Inspiring high precision dam water depth measurement with novel 'bubbler’ designs

Abstract

[Abstract]: Over time and due to enhancements in technology, a number of water level measuring systems have been developed for the purpose of improved water management. One of these methods is the “bubbler” arrangement incorporated with a pressure sensitive transducer and relay equipment. This project intends to optimise the accuracy and precision of the “bubbler” arrangement method through testing and evaluation of novel bubbler/water interface configurations. A gas bubbler system can measure both stream and dam water levels. The water level is determined by measuring the pressure head of gas bubbling from the bottom a dam. An air line is attached securely below the water surface and the pressure required to force air out the capillary line in the form of bubbles is registered on a pressure transducer tapped into the control board. From this pressure, the height of the liquid column above the point of measurement can be determined. When this measured pressure is magnified, a saw tooth plot of pressure over time can be seen. This is due to the change in pressure during the bubble formation at the end of the capillary. In order to optimise this arrangement, this variation in pressure over time as the bubble forms and grows needs to be reduced. The pressure variation is also known as the effective bubble pressure. The effective bubble pressure is the excess pressure required to overcome the head loss due to the surface tension of the water. To try minimise this effect, an experimental apparatus was designed and built following the principles of a bubbler arrangement. A laboratory measurement program was also implemented. From the different tests that were undertaken, it was found that a 12.5 mm diameter bare ended tube with a cut at an angle of 60°, was found to be the most accurate and precise interface. This was determined by undertaking a statistical analysis on each of the test results including, means, standard deviations, maximums, minimums and ranges. The temperature of the water was also recorded prior to and during each test. The test results also agreed with some of the relevant surface tension and bubble physics theory.