Sunday, 12 December 2010

The Upper Kennet 'winterbourne' extension

A snapshot looking at the Upper Kennet from George Bridge (just south off the A4 at SU 132 684) over the last couple of years might suggest that at least 4km of the main river below Swallowhead should now be regarded as a seasonal winterbourne in its own right.

The view today.  The rainfall accumulation record for the region for January to September 2010 shows a below average figure (only 93% of the 1971-2000 average), and for the last quarter to date this area has also been fairly dry, so is this an unusual scene for the time of year?

In early January 2009 (before the gate replaced an old barbed wire fence) the river displayed a reasonably healthy level...

...and whilst by the end of August 2009 it was once more parched... this time last year flows had returned (mid-December 2009). 

2010 started out by adding still higher levels (mid-January 2010)...

...but, although there was still water in mid-June 2010,...

...the bed was dry again by the end of August, which it is how it has stayed up to today.

The River Kennet is now dry until a trickle of water is added by springs near Lockeridge (the new perrenial head), but even then it remains a shadow of what might be expected during winter.  The official record shows that from January to September 2010 the river flow accumulation for the Kennet as a whole was marginally above the long term average, but with "precipitation levels [...] generally expected to be close to or slightly below average" for the rest of the winter, that position might not be repeated next year.