The uncertainty of the calculative value of the volumetric flow rate in
open channels
Abstract
The well-known Manning formula is usually used for the calculation of
the volumetric flow rate (discharge) in a river or open canal. The
discharge depends on the geometry of the channel, i.e. the water area,
the wetted perimeter and the slope, as well as on the roughness
coefficients. All these quantities are determined with some uncertainty.
If these uncertainties are taken into consideration in the process of
discharge calculation, then, as has been demonstrated for a hypothetical
river channel, the ratio of the uncertainty to the calculated value of
the discharge will change from several dozen percent in case of small
flows to about ten percent in case of big, flood flows