Manager allows the engineer to obtain a visual picture of the size and location of the 

 shoal. Upon completion of this task, the engineer then consults the DMS-Manual. 

 Having obtained a visual image of the shoal, the engineer compares this image with the 

 general drawings and example photographs. This process results in the selection of one 

 or more classifications that may describe the shoal. Upon reading the description of the 

 shoal and the physical processes that created it, the engineer should be able to narrow the 

 choice even further. Obtained before application of the DMS, knowledge about the 

 physical processes in the watercourse (e.g., wind and wave climate, storm history, and 

 current strength and patterns) further simplifies this process. 



Identification of the type of shoal is the first step in obtaining more appropriate and 

 cost-effective shoaling mitigation methods. By identifying the type of shoal, the engineer 

 has also identified the processes that led to shoal creation. Addressing the processes (the 

 disease) rather than the shoaling (the symptom) greatly increases the probability of 

 finding an effective shoaling mitigation method (the cure) in the DMS approach. 



Sometimes, shoals may result from several different mechanisms acting in concert. 

 In such cases, the manual lists the shoal under more than one classification. Here, 

 addressing either one or both of the processes provides a successful mitigation method. 

 For example, shoaling occurs in a channel that crosses perpendicular to tidal currents. 

 However, the sediment in the shoal originates from an upstream shoreline exposed to 

 waves. Waves erode the shoreline, and tidal currents transport the sediment towards the 

 channel where the sediment gets deposited because of vertical expansion. Here, the 

 physical processes at play include tidal currents and waves. By only addressing the 

 waves, the engineer may be able to cut off the sediment source rather than try to treat 

 both waves and currents. Regardless, in situations where more than one shoal 

 classification applies, the manual recommends a more detailed analysis by means of 

 using the DMS-Analytical Toolbox. 



Example Application - East Pass Inlet 



As identified in Figure 5, the maintained channels at East Pass Inlet exhibit three 

 areas of chronic shoaling. In this example, the type of shoaling in each of these areas is 

 identified using the DMS-Manual and the information collected and contained in the 

 DMS-Data Manager. 



Area 1 : Outer Bar 



This shoal is located in the maintained channel south of the jetty tips where the 

 channel crosses the ebb shoal. According to dredging records (Table 2), approximately 

 16,000 cu yd/year are dredged from this location. Figure 7 illustrates the location of the 

 outer bar shoal in 1990. Based solely on the shoal's location, the most likely 

 classification is Horizontal Expansions: Expansion Into Ocean - Ebb Tidal Shoal 

 (Figure 9). The sample manual page describes the shoal as follows: "Crescent- or box- 

 shaped shoal that forms at the seaward end of a tidal inlet. Shape of this shoal depends 

 on the area's wave climate." This description exactly matches the morphology 

 encountered at this area. Comparing the generalized figure with Figure 7 further 

 validates this choice. 



With the shoal type identified, the next step in the DMS is to identify the shoaling 

 mechanisms and investigate possible shoaling mitigation methods. In this case, the 



Chapter 3 DMS-Manual 29 



