Anniina Kittilä, ETH Zürich, Institute of Geophysics, Geothermische Energie u. Geofluide. Sonneggstrasse 5, 8092 Zürich, Switzerland e-mail: anniina.kittila(at)erdw.ethz.ch
The bucket method is a simple and fast volumetric technique to measure the flow rate in small streams or in springs. For the bucket method it is needed a bucket of known volume, a stopwatch, and preferably at least two people to carry out the measurements.
Description of the method
This simple, direct measurement of flow rate is based on the time to fill a bucket of known volume. The entire flow is diverted into a suitable size bucket, and the time to fill the bucket is measured with a stopwatch (Mustonen 1986, Wolkersdorfer 2008). The flow rate is obtained by dividing the volume of the bucket by the filling time. For more accurate results it is good to repeat the procedure approximately five to seven times to get an average for the filling time. The results are usually obtained in litres/second (l/s) or in litres/minute (l/min) (Wolkersdorfer 2008).
The method is suitable for measuring the flow rate in small streams or channels, where the entire flow can be diverted to the bucket. The results obtained can be very accurate, and the method is used to calibrate instruments that measure flow rate, in model scale laboratories, and in other equivalent procedures (Mustonen 1986). The bucket should not be filled by holding it below the water surface because this does not give true flow rate values. The restraints of the method for measuring only small flow, approximately 5-6 l/s, come from the need to divert all the flow into the bucket, which might be very challenging for streams with high flow rates, and secondly, the accuracy can suffer if the filling happens too fast, especially if it takes only some seconds. The variations in filling times between separate measurements give good indication of the accuracy of the results (Wolkersdorfer 2008).
The ideal location for using bucket method is in the natural waterfall of the stream, but one can be constructed using a weir or a small earth dam where the water flows through a single pipe. In case there is a need for constructing a separate waterfall, other methods, such as a V-weir, might be more suitable to measure the flow rate in that particular stream. Additionally, sometimes the measurements might be interfered with heavy debris flow, distorting the accuracy of the flow rate results.
This method does not require scientific equipment or difficult installation. Neither does it affect the environment because it can be done in small scale and relatively quickly, although the need for constructing a separate waterfall may indicate that other methods are more suitable in that stream. The accuracy of the measurements is very high once performed properly, and practically no maintenance is needed other than water proof bucket.
The use of bucket method does not require expertize in conducting flow rate measurements, and it is actually a very common “do-it-yourself” technique, easy to be done with common household objects. The investment for measuring the flow rate with this method is very minimal, but for long-term monitoring other methods are recommended, as it is not possible to get, for example, automatic digital measurement data with bucket method.
Mustonen, S. 1986. Sovellettu hydrologia. Vesiyhdistys r.y., Helsinki, 436 p. (In Finnish)
Wolkersdorfer, C. 2008. Water Management at Abandoned Flooded Underground Mines. Springer, 465 p.