The next step of the current adjustment consists o£ operating the 

 model with saltwater in the ocean. For a representative tide, the model 

 roughness distribution is refined to achieve accurate reproduction of 

 velocity distribution both laterally and vertically. During this phase, 

 the lateral distribution of velocity (model and prototype) is determined 

 at various depths across each velocity range rather than as a depth aver- 

 age. It is sometimes necessary during this phase of the model adjustment 

 to bend some (or most) of the vertical roughness elements in half in order 

 to concentrate more of the flow resistance near the bed. 



If the prototype velocity data have been collected over a long period 

 of time, there may be no short term (i.e., 1 week or less) during which 

 sufficient velocity data were collected throughout the entire estuary. 

 In this case, reproduction of velocity distribution rather than absolute 

 magnitude is emphasized to avoid the necessity for reproducing all the 

 combinations of tide and freshwater inflow during which prototype veloc- 

 ity data were obtained. After the velocity distributions have been satis- 

 factorily reproduced, a few prototype tide-inflow conditions must be 

 reproduced to ensure that velocity magnitudes are accurately reproduced 

 in various areas throughout the estuary. If the prototype velocity data 

 have been collected in comprehensive, short-term surveys, greater emphasis 

 can be placed on the reproduction of velocity magnitudes. As discussed 

 previously, a single tide from each short-term survey is selected as rep- 

 resentative of that survey, and only this tide is reproduced in the model. 

 Since the magnitude of current velocity is strongly influenced by tidal 

 range, an adjustment to many of the prototype velocities may be neces- 

 sary to represent conditions for the tide reproduced in the model. The 

 prototype velocity adjustment can often be based on a simple correlation 

 between tidal range and maximum ebb and flood velocities at a given sta- 

 tion (Fig. 3-25). The maximum ebb and flood velocities for the tide being 

 reproduced can be determined from such a plot and compared to the maximum 

 velocity observed. The appropriate percentage correction is then made to 

 all velocities observed at that station. 



Two particular difficulties are often encountered during the velocity 

 verification. Depending on the type of prototype velocity meter used, 

 vertical motion of the survey boat can cause the recorded velocity to 

 be considerably greater than the actual velocity. This is particularly 

 troublesome in the entrance to an estuary, where the survey boat is sub- 

 ject to continuous wave action. In this case, model reproduction of the 

 lateral and vertical velocity distributions must be emphasized rather than 

 velocity magnitude. In confined channels of tributaries or the upstream 

 reaches of the estuary, current velocities are greatly influenced by the 

 magnitude of the freshwater inflow. If the reported prototype freshwater 

 flow rate is inaccurate, an accurate velocity verification in such areas 

 cannot be achieved. The freshwater inflow rate must then be adjusted as 

 necessary to obtain the proper velocities. 



Although a further refinement of model roughness may be required 

 during the salinity verification, velocities are checked to ensure that 



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