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UNIT I PRECIPITATION 1. Define Hydrology. Hydrology means science of water. It is the science that deals with occurrence, distribution and movement of water is on, above and beneath the earth.

evaporation,

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2. What is the objective of the hydrological study? * Estimation of water resources * Study the processes such as precipitation, runoff, transpiration, infiltration and their interactions. * Study of floods, droughts and strategies to combat them * Hydro power

3. What is the importance of hydrology? The importance of hydrology is the assessment, development, utilization and management of water resources of any region.

iii) Evaporation

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4. Enlist the various phases of a hydrological cycle? i) Precipitation ii) Infiltration iv)Transpiration v) Runoff

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5. Define Precipitation? Any form of moisture reaching the earth surface is called precipitation. The usual forms of precipitation are rainfall, snow, hail, sleet, frost, dew etc.

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6. Define infiltration? It is defined as the process by which water enters the sub-surface strata of the earth. The infiltrated water first meet the soil moisture deficiency and there after moves vertically downwards to reach the ground water table. 7. Define evaporation? It is the process by which water from liquid state passes into vapour state under the action of sunrays.

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8. Define transpiration? The process by which water passes from liquid to vapour through plant metabolism is termed as transpiration.

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9. Define runoff? It is the precipitation excess after meeting the demands of evaporation, transpiration and infiltration 10. Enlist the various forms of precipitation? The usual forms of precipitation are i) Rainfall ii) Drizzle v) Glaze vi) Snow

iii) Hail vii) Frost

iv) Dew

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11. What are all the types of precipitation? i) Cyclonic precipitation ii) Convective precipitation iii) Oragraphic precipitation iv) Frontal precipitation 12. How the precipitation can be measured? It can be measured by rain gauge. The rain gauge may be i) Recording type rain gauge ii) Non- recording type rain gauge

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13. What are all the demerits of Non- recording type rain gauge? It does not give information regarding  Beginning of the rain   End of the rain   Intensity of rainfall   14. Enlist the three types of recording type rain gauge? * Tipping bucket * Weighing bucket * Floating bucket

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15. Write short notes on rain gauge density? It is the no. of rain gauges is to erected in an given

area Rain gauge density = No. of rain gauges / Area

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16. What are all the methods available to find the average depth of precipitation over an area? i) Arithmetic mean method ii) Thiessen polygon method iii) Isohyetal method

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17. Define isohyet? An isohyet is the line joining the points of equal rainfall.

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18. What is the use of Double mass curve? It is used to check the consistency of the rainfall record. In double mass curve a graph is drawn between the cumulative value of average rainfall of base stations as the abscissa against the corresponding cumulative value of rainfall of the station under test as ordinate.

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19. Define Hyetograph? It is a plot of rainfall intensity against time interval. It is derived from mass curve and is usually represented as bar chart. It is used to predict the extreme floods. 20. Write short notes on intensity-duration curves? Short duration – High intensity Long duration – Less intensity

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21. What is the use of frequency analysis? It is used to find the probability of occurrence of extreme rainfall. The probability of occurrence of rainfall whose magnitude is equal to or greater than specified magnitude is given by T = N+1/m where T = Return period m= Rank N= No. of years of rainfall record 22. State Hydrologic equation? The Hydrologic equation is simply the statement of the law of conservation of mass and is given by

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I=0+S Where I = Infolw O = Outflow S = Change in storage

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23. What are the basic data required for hydrological studies? The basic hydrological data required are i) Climatological data ii) Hydrometeorological data iii) Precipitation records iv) Stream flow records v) Ground water table vi) Evaporation data vii) Crops and their pattern viii) Water quality data etc., 24. Define air mass? A vast and deep body of water in which temperature and humidity characteristics are relatively homogeneous at any given elevation is called an air mass.

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25. Define air front? The surface of contact between two air masses or between an air mass and the surrounding atmosphere is called air front.

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26. Define Cyclone? A cyclone is a more or less circular area of low pressure in which wind blows spirally inward in counter clockwise direction in northern hemisphere and clockwise direction in southern hemisphere.

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27. Distinguish between continental air mass and maritime air mass? Sl. No Continental air mass

Maritime air mass

Originated from land

2 3

Usually dry Fluctuations in temperature

Originated from water bodies such as oceans, lakes, rivers etc Almost moist Uniform temperature

4

Unstable

Stable

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