ISO 1070:2018

This document specifies a method of determining discharge in open channels from observations of the surface slope and cross-sectional area of the channel.
It is applicable to use under special conditions when direct measurement of discharge by typically more accurate methods, such as the velocity-area method, is not possible. Generally, the method can be used to determine discharge
a)    for a peak flow that left high-water marks along the stream banks,
b)    for a peak flow that left marks on a series of water-level gauges or where peak stages were recorded by that series of gauges, and
c)    for flow observed at the time of determining gauge heights from a series of gauges.
The method is commonly used to undertake the extension of stage?discharge relationships above the highest gauged flows.
It does not apply to determining discharges in tidal reaches.