Portable in-sewer Doppler velocity measuring equipment has been available for a number of years. However in large sewers (typically greater than one metre diameter) the accuracy of these devices for large flow depths can be very poor. This paper describes a system, developed by the authors, that enables the determination of a velocity profile across the section of the flow in a large sewer. The velocity profile information obtained can then be used to determine a more accurate estimation of the mean velocity of flow in the large sewer.

In the paper the hardware and software developed to form the Doppler Transducer Velocity Array System is discussed. Installation of the system in a large sewer and subsequent field testing of the system are also discussed, with results of the field testing included. The paper also shows how the results obtained were used to produce 3-dimensional surface plot graphs that show the variation of velocity against time across a section of the sewer flow.

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