98. Reference elevation . The reference elevation Zt is the horizontal 

 datum for specifying water surface elevation and channel geometry. Mean sea 

 level (MSL) , mean low water (MLW) , National Geodetic Vertical Datum (NGVD) , or 

 any other suitable horizontal datum can be chosen as the reference elevation. 

 If MSL is selected as the reference elevation, the water surface elevation z 

 would be the difference in elevation between the water surface and the mean 

 sea level. The aforementioned tidal datums are the most commonly used in 

 practical engineering studies of inlets. 



99. Lateral inflow rate . The lateral inflow rate q is the rate at 

 which water enters or leaves the channel at a cross section from the channel 

 banks or bottom by seepage, or enters or leaves the water surface by evapora- 

 tion or precipitation. Flow from a minor tributary stream can be represented 

 by specifying values of lateral inflow. An examination of the flow records at 

 the two ends of a channel reach can be used to evaluate lateral inflow rate. 

 In the present version of DYNLETl , q can be represented as a different 

 constant value at each node. 



100. Channel alignment angles . The channel alignment angle is defined 

 as the angle that the channel axis makes with a reference axis. The reference 

 axis may be, for example, the bottom edge of the hydrographic map for the 

 inlet. The angle is measured counterclockwise from the reference axis and is 

 given in degrees. Values of channel alignment angle must be specified at each 

 node . 



101. Transition loss coefficient . The value of the transition loss 

 coefficient K^, the coefficient assigned to describe turbulent losses caused 

 by flow expansion and contraction, must be specified at all nodes. If these 

 losses are to be omitted, K^ must be set to zero. Such losses must be 

 accounted for to accurately represent turbulent losses produced by sharp 

 channel contractions and expansions, bridge pilings, culverts, etc. A cross 

 section that produces flow contraction during ebb flow will produce flow 

 expansion during flood flow. The maximum values for the contraction coeffi- 

 cient is 0.5, and the maximum value for the expansion coefficient is 1.0. 

 Values of 0.5 for both contraction and expansion coefficients are recommended 

 as initial values in model calibration. For modeling the flow around 

 important structures, such as bridges, it may be necessary to calibrate these 

 coefficients with field data. 



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