how nozzle's inlet flow speed change in an ocean situation
 

Folks,
I got the difficulty to understand how flow's speed change in nozzle's inlet when it is in ocean tidal situation.
For example, if tidal free stream velocity is 5m/s, and nozzle inlet diameter is 10cm, will the inlet velocity decrease? that's my calculation result but I cannot explain why. Is there any one here can help me to understand it?
thanks.

could you please elaborate on the setup, such as the location of the nozzle and the direction of flow, etc? thanks.