Irrigated fields need good surface drainage so that fieldwork is timely and excess water is removed in reasonable time. Poor internal drainage can cause rooting restrictions, diseases, fertility problems, reduced yields, and other soil related problems because of a high water table in excessively wet periods. Surface drainage is an absolute must where internal drainage is a problem. Also, the more water-application control achieved, the better aerated the soil. Topography of a field is a decision aid in the type of irrigation system selected or size of irrigation system installed.
Sprinklers fit rolling topography, but surface irrigation systems require graded fields.
An adequate water supply to meet crop demand is important for ease of operation and for management of an irrigation system. With probability of rainfall at almost any time, a water supply should be large enough to meet crop demand when the root zone reaches the level of depletion desired. The water source for irrigation should be as clean as possible. Surface water often carries sediments and trash. Large particles should be screened out, letting fines pass.