Civil Engineering October 2022 | Vol 30 No 9

24 October 2022 Civil Engineering S taff gauges are gauges that are made of metal or plastic strips, approxi- mately 8 cm to 15 cm wide and 1 m to 2 m long. They have numbered markings at linear inch/foot or cm/m intervals. Theses gauges are permanently installed markers for measuring water depths of rivers, streams, lakes, ponds, dams and swamps. Also named water depth gauges, water flow gauges, flow meters, ramp gauges or limnimetric staff gauges, these gauges are suitable for studies of water levels and water flows by environmental scientists and hydrologists. Manning’s formula, ASTM Velocity Area Method, ISO Slope Area Method and others are some of the procedures of the measurements used to calculate the flow rates. For engineers and process controllers working in the water and sewage field, a more vigorous approach to flow measurement is required. With a calibrated staff gauge the flow (ℓ/s) can be directly read off the gauge with no need to consult flow equations and can be used to check the accuracy of the secondary monitoring device. THE HISTORY OF STAFF GAUGES The staff gauge has a long history of visu- ally determining water depths and levels, particularly in the USA where the ma- jority of present-day standardised flumes originated and where ‘gauges’ are ‘gages’. The history and reason is outlined in the following statement from the United States Geological Survey (USGS): “In 1888, USGS Director John Wesley Powell met a very forward-thinking graduate student named Frederick Haynes Newell. Powell was so impressed that he made Newell the first full-time appointee to the new Irrigation Survey, which was created to investigate the potential for dams and canals in the western United States. At that time, there were no practical and systematic techniques for obtaining daily stream flow (or discharge) records, so Newell set up a training camp on the Rio Grande River at Embudo, New Mexico. Newell’s Camp of Instruction developed water measurement methods that are widely used by the USGS today. During the next ten years, Newell continued to play an important role in the development of stream flow gaging techniques and methods, and he eventually became the first Chief Hydrographer of the USGS. Newell is purported to be the person responsible for the adoption of the USGS spelling of ‘gage’ instead of ‘gauge’. Around 1892, Newell reasoned that ‘gage’ was the proper Saxon spelling before the Norman influence added a ‘u’. USGS historian Robert Follansbee speculated that Newell might have also been influenced by the adoption of ‘gage’ in the Standard Dictionary (the first dictionary pro- duced by Funk and Wagnalls).” DESIGN OF CALIBRATED STAFF GAUGES TO INDICATE FLOW RATES The standard rating unit for all flume and weir calculations is litres per second (ℓ/s) and this is the suggested standard for the calibration of a calibrated staff gauge. Calibrate, in this case, is defined as a unit of measurement on an instrument that can measure a particular function accurately and precisely, determined by comparison with a standard – in this case, flow in ℓ/s. With curved/sloped sides (Palmer-Bowlus, U-shaped or trapezoidal flumes) the calibration must make compensation for the flume curvature or side slope to give an accurate vertical reading. Taking into account the international standard, the calculation of the measurement is taken Peter van der Merwe Pr Tech Eng Consultant for Flumes and Weirs flumesandweirs@gmail.com Open channel flow measurement and monitoring: staff gauges H-flume gauge Palmer-Bowlus gauge