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Hydrology

TermDefinition
hydrology it is the science whihc deals with the occurence, circulation and and distribution of water on earth's surface and atmosphere.
hydrologic cycle it is a cycle in which water moves from one phase to another having different residence time.
residence time it is time taken by water molecules to cross one particular phase of hydrologic cycle.
time in terms of volume and discharge. t=V/Q
catchment area/watershed the area between two ridge line/water divide/divide.
water budget equation It is based on law of conservation of mass Mass inflow-mass outflow=change in storage.
Depth from volume and area depth=V/A
forms of precipitation rain,drizzle, glaze, sleet, snow, hale
rain types of rainfall this is the principal mode of precipitation and consists of water droplets ranging from 0.5 mm to 6mm.light rainfall-<2.5 mm per hour,medium rainfall=2.5 to 7.5, heavy->7.5 mm.
1)rainfall sample collection time and when it is called rainy day. 2) the maximum rainfall occurs in the form of which rainfall. 3) highest rainfall place in india. 1)8:30 AM. If rainfall>2.5 mm/hour, the dai is called rainy. 2) Orographic rainfall (rainfall obstructed by mountains). 3) Monsenram.
Cloud cover is measured in terms of Octa i.e 1/8th.
1)Average rainfall of india 2) Mawsynram rainfall 1) 110 cm. 2) 1200 cm.
Drizzle These are fine drops havings size smaller than 0.5 mm and when rain intensity is less than 1mm/hour.
Glaze when droplets come in contact with cold surface (approx 0 degree temperature), the drops are converted into ice which is called galze.
sleet these are frozen raindrops of transparent nature.
Snow These are ice crystals of density of 0.1 gm per cc.
hail these are lumps of ice whose size is more than 8 mm.
1). Daily rainfall. 2) Annual rainfall. 3) Average annual rainfall. 1). The amount of rainfall collected by raingauge in last 24 hours is called daily rainfall. 2) The amount of rainfall collected by raingauge in one year is called Annual rainfall. 3). Average of annual rainfall of last 35 years.
Index of wetness. It is used to find the rainfall variation of particular year. Index of wetness= Rainfall in a year/average annual rainfall × 100.
If index of wetness comes 60% of particular year, it means rainfall deficiency for that year is 40%.
Rainfall deficiency classification 1). 30-45 % = large deficiency. 2). 45-60% = Serious deficiency. 3) >60% = Disastruos deficiency.
1). If index of wetness is 100%, the year is called 2) If > 100%, then 3) If < 100%, then 1). Normal year. 2) good year. 3) bad year.
Index of wetness cannot be directly correlated with flood or drought.
Drought it is the climatic situation characterized by deficit supply of moisture.
Drought classification 1). Meteorological drougth. 2). Hydrological drought. 3). Agricultural drought.
Meteorological drought deficiency in precipitation is M.D. If precipitation is less than 25%, it s called drought. 2) If 25-50%= Moderate drought. 3) If >50%= Severe drought.
Drought year. A particular year is called drought year if more than 20% of the whole country area is under drought.
Drought prone area. If the drought occurs over an area with probabilty of 0.2 to 0.4, then that area is called drought prone area.
Hydrological drought. This is drought in whhc there is below level of stream flow, water content in lakes, reservoirs, underground water etc.
Agricultural drought. In this, there is deficiency of water available for plant growth. This is calculated using aridity index.
Aridity index. P.E.T-A.E.T/P.E.T *100.
1). P.E.T 2). What is its other name. 1). Potential evapotranspiration is the water consumed by the plant during its growth time when sufficient amount of water/moisture is available. 2) Consumptive use.
A.E.T Actual evapotranspiration is the actual water available under prevailing conditions.
Classification of Arid region based on A.I 1). 0-25 % = Mild Arid region. 2). 20-50 % = Moderate arid region. 3) >50 % = Severe arid region.
The network density of raingauge depends on what factors. 1). Magnitude of rainfall. 2). Topography of the region. 3). Desired accuracy.
Measurement of rainfall is done in which term. It is done in terms of depth of rainfall when all rain water would be allowed to stand/collect on the given area.
Rainfall measurement instruments different 5 names. Raingauge Pluviometer. Ombrometer. Udometer. Hyetometer.
What are requirements of installing raingauges. 1). The raingauge should be placed in an open fenced area of 5.5 m * 5.5 m. 2). The raingauge should be placed atleast 30 m or twice the height of the building.
Classification of raingauge. 1). Non-Recording raingauge. 2). Recording raingauge.
Define non-recording raingauge. It is the raingauge which is cylindrical in shape of known area and graduations and Symon's gauge is commonly used. It has a diameter of 127 mm (5 inches) which collects water and give its measurement in terms of depth.
Define recording raingauge. The most commonly used is float type. It records both rainfall with time. It could be used for measuring rainfall for a particular time period. Hence, with this, a graph between rainfall and time could be made.
What are latest improvements in raingauges. 1). Telemetring raingauge- It has an electronic unit with which measurement after recording could be send to the base station for analysis.2). Radar technology- With this areal extend, location and movement of rainstorms could be done.
Define radar technology. With this, meteorological radars could measure raifall of area with better accuracy. Meteorological radars works at a wavelength range of 3 to 10 cm. 3 cm wavelength is used for light rainfall and 10 cm wavelength is used for heavy rainfall.
What are recommendations of WMO for raingauge density. 1). for flat tropical,temperate and mediterranean regions= 1 per 600-900 SKM. 2) For mountaneuos " " " " " = 1 per 100-250 SKM. 3). For polar and arid region= 1 per 1500-10000 SKM.
What are IS on raingauge density. 1). For flat regions= 1 per 520 SKM. 2) For regions with average elevation of 1000 m= 1 per 260 SKM. 3) For hilly region with heavy rainfall= 1 per 130 SKM.
1). India density of raingauge. 2). World's highest density is in which country and what is it. 1). 1 per 600 SKM. 2). Israel= 1 per 37 SKM.
In india, the maintenance of raingauge is done by which departments. 10 % is maintained by IMD. Rest maintained by state government and others by its owners of independent agencies like AAI, Railway etc.
The average value and interval of value of Cv. Cv= Coefficient of variation. 30 and 15-70.
Out of total rainguages, what percentage should be recording raingauge. 10 %.
Isohyets. these are imaginary lines joining points of equal rainfall.
Methods for determination of average rainfall when more than one raingauge station are available. 1). Arithmetical mean method. 2). Thiessen method. 3). Isohyetal method.
losses from precipitation. In hydrology, runoff is of prime concern whereas evaporation, transpiration, interception loss, depression storage etc are termed as losses.
What are methods to reduce evaporation losses. 1). By reducing surface area- by increasing height. 2). By providing mechanical covers like shed etc. 3). By providing chemical covers like cetyl alcohol which can reduce upto 60% evaporation.
Methods to determine evaporation. 1). Class A evaporation pan. 2). ISI standard pan. 3). colarado Sunken pan.
Class A pan this pan has been developed by US weather department. The pan is made up of unpainted GI. It is 255 mm high with diameter of 1210 mm. In case of persistent corrosion, monel metal (Nickel +copper) is used.
ISI standard pan. The pan is similar to class A evaporation pan. It is modified form. Has diameter of 1220 mm. It is made of copper of thickness 0.9 mm. It has hexagonal wire kneading on top of the pan so that it could not be disturbed by animals.
Colarado Sunken pan This pan is used in actual areal and thermodynamic condition. Only 50 mm of pan is outside the ground and water to fill after one day till the level of 50 mm below of top pf pan is the evaporated water.
What is pan coefficient and what are pan coeff. for Class A, ISI standard and Colarado Sunken pan. Pan coefficient is used to change pan evaporation into lake evaporation. Class A= 0.7. ISI= 0.8. Colarado= 0.78.
Which pan has highest evaporation. Class A as compressed by 0.7 to reduce.
IMD has how many pans. 220.
Empirical method to determine evaporation. E= Km(ew-ea)(i+V9/16). E= Evaporation rate in mm/day. Km= coefficient whose value depends on size of water bodies and whose value is 0.36 for deep water bodies and 0.50 for shallow water bodies.
How to find velocity at different heights. If wind follows the 1/7th power law, the velocity at any height can be computed. V9/V1= ch9(1/7)/ch1(1/7).
1). Evapotranspiration. 2). Transpiration is confined to which hours. 3). Evaporation is confined to which hours. 1). Evapotanspiration is the water whihc leaves the living plnts and reaches the atmosphere as water vapur. 2). Transpiratioj is confined to mainly day light hours. 3). Evaporation is confoned to both day and night hours.
Methods of determining evapotranspiration. 1). Lysimeter(it is a water tight tank). 2). Field plots. 3). Penman's equation. (It is based on energy transfer and mass balance method). 3). Blanney criddle method (extensively used by field engineers).
Isopleths. These are lines joining places of equal depth of evapotranspiration.
P.E.T is maximum for which place in India. Rajkot (Gujarat).
Created by: ajay1