Contents preface (VII) introduction 1—37

Fig. 2.2 Symon’s rain gauge

42 IRRIGATION AND WATER RESOURCES ENGINEERING
Recording rain gauges automatically record the intensity of rainfall and the time of its occurrence in the form of a trace (or graph) marked on a graph paper wrapped round a revolving drum. Following three types are the most widely used recording rain gauges :
(i) Tipping bucket rain gauge,
(ii) Weighing bucket rain gauge, and (iii) Siphon rain gauge.

(i) Tipping bucket rain gauge : A 300 mm diameter funnel collects rain water and conducts it to one of the two small buckets (Fig. 2.3) which are so designed that when 0.25 mm of rainfall is collected in a bucket, it tilts and empties its water into a bigger storage tank and, simultaneously, moves the other bucket below the funnel. When any of the two buckets tilts, it actuates an electric circuit causing a pen to make a mark on a revolving drum. The recording equipment can be remotely located in a building away from the rain gauge. At a scheduled time, the rain water collected in the storage tank can be measured to yield total rainfall in the measuring duration. The rainfall intensity (and also the total rainfall) can be estimated by studying the record sheet on which each mark indicates 0.25 mm of rain in the duration elapsed between the two adjacent marks.

30 cm

Receiver

Funnel

Tipping bucket

Storage tank

Measuring tube