Wave Action and Bottom Movements in Fine Sediments

Abstract

Mudbanks have been observed to have an extraordinary calming effect on the sea surface. In certain cases this effect is due primarily to the transfer of energy through the sea/mud interface and its frictional dissipation within the bottom sediments. This paper describes an experiment that measured wave characteristics and the resulting sea floor oscillations in an area where the bottom is composed of fine-grained sediments. The energy lost by the waves at the position of the experimental setup is calculated and compared with a direct measurement of the net energy lost by the waves in going from the point of the experiment to a station 3.35 km inshore. Results show that bottom motions in the range of wave-induced bottom pressures from near zero to 2.39 x 10-3 Pascal have the appearance of forced waves on an elastic half space. The apparent effect of internal viscosity is seen in a phase shift between the crest of the pressure wave and the trough of the mud wave. Measurements show this angle to be 22° (ill") for the peak spectral component (T = 7.75 seconds). The energy lost to the bottom by the waves at the field site was found to be at least an order of magnitude greater than that resulting from the processes of percolation or that caused by normal frictional effects. This newly observed mechanism for the dissipation of wave energy is particularly important for waves in intermediate-depth water and could be a prime factor in determining design wave heights in muddy coastal areas.

Storm deposits and storm‐generated coarse carbonate breccias on a pelagic outer shelf (South‐East Basin, France)

“…However, it is well known that deep‐water waves begin to react with the sea floor and undergo shoaling transformations as a result of wave–sea floor interaction when they move shorewards (Friedman & Sanders, 1978). After the pioneer work of Putman & Johnson (1949), soil engineers have studied wave–sea floor interactions using analytical approaches (Gade, 1958; Dalrymple & Liu, 1978; Hsiao & Shemdin, 1980; Yamamoto et al ., 1983; Clukey et al ., 1988), tank experiments (Yamamoto & Schuckman, 1984) or in situ observations (Suhayda, 1977; Tubman & Suhayda, 1977; Forristal & Reece, 1985; Trevorrow et al ., 1988; Hooper, 1996). Wave attenuation is the decrease in wave height and wave period as a function of the distance travelled by the waves.…”

Observations of nearshore wave dissipation over muddy sea beds

“…Bottom sedimentary fabric should have negligible effect on short waves, which interact weakly with the bottom. The long wave paradigm has also influenced the planning of field experiments [ Tubman and Suhayda , 1976; Forristall and Reece , 1985], with instruments typically deployed at two locations along the long wave propagation path, in deep and relatively shallow water (e.g., 312‐m and 20‐m isobaths from Forristall and Reece [1985]). Focusing on long wave propagation alone simplifies the problem by eliminating the need to account for wind input and wave breaking.…”

Gulf of Mexico Shallow-Water Wave Heights and Forces

“…Excessive attenuation of wave energy in the Mississippi Delta area has been attributed to this dissipation mechanism by Gade (1958), , Tubman and Suhayda (1976), Schapery and Dunlap (1978) and others. Excessive attenuation of wave energy in the Mississippi Delta area has been attributed to this dissipation mechanism by Gade (1958), , Tubman and Suhayda (1976), Schapery and Dunlap (1978) and others.…”