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Flow diagram

Flow diagram

The gaugings carried out during a flood are part of a series of gaugings, ideally covering the full range of levels measured at the site.

A flow gauging consists of measuring:

  1. the cross sectional area of the water in m2. This is achieved by measuring the distance across the surface and between 20 to 25 depths across the river.
  2. the velocity at several points at each of these depth positions, from which the mean velocity m/s is calculated.

These measurements are multiplied to provide m3/s or cumecs Q (m3/s) = A(m2) x mV(m/s).  

These instantaneous flow measurements are used to create a mathematical relationship between level and flow (called a flow rating). Continuous flow data is then derived from the level data.