o 

 o 



MAXIMUM MIDDEPTH EBB AT STA 4 

 MAXIMUM MIDDEPTH FLOOD AT STA 4 



TIDE RANGE (ft) AT STATION 21 



Figure 3-25. Typical correlation between tidal range and maximum 

 velocity, Gastineau Channel model (Herrmann, 1972). 



the current reproduction is still accurate. Examples of velocity verifi- 

 cation achieved in various estuary models are presented in Figures 3-26 

 and 3-27. 



The flow predominance method of presenting current velocity reduces 

 magnitude, direction, and duration of the currents to a single expression 

 that defines what percentage of total flow at any given point is toward 

 the ocean (ebb) and what percentage is away from the ocean (flood) . This 

 expression is derived from a conventional plot of velocity versus time 

 over a tidal cycle at any given point. The areas subtended by both the 

 ebb and flood parts of the curve are measured (or calculated) and sum- 

 marized. The area subtended by the ebb part of the curve is then divided 

 by the total area to determine what percentage of the total flow is in 

 the ebb direction. This calculation is performed for both model and 

 prototype velocity data to determine the time-average vertical flow dis- 

 tribution. This information is used in addition to the time-varying 

 vertical velocity distribution in adjusting the model roughness. The 

 flow predominance data are useful in determining the vertical flow dis- 

 tribution at a given station (shown in Fig. 3-28), or in determining the 

 longitudinal distribution of flow along the length of the estuary at 

 particular depths (shown in Fig. 3-29). 



