In the table, A^ is the minimum cross-sectional area helow MSL in 

 square feet and P is the tidal prism in cubic feet for the spring 

 or diurnal tidal range reported in the National Oceanic and Atmospheric 

 Administration, National Ocean Survey Tide Tables (1976]'+. 



A solution of the appropriate tidal prism-channel cross-sectional 

 area equation from the table, and the hydraulic characteristic equations 

 using Figures 2, 3, and 4 for the tidal prism and channel area that 

 satisfy both criteria, will yield a predicted stable channel cross- 

 sectional area. It is possible, should the channel be too long or the 

 bay area or tidal range too small, that no common solution to the stabil- 

 ity and hydraulic criteria will be found, indicating that no channel 

 cross-sectional area would be stable. Any dredged channel at this loca- 

 tion would eventually close if sediment is available to fill the channel, 



V. EXAMPLE DESIGN PROBLEM 



************** EXAMPLE PROBLEM ************** 



GIVEN : A bay with a surface area of 2 x 10^ square feet (1.86 x 10^ 

 square meters) and an average depth of 20 feet (6.1 meters) is located 

 on the Atlantic coast. The tide is semidiurnal (T = 12.4 hours) with 

 a spring range of 4.4 feet (1.34 meters), as given by the National 

 Ocean Survey Tide Tables. An inlet channel, which will be the only 

 entrance to the bay, is to be constructed across the barrier beach 

 which separates the bay from the ocean. The inlet is to provide a 

 navigation passage for small vessels, dilution water to control bay 

 salinity and pollution levels, and a channel for fish migration. 

 The channel is to have a design length of 3,600 feet (1,097 meters) 

 with a pair of vertical sheet pile jetties that will extend the full 

 length of the channel. 



FIND : 



a. If the channel has a depth below MSL of 12 feet (3.66 meters) 

 and a width of 600 feet (183 meters), what are the maximum flow veloc- 

 ity, bay tidal range and phase lag, and the volume of water flowing 

 into and out of the bay on a tidal cycle (tidal prism) for a tide hav- 

 ing the spring range? 



b. Evaluate the potential stability of the proposed channel 

 cross section. 



^NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION, "Tide Tables, East 

 Coast North and South America, Including Greenland," and "Tide Tables, 

 West Coast North and South America, Including the Hawaiian Islands," 

 National Ocean Survey, Rockville, Md., 1976. 



17 



