Why are local variations found in the processes operating at Muriwai?

Muriwai Beach Otakamiro Point Give out student first student map. Students label Otakamiro Point and Muriwai Beach Otakamiro Point

MAP 1 Wave Processes Muriwai Beach OP “The focus here is to see how wave processes vary between Otakamiro Point and Muriwai Beach”. Ask students to consider how wave processes my vary between the two locations. Also consider what factors affect the way that waves approach the coastline. OP

The prevailing winds at Muriwai are south-westerly The prevailing winds at Muriwai are south-westerly. Generally, winds are 16kph or more. They have blown over a long fetch, so the swell can be high. This are some of the factors have an effect.

Muriwai Beach Instruct students not too add labels until the labels on your projected map are up. Ask students to consider what the waves are generally like around the headland. What about wave refraction? The prevailing winds at Muriwai are south-westerly. Generally, winds are 16kph or more. They have blown over a long fetch, so the swell can be high. Otakamiro Point

Around the headland (O. P Around the headland (O.P.) the waves are destructive – they are eroding.

Muriwai Beach Around the headland (O.P.) the waves are destructive – they are eroding. What features result from wave processes at the headland? The prevailing winds at Muriwai are south-westerly. Generally, winds are 16kph or more. They have blown over a long fetch, so the swell can be high. Otakamiro Point

This is due to wave refraction… the shape of O. P This is due to wave refraction… the shape of O.P. bends the waves, focussing their energy into the sides of O.P. This has resulted in a large cave to the N of O.P and an arch to the S. There is also a large stack and a wave-cut platform at the tip of O.P.

This is due to wave refraction… the shape of O. P This is due to wave refraction… the shape of O.P. bends the waves, focussing their energy into the sides of O.P. This has resulted in a large cave to the N of O.P and an arch to the S. There is also a large stack and a wave-cut platform at the tip of O.P. Muriwai Beach Around the headland (O.P.) the waves are destructive – they are eroding. Now ask students to consider how waves might approach Muriwai Beach differently. The prevailing winds at Muriwai are south-westerly. Generally, winds are 16kph or more. They have blown over a long fetch, so the swell can be high. Otakamiro Point

Most days of the year the waves approaching the beach are constructive, i.e less than 11 waves breaking per minute. Therefore, swash is more powerful than backwash, so sand is deposited to form beach.

Okiritoto Stream This is due to wave refraction… the shape of O.P. bends the waves, focussing their energy into the sides of O.P. This has resulted in a large cave to the N of O.P and an arch to the S. There is also a large stack and a wave-cut platform at the tip of O.P. Most days of the year the waves approaching the beach are constructive, i.e less than 11 waves breaking per minute. Therefore, swash is more powerful than backwash, so sand is deposited to form beach. Muriwai Beach Around the headland (O.P.) the waves are destructive – they are eroding. Students can now add labels The prevailing winds at Muriwai are south-westerly. Generally, winds are 16kph or more. They have blown over a long fetch, so the swell can be high. Otakamiro Point

Muriwai Beach Recapping the variation DESTRUCTIVE WAVES OP

CONSTRUCTIVE WAVES DESTRUCTIVE WAVES Muriwai Beach OP Recapping the variation. Ask students to consider what causes these variations in the wave processes. Think about rock types. DESTRUCTIVE WAVES OP

What are the reasons for these differences? Put this as a heading after your 1st map What are the reasons for these differences? Wave Processes The main reason is because of the relief/geomorphology (shape of the land): The headland is a highland coast – the land was uplifted millions of years ago and it is formed of more resistant rock, it hasn’t been eroded very quickly. It has maintained its shape and wave refraction and wave erosion occur around it. The beach is a lowland coast made up of softer rock, so over time the wide gently sloping beach at Muriwai has formed. Students stick map in and note down the reasons

MAP 2 Longshore Drift (LSD) Maori Bay Muriwai Beach OP Second Map. Again label the beach and O.P. “The focus here is to see how LSD varies between Maori Bay, Otakamiro Point and Muriwai Beach”. Ask students to consider what the variations are in the way that LSD operates between the three locations. OP Maori Bay

LSD is the process of transportation of beach material LSD is the process of transportation of beach material. At MCE, this black sand which originated from the volcanic central plateau of NZ Along the beach the prevailing winds are south-westerly, therefore waves normally approach the beach from the SW. In the surf zone the breaking waves (swash) transport the sand up the beach on a diagonal (NE) At the headland and Maori Bay the prevailing winds are still S-Westerly. However, the processes around the headland (wave reflection, refraction and rip current formation do not allow LSD to operate uniformly. So LSD does not occur in the northerly direction predicted. The backwash carries the sand straight down the beach. Therefore LSD occurs uniformly in a Northerly direction towards Kaipara Heads Give students handout of this slide and they need to cut out the text boxes and put them where they think they should go on their maps, adding various arrows (in pencil) at the same time.

The backwash carries the sand straight down the beach The backwash carries the sand straight down the beach. Therefore LSD occurs uniformly in a Northerly direction towards Kaipara Heads In the surf zone the breaking waves (swash) transport the sand up the beach on a diagonal (NE) Along the beach the prevailing winds are south-westerly, therefore waves normally approach the beach from the SW. At the headland and Maori Bay the prevailing winds are still S-Westerly. However, the processes around the headland (wave reflection, refraction and rip current formation) do not allow LSD to operate uniformly. So LSD does not occur in the northerly direction predicted. Muriwai Beach Students check their own maps against this one LSD is the process of transportation of beach material. At MCE, this is commonly black sand which originated from the volcanic central plateau of NZ. OP

Muriwai Beach Uniform LSD Recapping the variation OP

LSD in various directions Muriwai Beach Uniform LSD Recapping the variation. Ask students to consider what causes these variations in the LSD. Consider refraction and wave reflection. LSD in various directions OP Maori Bay

What are the reasons for these differences? Put this as a heading after your 2nd map What are the reasons for these differences? Longshore Drift The difference is again due to the geomorphology of the MCE: The beach is long and straight so wave processes can operate without interruption. Around the headland reflection, refraction and rips cause many currents in the water which cause LSD to occur locally around the headland in various directions. Students stick map in and note down the reasons

MAP 3 Sand Dune Formation Maori Bay Muriwai Beach Third Map. “The focus here is to see how sand dune formation varies between Maori Bay and Muriwai Beach”. Ask students to consider what the variations are in the way that SD formation operates between the two locations. Did they even see the sand dunes at Maori Bay? Maori Bay

Vegetation, such as spinifex grass traps the sand and over time large dunes have formed. At Muriwai Beach the tidal range is about 2m. At low tide this exposes up to 300m of the beach, as the beach has a gentle gradient. BEHIND MURIWAI BEACH THERE IS A LARGE SYSTEM OF WELL-ESTABLISHED SAND DUNES. At Maori Bay the beach is narrower and steeper. Therefore, at low tide less than 100m of beach is exposed. Less sand dries. Although winds are 16kph or more, less saltation takes place. AT MAORI BAY THERE IS ONLY A SMALL AREA OF DUNES ON THE NORTHERN END OF THE BEACH. Give students handout of this slide and they need to cut out the text boxes and put them where they think they should go on their maps, adding various arrows (in pencil) at the same time. The exposed sand dries and, as the winds at Muriwai are frequently 16kph or more, saltation takes place. Large amounts of sand are blown towards the back of the beach.

At Muriwai Beach the tidal range is about 2m At Muriwai Beach the tidal range is about 2m. At low tide this exposes up to 300m of the beach, as the beach has a gentle gradient. BEHIND MURIWAI BEACH THERE IS A LARGE SYSTEM OF WELL-ESTABLISHED SAND DUNES. Vegetation, such as spinifex grass traps the sand and over time large dunes have formed. The exposed sand dries and, as the winds at Muriwai are frequently 16kph or more, saltation takes place. Large amounts of sand are blown towards the back of the beach. Muriwai Beach Students check their own maps against this one At Maori Bay the beach is narrower and steeper. Therefore, at low tide less than 100m of beach is exposed. Less sand dries. Although winds are 16kph or more, less saltation takes place. AT MAORI BAY THERE IS ONLY A SMALL AREA OF DUNES ON THE NORTHERN END OF THE BEACH. Maori Bay

What are the reasons for these differences? Put this as a heading after your 3rd map What are the reasons for these differences? Sand Dune Formation Maori Bay is surrounded by cliffs, so there is limited space for dune development. In addition there is less saltation occurring at Maori Bay, therefore there is less sand available for dune formation.