I would be very interested in the results of that survey.
I'd particularly like to know if the current GPS height of the water in the ponds are at the same sort of level as they were when this was a canal.

If the level of the canal was for instants 8' higher than today then the reserve would have looked quite different 200 years ago.

If a GPS reading was taken outside WHSmiths or even the 'Tow-path' along Davids Rd, then that should give a good estimate (minus a couple of feet) for the height of the canal back in the good old days.