General circulation patterns inside inlets are more complex due to the 

 complexity of the interior inlet physiography. 



3. Inlet Currents . 



a. Hydraulic Currents in Inlets . This section presents methods for 

 calculating the time-dependent average cross-sectional velocity in an inlet 

 channel and the bay tidal level range, assuming that the inlet is sufficiently 

 small that inlet currents are hydraulically driven by differences in elevation 

 between inlet and bay vater level elevations. 



Required input data for these calculations include the ocean tidal period 

 and amplitude, the inlet channel length and hydraulic resistance, and the bay 

 surface area. An example is presented to demonstrate these calculations for a 

 hypothetical sea-inlet-bay system. 



Figure 4-74 shows an idealized sea-inlet bay system. The jettied inlet 

 channel has a length L , width B , average depth d , and cross-sectional 

 area A below mean sea level (MSL), and instantaneous average velocity V . 

 Flow in the system is generated by a sea tide having a period T and ampli- 

 tude a and results in a bay level response having the same period and 

 amplitude a^ . The time of high water in the bay lags behind the sea high 

 pn. 



water by a pnase lag e , usually given in degrees. 



is the bay surface 



area, and 2A,a, , the volume of vater that flows into and then out of the bay 

 on a tidal cycle, is commonly known as the tidal prism P . Parameters needed 

 to define the inlet channel hydraulics include entrance- and exit-loss 

 coefficients k and k^^ , a resistance coefficient f (Darcy-Weisbach) 

 or n (Manning), and the hydraulic radius R , which equals the cross- 

 sectional area divided by the wetted perimeter. The acceleration of gravity 

 is g . 



SEA 



Jellies 



PROFILE 



Figure 4-74. Sea-inlet-bay system, 

 4-161 



