Standards Development

Scope

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.

Purpose

Measurements of flow in open channel by conventional methods are costly, time consuming and hazardous. Noncontact methods of flow measurement are generally as accurate as conventional methods. Data can be obtained by these methods when data collection by standard contact methods are felt unsafe or cannot be obtained.

Use of the non-contact methods are techniques for measuring water surface velocity and liquid flow in open channels. The water surface velocity can be measured with technologies, such as Radar, or video images. Thereafter, the measured values are converted to the water discharge values. This method usually can be conducted either with or without human labours in the actual field measurements. Because of availability of different measurement systems, the systems need to be selected in terms of the site condition, such as the types of flow field, width of river and installations. Actually, water surface as well as river flow condition during targeted flood stages are key importance to select the system.