COASTAL ENVIRONMENTS Lessons 1 to 2 Defining Coast and Waves Lesson Objectives Success Criteria 1) Know what is meant )Define coast. by term the coast. 2)Draw an accurate 2) Understand waves. annotated wave diagram.
Starter: What is the coast? In pairs come up with a definition. Definition of the coast: a narrow zone where the land and sea overlap and directly interact. Factors affecting coasts: see next diagram Factors affecting coasts: Defining Coast and Waves
Lesson Objectives Success Criteria 1) Know what is meant 1)Define coast. by term the coast. 2)Draw an accurate 2) Understand waves. annotated wave diagram. Homework for next week! Read Geofile 297 Basic
coastal processes and make detailed notes using sub headings for next week. Waves Wave formation: Transfer of energy from wind blowing over water Tsunamis are an exception Increase wind strength causes increased frictional drag which creates larger waves Local waves caused by wind are known as sea
waves, whereas waves travelling from distant storms are swell waves Wave energy depends on 3 factors: wind velocity, period of time over which wind has blown, fetch Waves (continued) Fetch is the maximum distance of open water over which the wind has blown, so large fetches (e.g. across the Atlantic from SW to NE) produce high energy waves. Waves hitting parts of SW England have a fetch of 6000+Km
Waves (continued) Wave terminology: (see handout) Make sure you know the definition of:
Swell waves Sea waves Fetch Wave height Waver period Wave length Wave steepness Wave energy Waves (continued) Swell waves - result from distant storms and strong winds.
These waves can travel long distances. Characterised by waves with low wave height, gentle steepness, long wave length, and long period. Sea waves - result from local wind and therefore only travel short distances. Opposite characteristics to swell, occurring in higher energy waves.
Fetch - maximum distance of open water over which waves can develop. Longer fetch leads to more wind and waves with higher energy. Wave height (H) - the vertical distance between the wave crest, and the trough Wave period (T) - time taken for a wave to travel one wavelength. Wave length (L) - the distance between 2 successive crests. Wave velocity (C) - the speed of movement of a wave. Wave steepness (HL) - ratio of wave height to wave length, cannot exceed 1:7, or wave will break. Wave energy (E) - the energy possessed by a wave in deep water expressed as ELH2.
Waves (continued) Waves in deep water: Deep water = when depth is > than one-quarter of the wave length Wind drag on the sea surface causes water to move in an orbital motion Waves are surface features the size of orbits decreases with depth Waves (continued) Waves in shallow water: Water is shallow when the depth is less than
one-quarter of the wave length Friction with the seabed increases As the base of the wave slows down, the circular oscillations become elliptical Waves (continued) Waves in shallow water: Water is considered shallow if D In shallow water friction with the sea bed increases and as the base of the wave slows down The ellipse becomes more acute, as the water
depth decreases as does the wavelength. The steepness of the wave increases until the upper part spills over, or plunges over. At the plunge line, the depth of water and the height of the wave are almost equal. The water which rushes up the beach is called the swash, and the water retuning on the surface is called the backwash. Why a wave breaks: Waves (continued) Wave refraction
As waves approach an irregular coastline they are refracted i.e. they become increasingly parallel to the coastline (best seen in a bay between two headlands) The waves near the shore slow down due to frictional drag on the sea bed, whereas those in deeper water continue to move more quickly This causes the waves to bend (creating curved orthogonals) This process also creates longshore (or littoral) currents which carry sediment inshore from the headland
Task: Draw an annotated wave diagram. Plenary: 1)Draw an annotated wave diagram from memory that includes: Wave height Wave length Crest Trough Wave period 2) Swap diagrams and peer assess using the AFL sheet to help you set targets for improvement.
Staple AFL sheet to diagram. Defining Coast and Waves Lesson Objectives Success Criteria 1) Know what is meant )Define coast. by term the coast. 2)Draw an accurate 2) Understand waves. annotated wave diagram.
Wave Refraction and Tides Lesson Objectives Success Criteria 1) Understand what 1) Draw an accurate wave refraction is. 2) Understand and be
able to explain what different types of tide are caused by and their effects. annotated wave refraction diagram. 2) Draw an accurate annotated tide diagram.
Starter: What are the four most important things you remember about waves from last lesson? Homework for next week! Make revision cards on waves, wave refraction, tides, and storm surges for next week. In small groups look at the
wave refraction diagram and agree an explanation on what is happening to the waves and why? You have 5 minutes to prepare before feeding back. WAVE REFRACTION Effect of the sea floor on waves: Land As waves approach the shore, their
speed is reduced as they touch the sea floor. Wave refraction causes two main changes: The speed of the wave is reduced. 2. The shape of the wave front is altered. Shoreline Wave movement is slowed down in shallow water, and this causes the wave front to break Depth decreasing
onshore 1. Faster movement in deep water causes waves to break parallel to each other Wind direction If refraction is completed:
The wave fronts will break parallel to the shore. Wave refraction also distributes wave energy along a stretch of coast. On a coastline with alternating headlands and bays, wave refraction will concentrate destructive/erosive activity on the headlands, while deposition will tend to
occur in the bays. Sea Land Dispersed energy A1 Concentrated energy on B1 B1 bank
A1 Wave front Sea A A B B
Draw and annotate a Wave refraction diagram: Wave Refraction and Tides Lesson Objectives Success Criteria 1) Understand what 1) Draw an accurate
wave refraction is. 2) Understand and be able to explain what different types of tide are caused by and their effects. annotated wave refraction diagram. 2) Draw an accurate
annotated tide diagram. Tides: Tides are controlled by: The gravitational effects of the moon (mainly) and the sun (partly), together with the rotation of the Earth. The geomorphology of sea basins is locally significant The moon pulls water to the side of the earth nearest to it, creating a bulge or high tide, with
a complementary bulge on the opposite side of the earth Intervening areas experience a low tide Spring tides occur when the moon, the earth and the sun are in line (i.e. there is a new moon or a full moon) Neap tides occur when the moon, the earth and the sun form a right-angle (i.e. there is a half-moon) Tides diagram: Tides (continued):
Coriolis force (the effect of the earths rotation) is also significant it causes flows of air/water to be deflected to the right in the northern hemisphere. Tides flood around the British Isles in a clockwise direction The tidal range is also affected by the morphology of the coastline and the sea bed Where water is funnelled the tidal range will be higher (Severn estuary = 13m a macro-tidal environment) and extreme narrowing of estuaries can cause a tidal
Tides (continued): Small enclosed seas only have a minimal tidal range such as the Mediterranean (0.01m a microtidal environment) The offshore gradient will control the extent of the inter-tidal zone. Steep gradients have a small inter-tidal zone whereas shallow gradients have a large inter-tidal zone Tides (continued):
Storm surges: Storm surges are rapid rises in sea level which are caused either by intense areas of low atmospheric pressure and/or severe onshore winds They pose a major natural hazard on densely populated coastlines Two areas which are particularly prone are the southern North Sea (depressions) and the Bay of Bengal (tropical cyclones) Storm Surges - Case Study:
North Sea, 31st January1st February 1953: A deep depression (976mb) moved over the North Sea Intense low pressure caused the sea level to rise by 0.5m Gale force onshore winds produced waves over 6m high Water piled up in the southern North Sea This event coincided with a Spring Tide up to 2.5m in
the Thames estuary Rivers discharging into the North Sea were at flood level 264 people drowned in SE England, 1835 in the Netherlands Plenary: Draw and annotate a Tides diagram: Wave Refraction and Tides Lesson Objectives
Success Criteria 1) Understand what 1) Draw an accurate wave refraction is. 2) Understand and be able to explain what different types of tide are caused by and
their effects. annotated wave refraction diagram. 2) Draw an accurate annotated tide diagram.
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