ERDC/CHL CHETN-II-46
March 2002
Longshore Sand Transport Initial
Results from Large-Scale Sediment
Transport Facility
by Ping Wang, Bruce A. Ebersole, and Ernest R. Smith
PURPOSE: Accurate predictions of the total rate of longshore sand transport (LST) and its
cross-shore distribution pattern in the surf zone are central to many coastal engineering studies.
Present understanding and methods for calculating the LST rate are largely developed based on
field studies (e.g., Komar and Inman 1970; Inman et al. 1981; Kraus et al. 1982; Bodge and Dean
1987a, b; Dean 1989; Schoonees and Theron 1993; Miller 1998; Wang, Kraus, and Davis 1998;
Wang 1998; Wang and Kraus 1999; Miller 1999). The Coastal Engineering Research Center
(CERC) formula (Shore Protection Manual 1984), which is based on field measurements, is
often used to calculate the total LST rate. Accuracy of the CERC formula is believed to be
30-50 percent and several parameters that logically might influence LST are excluded in the
formula, such as breaker type and grain size. The GENESIS shoreline change model, a tool
commonly used in shore protection and beach-fill project design, utilizes the CERC formula. In
the GENESIS model, the cross-shore distribution of LST is assumed to be uniform across the
surf zone. Laboratory data (Bodge 1986; and Kamphuis 1991) and field data (Zenkovitch 1960;
Ingle 1966; Bodge and Dean 1987a, b; Miller 1998) suggest that the distribution is not uniform.
This technical note summarizes results of initial experiments conducted in the new Large-
scale Sediment Transport Facility (LSTF) (see Fowler at al. 1995; Hamilton and Ebersole 2001
for additional details about the LSTF). Experiments are underway to investigate the importance
of breaker type (spilling and plunging breakers) on LST, to examine the accuracy of presently
used methods for calculating the total LST rate, and to aid in developing improved predictors for
both the total LST rate and its cross-shore distribution patterns for varying surf conditions.
Initial results concerning the cross-shore distribution pattern for the two different types of
breaking waves are also presented. The LTSF experiments are intended to span the gap between
laboratory measurements and low-energy field measurements. The LSTF is capable of
simulating wave conditions that are almost directly comparable to annual averages along many
low-wave-energy coasts, for example a majority of estuarine beaches (Nordstrom 1992) and
many beaches along the Gulf of Mexico and the Great Lakes in the U.S.
BACKGROUND: A commonly used tool for predicting the total rate of longshore transport is
the CERC formula (Shore Protection Manual 1984),
5
3
Kl
sin ( 2θb )
H s2
Q=
ρg 2
(1)
b
16 γ
where γ is the breaker index, often taken to be 0.78, ρ is the density of water, g is gravitational
Previous Page
