The maximum is the irrigation time which allows water to pass the root zone at the top of the block. If the irrigation path is very long or if water is applied too slowly, the water at the top of the bay will have passed the root zone before the water has reached the end of the bay. This will render efficient irrigation impossible. The best way to design an efficient flood irrigation system is to find out the length of time it takes water to soak down to the root zone, then select a flow rate which permits water to reach the end of the bay within this time. In practice, flow rates are often not high enough or the bays too long.
Water passes the root zone, resulting in waste and causing environmental hazards.
While flood is often regarded as low technology, Intelligent Irrigation principles can still be applied. The mechanics of flood irrigation can be improved in several ways. Recycling of tail water, for example, is now common. Sequenced irrigation bays, in which bays are flooded one at a time, is used to give maximum flow and hence reduce the time that water soaks into the soil during irrigation. Surge irrigation applies water in a series of stages so the soil has time to expand and seal, thereby minimising soakage.