The river...

Fri 29 Nov, 18:46 (last edited on Fri 29 Nov, 18:47)

I knew someone would put me right Steve - I didn't fail maths and physics 'O' levels for nothing yaknow!

It's the height and width of the bridge arches and the 2 flood relief channels (without which some of us would be in deep doo-doos - or possibly these days deep in doo-doos) which of course determine the volume of water flowing through, not the width of the flood across the field.

So let's just agree there was a Heck of a Lot of Water headed downstream on Monday!

Thu 28 Nov, 11:27 (last edited on Mon 2 Dec, 13:18)

I don't know how you have done your calculations, but if it's 100 metres x 1 metres by 0.5 metres per second (about 1.1 mph), that's 50 cubic metres a second. The average discharge rate of the Evenlode is 3.7 cubic metres per second (222 cubic metres per minute).

According to Wikipedia, the highest discharge rate of the Evenlode was in December 1979, when it reached 26.7 cu metres per second averaged over 24 hours.

That is, of course, where it reaches the Thames, so there are other tributaries which join between the Evenlode after Charlbury, although as water flows out across the flood plain clearly the intermediate flow rates must be higher than discharge rate.

I think to do a more accurate estimate of the flow rate under he bridge at Charlbury, you would need an estimate for the cross-sectional area of the bridge arches (which were almost full on Monday afternoon) and the flow rate.

In any event, the flow rate is clearly far higher that 30 m^3 per hour. It would not surprise me if is was closer to 30 m^3 per second. Not fully that level, but definitely in the vicinity 20 m^3 per second or so. That's 20 tonnes a second of course, or about an Olympic swimming pool ever 2 minutes.

Thu 28 Nov, 11:06

... on Monday hit the highest level I've seen it in 10 years.  Now, I'm neither a mathemetician nor a physicist but try this, speed and distances etc estimated entirely by eye!

100m across (from Mill Lane to cricket field).  Average depth 1m (in the main river up to 4m); Speed of 1m3 every 2 seconds.  So, 30m3 per minute, or 1800 per hour or 43,200 over 24 hours - or 43,200,000 litres passing through.  An olympic swimming pool contains 2,500,000 litres.

Of course there are huge variables here - the rise and fall, and different flow speeds (much faster in the main channel) for a start.  And various solids in there somewhere!  But who can come up with something more accurate??