# Uses of rain gauge | Rain gauge types | Tipping bucket rain gauge

The uses of rain gauge are given below:-

• It is used to study the present as well as the future condition of water resources.
• It is used to determine the amount of rainfall with respect to the time at a particular place or area.
• It is used to predict the water precipitation at a particular place to make a stable structure like a dam, road, etc.
• Rain gauge help to design the drainage by showing the discharge of precipitation at given interval of time.

### Definition

The instrument used by hydrologists for the measurement of precipitation or total rainfall is called rain gauge.

Estimating and Costing

Design of septic tank

### Rain gauge types

There are two types of the rain gauge, they are

1. Non-recording rain gauge
2. Recording rain gauge ( Automatic )

#### 1) Non-recording rain gauge

It is defined as the gauge which is read manually. It doesn’t record rain itself but simply collects. Symon’s rain-gauge is the most common type of non-recording rain gauge. The collector is used above funnel leading into the receiving vessel.

The rainfall collected in the vessel is measured by a graduated measuring cylinder or dipstick to give a depth of rainfall. This type of rain gauge gives the amount of rainfall only. Such rain-gauge does not provide the information regarding the time, intensity and duration of rainfall.

The capacity of measuring glass is 25 mm and the least count is 0.1 mm.

#### A suitable site for rain gauge station

• The site should be in an open place.
• It should be at least 30m away from the obstruction.
• It should be level ground.
• The fence should be erected around the station.

#### 2) Recording rain gauge

##### A) Weighing bucket rain gauge:

It is the most common type of self-recording rain gauge. In this rain gauge rain falling on the receiving area is collected by a funnel and is let into a storage bucket, which rests on a weighing platform.

This gauge continuously records the weights of the bucket and the accumulated rainfall by means of a spring mechanism or a system of balance weights. In this method, the mechanical lever arm of the balance is collected with a pen that touches a clock mounted drum with a graph paper. The record shows the accumulation of rainfall over time.

##### B) Tipping bucket rain gauge

Tipping bucket rain gauge consists of a 30 cm diameter sharp edge receiver. A funnel is provided at the end of a receiver under which a pair of buckets are provided.  The buckets are provided in such a way that when one bucket receives 0.25 mm of preparation it tips discharging its contents into a reservoir bringing the other bucket under the funnel.

The disadvantages of tipping bucket type rainfall recorder are:

• For higher intensity, bucket tips rapidly and record tend to overlap.
• It takes 0.3s to complete the tip; this makes the intensity of rainfall recorded by the gauge less by some % for high intensity.
##### C) Float type ( with siphon arrangement )

It is also known as siphon type rain gauge as it uses the siphon mechanism to empty the rainwater collected in the float chamber. A funnel receives rainwater, which is collected in a rectangular container. The float is used at the bottom of the container.

The float rises when the water level rises in the container and its movement is recorded by a pen moving on a recording drum actuated by a clockwork. When the water level rises in the container then the float touches the top, the siphon comes into operation and releases the water.

#### Sources of error in recording

• A mistake in reading the scale.
• Loss resulting from rainfall splash
• Deficiency in measurement due to the wind.
• Lack of consideration of evaporation loss.
• Change of receiving area due to dents on the collector rim.

#### Optimum Number of Rain Gauge

If there are a number of rain gauge which are already installed in the region, the information obtained from these gauges can be used to determine the optimum number of rain gauges required for the area. The optimum number (N) depends upon the coefficient of variation (CV) of the mean rainfall at the existing station and the allowable degree is given by,

Where,

e = allowable degree of error ( expressed as a percentage ) or allowable percentage of error in estimating the mean areal rainfall, e is generally taken as 10%.

CV = Coefficient of variation

#### Rain Gauge Network

WMO recommends that the minimum area for 1 station under ideal condition and area to be covered under the difficult conditions in km² are presented in the table below.