OCEN682 – Coastal Sediment Processes: Spring 2010James M. KaihatuCE/TTI 808D862-3511; [email protected] DetailsCourse Details• Objective: Familiarization with the htitif tlditdcharacteristics of coastal sediments and the processes by which they are transportedtransported.• Class Time and Location: TR 2:20-3:35 CE134CE134• Grading: Irregularly-spaced homework (20%); takehome midterm (35%); project(20%); take-home midterm (35%); project (45%)•Office Hours:MW 10:00am12:00pm or•Office Hours: MW 10:00am-12:00pm or by appointmentCourse MaterialsCourse MaterialsTextbook: None requiredAdditional References:Additional References:• Dean, R.G., and Dalrymple, R.A. Coastal Processes with Engineering Applications, Cambridge University Press, 2004.• Fredsoe, J., and Deigaard, R. Mechanics of Coastal Sediment Transport, World Scientific, 1992.• Horikawa, K. Nearshore Dynamics and Coastal Processes, University of Tokyo Press, 1988.• Komar, P.D. Beach Processes and Sedimentation, Prentice-Hall•Nielsen PCoastal Bottom Boundary Layers and Sediment TransportWorldNielsen, P. Coastal Bottom Boundary Layers and Sediment Transport, World Scientific, 1992.• US Army Corps of Engineers, Coastal Design ManualCl N tAilbl liClass Notes: Available online: https://ceprofs.civil.tamu.edu/jkaihatu/teaching/ocen682/index.htmlWhy We Care About Coastal Sdi PSediment ProcessesEveryone’s moving to the coast…What is Beach Erosion?What is Beach Erosion?Beach erosionis a process whichBeach erosionis a process which removes sand from the beach• Natural causes (wind, waves, td )storm surge, undersea canyons)• Artificial causes (beach development, loss of sand supply)pppy)• Short term (seasonal, storm-by-storm)• Long term (subsidence, sea level rise, human error)Beach replenishment in Miami, FLMAJOR reason why we study coastal sediment processesIs All Beach Erosion Bad?Is All Beach Erosion Bad?•The beach responds toThe beach responds to forcing from waves• Large waves - lessening ggof beach slope – more area over which to dissipate energydissipate energy• Large waves – scoured sediment form bar–forcesediment form bar force waves to break further offshore• Summer beach profile –wider post recoveryBeach erosion is a natural process, so long as man doesn’t mess it up…Some Long Term Causes of Net BhLBeach LossSSea level riseDams – Impoundment of riverine sedimentHurricanes and other intense eventsPermanent sediment sinksBad coastal engineeringConsequences of Beach ErosionConsequences of Beach ErosionReduction in ability to protect coastal communities from strong stormsIncrease in damage to structures on coastBefore widescale erosionAfter erosionAfter erosion has begunReduction in tourismImpact on beach nesting speciesSo? I Don’t Live on the Beach!So? I Don t Live on the Beach!Yeah, well, neither did I…it came to me!Beach sand inside amp came to me!Circa 2003My GarageMy Amp!vacuum tubes!Lt ’My LivingMy Amp!Lots o’ beach sand!My Living Room !My Car!Bh dextra car!404 Carroll Ave, Bay Saint Louis, MS(0.6mi from beach)August Beach sand inside crankcase!new boat!(0.6mi from beach)g31, 2005Beach Sand!!1 Forcing Mechanisms1. Forcing MechanismsTides• Seasonal / long term effect on beach • Berm-building mechanism• Modulates ocean wave effects• Inlets –ebb and flood currents1 Forcing Mechanisms1. Forcing MechanismsHi /tKatrina’s trackHurricane / storm surgeCamille “Cut”track• Increased water BSL, MSlevels due to wind• Can inundate low lying areasSurge at I-10 in Bay Saint Louis lying areas, undercut bluffs• Increased wave setup adds toChandeleuryMSsetup adds to overall surge, increases destructivenessChandeleur Isles pre- and post-stormdestructivenessForcing MechanismsForcing MechanismsWavesCdbidbli•Caused by wind blowing on ocean surface• Longer waves (swell) run tf ti h dηHout of generation area ahead of shorter waves (wind sea)• Wave period T – time it tk f t t tHtakes for two crests to pass a point• Wavelength L – distance between crestst (s)η= elevation of ffbetween crests • Function of period and water depthfree surfaceL = wavelengthL=deep• Wave height H – distance between trough and crest of waveLo= deep water wavelengthForcingMechanismsForcing MechanismsVelocities, pressures under waves• To first order: orbital paths of particles are closed• Particle path circular in deep water, elliptical in shallow water• Size of path decreases with elevation in water column.ForcingMechanismsForcing MechanismsbWave Refraction and ShoalingboContours of Water Depthb2Wave TransformationT=15 sWave DiffractionTransformation over Irregular BathymetryDiffractionT=5 sForcingMechanismsForcing Mechanismsspilling breakersWave setupplunging breakerssurging breakersbreakersForcingMechanismsForcing MechanismsInfragravity WavesLongshore CurrentRip CurrentsCross Shore Current / UndertowSediment CharacteristicsSediment CharacteristicsSediment size di t ib tiφ= phi scaledistribution from samplesMφ= mean sizeσφ= std. dev.αφ= skewnessw=fall velocityFall velocity vsCD= drag coeff.Fall velocity vs. diameterR=Reynolds numberHow to Describe Sediment TTransport1) Macroscale2) MicroscaleCharacteristics of Beach EvolutionCharacteristics of Beach EvolutionOne-Dimensional CharacteristicsTwo-Dimensional CharacteristicsSedimentTransport MechanismsSediment Transport MechanismsFD=drag forceΨFL= lift forceW = immersed weight(bottom(bottom shear stress)Shields criterion for unsteady flowDiagram of force balance for incipient motion (steady flow)Shields numberReynolds numberSedimentTransport MechanismsSediment Transport MechanismsAtiFliAsymmetric Flow in Shallow Water Waves• Stronger shoreward flow than sea ard flothan seaward flow• Less dense material travels further seaward under troughunder troughModes of Transport• Bedload – enabled by granular interactions•Suspended load–enabled•Suspended load –enabled by turbulent fluctuations from breakingLongshore TransportLongshore Transport• Longshore transport dependent on averaged effects of local wave climate• Result of longshore current• Direction can be seasonal, depending on prevailing wavedepending on prevailing wave directions• Longshore transport occurs continually• “River of sand”Changes in transport lead to erosion•Changes in transport lead to erosion or accretion• Difficult to measure • Can be measured by volume impoundedCross Shore TransportCross Shore