Figure 7 . Navigation channel at Dillingham Harbor . View is toward Nushagak Bay 

 from a location near the sill (Fig. 6). 



per liter average suspended solids, the concentration of suspended sediment does 

 not appear to be a critical factor. Note that in all cases discussed the amount 

 of sand-sized material moving as bedload was negligible, except possibly near 

 Knik Atm in Eagle River and Ship Creek. Cross-sectional area is calculated for 

 the maximum water surface below which the ebb-tidal flow is capable of scouring 

 fine-grained sediment. For rivers and for a harbor basin entrance, it is MHHW; 

 for tidal-flat channels it is as shown in Figure 3. 



b. Cross-Sectional Shape . Harbor and river channel cross-section shapes 

 vary according to the hydraulic regime active within them. Channels, such as 

 those on the tidal flat which carry less than 6 x 10^ cubic meters per ebb 

 cycle are V-shaped, and the channel area is 



A = 



(4) 



in which z is the sidewall slope, and d is the channel depth, 

 depth of the channel is 



d = /AZ 



Thus, the 



(5) 



When Q > 1.4 X 10^ cubic meters per ebb cycle, the channels are parabolic 

 (concave-up sidewalls) , and as the discharge increases the channel bottom be- 

 comes slightly broader and flatter. The cross-sectional area of a parabolic 

 channel is 



A = -wd 



(6) 



