Changes

In arid and semi-arid regions, where precipitation is low or infrequent during the dry season, it is necessary to store the maximum amount of rainwater during the wet season for use at a later time, especially for agricultural and domestic water supply. One of the methods frequently used in rainwater harvesting is the storage of rainwater in situ. Topographically low areas are ideal sites for in situ harvesting of rainfall. This technique has been used in the arid and semi-arid regions of northeastern Brazil, Argentina, and Paraguay, primarily for irrigation purposes. The in situ technology consists of making storage available in areas where the water is going to be utilized.

Generally this technology is simple and easy to use. Governmental organizations and the agricultural community generally work together to support and promote the in situ rainwater storage. Educational and information programs should be provided to inform users of the benefits of this technology, and the means of implementing rainwater harvesting while preventing soil loss.

This technology increases water supply for irrigation purposes in arid and semi-arid regions. It promotes improved management practices in the cultivation of corn, cotton, sorghum, and many other crops. It also provides additional water supply for livestock watering and domestic consumption.

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All rainfall harvesting systems have three components: a collection area, a conveyance system, and a storage area. In this application, collection and storage is provided within the landscape. Topographic depressions represent ideal collection and storage areas. In many situations, such areas are impermeable, being underlain by clay soils that minimize infiltration. Methods of rainwater harvesting in situ, including site preparation of agricultural areas in Brazil, are described below.

The Guimarães Duque method was developed in Brazil during the 1950s, and uses furrows and raised planting beds, on which cross cuts to retain water are made using a reversible disk plow with at least three disks. The furrows are usually placed at the edge of the cultivation zone.

This technology requires very little '''maintenance''' once the site is chosen and prepared. Maintenance is done primarily during the course of normal, day-to-day agricultural activities, and consists primarily of keeping the collection area free of debris and unwanted vegetation. Where only parts of the rows are cultivated, rotating the areas that are plowed will enable more efficient maintenance of the available storage area.

The equipment used in the construction of the furrows and storage areas must be improved. Relatively inexpensive plows and tractors can reduce the cost of implementation and contribute to the more widespread use of this technology by small farmers. New methods of soil conservation should be explored.

====Contacts====

* '''José Barbosa dos Anjos''', Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA), Centro de Pesquisa Agropecuaria do Trópico Semi-Árido (CPATSA), BR-428 km 152, Zona Rural, Caixa Postal 23, 56300-000 Petrolina, Pernambuco, Brasil. Tel. (55-81)862-1711. Fax (55-81)862-1744. E-mail: [email protected].

* '''Aderaldo de Souza Silva''', Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA), Centro Nacional de Pesquisa de Monitoramento e Avaliacao de Impacto Ambientalt (NPMA), Rodovia SP-340 km 127.5, Bairro Tanquinho Velho, Caixa Postal 69, 13820-000 Jaguariuna, São Paulo, Brasil. Tel.(55-4198)67-5633. Fax (55-4198)67-5225.

[http://www.oas.org/dsd/publications/Unit/oea59e/begin.htm#Contents Source Book of Alternative Technologies for Freshwater Augmentation in Latin America and the Caribbean]. 1.2 Rainwater harvesting in situ. UNEP - International Environmental Technology Centre United Nations Environment Programme. Unit of Sustainable Development and Environment General Secretariat, Organization of American States, Washington, D.C., 1997.