Detailed study of inlets through barrier islands on the U.S. Atlantic and gulf coasts shows that the shape of the shoreline at an inlet can
be classified in one of four characteristic planforms. (See Figure 4-58,
adapted from Galvin, 1971.) Inlets with overlapping offset (Fig. 4-59)
occur only where waves from the updrift side dominate longshore transport.
Where waves from the updrift side are less dominant, the updrift offset
(Fig. 4-59) is common. Where waves approach equally from both sides, inlets typically hâve negligible offset. (See Figure 4-60.) Where the supply of littoral drift on the updrift side is limited, and the coast is
fairly well exposed, a noticeable downdrift offset is common as, for example, in Southern New Jersey and Southern Delmarva. (See Hayes, et al,,
(1970.) These planform relations to littoral processes hâve been found
for inlets through sandy barrier islands, but they do not necessarily hold
at inlets with rocky boundaries. The relations hold regionally, but temporary local departures due to inlet migration may occur.
4.82 FIELD STUDY
A field study of the problem area is usually necessary to obtain
types of data not found in the office study, to supplément incomplète
data, and to serve as a check on the preliminary interprétation and corrélations made from the office data. Information on Coastal processes may
be obtained from wave gage data and visual observations, sédiment sampling, topographie and bathymétrie surveys, tracer programs, and effects
of natural and manmade structures.
4.821 Wave Data Collection. A wave-gag in g program yields height and
period data. However, visual observations may currently be the best
source of breaker direction data. Thompson and Harris (1972) determined that 1 year of wave-gage records provides a reliable estimate of
the wave height frequency distribution. It is reasonable to assume that
the same is true for wave direction.
A visual observation program is inexpensive, and may be used for
breaker direction and for régional coverage when few wave-gage records
are available. The observer should be provided with instructions, so
that ail data collected will be uniform, and contact between observer
and engineer should be maintained.
/
Sédiment Sampling. Sédiment sampling programs are described in
ion 4.26. Samples are usually surface samples taken along a line
P rpendicular to the shoreline. These are supplemented by borings or
res as necessary. Complété and permanent identification of the samPle is important.
4.823 Surveys. Most engineering studies of littoral processes require
surveying the beach and nearshore slope. Successive surveys provi e
data on changes in the beach due to storms, or long-term érosion or
accretion. If beach length is also considered, an approximate vo urne
of sand eroded or accreted can be obtained which provi es m orma
for the sédiment budget of the beach. The envelope of a profile defin
4-147
be classified in one of four characteristic planforms. (See Figure 4-58,
adapted from Galvin, 1971.) Inlets with overlapping offset (Fig. 4-59)
occur only where waves from the updrift side dominate longshore transport.
Where waves from the updrift side are less dominant, the updrift offset
(Fig. 4-59) is common. Where waves approach equally from both sides, inlets typically hâve negligible offset. (See Figure 4-60.) Where the supply of littoral drift on the updrift side is limited, and the coast is
fairly well exposed, a noticeable downdrift offset is common as, for example, in Southern New Jersey and Southern Delmarva. (See Hayes, et al,,
(1970.) These planform relations to littoral processes hâve been found
for inlets through sandy barrier islands, but they do not necessarily hold
at inlets with rocky boundaries. The relations hold regionally, but temporary local departures due to inlet migration may occur.
4.82 FIELD STUDY
A field study of the problem area is usually necessary to obtain
types of data not found in the office study, to supplément incomplète
data, and to serve as a check on the preliminary interprétation and corrélations made from the office data. Information on Coastal processes may
be obtained from wave gage data and visual observations, sédiment sampling, topographie and bathymétrie surveys, tracer programs, and effects
of natural and manmade structures.
4.821 Wave Data Collection. A wave-gag in g program yields height and
period data. However, visual observations may currently be the best
source of breaker direction data. Thompson and Harris (1972) determined that 1 year of wave-gage records provides a reliable estimate of
the wave height frequency distribution. It is reasonable to assume that
the same is true for wave direction.
A visual observation program is inexpensive, and may be used for
breaker direction and for régional coverage when few wave-gage records
are available. The observer should be provided with instructions, so
that ail data collected will be uniform, and contact between observer
and engineer should be maintained.
/
Sédiment Sampling. Sédiment sampling programs are described in
ion 4.26. Samples are usually surface samples taken along a line
P rpendicular to the shoreline. These are supplemented by borings or
res as necessary. Complété and permanent identification of the samPle is important.
4.823 Surveys. Most engineering studies of littoral processes require
surveying the beach and nearshore slope. Successive surveys provi e
data on changes in the beach due to storms, or long-term érosion or
accretion. If beach length is also considered, an approximate vo urne
of sand eroded or accreted can be obtained which provi es m orma
for the sédiment budget of the beach. The envelope of a profile defin
4-147