The offshore bar constructed by storm waves is returned to the beach by subsequent swell waves in a matter of two or three weeks. During this process sediment suspension and littoral current are excessive, which results in a large pulse of littoral drift. Longshore transport at this time can be an order of magnitude greater than that throughout the remaining swell season. It is such pulsational movements that cause sand spits to form or enlarge across river mouths or embayments. Calculations of littoral drift from accretion assumed to be over a year can be grossly in error.

Littoral Drift Caused by Storms

https://link-springer-com-443.webvpn.jmu.edu.cn/content/pdf/10.1007%2F978-3-319-48657-4_134-2.pdf

Engineering Applications of Coastal Geomorphology

This study describes the formation and reduction processes of river deltas and their control. Based on the similarity process between the flow motion within the boundary layer and the nearshore currents within the surf zone, the concept of the boundary layer theory is introduced. The theory is authorized by two essential assumptions; they are the velocity profiles of longshore currents are similar and wave set-up is independent of longshore direction. Employing these assumptions, the nearshore current equations can be simplified to arrive a single equation for non-uniform longshore currents. This equation is similar to the boundary layer equation and contains integration coefficients which depend only on the velocity profiles oflongshore currents. Therefore, an experimental study on the similarity of velocity profiles in non-uniform longshore currents was carried out. The experimental results reveal that the coefficients which appeared in the equation of non-uniform longshore currents are not functions oflongshore direction nor time. An extension is made to Tsuchiya and Yasuda's formulation of longshore sediment transport rate to include the non-uniform terms. The new formulation of non-uniform longshore sediment transport includes the effects of sediment size, beach slope and bed, roughness, and has been verified with the field and laboratory data plotted in the well known Komar's figure. The physical description of river delta formation is investigated through studying two field cases: the Nile Delta coast, Egypt and the major river deltas in Lake Biwa, Japan. The formation process of river deltas is investigated analytically and experimentally. The effect of longshore variation of beach slope on the configuration of river delta is studied. The theoretical and experimental results reveal that; for river-dominated delta type, beach slope is remarkably varied along the river delta with steeper beach slope at the river mouth and milder one at the end sides of the river delta. Thus, the configuration of river delta is sharply formed. In the contrary, for wave-dominated delta type, the longshore variation of beach

The formation and reduction processes of river deltas and their control

Many methods used previously to reduce or prevent erosion have not worked effectively. It isnow necessary, due to rising costs of construction, to examine old methods and see if Nature hasindicated some direction in which to go. Limitations of groins, seawalls and beach reclamation aredescribed. The most effective natural method of controlling beach erosion by the formation of anoffshore bar is described. The need for normal return of this material to the beach is met by the zetashaped bays sculptured between headlands by persistent swell waves. Man can copy Nature byinstalling offshore breakwaters in order to form stable bays along an eroding coast. The indentationof these is limited and is predictable from the obliquity of the waves or the angle between the down-coast shoreline and the headland alignment. This method has been used successfully in Singaporein spite of the extreme obliquity of the incident swell.

/pdf/a-new-look-at-beach-erosion-control-4nu1dqhv26.pdf

Richard Silvester

Papers

A new look at beach erosion control