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How do evaporation and seepage cause losses of irrigation water?

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Large wheeled irrigation sprinkler sprays water over green crops in a field, with mountains and cloudy sky in the background. — Irrigation Specialized irrigation equipment watering crops in a field.

In the context of irrigation, evaporation and seepage are significant sources of water loss, particularly from surface supplies like reservoirs and canals.1

Evaporation

Evaporation involves the loss of water directly from the surface into the atmosphere. This process is driven by "evaporative demand," which is influenced by meteorological conditions such as solar radiation, temperature, wind, and atmospheric vapor pressure. In agricultural settings, water is also lost through evapotranspiration, which combines evaporation from the soil surface with transpiration from plant leaves. Techniques to mitigate these losses include applying alcohol films to water surfaces or installing solar panels over canals to provide shade.123

Seepage

Seepage refers to the movement of water through soil or the walls of containment structures. It occurs as water percolates through small openings in the ground or channel boundaries. The rate of seepage depends on the permeability of the soil and the pressure gradient acting on the water. To control this, irrigation channels are often lined with impervious materials such as concrete, asphalt, or plastic film.451