3 DMS-Manual 



This chapter describes the structure and use of the DMS-Manual. The 

 chapter also presents the manual's application to shoaling problems at East Pass 

 Inlet. 



Manual Description 



Manual structure 



The DMS-Manual is a tool for identifying the type of shoaling problem 

 encountered on a case-by-case basis. As envisioned, the multipage document 

 will serve as a field guide to shoaling problems. Each page of the manual 

 corresponds to a different shoaling pattern. At present, the manual has identified 

 six main shoal classifications or patterns: 



• Horizontal Channel Expansions. Horizontal expansions of channel 

 boundaries are most times accompanied by an increase in cross-sectional 

 area of the conveyance. Conservation of flow dictates an accompanying 

 decrease in velocity. If the currents are transporting sediment, a decrease 

 in velocity will reduce the sediment-transport capacity and therefore 

 cause sediment to come to rest. This deposition of sediment creates a 

 shoal. 



• Vertical Channel Expansions. Similar to the previous category, vertical 

 expansions of channel boundaries are also accompanied by an increase in 

 cross-sectional area of the conveyance. Again, conservation of flow 

 dictates an accompanying decrease in velocity. If the currents are 

 transporting sediment, a decrease in velocity will reduce sediment- 

 transporting capacity and, therefore, tend to cause deposition of 

 sediment. This deposition creates a shoal at and after the expansion. 



• Sheltered Areas. Protuberances (e.g., headlands and structures) in a 

 conveyance cause flow to accelerate at the obstruction by reducing the 

 channel cross-sectional area. This acceleration increases the sediment- 

 transport potential at the obstruction. Downstream of the obstruction, 

 complicated flow patterns create regions of low velocity and low 

 turbulence in addition to flow readjustment to the increased cross- 

 sectional area. Lower velocities reduce the sediment-transport potential. 

 This reduction increases the probability of sediment deposition. This 



Chapter 3 DMS-Manual 23 



