ISO 18481:2017

Hydrometry — Liquid flow measurement using end depth method in channels with a free overfall

Publication date:   Dec 8, 2017

General information

90.93 Standard confirmed   Mar 31, 2023

ISO

ISO/TC 113/SC 2 Flow measurement structures

International Standard

17.120.20   Flow in open channels

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Scope

ISO 18481:2017 specifies a method for the estimation of the sub-critical flow of clear water in a smooth, essentially horizontal channel (or a gently sloping channel), abruptly discontinued at bottom by a hydraulic structure, with a vertical drop and discharging freely. Such an overfall forms a control section and offers a means for the estimation of flow using the end depth measurement method. A wide variety of channel cross-sections with overfall have been studied, but only those which have received general acceptance after adequate research and testing, and therefore do not require in situ calibration, are considered. This document covers channels with the following types of cross-sections:
a) rectangular with confined and unconfined nappe;
b) trapezoidal;
c) triangular;
d) circular;
e) parabolic.
The flow at the brink is curvilinear; therefore, the measured depth at the drop is not equal to the critical depth as computed by the principle based on assumption of parallel flow. However, the end depth and the critical depth (as in the case of the assumption of parallel flow) have unique relation, which is used to estimate the flow through these structures.

Life cycle

PREVIOUSLY

WITHDRAWN
ISO 3847:1977

WITHDRAWN
ISO 4371:1984

NOW

PUBLISHED
ISO 18481:2017
90.93 Standard confirmed
Mar 31, 2023