CETN IV-15
Rev. September 1999
Montauk Point
=0
35
=
t
Q ne
ff
? Q
blu
V=
∆
Shinnecock
?
P=
N
fl)
15(
Inlet
+
bb)
e
77(
t=
Inle
=?
81
∆V
o2
Moriches
t
?
P=
19
=?
=?
=2
Inlet
R
Q sl
Q net
189
to
04
=1
Qn
et
9
=22
Q sl=?
Qn
et
Units: Thousands m3/yr
(not to scale)
Figure 2. Conceptual sediment budget for Shinnecock Inlet, New York
Example 2: Refine the conceptual budget for Shinnecock Inlet and the beaches +3.2 km east
and west of the inlet. Because of space limitations, uncertainty in the sediment budget will be
omitted (refer to CETN-IV-16 for estimating uncertainty within a sediment budget).
Background Information: The refined conceptual budget is shown in Figure 3, and details of its
formulation are presented here. At 3.2 km east of the inlet, wave refraction modeling indicated
that the ratio of QR to QL was approximately 1.9. The same ratio west of the inlet, also estimated
from wave refraction modeling, was 1.8. These ratios indicate a westerly directed net transport
that is slightly greater at the eastern boundary as compared with the western boundary. Based on
profile-survey data, the berm-crest level was 3.5 m relative to National Geodetic Vertical Datum
(NGVD), and the depth of closure was 7.0 m NGVD. The average shoreline change rate ∆y/∆t
for Adjacent Beach 1 (from inlet to 3.2 km east, hereafter noted as A1) was 1.40 m/year, and the
same quantity for Adjacent Beach 2 (from inlet to 3.2 km west, noted as A2) was 1.43 m/year.
Beach-fill placements for A1 and A2 were 13,000 and 25,000 cu m/year, respectively. The rate
of relative sea-level rise was 0.003 m/year, and the distance from datum to the depth of closure
Lc was approximately 760 m for A1 and A2. The inlet channel and shoals had a net volume
change of 111,000 cu m/year, with dredging averaging 2,400 cu m/year (Moffatt and Nichol
Engineers & URS Consultants 1999).
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