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...

...by 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.

Saturday 11 December 2010

Newbury Flood Alleviation Scheme (FAS) planned

To face the risk of a one-in-a-100-year (a 1% chance in any year) flood event in Newbury, provisional new plans have been laid out for consultation and comment by the Environment Agency.

Proposals forming part of the response to the 2005 Kennet Flood Risk Management Strategy will be appraised and selected for submission as a business case in March 2011, but the final determination as to whether the project will proceed will be made on the basis of its priority by comparison to other flood alleviation schemes across the country. A public exhibition of the proposals will be held in Newbury in February 2010.

The initial intention is to protect around 370 residential and 80 commercial properties, but in urging people to sign up to the EA's updated flood warning alert service on 29 November 2010, local MP Richard Benyon (and the Coalition Minister with responsibility for flood alleviation) noted that “There are 2,525 properties at risk of fluvial flooding in the Newbury constituency".  A more detailed map of the wider risk from Newbury down to Thatcham is available here.

In terms of the effects of any adopted plan on paddling on the start of the lower reach, there is probably little difference that would be noticed on a day to day basis.  Most of the proposals appear to involve raising towpath levels slightly along the side of the Navigation, and building walls or embankments to protect specific areas of low lying housing or grassed park.

The section of the floodplain between the A34 and the disused Lambourn Valley railway (c.240m to the west of the boat launch slip at the edge of Northcroft recreation grounds) is proposed to provide a compensatory storage area around the Speen Moors Plantation,using the remaining embankment as a semi-permeable bund wall.  Whilst water levels could be raised up to 2m in this 'holding' area during one-in 20-year flood event or higher risk periods, this would require a special structure that could be lowered into the River Kennet where it breaches the embankment [SU 459 671], and probable new embankment building to the south of this area to prevent bypassing re-entry of flood water to the Kennet & Avon Canal.

The stanchions in the river mark all that remains of where the Lambourn Valley Railway crossed the River Kennet west of Newbury.

This is not the most readily accessible area to undertake such works but should they proceed it would potentially bar the end of the riverine Kennet run down from Benham Weir (should you be considering exploring the new 'lake-scape' during such floods).

Just above the line of the old railway (note the flood plain beyond the river) is a riverwide bar, presumably intended to prevent navigation further upstream.  In normal water levels you can paddle over it river right...

...in lower water levels you can squeeze under the bar river left.  The proposed Newbury FAS might negate the need for this effort during periods of potential flooding.