I was back at Croasdale Beck last week and noticed a rather dramatic change to the meander just upstream from our regular sampling spot. If you look at the photograph that heads the post “A tale of two diatoms …”, you’ll see the stream flowing around this meander. Now, however, it has cut a new, shorter channel that bypasses the meander altogether. We visited the stream just a few days after Storm Ophelia had passed through although, judging by the grass growing on the gravel of the abandoned meander, it was not necessarily this particular event that reshaped the stream.
Croasdale Beck is an unruly tributary of the River Ehen, rising on the fells above Ennerdale Water and tumbling down across rough grazing land and some semi-improved pasture (as in the picture above) before joining the Ehen in Ennerdale Bridge. This is not the first time that we have seen conspicuous changes in the channel after a storm. The magnitude of the flood is illustrated by the hydrograph below, which went off-scale for a period, as the discharge exceeded 3000 mega litres per day (300 MLD is the approximate limit for safe wading, in my experience). I noticed that there was much less green algae present than we usually record at this time of year, although the diatom film was still quite thick. Some of the stones that I picked up to sample had the slimy biofilm on the underside, suggesting that they had been recently rolled by the flooded river. Croasdale Beck has no lake to buffer the rise and fall of the floodwaters and a huge amount of energy is carried down in a short period of time as the water surges downstream.
By the time we had arrived, the floodwaters had subsided and the sheep were contentedly grazing the surrounding land. The stream itself was almost back to base flow (in contrast to the River Ehen which was still only just wadable). Only the meander looked different …
The hydrograph for the River Ehen, as the aftereffects of Storm Ophelia make their way downstream.