available to estimate the friction factors a value of f = 0.03 may be 

 used. 



Losses caused by bridge piers, sills, channel bends, etc., must also 

 be accounted for in hydraulic calculations by adding a loss coefficient 

 similar to k and k „ in the equation defining F. Like k 



en 



and 



IX , this coefficient defines the number of velocity heads (V^/2g) lost 

 at a channel disturbance. 



IV. INLET CHANNEL STABILITY 



Some new inlets formed artificially or as a result of storms will 

 rapidly close while others will remain open for a period of time but 

 undergo variations in cross-sectional area, length, and location (dynamic 

 stability). Inlets "stabilized" by jetties will be more likely to remain 

 open in a fixed position but the channel may erode or shoal in response 

 to environmental conditions. Inlet channel behavior is the result of a . 

 complex response to tide and storm-generated flows which attempt to main- 

 tain the channel and wave-generated sediment transport to the inlet 

 which attempts to close the channel. 



However, several authors have demonstrated that a relationship exists 

 between the tidal prism and inlet throat cross-sectional area for many 

 stable jettied and unjettied inlets located on sandy coasts. Data 

 analyzed by Jarrett (1976)^ suggest the following relationships for 

 U.S. inlets (Table). 





Table. Inlet stability equations. 





Location 



Jetties 



Defining tide 



Equation 



Atlantic 



None or one 



Spring 



^o - 



5.37 X 10"^ pl-o/ 



Gulf 



None 



Diurnal 



^o = 



3.51 X 10-'+ pO-86 



Pacific 



None or one 



Diurnal 



^c = 



1.91 X 10-6 pi. 10 



Atlantic 



Two 



Spring 



^a = 



5.77 X 10"5 pO.95 



Gulf 



Two 



Diurnal 



^c = 



3.76 X 10-^ P°-85 



Pacific 



Two 



Diurnal 



A. = 



5.28 X 10-"+ pO-85 



3JARRETT, J.T., "Tidal Prism-Inlet Area Relationships," GITI Report 3, 

 U.S. Army, Corps of Engineers, Coastal Engineering Research Center, 

 Fort Belvoir, Va., and U.S. Army Engineer Waterways Experiment Station, 

 Vicksburg, Miss., Feb. 1976. 



16 



