海岸动力学英文Coastal Hydrodynamics_6.2.pptVIP

Chapter 6 Iwagaki formulated the following equation where B is the width of the littoral zone, Qx the lonshore transport rate, h the mean water depth in the littoral zone, hi the water depth which determines the offshore limit of the littoral zone,λthe bottom sediment porosity, and the x-aixs is taken in the longshore direction. Chapter 6 The above equation indicates that the coastal change has two contributions: the local change of longshore transport, and the time variation of hi which is determined by the time history of the incoming wave characteristics. Even on a coast where the local variation of longshore transport is zero, beach erosion can occur with increasing wave height. When the time variation of hi is zero, erosion or deposition will completely depend on the sign of the local change of longshore transport. Chapter 6 Based on these considerations, we can say the long-term variation in coastal topography is in general generated by the local variation in the longshore transport rate. Through use of the above rules, if the rate of sediment transport along a beach can be evaluated, equilibrium, erosional, or depositional regions along the coast can be determined as demonstrated in this figure. The above procedure is applicable to the prediction of the shoreline change due to the placement of coastal structures. Chapter 6 Long-term coastal changes deposition erosion equilibrium erosion equilibrium Chapter 6 If the budget of littoral sediments is known, the art of the approach is in evaluating the sources and losses such that their balance agrees with the beach erosion or deposition. An assessment of the long term state of a beach can be determined by considering the credits and debits of sand that pass through a coastal system. 4. Methods Chapter 6 INPUTS (credits) : + Longshore transport into beach + River supply + C