Measurement of rainfall and rain guage.pptx

Measurement of rainfall and rain guage.

1. To p i c To Measure Rainfall Depth Of a Storm Event Using And Automatic Rain Gauge.

2. Types of Rain-Gauges Fo ll o wi n g a r e t h e m a i n ty p e s o f r a i n -g auge s measurement of rainfall. u s e d f o r Non-automatic / Non-recording Rain-gauge Symon’s Rain-gauge Automatic / Recording Rain-gauge Weighing Bucket Rain-gauge Tipping Bucket Rain-gauge Float type Rain-gauge

3. Non-automatic (Non-recording) Rain-gauge ▪ These are called non-recording rain gauges because they do not record the rain but only collect the rain. The collected rain is then measured by means of graduated cylinders so as to directly represent the rainfall volume in cm of water depth, i.e. ▪ Depth of rain water in cm = Note: The amount of precipitation/rainfall is expressed as the depth in cm or inches. Volume of water collected in cm 3 Area of aperatureof the guage in cm 2

4. Symon’s Rain-gauge M o s t c o m mo n ty p e o f n o n - a u t o m a t i c r a i n - g a ug e . Consists of cylindrical vessel 127 mm ( 5”) dia w i t h a b a s e e n l a rg e d t o 21 m m ( 8 ” ) d i a . T h e t o p s e c ti o n i s a f unn e l pr o vi d e d wi t h c i r c u l a r br a s s r i m e x a c t l y 12 7 m m ( 5 ” ) i n t e rn a l dia. T h e f unn e l s h a n k i s i n s e r t e d i n t h e n e c k o f r e c e i v i n g bo t t l e w h i c h i s 7 5 t o 10 m m ( 3 t o 4 ” ) dia. Capacity of bottle is 75 to 100 mm of rainfall. T h e r a i n - g a ug e i s p l a c e d i n c on c r e t e b l o c k 60cm×60cm×60cm ( 2’ ×2’ ×2 ’). T h e r i m s hou l d b e 30 5 m m ( 12 ” ) a bo v e t h e ground surface. Water contained in the bottle is measured by s u i t a b l y gr a du a t e d m ea s ur i n g g l a ss , w it h a n accuracy up to 0. 1 mm.

5. Automatic (Recording) Rain-gauge ■ G a u ge s w h i ch c a n g i ve pe r m a n e n t a n d a ut o mat i c rainfall record without any bottle reading. ■ Man ha s n o t to g o to t h e ga u g e to m e as u re t h e amount of rain fallen. ■ There is mechanical arrangement by which the total amount of rain fallen, since the record was started, gets recorded automatically. ■ The gauge thus produces a record of cumulative rain vs. time in the form of graph known as Mass Curve of rain fallen.

6. Measurement of rainfall by an Automatic (Recording) Rain-gauge In general, automatic rain-gauge consists of rotating drum with a graph paper fixed around it. Th ere i s pe n i n c o n tact wi th gr a p h pap er, w h i ch mov e s u p wi th the c ol l ect e d ra i n, a n d t h us recording cumulative rain, with the passage of time. These are of three types Weighing Bucket Rain-gauge Tipping Bucket Rain-gauge Float Type Rain-gauge

7. 1.Weighing Bucket Rain- gauge ■ Consists of a receiver bucket supported by a s p ri n g o r le ve r b a l a n c e o r a n y o t he r weighing mechanism. ■ T he m ov e m e n t o f b uck e t d u e t o i t s i nc r e as i n g w e i g h t i s t r a n s m i t t e d t o a p e n which traces t h e cl o c k r e c o rd o n a driven chart.

8. 2.Tipping Bucket Rain-gauge Consists of 30 cm dia sharp edge receiver. At the end of receiver funnel is provided. Under the funnel a pair of buckets are pivoted (the central point which balances) in such away that when one bucket receives 0.25 mm (0.01”) of rainfall it tips (to fall or turn over), discharging its contents into reservoir bringing other bucket under funnel. Tipping of bucket completes an electric circuit causing the movement of pen to mark on clock driven revolving drum which carries a record sheet.

9. 3.Float Type Rain-gauge ■ Working is similar to weighing gauge bucket. Funnel receives the rain water which is collected in rectangular container. Float is provided at the bottom of container. Float is raised as the water level rises in the container. Movement of float is being recorded by a pen moving on recording drum actuated by clock work. When the water level in the container rises so that float touches the top, the siphon comes into operation, and release the water; thus all the water in the box is drained out. ■ ■ ■ ■ ■

10. Advantages of Recording Gauge over the Non-recording Gauge. ■ ■ ■ In r e c o rd i n g g aug e r a i n f a l l i s rec o r d e d a u t o m a t i c all y & therefore, there is no necessity of any attendant. Recording rain-gauge gives the intensity of rainfall @ an y t i m e w h i l e t h e non - r e cor di n g gau ge g i v e s the total rainfall in any particular interval of time. As no attendant is required such rain-gauge can be installed in far–off places also. Possibility of human error is obviated.

11. Disadvantages of Recording Gauge over the Non-recording Gauge. It is costly in comparison with non- recording gauge. Fault may be developed in electrical or mechanical mechanism or recording the rainfall.