Hydrology (Finals) Flashcards
is the process in which a liquid change to the gaseous state at the free surface, below the boiling point through the transfer of heat energy
evaporation
evaporation from water bodies and soil masses together with transpiration from vegetation
evapotranspiration
rate of evaporation is dependent on:
- the vapor pressures at the water surfaces and air above
- air and water temperatures
- wind speed
- atmospheric pressure
- quality of water
- size of the water body
rate of evaporation is proportional to the difference between the saturation vapor pressure (SVP) at the water temperature (ew) and the actual vapor pressure in the air (ea)
vapor pressure
John Daltonโs law of evaporation
rate of evaporation increases with an increase in the water temperature
temperature
the amount of water evaporated from a water surface is estimated by the following methods:
- using evaporimeter data
- empirical evaporation equations
- analytical methods
are water-containing pans which are exposed to the atmosphere and the loss of water by evaporation measured in them at regular intervals
evaporimeters
a pan of diameter 1210 mm and depth 255 mm and made of unpainted GI sheet
class A evaporation pan
the pan is placed on a wooden platform of height 15 cm above ground level to allow free air circulation below the pan
class A evaporation pan
a pan of diameter 1220 mm and depth 255 mm and is made of copper sheet 0.9 mm thick, tinned inside and painted white outside
ISI standard pan
the pan is placed on a square wooden platform of width 1225 mm and heigh 100mm above the ground level below the pan
ISI standard pan
920 mm square pan made of unpainted GI sheet, 460 mm deep, and buried into the ground within 100 mm of the top
colorado sunken pan
a square pan of 900 mm sides and 450 mm deep
us geological survey floating pan
supported by drums float in the middle of a raft of size 4.25 m x 4.87m, it is set a float in a lake with a view to simulate the characteristics of a large body of water
us geological survey floating pan
lake evaporation = cp x pan evaporation
class a land pan - 0.700, 0.60-0.80
ISI pan (modified class A) - 0.875, 0.65-1.10
colorado sunken pan - 0.805, 0.75 - 0.86
USGS floating pan - 0.760, 0.70-0.82
empirical evaporation equation
๐ธ๐ฟ = ๐พ๐(๐ข)( ๐๐ โ ๐๐)
f(u) = wind speed
meyerโs formula
๐ธ๐ฟ= ๐พ๐( ๐๐โ ๐๐)(๐ + ๐๐/16 )
water budget method
๐ + ๐๐๐ + ๐๐๐ = ๐๐๐ + ๐๐๐ + ๐ธ๐ฟ + ฮ๐ + ๐๐ฟ
analytical methods of evaporation
- water-budget method
- energy-balance method
- mass-transfer method
simplest but the least reliabe
water-budget method
is application of law of conservation of energy
energy-budget method
water volume lost due to evaporation from a reservoir
๐๐ธ = ๐ด๐ธ๐๐๐ถ๐
methods to reduce evaporation losses
- reduction of surface area
- mechanical covers
- chemical films
as the area increases the rate if evaporation also increases
reduction of surface area
permanent rods over the reservoir, temporary rods and floating roof such as rafts and light -weight floating particles
mechanical cover
application of cetyl alcohol (heaxdecanol) and stearyl alcohol (octadecanol)
chemical films
process by which water leaves the body of a living plant and reaches the atmosphere as water vapor
transpiration
important factors affecting transpiration are:
atmospheric vapor pressure
temperature
wind
light intensity
characteristics of the plants
the total amount of water loss in the form of water vapors into the atmosphere from surface of the soil. canopy interception, water bodies as well as from the aerial parts of the plants
evapotranspiration
if sufficient moistureis always available to completely meet the needsof vegetayion full covering the area
potential evapotranspiration
the real evapotranspiration occurring in a specific situation
actual evapotranspiration
is the maximum quantity of water that the soil retain against the force gravity
field capacity
is the moisture content of a soil at which the moisture is no longer available in sufficient quantity to sustain the plants
permanent wilting point
hydrologic budget
๐ทโ ๐น๐โ๐ฎ๐โ๐ฌ๐๐๐=ฮ๐บ
is a special watertight tank containing a block of a soil and seat in a field of growing plants
lysimeters
measurement are usually confined to precipitation, irrigation input, surface runoff, and soil moisture
field plots
it is calculated by multiplying the reference crop evapotranspiration by coefficient K, the value of which changes with the stage of the crop
potential evapotranspiration of any other crop
potential evapotranspiration of any other crop
๐ธ๐=๐พ(๐ธ๐๐)
Blaney - Criddle Formula
๐ธ๐=2.54๐พ๐น and ๐น= ฮฃ๐โ๐ฬ ๐/100
can be defined as a flow channel into which the surface runoff from a specified basin drains
stream
the science and practice of water measurement
hydrometry
streamflow measurement techniques
direct determination stream discharge
indirect determination stream flow
direct determination stream discharge
- area-velocity methods
- dilution techniques
- electromagnetic methods
- ultrasonic method
indirect determination stream flow:
- hydraulic structures
- slope-area
classifications of stream
- perennial streams
- intermittent streams
- ephemeral streams
water flows in these streams through out the year. the primary water source can be from ground water, surface water, or combination of both
perennial streams
For part or most of the year but may carry no water during the dry season
intermittent stream