Low-Flow Measurement in Water Treatment Settling Basins

The City of San Diego recently used a SonTek Acoustic Doppler Velocimeter (ADV) to evaluate the flow fields in the settling basins at the Otay Water Treatment Facility (Figure 1). The basins are fairly long, and are designed to pass water slowly so flocculated contaminants have time to settle during the water's transit through the basin.

The City was concerned that too much flocculated material exits the basin without settling, and considered that the basin design might be the cause. Because the currents are as low as 1 cm/s, the ADV's unique capability to measure in such low flows made it the perfect choice to investigate this theory.

The ADV was mounted to a pole and suspended from a movable bridge to map the entire flow field of the basins (Figure 2). There is still considerable data analysis to be done, but the City is pleased with the ability of the ADV to gather excellent data under these conditions.

• ADV