMENT (NATURAL PROCESSES (CLIMATOLOGICAL processes…
MURIWAI COASTAL ENVIRONMENT
LOCATION
The Muriwai coastal environment is located 41.3km by road West of Auckland City, around a 40 minute drive along State Highway 16. Muriwai is located at 36.8362'S, 174.4341'E. Muriwai beach can be found Northwest of Muriwai settlement and Southwest of Helensville.
Our study area extends from Maori Bay including Otakamiro Point (headland) to Okintoto Stream (approximately 3km to the North). It extends from offshore to the outer limits of the surf and approximately 5km inland to the road east of the golf course.
NATURAL PROCESSES
CLIMATOLOGICAL
processes that determine weather patterns (temperature, precipitation, air pressure, humidity)
BIOGEOGRAPHICAL
processes whereby one life cycle provides the catalyst for new life.
HYDROLOGICAL
processes pertaining to the water cycle whereby water (solid, liquid or gas) moves between air, water bodies and land.
PEDOLOGICAL
processes involved in the formation of soil types (ash, decomposed vegetation and corpses, water, eroded rock)
GEOMORPHOLOGICAL
processes that build the land
MURIWAI COASTAL ENVIRONMENT SYSTEMS
PROCESSES
5 higher order processes
1.Geomorphological
-land building and shaping
-plate tectonics
Hydrological
-tides and wave action
-long shore drift (transportation)
Climatological
-wind action (aeolian)
-wave formation
-sun drying sand
Biogeographical
-vegetation growth
Pedological
-sand, rocks, soils (sediment)
OUTPUTS
Features found at the MCE
Sand dunes
-beach
Headland
-shore platform
-cliffs
-caves
-stacks
-blowholes
INPUTS
-waves
-wind
-sediment
-rock type
-vegetation
-tectonic processes
-gravity
-suns energy
FEEDBACK
-energy (wind and wave)
-sediment
-changed typography (shape) of the land (change can be seasonal or over a long period of time)
MAIN SYSTEMS AT THE MCE
LONGSHORE DRIFT
Longshore drift is the movement of titanomagnetite sand along Muriwai beach at an angle. Because waves rarely approach the coastline at a right angle, and instead strike Muriwai beach at an oblique angle, a littoral current is created. This current transports material along the beach in a down drift direction, creating longshore drift. The swash runs up the beach face at an angle due to the oblique approach of the waves due to the prevailing SW winds. The backwash (which is stronger than the swash due to Muriwai's destructive waves) then runs perpendicular down the beach face due to gravity. A zig zag movement of sediment results. At Muriwai beach LSD is responsible for the supply of titanomagnetite that is originally washed into the Tasman sea by river originating from Mt Taranaki and the central plateau. LSD transports sediment northward along Muriwai beach and has resulted in the formation of a sand spit called Kaipara Peninsula. AT MCE the beach is long and straight so LSD processes can operate without interruption.
SAND DUNE FORMATION
5 higher order processes that form sand dunes:
Geomorphological
-central plateau of NZ is the source of sediment for Muriwai beach (volcanic origins)
Hydrological
-destrusctive waves
-longshore drift
-littoral zone
Climatological
-wind is prevailing SW/W 48% of the time
-large fetch (2000km)
-aeolian processes (suspension, saltation, surface creep)
-sun (dries out the sediement)
Pedalogical
-sediment (titanomagnitite, iron rich fine sand and quartz feldspar, coarse white sand)
Biogeographical
-vegetation (spinnafex, marram and pingao)
-zone of zero velocity
AEOLIAN PROCESSES
Aeolian processes are the way that sand dunes are created.
In short:
1.
Wave action and tidal processes create amounts of sediment that is dried by the sun.
2.
The wind blows and transports the sand.
3.
Vegetation stops and blocks the blowing.
4.
Wind dries out the sand and it forms dunes.
Aeolian processes are made up of 3 processes, suspension, saltation and surface creep. Aeolian transport is made up of 75% saltation and 25% surface creep.
Suspension:
0-2mm sand grains, light enough to be blown across the beach at heights.
Saltation:
fine/medium sand grains hop along the beach in winds above 5m/sec. lighter sand moves faster. Saltation is the colliding of sand grains with other grains, causing the impacted grains to be flung into the air.
Surface Creep:
heavier grains roll along the beach as they're too heavy to be picked up and blown.
HEADLAND PROCESSES
EROSIONAL PROCESSES
MURIWAI FACTS AND FIGURES
WIND
Winds at MCE blow at 11 knots more than 50% of the time. This is the velocity needed to move the titanomagnetite sand.
70% of winds blow onshore, this is a vital factor in wind and wave action.
Winds at MCE are prevailing West and South West 48% of the time.
WAVES
Waves approaching Muriwai have 300,000kj of energy.
Average wave height is 2.5m.
MCE has destructive waves (which break vertically downwards and produce stronger backwash than swash.)
Fetch at MCE is 2000km across the Tasman Sea.
MCE has strong backwash and weaker swash.
The difference between high and low tide (tidal range) is 3m vertically.
The size and energy of a wave is influences by:
-how long the wind has been blowing
-the strength of the wind
-how far the wind has travelled (fetch)
SEDIMENT
High concentrations of very fine (0.25mm) titanomagnetite sand, which is dark grey/black due to its iron content.
The main source of sediment is from Mt Taranaki and volcanic sediment from the central plateau region, from the Waikato river.
Other sediment is fine (0.5mm) quartz feldspar, a white sand
VEGETATION
3 types of vegetation: spinifex, pingao (both NZ natives) and Marram grass)
The vegetation at MCE must be able to tolerate a hostile environment of high winds, salt spray, sand blast, coverings by sand and little water.
Vegetation plays an important part in the formation and stabilisation of sand dunes