Types of rain gauges with sketch

Rain gauges measure the depth of rainfall (mm) at a point. They are of two kinds: non-recording and recording.

A. Non-recording (Symons') gauge

A funnel of 12.7 cm diameter sits on a cylindrical vessel and collects rain into a bottle; the depth is read by a graduated measuring jar once a day (8:45 am in Nepal).

   |<-- 12.7 cm -->|
    \             /   Funnel
     \___________/
      |  bottle  |   <- collecting can
      |__________|
   ========ground=======

It is cheap and simple, but gives only daily totals and needs an observer.

B. Recording gauges

1. Tipping-bucket gauge: Rain falls through a funnel onto a two-compartment bucket balanced on a pivot. When 0.25 or 0.5 mm of rain fills one compartment it tips, empties, and brings the other under the funnel. Each tip closes a switch and is recorded electronically. It gives the intensity but may under-record in very heavy rain.

     funnel
       \ /
     [ \/ ]   two-compartment bucket
      /\  tips at fixed volume
   pivot   -> pulse to recorder

2. Weighing-bucket gauge: The collecting bucket sits on a spring balance; the increasing weight moves a pen over a clock-driven drum chart, giving a continuous mass curve. It records snow and hail also.

3. Float-type (natural siphon) gauge: A float in a chamber rises with the rain collected, moving a pen on a rotating drum. When the chamber is full, a siphon empties it automatically and the pen returns to zero. It gives a continuous mass curve (Dines or Hellman type).

Comparison

Siting

The gauge is placed on open level ground, with its funnel rim horizontal 30 cm above the ground, away from obstructions at a distance of at least twice their height.