Belstead Brook Water Level Gauging Station

Image: © Nigel Mykura Taken: 23 Jun 2014

This is the flow gauging weir at Belstead Brook, 40 metres upstream of Belstead Bridge. It is a Compound Crump weir, that is, it is triangular in cross section with a precise triangular profile often used for discharge monitoring (after E S Crump, who defined the characteristics of this shape of weir). Normally a Crump weir will have a slope of 1:5 downstream and 1:2 upstream. This is a compound weir because it has a pair of flumes in the centre of the weir. When used to measure the flow of water in open channels such as here at Belstead Brook, a flume is defined as a specially shaped, fixed hydraulic structure that under free-flow conditions forces flow to accelerate in such a manner that the flow rate through the flume can be characterized by a level-to-flow relationship as applied to a single head (level) measurement within the flume.The flow is measured by a float with a counterweight. This method requires a float to be installed in a well on the stream bank connected to the weir by a pipe. The well provides a stable environment undisturbed by wind or water movement for a small float attached to a moving line and a counter weight so the movement in stream level can be measured by rotation of a wheel. Typically the wheel rotation is measured very accurately by light or laser encoder, in the instrument. A few metres away from the brook at this point is a cabinet of electrical equipment whereby the flow details are transmitted to the river authority monitoring centre.

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