In message , at 07:05:35 on Fri, 8
Jan 2016, Clive D. W. Feather remarked:

One of the reasons I'm not convinced that the New Bedford is tidal in
the sense of going up and down twice a day is that when it floods at
Welney the water doesn't flow away to the Wash for weeks.

But is that the New Bedford flooding or the Old Bedford or Delph?

Anyway, heavy flow from upstream could overwhelm the tidality.

The point at which "flooding is possible" measured on the New Bedford is
2.4m AOD, and it's pretty much spot on that today.

The peak tides at Kings Lynn are currently is 2.2m (and the average
around 0.6m) so that's not going to be flowing inland as far as Welney,
nor does the chart for Welney show any indication of waters backing up
in tune with the tides.

We should revisit this in the summer when it's drier (or perhaps find
some historic data).
--
Roland Perry