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How Does a Tipping Bucket Rain Gauge Work?A Lesson in the Weather Instruments HOW-TO SeriesBy Rachelle Oblack, About.com Guide

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Each time the bucket fills with rain, the see-saw tips. The total rainfall is measured by counting how many times the bucket tips.

Copyright www.weatherhut.com 2007. Used with permission.by Guest Writer Jenni Worboys

What is a Tipping Bucket Rain Gauge?

A tipping bucket rain gauge is a meteorological device that measures the amount of precipitation, or rain, that has fallen. It is one of the most common tools used to measure rainfall. Tipping bucket rain gauges are a really interesting and fun way for you and your children to learn about the weather, and predict what the weather will be in your area.

How a Tipping Bucket Gauge Works

A tipping bucket rain gauge has several components that allow it to accurately measure of rainfall. As rain falls it lands in the funnel of the tipping bucket rain gauge. The rain travels down the funnel and drips into one of two very carefully calibrated ‘buckets’ balanced on a pivot (like a see-saw).

The top bucket is held in place by a magnet until it has filled to the calibrated amount (usually approximately 0.001 inches of rain). When the bucket has filled to this amount, the magnet will release its hold, causing the bucket to tip. The water then empties down a drainage hole and raises the other to sit underneath the funnel. When the bucket tips, it triggers a reed switch (or sensor), sending a message to the display or weather station.

Go to the Tipping Bucket Rain Gauge Animation

The display counts the number of times the switch is triggered. Because it knows how much rain is needed to fill the bucket, the display can calculate the rainfall. Rainfall is measured in inches; 1" of rain would fill a container with straight edges to a level of 1".

Getting the Best Results from Your Rain Gauge

To get the most accurate results from a tipping bucket rain gauge, you need to properly install the rain gauge.

1. The rain gauge must be positioned on a flat surface – if the surface isn’t flat, the see-saw may tip before the bucket has filled to the calibrated level, or not tip at all. If the bucket doesn't tip at the calibrated level, the rainfall calculated will not be correct. Use a spirit level to determine whether a surface is flat, and then fix the gauge to the flat surface to ensure you are getting an accurate reading.

2. The rain gauge must be positioned on a surface that does not vibrate – surfaces such as a porch or fence can move and vibrate. The tipping bucket is very sensitive and any vibrations could cause the gauge to tip even if it is not raining.

3. The instrument must not be positioned near trees – being positioned near trees could allow leaves or pollen to fall inside the funnel and block it, causing an inaccurate reading.

4. It must not be positioned in a sheltered area – Being positioned in a sheltered location (such us beside your house or a fence) could significantly increase or decrease the amount of rain depending on the wind direction, and cause an inaccurate reading. The gauge should be positioned at least twice as far away from the object as the object’s height (e.g. if the fence is 6 feet high, the gauge should be positioned at least 12 feet away).

5. Your weather equipment must not be located near any magnetic, steel, or iron objects – magnetic, steel, or iron objects can affect the amount of time the magnet will hold the bucket or whether it will hold it all, causing an inaccurate reading.

Go to the Tipping Bucket Rain Gauge Animation

Will a Rain Gauge Measure Snow?

If it snows where you live, most rain gauges will not be able to measure the snow fall; snow will block the opening of the collection funnel. However, special snow gauges are available to measure this.

Following these recommendations should ensure your get an accurate result from your tipping bucket rain gauge.

Rain Gauge – Its Types And StandardsWhat is a rain gauge? What is its use? Who uses it? Perhaps you have heard of it a hundred times already. Hence, for someone like you who doesn't know much about what this instrument is for but it is clear that you are after the helpful bunches of data about it, then, you just found the perfect article that will suffice your queries.

The Types of Rain Gauges

Among the popular and commonly used types of rain gauges are the weighing gauges, graduated cylinders, simple buried pit collectors, and the tipping bucket gauges. They all have their own share of pros and cons in line with the collection of rain data.

A Look at the Standard Rain Gauge

The standard type of this instrument was developed at approximately the beginning of the 20th century. It particularly consisted of a funnel that was attached to a graduated cylinder that suited into a bigger container. Almost all modern rain gauges are patterned to this early model.

Moreover, the design allows the outside container to catch the water that overflows from the smaller-sized graduated cylinder. As it is measured, the water that is collected in the graduated cylinder will be gauged. The excess rain water will be placed in a different cylinder and will be measured as well.

Typically, the cylinder uses the millimeter unit of measurement. The bigger container is the one that is used to gather the rainfall that amounts to more than 25mm which flows out from the tiny hole located on top of the smaller cylinder. There is a metal pipe which is affixed to the container that is flexible and adjustable to guarantee that the rain gauge is showing the appropriate level. The pipe is then fitted over some kind of a metal rod which has been originally affixed in the ground.

The Weighing Precipitation Gauge

The weighing type precipitation gauge is made up of a storage bin that is used to record the mass. There are models which gauge the mass with the use of a rotating drum or pen or by means of a vibrating wire that is connected to a data logger. Its primary advantage is that it rarely underestimates the extreme rain and it can still gauge other kinds of precipitation like snow, hail, and rain. However, they are more costly and needs higher maintenance level.

Likewise, this type bears a kind of device that promotes the measurement of the amount of chemicals that are contained in the atmosphere of a particular location. Scientists who study the greenhouse gas effects as well as their effects on the acid rain levels find it very helpful.

The Tipping Bucket Rain Gauge

This type is composed of a big copper cylinder which is normally secured to the ground.

At the top is the funnel which responsibly gathers and then channels the precipitation. The latter then falls into one of either the levers or small buckets that are balanced like the scale. When there is about 0.2 mm precipitation amount, the lever tips fall and then an electrical signal is transmitted to the recorder.

There are of course several modern models being used these days. Their designs may vary but what remains alike is the purpose that they serve. Professionals also have their own methods of reading the data and providing accurate records.

Self-Recording Rain GaugeRecording raingauges are used to obtain a continuous record of daily or weekly rainfall.  It consists of a funnel-shaped collector at the top of the gauge and a float syphon chamber and recording mechanism just below it.  the rain water collected by the collector is led into the float chamber.  The float is having a central stem on which a pen assembly is fixed.  The pen is moving over a daily (or weekly) chart wound over a clock drum.  After every one centimetre of rainfall syphoning occurs and recording of rain starts afresh.

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The intensity of rainfall is the rate at which the rain is falling and it is expressed in cm/hr. For example, during a particular event of rainfall occurred for 10 minutes the quantity of rainfall is 2 cm, then the intensity of rainfall of that rain event is 12 cm/hr. 5 cm/ hr intensity of rainfall means an average rainfall rate of 5 cm per hour duration. The rainfall particulars are recorded with either non-recording rain gauges or automatic recording rain gauges or by Meteorological Department (IMD).

World Anual Rainfall

 Rainfall Recording Non-recording gauges

In non-recording gauges the rainfall for the past 24 h is measured and recorded as cm of rainfall during the last 24 hours. These data give only average intensity and not the actual intensity of rainfall of the rain event, which might have last for only 10 to 15 minutes. This type of rain gauges does not record the rain but only collect the rain. Symon’s type instrument is most commonly used. The rain gauge consists of a collector, with a gun metal rim, a base and a polythene bottle. The collector and the base are made of Fibre Glass Reinforced (FRP). The collectors have aperture of either 100 cm2 or 200 cm2 area and are so made that they are interchangeable. The polythene bottles are of three sizes having capacities of 2, 4 and 10 litres of water respectively. The rain gauge should be fixed on a masonry or concrete foundation 60 x 60 x 60 cm sunk into the ground. The base of the gauge should be embedded in the foundation, so that the rim of the gauge is exactly 30 cm above the surrounding ground level. The rim of the gauge should be kept perfectly level. The horizontality should be checked with a spirit level laid across the rim.

At the time of recording rainfall, remove the funnel of the rain gauge and take out the polythene bottle. Place the measuring jar in an empty basin and slowly pour the contents of the receiver into the measuring jar taking care to avoid spilling. If, however, any water is spilled into the basin, add it to the water in the measuring jar before arriving at the total amount collected. While reading the amount of rain, hold the measuring jar, upright between the thumb and the first finger or place it on a table or other horizontal surface. Bring the eye to the level of the water in the measure glass and take the reading of the bottom of the meniscus or curved surface of the water. The amount of rainfall should be read in millimeters and tenths. It is extremely important to note that the correct type of measuring jar appropriate to the type of rain gauge funnel in use should be used for measuring the amount of rainfall, to avoid errors in the results. Enter 0.0 for no rain and a ‘t’ (meaning trace) for rainfall below 0.1 mm.

The collector of the rain gauge the receiving bottle and measuring cylinder are always kept clean. They should be emptied regularly of sediment or other material that may have fallen into them and cleaned periodically. The grass around the gauge should be kept short. No shrubs or plants should be allowed to grow around the gauge.

Automatic Recording gauges

Automatic ram gauges record continuously the cumulative amount of water with time on a graph paper. After the collection in the bottle has recorded 10 mm of rain, the bottle gets emptied and the line representing cumulative rainfall vertically falls down. Hence, while estimating the amount of rain fallen during any time interval, this fact must be kept in view. The graph of the automatic rain gauge shows the time taken for each 10 mm of rain. The total rainfall in any particular hour can be obtained from the graph.

Recording type of rain gauges are those which can give a permanent automatic rainfall record without bottle reading. In this type of rain gauges, a man need not go to the gauge to measure or read the amount of rain fallen. A mechanical arrangement by which the total amount of rain fallen, since the record was started, gets recorded automatically in graph paper. Thus the gauge forms a record of cumulative rain vs time in the form of a graph and which is known as the mass curve of rain fallen. The curve will also help in indicating the times of onset and cessation of a rain and its duration.

The slope of the curve gives the intensity of rainfall for any given period.

                                            do     _(P2—

The intensity of rainfall,            — (1, ii)

Since such gauge represent the cumulative rain, they are called as integrating rain gauges. There are three types of recording rain gauges. They are

1.   Tipping bucket gauge,2. Weighting type,3. Floating type.

Tipping bucket gauge

The arrangement of a tipping bucket rain gauge. In this type of rain gauge, the rainwater is collected in the collector and then passed through a funnel. The funnel discharges the water into a two compartment bucket. If 0.1mm of rainwater gets filled up in one compartment, the bucket tips emptying in to a reservoir and moving the second compartment into place beneath the funnel. The tipping bucket completes an electric circuit, causing a pen to mark on a revolving drum. These types of gauges are generally in hilly and inaccessible areas, where they can supply measurements directly to control room. No graph paper or drum is installed in the gauge and the rainfall measurements are directly recorded at the control room.

Weighting type gauge

This type of gauge weights the rain which falls into a bucket placed on the platform of a spring or a lever balance or any other weighting mechanisms as shown in fig. When the

weight of the bucket increases, that helps in recording the increased quantity of rain with time by moving a pen on a revolving drum.

Floating type gauge

In this type of gauge, the rise of gloating body due to increasing rain catch helps in lifting the pen point, which goes on recording the cumulative rain with time in a graph paper wrapped round a rotating drum. Nowadays various types of floating type recording rain gauges are available. Natural Syphon recording rain gauge is widely used in India.

The rainwater entering the gauge at the top of the cover is led via the funnel to the receiver, consisting of a float chamber and a siphon chamber. A pen is mounted on the stem of the float, and as the water level in the receiver rises, the float arises and the pen records, on a chart wrapped round a clockwise rotating drum, the amount of water in the receiver at any instant. The rotating drum completes one revolution in 24 hours (one day) or sometimes in 7 days. Syphoning occurs automatically when the pen reaches the top of the chart, and as the rain continues, the pen rises again from the zero line of the chart. If there is no rain, the pen traces a horizontal line from where it leaves off rising.

The siphon recording rain gauge is an instrument designed for continuous recording of rainfall. In addition to the total amount of rainfall, the onset and cessation of rain (and therefore the duration of rainfall) are recorded.

The gauge should be installed in such a way that the rim of the funnel is horizontal and set at a height of exactly 75 cm above ground level. For setting the pen at the zero mark, pour sufficient water into the receiver till the pen reaches the top and water siphons out. After all the water is drained out, the pen should be on the zero line; if not, it should be adjusted.

Rainfall enters the gauge at the top via a funnel and passes through a receiver consisting of a float chamber and a siphon chamber. A pen is mounted on the stem of the float, and as the water level rises in the receiver, the float rises and the pen records the level of water in the chamber on a chart wrapped round a clockwise rotating drum. The rotating drum completes one revolution in 24 hours (one day) or sometimes in 7 days. Siphoning occurs automatically when the pen reaches the top of the chart, at the 10 mm mark, and then the pen comes down to the zero line of the chart. The pen rises again with the onset of rainfall. When there is no rain, the pen traces a base horizontal line of the chart.

The siphon is arranged concentrically so that the long discharge tube being surrounded by the shorter siphon chamber and is directly connected to the float chamber. A glass piece is placed over the joint of these tubes and the passage connecting two tubes at this joint is of almost capillary dimensions, but the sectional area is large enough to discharge the water collected in the receiver with enough speed. When the upper end of the water level falls to a certain depth, the siphon ceases to act, the water column is broken at a definite stage by a bubble of air which gets into the capillary and freedom from dribbling is thus ensured. There is just sufficient water to float the float after siphoning.

The chart should be changed daily (in India at 08 30 IST) as a routine observation irrespective of the rainfall occurrence. The observer should see that the pen trace matches the base horizontal line of the chart without an error after every siphoning operation. The instrument should be checked daily once for correct siphoning operation.

Duration of Rainfall

The duration of rainfall is the time period for which the rain event occurs at that given intensity of rainfall. From the historic records of the automatic rain gauge station (of graphs) for 30 to 50 years the intensity of rainfalls for different time intervals such as 5 minutes, 10 minutes, 15 minutes, 20 minutes, 60 minutes, etc., could be obtained.

Frequency of Rainfall

The frequency of rainfall is the number of times the rainfall of a particular intensity and duration occurred in the past based on the historic records. Frequency of rainfall is also know as the recurrence interval of a particular rainfall.

 Time of Concentration

During a rainfall only a certain amount of water from the adjacent area will reach the outlet initially, but after sometime the rain water from the entire area of the catchment will start reaching the outlet and the runoff rate would become maximum and equal to the rate of rainfall. The period after which the entire area will start contributing to the runoff is called the time of concentration. Time of concentration generally consists of two parts: viz., the inlet time and the channel flow time.

The inlet time (Ti) is the time taken by the water to flow overland from the critical point up to a point where it enters the drain mouth.

Where T = 0.885 L3 \ 0.385 Equ.

 

Ti is inlet time in hours,

L is the length of overland flow in km,

H is the total fall in level from the critical point to the mouth of the drain.

The channel flow time is the time taken by the water to flow from the mouth of the channel to the considered point. This is obtained by dividing the length of the drain by the velocity of flow in the drain.

Unless otherwise determined by overland flow charts or nomographs, the Time of Concentration (Tc) for inlets of storm water collection systems may be used as follows as furnished in Table

Time of concentration for different areas

Characteristics of the area Time of Concentration, minFlat terrain Steep terrain

Residential and undeveloped areas 15 10Residential and developed area 10 8

 At no time the Time of Concentration shall be greater than 30 minutes for design of storm inlets. The runoff resulting from a rainfall having duration equal to the time of concentration will be the maximum and that duration of rainfall is called the critical rainfall duration.

Design Storm Duration

Although the design storm must reflect required levels of protection, the local climate, and catchment conditions, it need not be scientifically rigorous. It is more important to define the storm and the range of applicability fairly precisely to ensure safe, economical and standardised design.

Two types of design storm are recognised: synthetic and actual (historic) storms. Synthesis and generalisation of a large number of actual storms is used to derive the former. The latter are events which have occurred in the past, and which may have well documented impacts on the drainage system. However, it is the usual practice in urban stormwater drainage to use synthetic design storms. Design storm duration is an important parameter that defines the rainfall depth or intensity for a given frequency, and therefore affects the resulting runoff peak and volume.

Current practice is to select the design storm duration as equal to or longer than the time of concentration for the catchment (or some minimum value when the time of concentration is short). Intense rainfalls of short durations usually occur within longer-duration storms rather than as isolated events. It is common practice to compute discharge for several design storms with different durations, and then base the design on the “critical” storm which produces the maximum discharge. However the “critical” storm duration determined in this way may not be the most critical for storage design.

Recommended practice for catchment containing storage is to compute the design flood hydrograph for several storms with different durations equal to or longer than the time of concentration for the catchment, and to use the one which produces the most severe effect on the pond size and discharge for design.

Rainfall Intensity-Duration-Frequency (IDF) Relationships

The total storm rainfall depth at a point, for a given rainfall duration and ARI, is a function of the local climate. Rainfall depths can be further processed and converted into rainfall intensities (intensity = depth/duration), which are then presented in IDF curves. Such curves are particularly useful in stormwater drainage system design because many computational procedures require rainfall input in the form of average rainfall intensity.

The three variables, frequency, intensity and duration, are all related to each other. The data are normally presented as curves displaying two of the variables, such as intensity and duration, for a range of frequencies.

Rainfall Intensity-Duration-Frequency

 These curves shall be developed by the IMD based on the automatically recorded rainfall data for a long period. The IDF curve is then used for determining the design intensity of rainfall for the duration of rainfall which is equal to the time of concentration. This design intensity of rainfall is used for the computation of storm runoff.

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SELF RECORDING RAINGAUGE. (SI-SI-7032)

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Rain Gauge Recording Type : this natural siphon type recording rain gauge is designed to give continuous record of rain fall. It is generally used in conjunction with an ordinary rain gauge ( non recording type ) exposed close by. Rainwater enters the gauge at the top of the cover and is carried through the funnel to float chamber provided with a float. The recording pen is mounted on the stem of the float. As the water level rises in the receiver, the float rises and the pen records rain on a chart placed on a clock drum which revolves once in 24 hours. The recording mechanism is mounted on the base and the base cover is provided with a gunmetal rim of about 203 mm. Dia. The funnel lifts of the base and carries a hasp, which is engaged with a staple on the base and pad locked. An angle iron piece with foundation bolt is provided for anchoring the rain gauge base to the ground. The dimensions of the base, collector, funnel, float chamber float chamber, float etc. are as per ISI specification and also as per IMD specification. The unit is supplied with 100 graph paper sheet, a phial of special recording ink, recording pen, filter, clock movement with drum and key, float chamber with float, foundation angle iron and literature booklet.

(a) Spare Rain Gauge Charts: per packet of 100 chart sheets.

(b) Spare Recording Ink: phial containing about 20 ml. of the special type of ink.

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Precipitation Measurement - Ppt rate Advertisements

All the forms of precipitation are measure on the basis of vertical depth of water that would accumulate on a level surface of precipitation remained where it fell.

In metric system precipitation is measure in millimeters and tenths.

Any open receptacle with vertical side can be used as a gauges for measuring rainfall. These refined receptacles with vertical side can be used as a gauges for measuring rainfall.

Rain gauges for measurement of precipitation are of two types

1

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1. Recording rain gauges2. Non-Recording rain gauges

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1. Non-recording rain gauges:Non-recording rain gauges are commonly used. They do not record the data and collect only rain and this collected rain is then measured in a graduated cylinder.

Depth of rain = volume of rain collected in cm3 /area of aperture of gauges in cm3

This type of gauges measures precipitation for only a specified period. Any open receptacle with vertical sides may be used for precipitation measurement but because of varying wind and splashing effect.

The measurements are not compatible unless the receptacles of same size, shape and exposed in a similar manner. The US national weather service gauges is type of non recording gauges.

Types of Precipitation Methods Precipitation factors Mechanism of Precipitation Hydrological Cycle Catchment & Basin Mechanism of Precipitation Double Mass Curve Theissen Isohytel method History Forms of Precipitation

It consists of:

Collector (receiving 8" 20.3 cm diameter) Overflow can Cylindrical measuring tube of area of 1/19th of collector Measuring scale

Measuring tube is placed in overflow can and with measuring sticks; the depth of rainfall can be measured. As area of M-Tube is 1/10th of collector, therefore 1" depth of rain in M-Tube corresponding to 0.1" of rainfall. In case of snow the M-Tube and the collectors are removed and the snow is collected, melted and poured in M-Tube and measured.

2. Recording gauges:Are those which automatically record rainfall without any bottle reading. The worker is not required to record the reading but instead mechanical arrangements are there by which total rainfall is recorded automatically on graph paper.

A graph of total rainfall VS time which is known as mass curve of rainfall is plotted by the gauges.

Its three types commonly used are:

1. Tipping bucket gauges2. Weighing type gauges3. Float recording gauges

1. Tipping bucket gauges:

In TBG the collector is funneled into two compartment buckets. When one compartment of bucket is filled with rain water it becomes over balanced and tips such that the other compartment takes its place beneath the funnel.

As the bucket is tipped it automatically activates an electronic circuit.This type of gauges is not suitable for measuring snow (without heating the collector).

2. Weighing type gauges:

It consists of a storage bin, which is weighed to record the mass. It weighs rain or snow which falls into a bucket, set on a platform with a spring or lever balance. The increasing weight of the bucket and its contents are recorded on a chart. The record shows accumulation of precipitation.

3. Float recording gauges:

The rise of float with increasing catch of rainfall is recorded. Some gauges must be emptied manually while others are emptied automatically using self starting siphons. In most gauges oil or mercury is the float and is placed in the receiver, but in some cases the receiver rests on a bath of oil or mercury and the float measures the rise of oil or mercury displaced by the increasing weight of the receiver as the rainfall catch freezes. Float may get damaged by rainfall catch freezer.

Storage gauges are used in remote areas where frequent servicing is not possible. Weighing type storage gauges operate for 1 or 2 months without any servicing required.

Weighing type storage gauges are designed to operate for entire season without attention. WTSG located in heavy snowfall areas should have collectors to prevent wet snow from clinging to the inside of walls and clogging the orifice. The orifice should be above the maximum snow depth expected.

Gauges are initially dry and require moisture for funnel and inside surfaces.

During rainfall of 5" to 6"/hr (12.5 to 250 mm/hr) the bucket of tipping bucket gauges tips every 6 to 7 seconds and takes about 0.3 seconds to complete the tipping procedure, during which some water is still pouring into already filled compartments. The recorded ratio is 5% too low.

Error caused by wind in gauges reading When gauges are installed on the ground, it is inclined against the wind and thus

catches less precipitation. Towards the wind it will catch more precipitation. Obstruction due to trees, buildings and un-even topography.