ERDC/CHL CETN-IV-28
September 2000
Table 1
Present Content of DMS Manual
1. Horizontal Channel Expansion
5. Multiple Channels
Ebb Tidal Shoal
Branches
2. Vertical Channel Expansions
6. Enhanced Sediment Forcing
Littoral Drift
3. Sheltered Areas
Downstream of Erodible Features
Sediment Transport
4. Changes in Channel Alignment
Inside of Channel Bends
Breaching
Figure 1 is a sample page from the Manual, Category 1 "Horizontal Channel Expansion," and
subcategory of "Expansion into Bay Flood Tidal Shoal." Two examples are given on this
particular page, for Bakers Haulover, FL, and Shinnecock Inlet, Long Island, NY. At both
locations, the flood shoal is growing with associated deposition in the adjacent navigation
channels. The sketch and photographs allow identification and categorization of the shoaling
process.
Growth of large flood shoals indicates a possible flood dominance, that is, the flood flow is
stronger but of shorter duration than the ebb flow. An example is shown in Figure 2, which is a
plot of velocity measured in the middle of Shinnecock Inlet. Because the sediment transport rate
is proportional to some large power of the velocity, for example, the velocity cubed, the stronger
flowed flow will tend to sweep bayward sediment that is deposited into the channel by the
longshore current. The plot in Figure 2 is translated upward (toward flood), indicating a mean
trend toward filling of the bay during that time. Prior to the time interval shown in this plot, the
bay level had been lowered by a wind that had forced water out of the inlet.
Depending upon the situation, possible solutions for the grown of flood shoals that may encroach
into bay side navigation channels include: moving the channel further bayward from the inlet
and the flood shoal; dredging a deposition basin between the channel and the flood shoal, from
which captured sediment might be pumped to the downdrift beach as nourishment; and to modify
the jetties or channel in such a way as to reduce the flood dominance.
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