Engineering Hydrology

 Do you Know?

👉Evaporation Measurement

(a) Using Evaporimeter Data

(b) Empirical Evaporation Equation

(c) Analytical Methods

👉Types of Evaporimeter

(a) Class A Evaporation Pan (US Weather Bureau)

(b) ISI Standard Pan (Used in India)

(c) Colorado Sunken Pan 

(d) US Geological Survey Floating Pan

👉     Lake Evaporation = Pan coefficient x pan evaporation

👉          Types of Pan                   Average value               Range

            Class A Land Pan                    0.70                           0.60-0.80

        ISI Pan (Modified Class A)         0.80                           0.64-1.10

        Colorado Sunken Pan                  0.78                           0.75-0.86

        US GS Floating Pan                     0.80                          0.70-0.82

👉Empirical Formulae

Empirical formulae are based on Dalton's Law.

(a) Meyer's Formula

👉Analytical Methods

(a) Water-Budget method

(b) Energy-balance method

(c) Mass-transfer method

👉Measurements of Actual Evapotranspiration

(a) Phytometer (Measures only transpiration)

(b) Lysimeter 

(c) Field experimental plots

👉Estimation of Potential Evapotranspiration 

(a) Penman's Equation

Based on combination of the energy-balance and mass-transfer approaches.

(b) Blanney-Criddle Formula

👉Measurement of Infiltration

(a) Flooding type infiltrometer

(b) Rainfall simulator

👉Empirical Infiltration Equations

(a) Green-Ampt method

(b) Horton Infiltration Equation

(c) Huggins-Monka Equation

(d) Soil Conservation Service Practice

(e) Antecedent Precipitation Method

👉Horton's Equation

  

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