TRADITIONAL FLOOD IRRIGATION WHY FLOOD IRRIGATE Flood irrigation sees water delivered to the field by means of a ditch or pipes. The water is then released to flow freely over the land and through the crops. About half of the water applied to the field actually irrigates the crops, and the other half is lost through evaporation, runoff, transpiration, weeds, and infiltration of uncultivated areas. The efficiency of flood irrigation is therefore not very high and because of this, it is primarily used in areas where there is an abundance of water. It is also used in areas where the farmer cannot afford a pressurised irrigation system and this is the only means they have to irrigate and grow the required crops. There are several issues that farmers deal with when performing flood irrigation. Some of the more important concerns are distribution uniformity, field flooding and environmental impacts on crops. This type of irrigation naturally has low distribution uniformity, because all of the water is applied at one section of the field. The top of the field will naturally have more time to absorb water than the bottom of the field. THE FLOOD IRRIGATION PROCESS CONSISTS OF FOUR MAIN TIME INTERVALS Phase 1 – the advance phase: The length of time it takes for water to be applied to the top end of a field and flow over the field length. Phase 2 – the storage phase: The time between the end of the advance phase and the shutoff of the interflow. Phase 3 – the depletion phase: The short period after shutoff, while the field is still submerged in water. Phase 4 – the recession phase: The period where the waterfront is retreating towards the downstream end of the field.
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