Evaporation And Infiltration Flashcards
Factors affecting evaporation
- radiation/sensible heat/temperature
-saturation deficit
-supply of water
-removal of saturated air(wind and turbulent mixes)
-nature of evaporating surface
E0
Open water surface evaporation
Fraction of E0
Land surface evaporation
Evapotranspiration
ET = E + T
Depends on soil type, soil water, crop/plant type and seasons
Potential evaporation (evapotranspiration)
PET
Where E or ET with sufficient water supply
Is soil is unlimited then we get potential ET
Actual ET is less that PET because limit on supply of water at various parts and growing seasons
Water budget
Equation: P-ET-R=0
-comped procedure, often with remote sensing (satellite)
-subject to local situation
Empirical equations
- should reflect relevant factors: saturation deficit, wind effects
- use parameters (coefficients) to fit the equation using observations
Estimating ET
Involves adapting Penman eqn and introducing more empirical eqns
Factors affecting Infiltration
- precipitation: higher intensity rainfall can cause more surface runoff
- soil type: particles and porosity
- soil water content: saturated?
- vegetation cover
- slope of the ground
Soil types
In hydrology…
Classes as either run off potential or infiltration potential
Measurement - Flooded method
- Easy to use
- Soil structure could be distrusted
Measurement - rain simulating method
- No disturbance to soil structure
- Close to true rainfall impact
- High cost
Infiltration capacity
- to measure how fast the rainwater can infiltrate through a given soil type in terms of infiltration rate fc (mm/h or mm/min)
-infiltration rate f tends to gradually decrease as soil becomes saturated
Methods to estimate f - Hortons
ft = fc + (f0-fc)e^-kt
where
ft: infiltration capacity at time (mm/h)
f0: initial infiltration capacity (mm/h)
fc: final infiltration capacity (mm/h)
k: empirical constant for a given soil texture (h^-1)
