DESIGN AND CALIBRATION OF TIPPING BUCKET SYSTEM FOR FIELD RUNOFF AND SEDIMENT QUANTIFICATION

This paper describes a low cost tipping bucket system for measuring ru noff and soil loss from field plots ranging in size from 25 to 50 m(2) (29.89 to 59.79 yd(2)). It been designed to minimise errors due to si ltation caused by slow flow rates and errors due to instability caused by high flow rates. The resolution of this system for a 50 m(2) (59.7 9 yd(2)) plot is 0.06 mm (0.0023 in) of runoff and is capable of measu ring a maximum rate of 110 mm h(-1) (4.33 in h(-1)). The number of tip s can be monitored manually by a magnetic counter or automatically in real time by a data logger. Soil loss is sampled by either a sediment pipe or a cotton bag. Field calibration indicates the maximum error in estimating flow rate is 2% and is close to the value observed by manu al measurements. At a soil loss of 7 t ha(-1) (3.125 t ac(-1)), the sa mpler pipe overestimated soil lass by 10%, compared to 6% by bag sampl er, and 33% by manual measurements. The main advantage of the pipe sam pler ic the ability to measure high rates of soil loss, with a maximum of 81 t ha(-1) (36.16 t ac(-1)), whereas the bag sampler is more suit able for low soil loss, less than 8 t ha(-1) (3.57 t ac(-1)), and is l ess laborious than the pipe sampler.