Basin irrigation Level basin irrigation has historically been used in small areas having level surfaces that are surrounded by earth banks. The water is applied rapidly to the entire basin and is allowed to infiltrate. In traditional basins no water is permitted to drain from the field once it is irrigated. Basin irrigation is favored in soils with relatively low infiltration rates. This is also a method of surface irrigation. Fields are typically set up to follow the natural contours of the land but the introduction of laser levelling and land grading has permitted the construction of large rectangular basins that are more appropriate for mechanised broadacre cropping.
Drainback level basins Drainback level basins (DBLBs) or contour basins are a variant of basin irrigation where the field is divided into a number of terraced rectangular bays which are graded level or have no significant slope. Water is applied to the first bay (usually the highest in elevation) and then the desired depth of applied water is permitted to drain back off that bay and flow to the next bay which is at a lower elevation than the first. Each bay is irrigated in turn using a combination of drainage water from the previous bay and continuing inflow from the supply channel. Successful operation of these systems is reliant on a sufficient elevation drop between successive bays. These systems are commonly used in Australia where
rice and
wheat are grown in rotation.
Furrow irrigation Furrow irrigation is conducted by creating small parallel channels along the length of the field parallel to the direction of its predominant slope. Water is applied to the top end of each furrow and flows down the field under the influence of gravity. Water may be supplied using gated pipe, siphon and head ditch, or bankless systems. The speed of water movement is determined by many factors such as slope, surface roughness, and furrow shape, but most importantly by the inflow rate and soil
infiltration rate. The spacing between adjacent furrows is governed by the crop species, common spacings typically range from . The crop is planted on the ridge between furrows which may contain a single row of plants or several rows in the case of a bed-type system. Furrows may range anywhere from less than long depending on the
soil type, location, and crop type. Shorter furrows are commonly associated with higher uniformity of application but result in increasing potential for runoff losses. Furrow irrigation is particularly suited to
broadacre row crops such as
cotton,
maize, and
sugar cane. It is also practiced in various horticultural industries such as
citrus,
stone fruit, and
tomatoes. The water can take a considerable period of time to reach the other end, meaning water has been infiltrating for a longer period of time at the top end of the field. This results in poor uniformity with high application at the top end with lower application at the bottom end. In most cases the performance of furrow irrigation can be improved through increasing the speed at which water moves along the field (the advance rate). This can be achieved through increasing flow rates or through the practice of surge irrigation. Increasing the advance rate not only improves the uniformity but also reduces the total volume of water required to complete the irrigation.
Surge irrigation This type of irrigation is relatively new with research and development into its practice and modelling started in early 1980s. Surge Irrigation is a variant of furrow irrigation where the water supply is pulsed on and off in planned time periods (e.g. on for 1 hour off for 1½ hour). The wetting and drying cycles reduce infiltration rates resulting in faster advance rates and higher uniformity than continuous flow. The reduction in infiltration is a result of surface consolidation, filling of cracks and micro pores and the disintegration of soil particles during rapid wetting and consequent
surface sealing during each drying phase. The effectiveness of surge irrigation is soil type dependent; for example, many
clay soils experience a rapid sealing behaviour under continuous flow and therefore surge irrigation offers little benefit. In spate irrigation, water is diverted from normally dry river beds when the river is in spate. The flood water is then diverted to the fields. This may be done by free intakes, by diversion spurs or by bunds, that are built across the river bed. The flood water, typically lasting a few hours or a few days, is channelled through a network of primary, secondary and sometimes tertiary flood channels. Command areas may range from anything between a few hectares to over . Spate irrigation systems require huge management efforts to control and optimize the flow of water. Because fast-moving water is capable of moving very large amounts of sediment, the heights of river banks and the composition of their beds can change rapidly. Diverting the flow of a powerful force which is capable of moving rocks, soils and other materials used to divert the path of the water can prove difficult. == Issues associated with surface irrigation ==