Pressure transducer and river levels in Carlisle

We found this by the river in Denton Holme. The pressure at the bottom of the river is measured using a pressure transducer. I looked up how one of these works https://www.omega.co.uk/prodinfo/pressure-transducers.html Strain gauges are essentially wires that get stretched, making the wire longer and thinner. Since resistance = resistivity x length/cross-sectional area, the resistance changes as the shape changes. A Wheatstone Bridge is an array of 3 known resistors along with an unknown from the strain gauge, from which the unknown resistance can be calculated. Pressure varies with depth. Pressure = depth x density x g. So if the resistance of the strain gauge is calibrated for different pressures, the depth of the water can be known from the resistance.