102. Initial values of water surface elevation . Values of the water 

 surface elevation must be given at every node at the initial time. These 

 values are obtained from field measurements. For a cold start, a horizontal 

 water surface may be prescribed, best taken as the average measured value if 

 available . 



103. Initial values of volume flow rate . Initial values of volume flow 

 rates (discharges) at all nodes must be specified. These values are taken 

 from field measurements. For a cold start, the initial discharges may be set 

 to zero. 



Cross-section data 



104. Cross -section data provide information on the shape of the inlet 

 and the boundary or perimeter roughness. Cross section data consist of the 

 inlet geometry (bottom elevation, Zj,) and bottom friction coefficient (n) at 

 the station of each node. 



105. Inlet geometry . Geometric data for the cross section must be 

 obtained from maps or field surveys. The data are recorded as "distances" and 

 "elevations," where distance is an offset from the left bank and elevation is 

 the bottom elevation referred to the reference elevation discussed in 

 paragraph 98. 



106. Bottom friction coefficient . Manning's coefficient of friction n 

 is specified at every cross-section data point. These values are estimates 

 obtained from previous studies, experience, and judgment. Textbooks such as 

 Chow (1959) provide guidelines for selecting values of n according to the 

 physical conditions. Typically, a value n = 0.02 is used for sand. This 

 value may be increased to 0.025 if the boundary consists of coarse sand. If 

 the inlet channel contains vegetation, an initial value of 0.035 is recommend- 

 ed. Values of the friction coefficient are specified at every data point in 

 the cross section so that in a wide cross section consisting of part sandy 

 bottom and part vegetation, different friction coefficients can be assigned to 

 the sandy and the vegetated parts. Adjustment of the value of n at selected 

 locations is the main calibration procedure for DYNLETl. 



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