This paper presents the quantitative results of improving the uniformity of the flow field within the test section of a constant cross section, closed-loop water channel. Tomographic Particle Image Velocimetry (TomoPIV) and four flowrate sensors are used to determine the mean velocity and velocity fluctuations at two motor frequencies: 7.5 Hz and 10 Hz (an approximate free stream flow velocity of 0.11 m/s and 0.18 m/s, respectively). The flow field velocity determined by the flowrate sensors showed great agreements with the TomoPIV results. For instance, at the 10 Hz water channel motor frequency, the flowrate sensors and TomoPIV obtained velocity ranges of 0.191–0.202 m/s and 0.185–0.21 m/s, respectively. In order to reduce the flow speed variations within the studied TomoPIV measurement volume, improvements were implemented on the water channel to include an adjustable screen and deflector to the first set of turning vanes downstream from the water channel motor. The modification improved the 7.5 Hz motor frequency measured flow velocity from 0.16–0.172 m/s to 0.106–0.108 m/s resulting in a final variation of flow speed within the measurement volume reduced to 1%.