1 / 11

EQUILIBRIUM BEACH PROFILE

EQUILIBRIUM BEACH PROFILE. Conceptually the result of balancing constructive and destructive forces. Really a misnomer because equilibrium never reached. WHY? Sediment dynamics happen much slower than ever- changing hydrodynamics. EQUILIBRIUM BEACH PROFILE - APPROACHES.

elyse
Download Presentation

EQUILIBRIUM BEACH PROFILE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EQUILIBRIUM BEACH PROFILE • Conceptually the result of balancing constructive and destructive forces. • Really a misnomer because equilibrium never reached. • WHY? • Sediment dynamics happen much slower than ever- • changing hydrodynamics

  2. EQUILIBRIUM BEACH PROFILE - APPROACHES Kinematic: determine motion of each grain: impractical Empirical: Purely descriptive and data driven Dynamic: balance constructive and destructive forces What about details of processes? Don’t necessarily know

  3. DESTRUCTIVE FORCES Turbulence http://www.cruising-newcaledonia.com/images/SURF.JPG

  4. DESTRUCTIVE FORCES Undertow (Komar, 1998) http://www.cruising-png.com/IMAGES2/WAVE.JPG

  5. DESTRUCTIVE FORCES Gravity mgsin(b) b mg http://www.gc.maricopa.edu/earthsci/imagearchive/GSslope.jpg

  6. CONSTRUCTIVE FORCES Non-linear wave profile Net onshore stresses result from non-linear profile

  7. CONSTRUCTIVE FORCES Intermittent suspension Velocity variation under broken waves u t Wave Breaking Very rough sketch Sed concentration t Largest onshore velocities coincide with highest suspension

  8. CONSTRUCTIVE FORCES Boundary layer streaming δ1 δ2 δ3 • Flow is non-uniform in flow direction • Boundary layer thickness varies in flow direction • Induces small vertical velocity component • Time average of uw not zero since u and w not perfectly 90 degree out of phase • Finite but small additional shear stress induced

  9. EQUILIBRIUM BEACH PROFILE THEORY Turbulence is major destructive force F is wave energy flux h is water depth y’ is cross-shore coordinate (onshore-directed) D* is energy dissipation per unit volume (dependent on grain size) Solve for h(y) h varies as cross-shore coordinate to 2/3 power A is the profile scale factor (function of grain size)

  10. d = 0.1 mm d = 0.5 mm d = 1.0 mm EBPs Larger particles have steeper slopes: Can withstand energy better

  11. d = 0.1 mm d = 0.5 mm d = 1.0 mm EBPs, BEACH SLOPE UH OH. Slope goes to infinity as shoreline approached

More Related