Cross-shore sediment transportChang Hsien Kuo

10259

NRCESTcross- and long-shore sediment

beach profile vs. cross-shore sediment

beach profile vs. cross-shore sediment

depth of closureHallermerier (1978, 1981)

annul mean significant wave height + standard deviation

Birkemeier (1985)cross-shore sediment transportMadsen and Grant (1976): sediment transport for half wave period

Watanabe et al. (1980): net sediment transport

cross-shore sediment transportSunamura (1982): Dominant sediment transport

Bar formationKeulegan (1945)

Bar formationSix types of longshore bars

Bar formationKeulegan (1945)

Bar formationKeulegan ratio=ht/hc~1.69

Bar formationNayaks criterion for longshore bars:Wave steepness (H/L) vs. wave height (H/h)

Bar formationStanding wave and wave reflection

Bar formationPartterns of secondary currents associated with different types of three dimensional longshore bar

Beach cuspBeach cusps were first described by Palmer (1834)

Beach cuspCusp spacing is about one-half the wavelength of edge waves

transverse sand bars

transverse sand barsTen years (1987-1996) of time exposure vidieo images of nearshore region at Duck, NC were used to study transverse sand bars.

transverse sand barsTransverse bar spacing :mean longshore current and beach slope

Komar (1998)

transverse sand barsPredicted values were much less than the measured values

Bed shear stress

Bed shear stress

Bed shear stress

Soulsby, 1997: free stream velocity

23Bed shear stress

Nielsen, 2002: shear velocity

Bed shear stress

Dick and Sleath, 1991: Momentum-integral method

Sedimment/fluid mixtureDixen at al., 2008: Log-fit method (Law of the wall)The velocity profile can be approximated by a logrithmic function

Bed shear stress

Phase lagfluctuationApplication to predict sand transport rate

Nielsen, 2006: Bedload formulation

Momentum integral methodSymbols : testsTop: skewness of shear stressBottom: phase lead of shear stress to free stream velocityBed shear stress

Four kinds of formulas for shear velocityRecent study-1

Net transport rate : velocity-load equationRecent study-1

Watanabe and Sato, 2004:Half-wave cycleRecent study-1

Shields parameter

Recent study-1

Wave-current friction factor (Ribberink, 1998)

Recent study-1Sediment load between half cycles: Phase lag parameter

Phase lag parameterRecent study-1

Recent study-1

For velocity-skewed oscillatory sheet flows with d > 0.2mmData: 32Goodness:R2:0.78 Fac2%:97%Fac5%:100%Recent study-1For acceleration-skewed oscillatory sheet flows with d > 0.2mm

Data: 32Goodness:R2:0.87 Fac2%:84%Fac5%:97%Recent study-1

For oscillatory sheet flows with d < 0.2mmData: 29Goodness:R2:0.80 Fac2%:86%Fac5%:93%Recent study-1

For oscillatory sheet flows over rippled bedData: 50Goodness:R2:0.65 Fac2%:62%Fac5%:89%Recent study-1

For oscillatory sheet flows with colinear currentsData: 50Goodness:R2:0.84 Fac2%:70%Fac5%:86%Recent study-1Steady sheet-flow