Coastal Engineering 48 (2003) 51 65
Limiting slopes and depths at ebb-tidal shoals
Frank S. Buonaiuto a, Nicholas C. Kraus b,*
Marine Sciences Research Center, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
US Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, 3909 Halls Ferry Road, Vicksburg,
MS 39180-6199, USA
Received 19 November 2001; received in revised form 23 October 2002; accepted 15 November 2002
Dense bathymetry surveys obtained by LIDAR at 13 small to medium coastal inlets of the continental United States were
analyzed to quantify limiting (maximum) bottom slopes of ebb shoals and entrance channels. The LIDAR data were supplemented
with conventional bathymetry measurements from five large inlets to obtain predictive relationships for the limiting (minimum)
depth over crest of the ebb shoal. The sites, all located on sandy coasts, were chosen to cover a range in tidal amplitude, tidal prism,
and average annual wave height. Wave-dominated inlets exhibited steeper slopes on their seaward margins than tide-dominated
inlets. Slopes on ebb shoals typically do not exceed 4 6j, with seaward slopes being 1 2j steeper than landward slopes. Dredged
entrance channels have steeper slopes than natural channels, with maximum slopes immediately after dredging reaching 6 8j. At
one inlet having a series of LIDAR surveys, entrance channel maintenance dredging created 3 5j side slopes that decreased 0.5
1j/year for the next 2 years to achieve a typical slope of 3j along much of the channel. Greatest bottom slopes are found in scour
holes near jetties (10 12j) and at the entrance bars (8 10j) of (tideless) Great Lakes harbors. Limiting depth over crest of the ebb
shoals is predicted well by the parameter (HSP)1/4, where HS is the average annual significant wave height, and P is the spring tidal
prism. High correlation was also found between limiting depth and prism, and with limiting depth and wave height.
D 2002 Elsevier Science B.V. All rights reserved.
Keywords: Channels; Coastal inlets; Ebb-tidal shoals; Lidar; Limiting depth; Slopes
controlling inlet morphology. Development of the ebb
shoal also depends on the slope of the inner shelf and
The ebb shoal, channel, and related morphologic
asymmetry of the tidal wave at the particular site. Des-
features at coastal inlets evolve under the action of the
pite the complexity of the physical processes (FitzGer-
tidal current (or current associated with seiching on the
ald, 1996; FitzGerald and FitzGerald, 1977), morpho-
Great Lakes of the United States), waves and wave-ge-
logic characteristics of inlets, such as minimum channel
nerated currents, and surrounding geologic framework.
cross-sectional area and volume of the ebb shoal, have
Storms, river flows, wind-generated currents, jetties,
been successfully quantified in terms of just a few
parameters of which tidal prism plays a leading role.
and dredging are other mechanisms and interventions
Empirical relations are available for estimating a
large number of long-term average morphologic prop-
* Corresponding author. Fax: +1-601-634-2055.
erties of coastal inlets (Table 1). Many of the relations
E-mail address: firstname.lastname@example.org
presented in Table 1 pertain to inlets of the United
0378-3839/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.