Field Investigation of Longshore Transport Distribution

Abstract

Following a change in wave direction, the active contours in an idealized pocket beach respond by rotating such that they approach a perpendicular orientation relative to the incoming wave rays. Assuming that cross-shore sediment transport does not contribute to this contour rotation, and that the contours are in the early stages of this equilibration process, the amount of contour rotation can be interpreted as the cross-shore distribution of the longshore sediment transport. As part of the Nearshore Sediment Transport Study, detailed nearshore profile measurements were conducted at Santa Barbara, California. Twenty-two of these profile lines were located on Leadbetter Beach, which is a quasi-pocket beach. To explore the concept described above, two of the nine intersurvey periods were selected due to their strong indications of wave direction change. Analysis of these data sets yielded two estimates of cross-shore distribution of longshore sediment transport which were compared with those presented by Komar, Fulford and Tsuchiya. Although these three distributions differ significantly, the effect of the tidal variations is to "smear" the differences in the inferred distributions as evident in the contour displacements. It was found that none of the relationships for longshore transport distribution predicted the amount of transport inferred in water depths greater than one meter. It is possible, especially for one of the intersurvey periods that the changes in contour locations were so extreme that substantial crossshore sediment transport was induced and would be interpreted as longshore transport occurring in water depths greater than had actually occurred. The method introduced here should be useful in other field and laboratory programs to investigate the cross-shore distribution of longshore sediment transport.

Coupling cross-shore and longshore sediment transport to model storm response along a mixed sand-gravel coast under varying wave directions

“…The LST distribution for k = 2 is the most uniform with the maximum located in the middle between the total run-up limit and the breaking line (at x/x b = 0.5). This distribution is similar to that previously observed on sandy beaches (Berek and Dean, 1982;Bayram et al, 2001). The LST distribution for k = 10 is the most asymmetrical with the maximum located at x/x b = 0.1, concentrating most of the LST in the inner nearshore region (Figure 10a3-d3).…”

“…In these coastal areas, it is particularly important to consider not only the crossshore sediment transport, but also the effects of LST (De Alegría-Arzaburu and Masselink, 2010;Masselink et al, 2016). Recent advances are available to estimate LST on sand, gravel and shingle beaches (Van Rijn, 2014); but the cross-shore distribution of LST, widely studied on sandy beaches (e.g., Berek and Dean (1982); Komar (1983); Kamphuis (1991); Bayram et al (2001)) and relevant for modelling coastal response, has not been investigated in depth on gravel and MSG beaches (Van Wellen et al, 1998;Van Wellen et al, 2000).…”

Longshore Sediment Transport Rate Measured by Short-Term Impoundment

“…Streamer traps measure the transport rate by quantifying the sediment flux through the water column and across the surf zone over measurement intervals of 5 -10 min (Kraus 1987;Rosati and Kraus 1989;Wang 1995Wang , 1998. The impoundment method measures the longshore transport rate by quantifying morphological change by either blocking sand movement with a shore-normal structure or reducing the transport with a shoreparallel structure (Berek and Dean 1982;Bodge 1987;Bodge and Dean 1987;Dean 1989). Long-term impoundment studies (Berek and Dean 1982;Dean 1989) involve measurement of material blocked by permanent coastal structures, and the transport rates obtained typically represent averages over months.…”

“…The impoundment method measures the longshore transport rate by quantifying morphological change by either blocking sand movement with a shore-normal structure or reducing the transport with a shoreparallel structure (Berek and Dean 1982;Bodge 1987;Bodge and Dean 1987;Dean 1989). Long-term impoundment studies (Berek and Dean 1982;Dean 1989) involve measurement of material blocked by permanent coastal structures, and the transport rates obtained typically represent averages over months. Watts (1953) correlated transport rates with the amount of sediment hydraulically bypassed at an inlet.…”

Rehabilitation of the South Jetty, Ocean City, Maryland

“…The majority of these investigations attempted to obtain an actual measured distribution from physical model and/or field studies to test analytical techniques of predicting the distribution. The technique used, placement of bed load sand traps across the surf zone, generally met with limited success.More recent investigations byFulford (1982),Berek and Dean (1982), and Bodge and Dean (1987) concentrated on obtaining the longshore distri bution of sediment transport across the surf zone by measuring the updrift accretion at a total littoral barrier in both the offshore and alongshore directions.…”