The tidal discharge volume for river channels is computed using the water 

 volume measured between high water elevation and low water elevation throughout 

 the tidal reach of the river above the cross section. This is obtained using 

 topographic data for the river from the site of observation to the head of tide- 

 water plus river discharge and tide data. 



III. 



EXAMPLE 



Two streams, Eagle River and Ship Creek near Anchorage, Alaska, and a series 

 of tidal-flat channels at Anchorage, illustrate the method used to obtain a 

 channel cross-sectional area/ebbtide discharge relationship that can, in turn, 

 be used to predict the stable cross-sectional area of a harbor navigation chan- 

 nel. The channel area of Dillingham Harbor, Alaska, is used to test the rela- 

 tionship. Sediments through which the channels flow are similar in each region 

 and composed of well-compacted mud and silt-sized, glacial-fed material with 

 less than 2 percent clay minerals. Channel and streambank elevations were in 

 all cases less than 1 meter above mean higher high water (MHHW) . 



1. Anchorage Tidal-Flat Channels. 



Channels were studied on a tidal flat in Knik Arm, the estuary serving the 

 Port of Anchorage at the northeastern end of Cook Inlet (Fig. 1). Knik Arm 

 carries an average suspended-sediment concentration of about 1,300 milligrams 

 per liter (Everts and Moore, 1976), and has a median tidal range of 8.8 meters. 

 Near Anchorage, the tidal flats are shore-connected, composed primarily of silt- 

 sized material, and variable in width with a maximum extension of 600 meters 

 into Knik Arm channel. 



Intertidal 

 Zones 



Figure 1. Location map of study area, Anchorage, Alaska. 



Flow in the tidal-flat channels occurs primarily during ebbtide. During the 

 flood part of the tide, water rises over the tidal flat as a sheet and is not 

 carried preferentially in the channels. Figure 2 is an aerial view of the study 



10 



