accurately measuring water flow speed?

[magpie patrick]

Barking Creek and the Darenth used to be navigated on the tide - that is, just letting the thing drift. The lock at Dartford and the semi-tidal doors at Barking would have spoiled this. In any event I doubt they were all that fast given they are comparatively small compared to, say the Thames. Boats drifting along are relatively uncontrollable and liable to bang into other boats. On the Thames (which can run at a fair lick under the bridges) avoding action was easy, on these it was not.

 

Sure you realise that if the current gets the better of you then make for the side, don't try and fight it! This applies even as the Thames Barrier slips away into the distance...