type of shoaling is usually accompanied by a region of scour or erosion 

 upstream of the shoal. 



Changes in Channel Alignment. Changes in channel alignment can refer 

 to either natural changes (meandering) or artificial changes (e.g., struc- 

 turally redirected flows). A change in channel alignment redirects the 

 flow momentum. Conservation of momentum dictates the establishment 

 of secondary currents within the conveyance that spin about the flow 

 axis. These vortices tend to erode sediment from the outer bank of a 

 bend and deposit it at the inner bank. 



Multiple Channels. Intersections of watercourses can create complicated 

 flow patterns. Often, these patterns include areas of flow acceleration 

 and deceleration. Decrease in velocity implies a decrease in sediment- 

 transport potential and hence an increase in the probability of shoaling. 

 Shoaling probability increases where one of the intersecting channels is a 

 riverine sediment source. 



Enhanced Sediment Forcing. This miscellaneous category of channel- 

 shoaling classification includes mechanisms that do not fall into the 

 above categories. These shoaling mechanisms include sediment 

 transport by winds, waves, storms, and large-scale current patterns. 



In the future, each of the above categories is expected to be further divided into 

 subcategories. Each page of the manual will be devoted to one of the 

 subclassifications of channel shoaling. As an example, the Horizontal Channel 

 Expansions category may be divided into three subclassifications: (a) Expansion 

 into Ocean - Ebb-Tidal Shoal, (b) Expansion into Bay - Flood-Tidal Shoal, and 

 (c) Areas of Shoreline Recession. 



Each page of the manual will feature the same format. Figures 9 through 12 

 show examples of envisioned manual format. At the top of each page is the main 

 shoaling classification and subclassification. Below this heading on the left of 

 the page is a general diagram of the shoaling patterns and forcing mechanisms. 

 These diagrams are drawn as simply as possible to aid in identification of 

 shoaling patterns that can vary significantly in size and shape. Below the 

 drawing is a short description of the shoal. Below this is a short narrative 

 describing the physical processes that create the shoal. At the bottom left is a 

 reference containing a case study dedicated to an example of this type of shoal. 

 An aerial photograph depicting the shoal pattern is located on the right of the 

 page, below the heading. Below the photograph is a description of the depicted 

 site, the date of the photograph, and a description of the project and shoaling 

 history. 



Manual use 



The DMS-Manual is a diagnostic tool. The engineer responsible for channel 

 maintenance begins the shoal-classification process by collecting all pertinent 

 data about the channel. These data will include aerial photographs, channel 

 hydrographic surveys, and dredging history. Data collection in the DMS-Data 



24 Chapter 3 DMS-Manual 



