Just before you get to all this there is Clyce Hole ('Clyce' is an old word meaning a sluice). Here the river has clearly been heavily engineered in fairly recent times, and when the river is full there is a substantial rush down an artificial waterfall. There's also the beginning of the Mill Stream, which is not actually joined to the main river though I'm sure that once it was. The Mill Stream used to power the mills at Northover and Beckery.
Beyond Pomparles Bridge the main river channel flows past Bride's Mound (also known as 'Beckery island') and then takes an unnaturally straight course towards Mere. This is the beginning of the medieval canal works. I imagine that before the river was diverted it used to split into two channels either side of Bride's Mound. One would have approximately followed the course of the present Mill Stream (to the right of the Mound); the other would have gone to the left, and met up with it somewhere near where Snow's Timber yard is now.
The County Council's notice boards on Bride's Mound give dubious information.
For instance, the river was not diverted towards Mere around 900 AD. Historians give different possible dates, but all between about 1250 and 1320.
The ancient course of the Brue is very unlikely to have been as shown on the Council's board. They show it flowing north through the Bleadney gap (as I'm sure it did), but then back into the Brue valley below Wedmore, following the modern course of the Brue to the sea at Highbridge. Every book I've read on the subject suggests that it joined up with the Axe the other side of Bleadney, and so it would have reached the sea near Brean Down.
It may be true that the Brue ran through a huge swamp here, but that changed considerably over time and also depending on the time of year. Once the Roman causeway had been built it would have held a lot of the water back on its upstream side, so that by the fifth century (if you are interested in either Sir Bedivere or St Bridget) it would probably have been flooded below the bridge in winter but not in summer. I prefer the idea of a lake with a lady to that of a gigantic swamp.