Monday, July 31, 2017

Disappearing water

The schools have broken up and now it seems to want to rain.  Aah well, it does that.  The July CRT Reservoir Watch figures show quite a variation in the change in water holdings for the canals. Over June The Oxford dropped 16.8%, GU North dropped a somewhat alarming 26% while the GU South dropped 11%.  How do you work that one out?  At least holdings are still somewhat above 2010/11 levels when we were all worried about being left high and dry.

Last week we had an interesting episode at Grant’s Lock, that’s the first one south of Banbury, where the overspill weir pours under the lock cottage floor.  I had the lock empty ready for Kath to bring Herbie in when a lady appeared asking if we would kindly let some water down because the pound below, which includes Twyford Wharf, was very low.  No surprise there, I thought, it’s always really shallow down there (don’t go near the sides or you’ll be aground in no time).  So, anyway we had a bit of fun bringing Herbie into the lock with the top paddles open for a few minutes.  I think Kath enjoyed driving her in hard against the current and I suppose we donated a few thousand gallons to the pound below.

It turned out the the lady was one of the owners of Twyford Wharf where they have a little hire fleet.  She was convinced that there must be a groundwater leak in that pound although she couldn’t find where it might be.  Certainly round the corner south of the wharf, the canal sits on a high towpath side embankment above the Cherwell, so there’s plenty of chance for gravity to take away any leakage.  Actually Grant’s lock is fourteen inches less deep than King’s Sutton (Tarver’s) lock which is the next one below so that according to my calculations that would account for a fifty gallon loss each time a boat passes through, but, if I recall rightly the overspill weir at Grant’s lock was flowing so that would make up fifty gallons in no time.  I think the lady is right, the water is escaping somewhere.

Meanwhile I wonder if this recent spell of unsettled weather will make much difference to the reservoirs.  I doubt it somehow.

2 comments:

Rick said...

I think you'll find that it's 3,557 gallons.

Or 42.7 bathtubs!

Rick

Neil Corbett said...

Aah yes, i know the mistake i mafe, i forgot to multiply by the 70ft length of the lock. Stupid boy.