How is flow estimated?

EA SHEPPERTON Downstream graph
EA SHEPPERTON Upstream graph


from
 
Environment Agency Guide 2012-2013

1910: Shepperton & Weybridge in Thames Villages by Charles Harper.

Shepperton Lock

Right bank lock, tel:01932 221840, length: 174'5", width: 19'10"
Shepperton Weir for canoists. See also.

Canoists:
One of the biggest weirs on the Thames, Shepperton Weir consists of 10 vertical sluices in a row, which, when the conditions are right, produce a large, powerful, challenging, bowl shaped green wave.
The legendary Shepperton wave is generally reckoned to be one of the best play waves in Europe, and with good reason. When the conditions are right, with approaching 100 cumecs dropping 7-8ft through the middle 8 gates, the weir generates an awesome 40 ft wide, 5ft high bowl shaped wave with breaking central pile and well defined green shoulders. If you can handle it, and this is not the ideal venue for beginners or intermediates, this is the perfect venue for pulling all the latest new school green wave moves.

1813:  Shepperton Lock built “at Stoner’s Gut”
1846 -

A pleasant hour might be spent about the weir and lock of Shepperton.  A boat may be hired of Keane, a fisherman, who should accompany the party, for the navigation down the rapids of Halliford Reach is troublesome, even dangerous, to those who are not familiar with the surroundings;  even a crack London sculler looks foolish tugging against the current.  The passing of the towing barges does not lessen the difficulty.

1859:  The lock keeper received an official letter -

desiring that in all communications with the public using the Lock his language and behaviour may be courteous ...

1859: The Thames, Mr & Mrs Hall

The Wey enters the Thames at a mill in the curve of the stream, but the ordinary course for boats is to the lock at Shepperton. The woody grounds of Oatlands now begin to rise on the right

1870:  Shepperton Lock by Henry Taunt -

Shepperton Lock, 1870, Taunt
Shepperton Lock, 1870, Henry Taunt
© Oxfordshire County Council Photographic Archive; HT1488

1888: 'The Strange Adventures of a House Boat' by William Black -

... our escapade at Shepperton was entirely lamentable and ignominious. Here the tow-path shifts to the Middlesex side, and the horse has to cross by ferry ; and here, once more, Palinurus detaching the rope prematurely, we were left helpless in mid- stream, with a strong current carrying us down.
Now, a man may use a boat-hook as an oar, even as he may use a walking- stick in place of an umbrella ; but neither will avail him much ; accordingly, we found ourselves drifting broadside on to an island.
"Kott pless me!" we heard Murdoch muttering to himself as he was vainly endeavouring to reach the bottom with one of these sticks, "what iss to be done with a boat like this?
Then a man comes running along the bank. "Throw us a line, guv'nor!"
Jack Buncombe, who is at the bow, coils up the towing-rope, and heaves it, just getting it ashore. The next instant our opportune friend (his soul no doubt exultant with hopes of a shilling and subsequent beer) has got the line looped round his shoulders; gradually he gets a little way on the boat; Murdoch has to take the tiller again ; and in this humiliating fashion we gain entrance to Shepperton Lock.

1889: Three Men in a Boat Jerome K Jerome -

The lock is just opposite the town, and the first thing that we saw, when we came in view of it, was George's blazer on one of the lock gates, closer inspection showing that George was inside it.

1890:  Two photos of Shepperton Lock, Francis Frith -

1890:  Shepperton Lock, Francis Frith
1890:  Shepperton Lock, Francis Frith
 
1890:  Shepperton Lock, Francis Frith
1890:  Shepperton Lock, Francis Frith

1999: In Shepperton Lock -

Shepperton Lock 1999
Shepperton Lock in 1999

Notice that for once the sun is out and passing a lock is a moment of relaxation! The pole floating in the water is there on purpose to keep it wet. With a wooden pole on a hot day, the pole dries and the hands suffer! Punters need to keep their hands wet!
This photo was taken from the deck level of a neighbouring boat. It must be very different seeing the Thames from that height!