Laserfiche WebLink
Evaluation of Measurement Methods <br />In the first few days of the 2004 autumn water level collection program, the water level <br />measuring probe became tangled with electrical wires in the well. In an effort to eliminate the <br />potential for entanglement and improve efficiency during this and future bedrock water level <br />data collection efforts, a sonic water level meter was used to measure water levels in a subset of <br />wells. <br />The sonic meter was used in combination with another water level measuring device to <br />evaluate the accuracy of the sonic meter. The sonic meter is a small portable handheld meter <br />that requires only a small opening at the top of the well and a few seconds to obtain a water <br />level measurement. The sonic meter is anon-obtrusive method of measuring the water level <br />and eliminates the possibility of a meter or steel tape getting caught on cables within the well. <br />The sonic meter was used to collect water levels at 26 sites. The results and a comparison to a <br />steel tape or m-scope measurement are presented in Figure Al and Table A1. As can be seen <br />from Figure A1, the water level measurements obtained from the sonic meter have a 99 percent <br />correlation to the steel tape or M-scope measurements. Table Al shows that most of the <br />measurements collected from the sonic meter are within 2 feet and 2 percent of values obtained <br />from other measurement devices over a large range in depth to water. The measurement <br />accuracy of the sonic meter is 0.2 percent of the reading. The estimated measurement accuracy <br />of the steel tape and M-scope are 0.1 and 0.5 feet, respectively. From these we conclude that an <br />acceptable difference in measurement between the sonic meter and the other devices should be <br />less than 0.5 feet. <br />700 <br />600 <br />500 <br />w <br />a <br />0 <br />v <br />~ 400 <br />w <br />w <br />N <br />w <br />R <br />~ 300 <br />0 <br />r <br />a <br />w <br />0 <br />200 <br />100 <br />Depth to Water (Sonic) <br />Figure Al -Comparison of Sonic Meter and Other methods <br />0 100 200 300 400 500 600 700 <br />