A case study is presented describing the sump model test of a wet well in an existing sewage pumping station at the Regional Municipality of Ottawa–Carleton Green Creek Pollution Control Centre in Ottawa, Ontario. The purpose of the test was to determine whether the existing sump could accommodate projected flow increases of up to 83% associated with the proposed expansion of the plant. It was anticipated that the (low increases could cause the formation of localized flow disturbances such as vortices and eddies, which might induce unacceptable cavitation and (or) vibrations in the proposed new larger pumps. The sump model was constructed entirely of Plexiglas to facilitate flow visualization enhanced by a dye tracer. Of particular interest was the use of a laser Doppler anemometer to measure velocity distributions at critical locations such as the pump intakes. This provided a significant improvement in accuracy and convenience over more conventional velocity-recording devices such as a pitot tube or hot-wire anemometer. The methodology and considerations in the selection of the model scale are described.Key words: model, sump, similitude, vortices, pumps.