NEARSHORE CURRENT SYSTEMS

NEARSHORE CURRENT SYSTEMS Water Motion Under Waves vs Water Depth DEEP WATER Wave Direction Wave Base Water Particle Movem ent SHALLOWER WATER Nielsen and Nielsen, 1978 Java: Uni of Texas Animated Demos Stokes' 2nd order Wave Theory Nearshore Circulation System Komar, 1976 Radiation Stress Radiation stress = ”The excess flow of momentum due to the presence of the waves” (Longuet-Higgins & Stewart 1960)  Sxx   ( p  u d  2kh 1 1  )dz   p0 dz  E     E  2n   2   sinh(2kh)  d  kh  1  S yy  E    E n      sinh(2kh)  Rip Currents & Cell Circulation Shallow water S xx  3 E  gH 2 16 Momentum balance in cross-shore direction: S xx h  g (  h)  x x S xx x balanced by h x ! Komar, 1976 Rip Currents & Cell Circulation h H Komar, 1976 Edge Waves & Cell Circulation H H Komar, 1976 Shoals & Cell Circulation (Sonu 1972) Longshore Currents & Oblique Breaking Waves Longshore component of wave forcing = where Sxy d x (1) n Sxy  En sin  cos   gH cos  sin  Frictional drag on flow = (1) = (2)  vl  Ry  C f um vl  (2) 5 tan *  b gd sin  cos  16 C f αb vl vl ,mid  2.7um sin b cos b (Komar and Inman 1970) (Longuet-Higgins 1970) Longshore Currents & Oblique Breaking Waves Longshore current profiles (solid line - no lateral mixing; dashed lines - with lateral mixing) (Longuet-Higgins 1970) Tidal Currents Shinnecock Inlet, Long Island, NY 50 km Flood-tidal Current Open-Coast Tidal Currents Tidal-Inlet Influenced Currents Ebb-tidal Current x Longshore Component of Tidal Current (x) 0.6 Channel/10 12 m 0.4 Current Velocity (m/s) 60 m 140 m 0.2 500 m Flood Open-Coast Ti dal Currents Tidal -I nl et Influenced Currents 0.0 -0.2 x -0.4 Ebb Ebb Flood -0.6 10 12 Time (hr) References Komar, P.D and Inman, D.L 1970 ”Longshore Sand Transport on Beaches,” J Geophys Res., (75):5914-5927 Komar, P.D 1976 ”Beach Processes and Sedimentation,” Prentice Hall, NJ Nielsen, J and Nielsen, N 1978 ”Kystmorfologi,” Geografforlaget, Brederup, Denmark (in Danish) Sonu, C.J 1972 ”Field Observations of Nearshore Circulation and Meandering Currents,” J Geophys Res., (77):3234-3247 ... NY 50 km Flood-tidal Current Open-Coast Tidal Currents Tidal-Inlet Influenced Currents Ebb-tidal Current x Longshore Component of Tidal Current (x) 0.6 Channel/10 12 m 0.4 Current Velocity (m/s)... 1970) Longshore Currents & Oblique Breaking Waves Longshore current profiles (solid line - no lateral mixing; dashed lines - with lateral mixing) (Longuet-Higgins 1970) Tidal Currents Shinnecock... Rip Currents & Cell Circulation Shallow water S xx  3 E  gH 2 16 Momentum balance in cross-shore direction: S xx h  g (  h)  x x S xx x balanced by h x ! Komar, 1976 Rip Currents