CEE 1030 1nd Edition Lecture 20 Shorelines Outline of Last Lecture I Distribution of land II Key questions in deserts a What is a dry climate b Where are deserts located c How does erosion occur III Types of deserts IV Wind deposits V Types of sand dunes VI Review Outline of Current Lecture I Land sea boundary II Waves III Shore zones IV Wave erosion V Beaches VI Coastal features VII Wave refraction VIII Shoreline stabilization Current Lecture I Land sea boundary a Interface boundary between different parts of a system b Constantly changing modified by waves c Sites of intense human activity i Construction ii Living iii Vacationing d Dynamic interfaces i Shoreline line that marks contact between land and sea ii Coastline the coast s seaward edge landward limit of the effect of the highest storm waves on the shore e Moving shorelines i Shoreline migrates up and down each day as the tides rise and fall These 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 coastlines iii Coastline marks most inland evidence of ocean waves iv Coastlines change mainly as a result of storm erosion and sea level change v Foreshore area exposed when the tide is out and submerged when the tide is in vi Backshore landward of the high tide shoreline usually only affected by waves during storms II Waves a Wind provides most of the energy that shapes and modifies coastal zones b Anatomy of a wave i Crest high point of a wave ii Trough low point between waves c Measuring waves i Wave height distance between trough and crest ii Wave length horizontal distance between crests iii Wave period the time interval between the passage of two successive crests d Predicting wave size i Main factors 1 Wind speed 2 Length of time wind has blown 3 Fetch distance wind has traveled across open water 4 Water depth e Formation of surface waves i Circular orbital motion water passes energy along by moving in a circle ii As wind blows energy is transferred from air to water by pressure and friction iii Water molecules are displaced in the direction of the wind but snap back due to molecular cohesion f Oscillation waves i Wave form advances but water does not advance from the original position ii Occurs in the deep ocean no blockages deep water g Effect of water depth i Water particle movement decreases with increasing water depth ii Below a depth equal to one half the wavelength there is negligible water movement h Effects of shallowing i Faster waves farther out to sea catch up as wave approaches shore so wave length becomes shorter and crest height increases ii Eventually crests become unstable and the steep breaks III IV V VI VII iii As wave crest breaks forward turbulent water advances up shore and forms surf i Translation wave turbulent advance of water created by breaking waves Shore zones a Offshore seaward of where waves break at low tide b Nearshore zone between where waves break at low tide to low tide level c Foreshore area between low tide shoreline and coastline d Backshore area inland of foreshore affected by storm waves and atypical high tides Wave erosion a Breaking waves exert great force b Erosion caused by shocks pressure and fractures in rock Beaches a Beaches waves act to accumulate local sediment along the landward margin of an ocean or lake b Beach formation i As breaking waves move water up the shore and then back down sediment is pushes large quantities of sand along the beach ii Differential sorting and transport of sediment grains by wind and wave action c Foreshore features i Beach face sloping section of beach below berm ii Berm nearly flat area inland of the beach face d Backshore features i Dune hill or ridge of wind deposited sand Coastal features a If coast rises or sea level drops land once covered by sea emerges to form part of the landscape b Wave erosion at sea level undercuts cliffs leading to collapse of cliff face c 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 estuaries ii Hilly terrains become islands d If coast is composed of rocks at different hardness different areas will erode at different rates i Result is a sea cave Wave refraction a Wave energy is concentrated against the sides and ends of headlands b 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 zone d Longshore currents VIII i Longshore currents tend to be slow and turbulent in areas where the shore curves inland ii As deposit builds out from a shore it forms a sandbar iii Over time sandbar can build out into the mouth of a bay as a spit iv Baymouth bar a sand bar that completely crosses a bay v Tombolo a ridge of sand that connects an island to the mainland or another island vi Rip currents 1 Usually flow from shoreline out to beyond area where waves break vii Signs of a rip current 1 Choppy channel with churning motion 2 Line of sea foam seaweed or debris moving steadily out to sea 3 Disrupted pattern of incoming waves Shoreline stabilization a Seawall barriers constructed parallel to the shore close to the beach b Breakwater barrier built offshore and parallel to the shore c Groin short wall built at right angle to shore and close to the beach to trap moving sand d Jetties pair of structures extending into the ocean at the river or harbor entrance e Hard stabilization can be built but it can disrupt ecosystems and water circulation patterns