Why can flood irrigation waste large amounts of water?

Flood irrigation can lead to significant water waste due to several factors inherent to the method's reliance on surface flow across fields.

• Evaporation: Because flood irrigation involves spreading water over the entire surface of a field, a large area of water is exposed to the atmosphere, leading to substantial losses through evaporation.1
• Seepage: When water is transported to and across fields via surface systems, it is susceptible to seepage into the ground from reservoirs and canals, particularly if these channels are not lined with impervious materials like concrete.1
• Excess Application: In surface irrigation systems, water is applied at the edge of a field and moves across the surface. If the land is not perfectly graded or if the application is not carefully managed, excess water may accumulate, necessitating the use of waste-water ditches to prevent waterlogging.2
• Salinity Management: Ironically, flood irrigation may require the use of "excess water" to leach accumulated salts from the soil, a process necessary to maintain a favorable salt balance for crop survival.3