physical processes that build the shoal involve the transportation of sediment offshore by 

 the ebb jet. The sediment source is the littoral drift on either side of the inlet. Because 

 the only access to Choctawhatchee Bay from the Gulf of Mexico is through the jetties, 

 location of the channel over the ebb shoal is unavoidable. In dealing with channels over 

 ebb shoals, the most common means of lowering dredging costs is to perform regular 

 surveys of the ebb shoal and situate the channel such that it crosses the shoal at the 

 deepest point. The Mobile District has already incorporated this practice into its regular 

 maintenance of the channels at East Pass Inlet in its dredging optimization procedure. 



Area 2: Channel Bend 



Beginning approximately 1,000 ft north of the jetty tips and continuing for 2,000 ft in 

 a north and then north-northwest direction, this shoaling hot spot is centered around the 

 southern bend in the project channel. Dredging records do not specify the exact amount 

 removed from this area. One can safely assume, however, that shoaling in this area 

 contributes greatly to the -38,000 cu yd/year (East Pass Channel plus Entrance Channel 

 categories denoted in Table 2) dredged from the inlet throat. Consultation of the manual 

 gives two possible categories for shoal classification. The first possible classification is 

 Horizontal Channel Expansions: Areas of Shoreline Recession (Figure 10). The 

 configuration of the converging jetties (which diverge as one moves south to north) 

 prompts selection of this category. Under this classification, sediment-laden currents 

 travel from an area of flow constriction (between the jetty tips) to an area of low velocity 

 (north of the jetties where the throat becomes wide). Here, with the transport potential 

 reduced, deposition occurs. The sediment source may be either the sediment eroded from 

 the channel between the tips of the jetties or (more likely) the suspended sediment 

 resulting from the inlet's interruption of littoral drift. 



The second possible classification is Vertical Expansions: Cross Channel Flow 

 (Figure 11). Under this category, shoals form where flow crosses the channel at an angle 

 to the channel's axis. Currents carrying sediments cross from areas of shallow depths to 

 areas of deeper depths. The change in depth is accompanied by a reduction in velocity 

 and hence a reduction in sediment-transport potential. Sediment, therefore, deposits 

 immediately beyond the change in depth. At this channel location, the channel bends 

 from a north/south to a north-northwest/south-southeast orientation. This change in 

 orientation increases the likelihood that, at some point (either on flood or on ebb), 

 currents will cross the channel in a direction other than in line with the channel axis. 



Given that the DMS-Manual has identified two possible shoal classifications, this 

 shoaling hot spot is a good candidate for further investigation using the DMS-Analytical 

 Toolbox. 



Area 3: Old Pass 



Figure 5 shows the location of Old Pass channel. The channel attaches to the main 

 channel just south of the Highway 98 Bridge. From there, the channel runs in a east- 

 northeast direction until it reaches the tip of Norriego Point. At the tip of the point, the 

 channel bends south acquiring a southeast orientation as it enters Destin Harbor. From 

 1969 to 1995, this short channel has accounted for approximately one-third of the 

 dredging activity at the inlet. 



30 Chapter 3 DMS-Manual 



