In some countries, water is routinely transported from regions where it is plentiful to regions where it is scarce. Several water conveyance and distribution techniques are available, and are actively used in many countries of Latin America and the Caribbean.
Technical Description
Among the most common water conveyance methods are tanker trucks, rural aqueducts, and pipelines. In some cases, this involves the transfer of water from one portion of a river basin to another, or between river basins. Each of these methods is described below.
· Tanker Trucks
Tanker trucks are fitted with a cistern or storage tank to transport and distribute water from a point of supply to the point of use, particularly to suburban and rural areas not served by a piped supply. If water is not supplied from a central treatment facility, it is usually extracted from the closest natural source (rivers, canals, reservoirs, or groundwater sources) and transported by the trucks to the point of use. Water thus transported may be pumped into a storage cistern, dispensed directly into household or other containers, or discharged into a small-scale treatment facility for centralized distribution. The tanks on the trucks are usually manufactured locally, and some trucks are equipped to carry portable pumps to extract the water from its source.
· Pipelines
Water may conveyed through pipelines by gravity flow or by pumping. The latter system will be significantly more expensive to construct, operate and maintain than similar gravity-flow systems. Large-diameter pipelines can be used to convey water over large distances, while smaller-diameter pipelines can be used to provide bulk or individual supplies at the point of use.
· Aqueducts
Aqueducts are canals used to bring water from a river or reservoir to a water distribution center. The main factors to be considered in the design of an aqueduct are the demand to be met, the source of the water, the topography in the area in which the aqueduct is to be built, the size and nature of the storage facilities, and the size and location of the distribution network. Aqueducts are best suited to meeting large-scale demands in areas with a fairly flat or gently sloping landscape suitable for conveying water to the point of use by gravity.
Extent of Use
Tanker trucks are used in most rural and urban areas of Latin American countries and in some Caribbean islands. Most trucks are privately owned; in some cases government sells the water to truck owners who then resell it to users.
Rural aqueducts have been built throughout the region and have been used to supply water for agriculture and domestic use in rural areas. Interbasin transfers using pipelines are common throughout the Latin American region.
Operation and Maintenance
Pipelines and aqueducts, whether operated by gravity or by a pumping system, need regular maintenance and repair of the pumps, pipes, and canals, and periodic upgrading of the facilities. Problems with water leaks, pumps, and storage facilities require immediate attention in order to avoid interruption of services.
Maintenance of the distribution system includes servicing the pumps and other treatment plant components, inspecting the diversion systems and pipelines, repairing leaks, and replacing electrical motors and other moving parts. A number of problems were encountered in the operation and maintenance of a distribution system in Jamaica.
The level of skill needed to operate these systems is medium to high, and involves some technical training of the operators.
Level of Involvement
In Jamaica, water distribution projects using pipelines have had a high level of government participation. The projects were conceived and designed by the government, funded by an international agency, and constructed by a group of engineering consultants, with overall project coordination provided by government. Easements to permit the pipelines to traverse private property were purchased by the government.
Costs
The costs of these conveyance systems vary depending on their capacity and complexity, as a function of the terrain, the availability of labor, and the demand to be met. For example, in Panama, a small aqueduct system designed to serve a few families cost $500. In Jamaica, the cost of gravity and pumped-source pipeline conveyance system is shown in Table 3.
Table 3 Cost of a Pipeline Water Transfer System
|
Source Type |
Project Capacity |
Length of Pipeline |
Diameter of Pipeline |
Capital Cost |
|
Pumped |
45 400 m3/day |
6.5 km |
76.0 cm |
$30 million |
|
Gravity |
104 000m3/day |
30.6 km |
96.5 cm |
$15 million |
Operation and maintenance costs are a function of the specific problems that can affect each project, such as clogging of intake pipes, or high turbidity and/or high values of coliform bacterial in the source water that requires treatment prior to use.
Effectiveness of the Technology
This group of technologies spans a number of scales of application. Tanker trucks are an extremely effective means of distributing potable water to urban and rural populations, especially as an emergency measure. Their use on a day-to-day basis is more costly in the long term than providing a piped supply, but, again, the method provides an effective short-term solution to a water supply problem. On a larger scale, use of aqueducts and pipelines can provide bulk water to users at a competitive cost. While these latter technologies are limited by the cost of operation to less-steep terrain, they are widespread throughout Latin America and the Caribbean. By varying the diameter of the pipes (and, to a lesser extent, the geometry of the channels), these technologies can span the range of requirements from large-scale source-to-treatment-works applications to individual user delivery applications.
Suitability
This technology is suitable for use in areas where piped water service is not available or has been interrupted. The use of aqueducts is well-suited to transporting large volumes of water over great distances. They are usually associated with impoundments, and are most often used in arid and semi-arid areas.
Advantages
Tanker trucks:
· Transporting water obviates the need for more complex water supply projects.
· The technology can efficiently provide water in small quantities to less accessible areas.
Pipeline and aqueduct systems:
· Large quantities of water can be transported without degradation in quality or evaporative losses.· Electricity can be generated along the pipeline route if there is significant head and flow.
· Industrial and agro-industrial enterprises can be situated where water is otherwise unavailable if economic factors are favorable.
· The technology has a low operation and maintenance cost.
· Agricultural production can be improved and increased by transporting water to irrigate crops.
· Compared to open channel methods, transportation of water by pipeline reduces water loss from evaporation, seepage, and theft.
Disadvantages
Tanker trucks:
· Water prices are increased because of the expense of transporting relatively small quantities by road.· There is a lack of quality control.
· Water distribution is costly and slow.
· Adequate roads are required to transport water from one region to another.
Pipeline and aqueduct systems:
· The capital cost is high; it usually requires borrowing, thus adding to the country's national debt.· The skilled personnel needed to operate and maintain the project are not always locally available.
· If the water transported is of poor quality, it will contaminate the water resources of another basin where the necessary treatment to rectify the problem may not be available or affordable.
· River diversion projects can create environmental problems downstream for aquatic life and water users, and can result in the transfer of nuisance species from one basin to another, exacerbating water quality problems throughout a country.
· Transporting large quantities of water can deplete the resources available within the supplying basin.
· Vandalism of the pipeline and appurtenances can occur unless the communities through which the pipeline passes are served by the water supply.
· Environmental impacts, such as threats to endangered species, must be carefully considered and actions taken to minimize negative impacts.
Cultural Acceptability
Tanker vehicles, pipelines, and aqueducts are centuries-old technologies for transporting water and are well accepted by all communities.
Further Development of the Technology
Development of improved, more durable, and less costly piping materials will improve community access to this technology, and increase the use of this method of water conveyance. Training and development of skills among local users is needed to facilitate the construction, operation, and maintenance of future projects. Better methods for water quality control need to be implemented in all water conveyance systems.
Information Sources
Contacts
Satney Martin, Senior Agricultural Engineer, Agricultural Engineering Services Divison, Ministry of Agriculture, Lands, Fisheries and Forestry, Castries, Saint Lucia.
Gerd Dercon, Profesor Universitario en la Cátedra de Riego, Universidad de la Cuenca, Laboratorio de Hidraulica, Quito, Ecuador. Tel. (593-7)831-688 ext. 236. Fax (593-7)832-183.
Basil P. Fernandez, Hydrogeologist and Managing Director, Water Resources Authority, Hope Gardens, Post Office Box 91, Kingston 7, Jamaica. Tel. (809)927-1878. Fax (809)977-0179.
Jorge Faustina Manco, Líder, Proyecto RENARM/Cuencas, Centre Agronómico Tropical de Investigación y Enseñanza (CATIE), Apartado 7170, Turrialba, Costa Rica. Tel (506)556-6279/556-7830. Fax (506)556-1576/556-1533. E-mail: jfaustin@catie.ac.cr.
Icela Ibeth Márquez Solano de Rojas, Profesora Regular Titular en la Universidad Tecnológica de Panamá, Calle 64 Norte, Penonomé, Provincia de Coclé, República de Panamá. Tel. (507)997-9371. Fax (507)997-9182. E-mail: irojas@keops.utp.ac.pa
William Murillo Montero, Ingeniero Civil, Director de Ingeniería, Servicio Nacional de Aguas Subterráneas, Riego y Avenamiento (SENARA), Calles 18-20, Av. 12 Transversal, Apartado 5262, San Jose, Costa Rica. Tel (506)257-9733. Fax (506)222-8785.
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