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Evaporation from water bodies and soil masses together with transpiration from vegetation
evaporation, transpiration, infiltration, surface detention and storage.
All abstractions from precipitation are those due to ____________, ___________, _____________, ________________, and ____________
process in which a liquid change to the gaseous state at the free surface, below the boiling point through the transfer of heat energy.
Rate of Evaporation
proportional to the difference between the saturation vapor pressure (SVP) at the water temperature, (ew ) and the actual vapor pressure in the air (ea)
it helps in removing the evaporated water vapor from the zone of evaporation, thereby creating greater scope for evaporation.
a decrease in _________________ (as in high altitudes areas) increases the evaporation rate.
The rate of evaporation increases with an __________ in the water temperature
solute, less than
When a ______ is dissolved in water, the vapor pressure of the solution is _______ that of pure water and hence it causes reduction in the rate of evaporation.
________ bodies have more heat storage capacity than shallow water bodies.
effect of heat storage
The _________________ is to change the seasonal evaporation rates and the annual evaporation remains more or less unaltered.
water-containing pans which are exposed to the atmosphere and the loss of water by evaporation measured in them at regular intervals.
noted along with evaporation measurement in evaporimeters
Class A Evaporation Pan
A pan of diameter 1210mm and depth 255mm
1210mm and depth 255mm
diameter of Class A Evaporation Pan
18 and 20cm
Depth of water in Class A Evaporation Pan is maintained between _____________
unpainted GI sheet
Class A Evaporation Pan is made of ____________
placed on a wooden platform of height _____ above ground level to allow free air circulation below the pan
measured by measuring the depth of water in a stilling well with a hook gauge.
ISI Standard Pan
A pan of diameter 1220mm and depth 255mm
1220mm and 255mm
diameter of ISI Standard Pan
The ISI Standard Pan is made of copper sheet _____ thick, tinned inside and painted white outside
The ISI Pan is placed on a square wooden platform of width _______ and height ________ above ground level to allow free air circulation below the pan
A fixed-point gauge
it indicates the level of water
Colorado Sunken Pan
920mm square pan made of unpainted GI sheet, 460mm deep, and buried into the ground within 100mm of the top
this pan's main advantage is its aerodynamic and radiation characteristics are similar to that of a lake
this pan's disadvantages are difficult to detect leaks, expensive to install, extra care is needed to keep the surrounding area free from tall grass, dust, etc.
US Geological Survey Floating Pan
A square pan of 900mm sides and 450mm deep.
900mm sides and 450mm deep
dimension of US Geological Survey Floating Pan
Supported by drum floats in the middle of a raft of size 4.25m x 4.87m, it is set afloat in a lake with a view to simulate the characteristics of a large body of water
Water level in the pan is maintained at the same level as that in the lake, leaving a rim of _____.
provided in the pan to reduce surging in the pan due to wave action
this pan's disadvantages are High cost of installation and maintenance, difficulty in making measurements.
are not exactly models of large reservoirs
simplest but the least reliable.
application of law of conservation of energy.
Reduction of surface area
as the area increases the rate if evaporation also increases
permanent roods over the reservoir, temporary roods and floating roof such as rafts and light – weight floating particles
application of cetyl alcohol (hexadecanol) and stearyl alcohol (octadecanol)