Quantitative precipitation estimations using rain gauges and radar
Precipitation and rain gauges
-
Upload
nikhil-holsamudrkar -
Category
Documents
-
view
573 -
download
5
Transcript of Precipitation and rain gauges
![Page 1: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/1.jpg)
SUBMITED BY:-
1) Nikhil Holsamudrkar (BE11F01F017)
2)Suresh Hatkar(BE11F01F015)
3) Swapnil Dhakane(BE11F01F013)
4) Mamta Ingole(BE11F01F018)
GOVT.COLLEGE OF ENGINEERIG
AURANGABAD.
GUIDED BY:-PROF .K. A.PATIL
Topic :- MESUREMENT OF PRECIPITATION
![Page 2: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/2.jpg)
PRECIPITATIONIntroduction
![Page 3: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/3.jpg)
PRECIPITATION
All forms of water that reaches earth’s surface is known as precipitation.
It is expressed in terms of depth to which rainfall water would stand on an area if all the rain were collected on it.
In case of snowfall equivalent depth of water is considered as depth of precipitation.
Rain gauges are used for measurement of precipitation.
![Page 4: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/4.jpg)
PRECIPITATION
In India ‘Indian Meteorological Department (IMD)’ is responsible for all weather and rainfall predictions.
It occurs due to:
1. Lifting of air mass2. Cooling of warm air3. Condensation
![Page 5: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/5.jpg)
PRECIPITATION
Lifting of air occurs mainly due to three causes:
1. Cyclonic precipitation:- It is caused by lifting of an air mass due to pressure difference.
2. Convective precipitation:- It is caused due to the upward movement of air that is warmer than it’s surroundings. Generally this kind of precipitation occurs in tropics.
![Page 6: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/6.jpg)
PRECIPITATION
3. Orographic precipitation:- It is most important precipitation and responsible for most heavy rains in India. It is caused by air masses which strike some natural topographic barriers such as mountains and can’t move forward hence rise up, causing condensation and precipitation.
![Page 7: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/7.jpg)
RAINGAUGES
1. Recording type2. Non recording type
Most rain gauges used in India are recording type i.e. Symon's raingauge.
Recordings are taken at 8:30 am And if rainfall is more then intermediate
readings are taken at 5:30pm
![Page 8: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/8.jpg)
PRECIPITATIONMeasurement, Estimation and Probability
![Page 9: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/9.jpg)
PRECIPITATION DATA
Necessary for various fields Municipal Industrial Agricultural Forestry Flood prevention Recreation
![Page 10: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/10.jpg)
1) Nonrecording gauge:-Symons’ Raingauge Extensively use in
India
Accuracy 0.1mm
At 8.30am
Capacity is10cm
Incase of Heavy rainfall
Low Maintenance
![Page 11: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/11.jpg)
![Page 12: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/12.jpg)
2)RECORDING RAIN GAGES
Weighing bucket type
Tipping bucket type
Natural-syphons type
![Page 13: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/13.jpg)
TIPPING BUCKET TYPE 30.5 cm size as per us weather bureau.
water collect from Tip bucket to storage tank
least count of 1 mm and gives out one electrical pulse for every millimeter of rainfall
Electric circuit
![Page 14: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/14.jpg)
TIPPING BUCKET TYPE
![Page 15: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/15.jpg)
![Page 16: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/16.jpg)
WEIGHING BUCKET TYPE
![Page 17: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/17.jpg)
Weighing bucket typeIt consists of a storage
bin, which is weighed to record the mass. It weights 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.
![Page 18: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/18.jpg)
FLOAT RECORDING GAUGES
![Page 19: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/19.jpg)
FLOAT RECORDING GAUGES
![Page 20: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/20.jpg)
![Page 21: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/21.jpg)
RAINGAUGE NETWORK
Since the catching area of the raingauge is very small as compared to the areal extent of the storm, to get representative picture of a storm over a catchment the number of raingauges should be as large as possible, i.e. the catchment area per gauge should be small.
There are several factors to be considered to restrict the number of gauge: Like economic considerations to a large extent Topography & accessibility to some extent.
![Page 22: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/22.jpg)
MINIMUM DENSITY OF RAINGAUGES ACCORDING TO IS 4987-1968
In plains : 1 station per 520 km2
In regions of avg. elevation of 1000m : 1 station per 260-390 km2
In predominantly hilly areas with heavy rainfall : 1 station per 130 km2
10% of total should be self recording raingauges
![Page 23: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/23.jpg)
ADEQUACY OF RAINGAUGE STATIONS
![Page 24: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/24.jpg)
RAINFALL ON A WATERSHED SCALE
3 common methods for estimating average rainfall.
1. Arithmetic Mean2. Thiesson
polygon method3. Isohyetal
method
i
ii
W
RWR
![Page 25: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/25.jpg)
P2 = 2.15”P4 = 2.26”
P6 = 1.81”
P5 = 2.18”
P3 = 1.80”
P1 = 1.62”
Watershed boundary
Measured Rainfall at Six Rainfall Gages
![Page 26: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/26.jpg)
ARITHMETIC MEAN METHOD
Pavg = [ Wi x Pi ] / Wi All gages given equal weight
Weight = 1 Pavg = (1.82 + 2.15 + 2.26 + 2.18 + 1.62 +
1.8) / 6 Pavg = 1.97 in.
![Page 27: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/27.jpg)
THIESSEN POLYGON METHOD
First: Draw straight dashed lines between each rainfall gage
Second: Draw solid perpendicular bisectors to these lines so that watershed area associated with each gage is enclosed by bisector lines These enclosed areas are known as Thiessen
Polygons The area within each polygon is closer to the
rain gage enclosed than any other rain gage. The rainfall measured in the polygon is
assumed to be representative of the rainfall in the entire polygon
![Page 28: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/28.jpg)
THIESSEN POLYGON METHOD
Third: Determine the area of each polygon The rain gage weight is the area of the polygon it is
located in Fourth: Calculate the average rainfall using:
Pavg = [ Wi x Pi ] / Wi
![Page 29: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/29.jpg)
P2 = 2.15”
P4 = 2.26”
P6 = 1.81”
P5 = 2.18”
P3 = 1.80”
P1 = 1.62”
Watershed boundary
Step #1: Dashed Lines Between Each Rain Gauge
![Page 30: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/30.jpg)
Watershed boundary
Step #2: Draw the Perpendicular Bisector Lines
![Page 31: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/31.jpg)
Watershed boundary
Step #3: Determine the Area of Each Polygon
A2= 150 ac
A3= 136 ac
A4= 269 ac
A5= 216 ac
A6= 65 ac
A1= 56 ac
![Page 32: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/32.jpg)
STEP #4: CALCULATE THE AVERAGE RAINFALL
Pavg = [ Wi x Pi ] / Wi
Pavg = [(65x1.81)+(150x2.15)+(269x2.26)+ (216x2.18)+(56x1.62)+(136x1.8)] / [65+150+269+ 216+56+136]
Pavg = 2.08 in.
![Page 33: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/33.jpg)
ISOHYTAL METHOD
Plot gauge locations on map; Subjectively interpolate between rain
amounts between gauges at a selected interval;
Connect points of equal rain depth to produce lines of equal rainfall amounts (isohyets);
![Page 34: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/34.jpg)
CALCULATION OF AVERAGE RAINFALL OVER CATCHMENT
![Page 35: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/35.jpg)
![Page 36: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/36.jpg)
COMPARISON BETWEEN METHODS FOR CALCULATING AVERAGE RAINFALL
Arithmetic mean method Assumes uniform rainfall distribution Very seldom occurs Easiest to use but least accurate
Thiessen polygon method Assumes linear variation Use when gages are not uniformly distributed Can use gages outside of watershed
Isohyetal method Theoretically the most accurate Most time consuming method Can use gages outside of the watershed
![Page 37: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/37.jpg)
DAD CURVES
DAD stands for Depth Area Duration curve.
DAD curves exhibit the depth and the area covered by the rainfall with a particular duration.
![Page 38: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/38.jpg)
There is a definite relation among depth, area and duration of rainfall.
The longer duration rainfall covers a wider area. Short time rainfalls normally cover small areas.
Rainfall rarely occurs uniformly over a large area.
![Page 39: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/39.jpg)
A depth-area-duration curve expresses graphically the relation between progressively decreasing average depth of rainfall over a progressively increasing area from the center of the storm outward to its edges for a given duration of rainfall.
![Page 40: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/40.jpg)
Purpose of DAD analysis of a particular storm is to determine the largest average depth of rainfall that fell over various sizes of area during the standard passage of time.
hydrologists and engineers require techniques whereby point rainfall amounts can be transformed to average rainfall amounts over a specified area
![Page 41: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/41.jpg)
DAD CURVE FOR ONE DAY RAINFALL OVER THE AREA 5000 KM2
![Page 42: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/42.jpg)
FREQUENCY OF THE RAINFALL
the frequency of the rainfall is the number of time that a given magnitude of the rainfall may occur in a given period.
The study of the probability of the occurrence of a particular extreme (such as 24-h maximum rainfall ) is of extreme important to determination of the design flood.
![Page 43: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/43.jpg)
The probability of an event bring equaled by the following formulae
•California formula : Pro = m/N
•Hazen formula : Pro = 2m-1/2N
•Weibull formula : Pro = m/N+1
Where N= no of years of recordPro = probability
![Page 44: Precipitation and rain gauges](https://reader035.fdocuments.us/reader035/viewer/2022081504/555d732fd8b42a0b778b5395/html5/thumbnails/44.jpg)
REFERENCES
• Introduction to Physical Hydrology, Martin R. Hendricks
• Hydrology and Floodplain Analysis, Bedient, Huber and Vieux
• National Geographic Magazine