24-hour Phone: 1 (800) 333-2252


A Comparison of the Dye Dilution Method to Continuous Wave Area Velocity and Clamp-On Ultrasonic Flow Meter Technology

We were recently called upon to perform flow validation in a wastewater treatment system at a power plant in Alabama. They were performing a dye dilution flow study and were looking for alternative methods to validate the flows derived from their dye study.

In the Dye Dilution method the flow rate is measured by determining how much the flowing water dilutes the added tracer solution. In this case a tracer was added at a constant rate of injection for a period of 24 hours while operators ran continuous samples to determine the concentration of the tracer solution, in this case a dye. The flow rate is determined by a formula involving the injection rate, and the measured plateau at the measuring site. This is a very labor intensive method yet accurate way to determine flow. The total flow calculated from the Dye Dilution study was 5.2 MGAL.

C. C. Lynch & Associates, Inc. was called upon to measure and validate the flow at two points in the process. The first location was an 18” pressurized line where we installed a Krohne Clamp on Style Transit Time Flow Meter.

A clamp on transit time flow meter will transmit sound through the pipe and fluid to determine the time flight difference between the signals transmitted with and against the flow. The total flow calculated by the Krohne meter was 5.337 Mgal.

At the 2nd location we installed Isco 2150 Continuous Wave Area Velocity Flow meters in two partially filled 30 inch culverts. This brief animation shows how the Doppler sensor measures the velocity.

The flow in the two culverts is fed from two sources. The pressurized line (measured with the Krohne clamp on flow meter) and the lined ditch both shown in the picture below. Note that the lined ditch has a Parshall Flume and Ultrasonic flow meter measuring a constant feed of 100 GPM.

The flow rate measured by the 2 Isco 2150 Area Velocity flow meters less the Parshall Flume flow was 5.207 MGAL

Method Total Flow
Dye Dilution Study 5.20 Mgal
Isco 2 each 2150 less flume flow 5.207 Mgal
Krohne Clamp on Transit Time 5.337 Mgal






As you can see from the table, the total flow volume reported by the Isco 2150 flow meters is within 0.1% of the dye dilution method and the total flow volume reported by the Krohne clamp on flow meter is within 2.5% of the dye dilution method.



Scroll Up