Open-Channel Flow Measurements at Water Treatment Facility

A major municipal water authority in China recently conducted a series of flow tests in a large treatment facility using a 5-MHz SonTek/YSI ADVOcean. They chose the ADVOcean because of its ability to measure precise 3-D currents at a focal point 18 cm from the transducer. The ADVOcean's heavy-duty construction made it ideal for this type of industrial application.

The ADVOcean was mounted on a stainless steel clamp (Figure 1), which was further supported on a pre-fabricated platform consisting of a trolley and winch system (Figure 2). The instrument was then lowered down at the clarifier outlet open-channel.

After obtaining the velocity profiles of the clarifier outlet open-channel, the water authority evaluated the total open-channel flow using the velocity-area method (ISO 748:1997 - Measurement of Liquid Flow in Open Channels -- Velocity-Area Methods). The results were then compared with the measurements made by the treatment plant's inlet dall-type flowmeter.

The open-channel was subdivided into 15 verticals. Three measurements were made in each vertical at depths of 0.2, 0.6, and 0.8 m. The flow rates derived from the tests were 438 Mld (megaliters per day) for the ADVOcean and 420 Mld for the inlet dall-type flowmeter. Given the dall-type flowmeter accuracy of 5%, this minor difference was considered acceptable in open-channel measurements for this field application. Figure 3 shows a flow profile in a cross section of the channel.

Figure 3. Flow Profile in a Cross Section of Channel

• ADVOcean