Formulation
The most fundamental activity in the process of developing a sediment budget is to
review and integrate existing knowledge of the site with the goal of developing a conceptual
sediment budget. The conceptual sediment budget represents a working hypothesis of
sediment-transport magnitudes and pathways. A conceptual sediment budget for the 1979
to 1995 period was formulated based on earlier studies and the initial analyses discussed
previously. The conceptual budget was formulated for the region as a means of
"bracketing" reasonable values for sources and sinks to the littoral system, and to discern
any potential problems with the available data and applied assumptions. The final
conceptual budget is shown in Fig. 4 for each primary morphologic reach. In Fig. 4, Qnet
is the net LST rate entering or exiting a cell; Qbluff is the source of littoral material from the
Montauk Point bluffs; Qsl is the beach loss attributed to relative sea level rise; Qbreach is the
cross-shore beach loss estimate due to breaches; and ∆V, P, and R are as defined in Eq. (1)
based on the Dec 1979 to Mar/Apr 1995 shoreline position data, except for the Montauk
Reach (discussed below). Note that the inlet cells include the inlet channel, ebb and flood
shoals, and adjacent beaches for approximately 3 km on both sides of the inlet.
Results
Montauk Reach. The ∆V and P values based on the 1979 to 1995 data (see Fig. 4)
applied in Eq. (1) require an eastward-directed net LST rate at the western boundary equal
to 55,000 + 33,000 m3/yr. Previous sediment budgets have estimated a westward-directed
net LST rate in the vicinity of Shinnecock Inlet for the 1955 to 1979 time period in the
Fire Island
Westhampton
Montauk
Qbluff=33+33
43 km
6 km
19 km
6 km
55 km
∆V= -96
∆V= -203
∆V= -4
∆V= 65
1979 to 1995 data:
P= 76
P= 94
P= 51
P= 63
∆V-P= -6
R= 21
R= 57
Modified:
∆V-P = -143 to -209
Qnet=349
Qnet=140
Qnet=117
Qnet=45
Qnet=115
Qnet=0
Qsl=11
Qsl=11
Qsl=38
Qsl=94
Qsl=88
Qbreach=62
Units: 1000s m3/yr
Note: ∆V and P for the barriers based
on data from 1979 to 1995 time period
except for Montauk Reach
Fig. 4. Final conceptual regional sediment budget (representative of 1979 to 1995 period).
range of 219,000 to 233,000 m3/yr. The conceptual budget requires a reversal (eastward-
directed) in the net LST rate east of Shinnecock to balance Eq. (1). This is not a
representative condition for the 1979 to 1995 period, indicating that other data and/or
assumptions for the Montauk Reach are faulty. The potential LST calculations conducted
Rosati et al.
10
Previous Page
