This technology was developed and applied in Mexico during the 1970s. It is essentially an intermittent gravity-flow irrigation system. It has been used almost exclusively for small-scale agriculture and domestic gardening.
Technical Description
Prior to the development of this technology, electronically controlled valves were used to produce intermittent water flows for irrigation. These valves are expensive and require some technical training to operate. The diabeto (from Greek diabetes or siphon) was developed for the purpose of replacing these valves with a device that would be more cost-effective and easier to operate and maintain with a minimum consumption of energy. The system consists of a storage tank equipped with one or more siphons, as shown in Figure 39. The storage tank must be designed to keep a predetermined head in the system to ensure that the water discharged during the siphoning process does not exceed the water flow into the storage tank, thereby draining the tank.
Another system that produces similar results is the use of a storage tank with a bottom discharge. This system as shown in Figure 40, is equipped with a floater, shown in Figure 41, which allows the cyclical opening and closing of a gate at the bottom of the tank. In effect, the operation of the floater is similar to the mechanism in the storage tank of a toilet flushing system.
The materials normally used in the construction of the water storage tanks are gravel, cement, and reinforced concrete. The siphons are usually built of a flexible plastic material; PVC is not recommended.
Figure 39: Schematic of an Automatic Surge Flow Irrigation System (Diabeto).
Source: P. Martinez Austria and R.A. Aldama, "Dispositive de Control para la Aplicación del Riego Intermitente," Revista Ingenieria Hidráulica en México, Mayo-Agosto, 1991.
Figure 40: Schematic Representation of a Gravitational Tank Irrigation System.
Source: V.N. García, Diseño y Aplicación del Riego Intermitente por Gravedad. Universidad Nacional Autónoma de México, Facultad de Ingeniería, México D.F., 1995 (Tesis para obtener el grado de Doctor en Ingeniería Hidráulica).
The design of these systems must consider irrigation water use, available hydraulic load, topographic characteristics in the area of application, physical dimensions of the irrigated land, slope and location of furrows, and soil characteristics. Design manuals, based on laboratory and field experiments, have been developed in Mexico.
Extent of Use
This technology has been used primarily in the arid and semi-arid regions of Mexico. The diabeto can be used in any gravity irrigation system, but has been particularly useful in the irrigation of 100 to 300 m2 fields, using furrow irrigation, and in domestic gardening. This technology is best suited for small-scale (< 4 ha) irrigation in rural areas. At present, it is widely used only in Mexico.
Operation and Maintenance
The diabeto and the gravitational tanks with bottom discharges function automatically, based on flow control devices, and do not need outside energy sources. The water is discharged into a channel that distributes it into the furrows and to the irrigated crops. Maintenance is very simple, requiring only periodic cleaning of the tanks, siphons, and/or discharge pipes.
Level of Involvement
Up to now, educational institutions, small private agricultural enterprises, and the Mexican Government have promoted this technology. However, it would be desirable if local communities got more involved in implementing it.
Figure 41: Schematic Representation of an Automatic Fluid Water Control Device used in Gravitational Tanks.
Source: V.N. García, Diseño y Aplicación del Riego Intermitente por Gravedad. Universidad Nacional Autónoma de México, Facultad de Ingeniería, México D.F., 1995 (Tesis para obtener el grado de Doctor en Ingeniería Hidráulica).
Costs
A surge flow, automatic irrigation device such as the one shown in Figure 37 costs about $600. This includes an 11.25 m3 storage tank, feeding system, and siphon. A device of this size can irrigate up to 4 ha. A similar gravitational tank irrigation system, with the same tank capacity, 150 m of piping, and gates, has an estimated cost of $1 500. A smaller system for domestic gardening can cost around $80. The operation and maintenance costs of these systems are practically nil.
Effectiveness of the Technology
With the surge flow, automatic irrigation systems and the gravitational tank technologies, irrigation efficiencies of over 75% have been achieved in the state of Zacatecas, Mexico. This represents a significant improvement over the 25% rate reported using traditional irrigation technologies. A saving of about 25% in energy consumption costs has also been observed.
Suitability
The technology is recommended for arid and semi-arid areas where low precipitation and high evaporation rates prevail, and where small storage areas and depleted aquifers exist.
Advantages
· This technology can utilize water from small wells of limited capacity, reused wastewater, and small streams.· Hydraulic energy is used as the driving force; these systems do not require external energy sources.
· The systems are low-pressure.
· Irrigation time and labor force requirements are small, as the systems are automatic.
· The technology is low in cost.
· It is easy to operate and maintain.
· It is applicable to small-scale agricultural systems.
· It is more efficient than traditional irrigation systems.
Disadvantages
· The technology is not recommended for furrow irrigation in fields with dimensions greater than 200 m long and 25 meters wide, as the volume of water required in such applications will require extremely large storage tanks.· For greater efficiency, the irrigated lands should be leveled.
Cultural Acceptability
The technology has been tried and tested in Mexico, although it has the potential to be used in many other countries. Governments and international institutions can help disseminate information on its use.
Further Development of the Technology
To improve the applicability of this technology to areas using drip irrigation, a device that will automatically mix fertilizers into the water stream provided by the diabeto is under development. Also, development of modular systems is under way. Ultimately, the development of educational programs on the implementation and effective use of this technology will be necessary.
Information Sources
Contacts
Polioptro Martínez Austria, Instituto Mexicano de Tecnología del Agua, Coordinación de Tecnología Hidráulica, Paseo Cuahunáhuac 8532, 62550 Jiutepec, Morelos, México. Tel. (52-73)19-3663. Fax (52-73)20-8725. E-mail: polioptr@tlaloc.imta.mx.
Alvaro Aldama Rodriguez, Instituto Mexicano de Tecnología del Agua, Paseo Cuahunáhuac 8532, 62550 Jiutepec, Morelos, México. Tel. (52-73)19-3663. Fax (52-73)20-8725.
Nahún García Villanueva, Instituto Mexicano de Tecnología del Agua, Subordinación de Hidráulica Rural y Urbana, Paseo Cuahunáhuac 8532, 62550 Jiutepec, Morelos, México. Tel. (52-73)19-4000, ext. 510.
José Natividad Barrios Domínguez, Universidad Autónoma de Zacatecas, Facultad de Ingeniería, Zacatecas, México.
Bibliography
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García, V.N. 1995. Diseño y Aplicación del Riego Intermitente por Gravedad. México, D.F., Universidad Nacional Autónoma de México, Facultad de Ingeniería. (Tesis para obtener el grado de Doctor en Ingeniería Hidráulica)
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