Continuous, Near-Bed Current Velocity Estimation Using Pressure and Inertial Sensing

The near-bed velocity is a key physical parameter in hydrological, ecological and geomorphological studies. Considering climate change, measurement methods capable of providing continuous observations are needed to assess and predict the effects of increasing uncertainty. Therefore, a technology gap remains for continuous near-bed measurements. To address this gap, we have developed a multimodal flow measurement device, the hydromast. The hydromast uses a combination of pressure and inertial sensing to measure the near-bed (< 30 cm) velocity. We have previously shown that the device can be used to classify river hydromorphological units. Encouraged by these results, we now show that the same device is also capable of continuously measuring the near-bed velocity in rivers. Ten hydromast prototypes were built and calibrated over the range of 0.01 – 2 m/s in a large-scale laboratory tow tank and validated under natural conditions (0.35 – 1.2 m/s) using 118 turbulent flow measurements in a river. It was found that the streamwise, time-averaged velocity mean estimation error from the hydromast in continuous tests with different methods was 0.095 m/s, as compared with a state-of-the-art acoustic Doppler velocimeter. The contribution of this study is a new method for continuous near-bed velocity measurements, verified with turbulent field data from a river.