transport. Intermittence in sediment supply as from reversal in transport may have
direct bearing on spit recurving. However, as a first step, the present work primarily
treats constant forcing through time.
Table 1. Parameters controlling inlet spit geometry and evolution, and the associated
processes
1
Spit Parameter
Short Term
Long Term
Sediment supply; geologic
Length
Longshore transport rate; proximity to inlet
controls; breaching (bayward or
channel; strength of channel current
seaward); cyclic & intermittent
forcing
2
Longshore transport rate; grain size;
Cyclic and intermittent forcing
Elongation speed
proximity to inlet channel; beach slope and
depth-contour gradients parallel to spit
Width
(see Overwash fans below)
Run-up elevation; tidal range; depth-
contour gradients perpendicular to spit
Dunes and other blocking
Overwash fans
Storm surge; frequency of storms
features; depth of receiving bay
or lagoon
Run up; tidal range
Elevation above
Aeolian transport; relative sea-
MSL
level change; tsunami
Depth of closure
Extreme storms; elapsed time
Wave height and period; tidal range; grain
size
Tendency to
Proximity to channel; channel current;
Cyclic and intermittent forcing
recurve
wave focussing; extreme storms
1.
Long-term processes encompass those of short-term processes in same category.
2.
Cyclic and intermittent forcing arises from seasonal and annual changes in wind and waves,
arrival of storms and weather fronts, annual and inter-annual change in water level, etc.
ANALYTICAL MODEL
In developing the analytical model of spit evolution, standard assumptions
entering shoreline-change mathematical modeling are applied (e.g., Hanson and
Kraus 1989; Larson et al. 1997). In particular, we assume (see Fig. 1 for notation):
The spit elongates solely by gradients in longshore sediment transport rate Q;
The spit maintains a constant width, W;
Active movement of the spit occurs within the vertical distance D composed
of the sum of the berm elevation B and depth of closure DC measured from a
common datum such as mean water level; and
Contours of the spit move in parallel over representative time scales.
Based on a laboratory physical-model study and interpretation of field evidence,
Meistrell (1972) introduced the concept of "spit-platform," comprised of a spit or
ridge above mean low water level that resides on the platform a sedimentary
structure elevated above the ambient shelf, but below mean low water. Meistrell
Kraus
3
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