CEE 1030 1nd Edition Lecture 20: ShorelinesOutline of Last Lecture I. Distribution of landII. Key questions in desertsa. What is a dry climate?b. Where are deserts located?c. How does erosion occur?III. Types of desertsIV. Wind depositsV. Types of sand dunesVI. ReviewOutline of Current Lecture I. Land-sea boundaryII. WavesIII. Shore zonesIV. Wave erosionV. BeachesVI. Coastal featuresVII. Wave refractionVIII. Shoreline stabilizationCurrent LectureI. Land-sea boundarya. Interface: boundary between different parts of a systemb. Constantly changing, modified by wavesc. Sites of intense human activityi. Constructionii. Livingiii. Vacationingd. Dynamic interfacesi. Shoreline: line that marks contact between land and seaii. Coastline: the coast’s seaward edge, landward limit of the effect of the highest storm waves on the shoree. Moving shorelinesi. Shoreline migrates up and down each day as the tides rise and fallThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.ii. Storms can result in abnormally high coastlinesiii. Coastline marks most inland evidence of ocean wavesiv. Coastlines change mainly as a result of storm erosion and sea level changev. Foreshore: area exposed when the tide is out and submerged when the tide is invi. Backshore: landward of the high-tide shoreline, usually only affected by waves during stormsII. Wavesa. Wind provides most of the energy that shapes and modifies coastal zonesb. Anatomy of a wavei. Crest: high point of a waveii. Trough: low point between wavesc. Measuring wavesi. Wave height: distance between trough and crestii. Wave length: horizontal distance between crestsiii. Wave period: the time interval between the passage of two successive crestsd. Predicting wave sizei. Main factors1. Wind speed2. Length of time wind has blown3. Fetch: distance wind has traveled across open water4. Water depthe. Formation of surface wavesi. Circular orbital motion: water passes energy along by moving in a circleii. As wind blows, energy is transferred from air to water by pressure and frictioniii. Water molecules are displaced in the direction of the wind, but snap backdue to molecular cohesionf. Oscillation wavesi. Wave form advances but water does not advance from the original positionii. Occurs in the deep ocean (no blockages, deep water)g. Effect of water depthi. Water particle movement decreases with increasing water depthii. Below a depth equal to one half the wavelength, there is negligible water movementh. Effects of shallowingi. Faster waves farther out to sea catch up as wave approaches shore, so wave length becomes shorter and crest height increasesii. Eventually crests become unstable and the steep breaksiii. As wave crest breaks forward, turbulent water advances up shore and forms surfi. Translation wave: turbulent advance of water created by breaking wavesIII. Shore zonesa. Offshore: seaward of where waves break at low tideb. Nearshore: zone between where waves break at low tide to low-tide levelc. Foreshore: area between low-tide shoreline and coastlined. Backshore: area inland of foreshore, affected by storm waves and atypical high tidesIV. Wave erosiona. Breaking waves exert great forceb. Erosion caused by shocks, pressure, and fractures in rockV. Beachesa. Beaches: waves act to accumulate local sediment along the landward margin of an ocean or lakeb. Beach formationi. As breaking waves move water up the shore and then back down, sediment is pushes large quantities of sand along the beachii. Differential sorting and transport of sediment grains by wind and wave actionc. Foreshore featuresi. Beach face: sloping section of beach below bermii. Berm: nearly flat area inland of the beach faced. Backshore featuresi. Dune: hill or ridge of wind-deposited sandVI. Coastal featuresa. If coast rises or sea level drops, land once covered by sea emerges to form part ofthe landscapeb. Wave erosion at sea level undercuts cliffs, leading to collapse of cliff facec. If sea level rises or land subsides, land once exposed will be submerged (submergent coasts)i. River valleys are inundated by ocean water and become estuariesii. Hilly terrains become islandsd. If coast is composed of rocks at different hardness, different areas will erode at different ratesi. Result is a sea caveVII. Wave refractiona. Wave energy is concentrated against the sides and ends of headlandsb. Wave energy is spread out and weakened in bas, often depositing sand (beach deposit)c. Oblique waves cause current to flow parallel to the coast in the surf zoned. Longshore currentsi. Longshore currents tend to be slow and turbulent in areas where the shore curves inlandii. As deposit builds out from a shore, it forms a sandbariii. Over time, sandbar can build out into the mouth of a bay as a spitiv. Baymouth bar: a sand bar that completely crosses a bayv. Tombolo: a ridge of sand that connects an island to the mainland or another islandvi. Rip currents1. Usually flow from shoreline out to beyond area where waves breakvii. Signs of a rip current1. Choppy channel with churning motion2. Line of sea foam, seaweed or debris moving steadily out to sea3. Disrupted pattern of incoming wavesVIII. Shoreline stabilizationa. Seawall: barriers constructed parallel to the shore, close to the beachb. Breakwater: barrier built offshore and parallel to the shorec. Groin: short wall built at right angle to shore and close to the beach to trap moving sandd. Jetties: pair of structures extending into the ocean at the river or harbor entrancee. Hard stabilization can be built, but it can disrupt ecosystems and water circulation