prEN ISO 24577

Hydrometry – Use of noncontact methods for measuring water surface velocity and determining discharge (ISO/DIS 24577:2026) prEN ISO 24577

Publication date:   Apr 30, 2026

Scope

Scope of the proposed deliverable

To determine liquid flow, the following steps are necessary:
1) Measure water surface (or near surface) velocity with techniques using radar, laser or video images;
2) Adjust wind effects to the water surface velocity;
3) Translate the adjusted velocity to an averaged velocity by applying the velocity index or numerical computation;
4) Determine the area of the wetted cross section from the stage area relationship; and
5) Obtain water discharge by multiplying the averaged velocity by the wetted cross sectional area.

This procedure is applicable to different kinds of channel and river section.

Applications include:
•Rivers and streams;
•Artificial channels such as drainage ditches and irrigation channels;
•Wastewater flows discharging to sewer or the environment through channels or partially filled pipes;
•In sewer measurements;
•Process flows on wastewater treatment plants.

For any individual site the method to measure water surface velocity should be selected appropriately, based on the site conditions, nature of the application and uncertainty required. Take a special note
that non-contact methods should NOT be used where a tidal phenomenon is present.