Types of efficiencies

 a. Water conveyance efficiency ( η_c):

             η_c = Wf/Ws   x 100%

Where, W_f = Volume of water

W_s = Volume of water delivered to the conveyance system at the supply source.

• It depends on conveyance losses, evaporation and seepage.

b. Water application efficiency ( η_a):

η_a =  Wf/Ws x 100%…………….. (i)

Where,

η_a = water application efficiency

W_s = volume of water stored in the root zone of the plants.

W_f = water delivered to the area.

But, W_f = W_s + deep percolation (D_F) + Surface runoff (R_F)

Or,  W_F = W_s + D_F + R_F

Or, W_s = W_f – (D_F + R_F).

Therefore, equation (i) becomes,

η_a =  [Wf- (Df + Rf)]/Wf……………. (i)

• In general, water application efficiency of surface method of irrigation is of 60%, that of well designed sprinkle and drip irrigation system is more than 70%.

c. Water Storage Efficiency (η_s):

η_s = Ws/Wn  x 100%

where,

η_s = water storage efficiency

W_s = water stored in the root zone during irrigation

W_n = water needed in the root zone prior to irrigation.

• It is important when water supplies are limited or when excessive time is required to secure adequate penetration of the water into the soil.
• Water storage should be kept high to maintain a favorable salt balance in salt problem soil.

d. Water distribution efficiency (η_d):

η_d = ( 1- r/d ) x 100

where,

η_d = water distribution efficiency (%)

d = average depth of water stored along the run during irrigation.

 = Average numerical deviation from d.

e. Water use efficiency (Wu):

i. Crop water efficiency = Y/Cu ( in kg / ha -cm)

Where,

Y = crop yield ( Kg/ha)

Cu = consumptive use or evapotranspiration ; cm.

ii. Field water efficiency ( Eu) =  Y/WR= Y/(G+ET+D)

Note : Crop yield : It may be defined in terms of growth or in terms of marketable product. It is expressed in kg / ha.