In countries like Brazil and Argentina, with semi-arid climates in which the amount and frequency of precipitation are small and variable, it is important to capture and store as much rainwater runoff as possible for later use. In Brazil, runoff from paved and unpaved roads is captured by street gutters and stored in subsurface galleries or dams strategically distributed along the roadsides. Since 1935, underground barriers have been built in Brazil to capture runoff. In 1965, an underground barrier was built along the bed of the Trici River with the objective of storing runoff water to provide water for domestic use in the municipality of Taua. In Argentina and Venezuela, this technology has been used to provide water for trees along the roadsides and for water-supply augmentation.
Paved and unpaved roads tend to shed water to their outside edges because they are "crowned" or cambered. The runoff can be captured in drainage ditches or underground galleries. A number of methods have been used for this purpose. In most of these systems, the components include a collection area, drainage system, storage area, and distribution system.
When formalized, most gutters are of trapezoidal shape with a length of 40 m, a width of 1 m, and an average depth of 1 m, as shown in Figure 9. They are either parallel or perpendicular to the roads. The roadside ditches store water temporarily, dissipate hydrologic energy through the use of stones or other structures designed to slow the velocity at which the water runs off the road surface, and convey the runoff to storage areas. Storage areas may be constructed perpendicular to the drainage ditches, and take the form of other conduits or underground galleries. These are generally about 15 m in length and 1.3 m in depth and width. A stone masonry wall is placed at the inlet of the gallery. This wall is solid to a depth of approximately 0.8 m, below which the wall is perforated to allow the water to enter the gallery while screening out large particulates, animals, or debris. The base is a stone bed, approximately 0.4 m thick.
In the Province of Mendoza, Argentina, runoff is collected and stored in drainage ditches or V-shaped swales along paved roadways. Water harvested in this manner is used primarily to cultivate trees planted in the swales. The trees most commonly planted along the roadsides are carob and pepper trees.
Paved roads are used also as dikes to divert runoff into impoundments along the roadsides, as is done on the Macanao Peninsula in Venezuela.
Extent of Use
This method of runoff capture has been used in semi-arid regions of Brazil, Argentina, and Venezuela.
Operation and Maintenance
The ditches and swales must be cleaned periodically by removing branches, leaves, litter, and sediments. Ant infestation is a problem that needs to be controlled in some areas. Whenever the roads are repaved or rebuilt, the gutters, ditches, and/or swales should also be rebuilt or repaired. The storage facilities, if used, should be inspected on a regular basis, and cracks or other problems corrected. Litter and debris should be removed from the gallery entrance.
Figure 9: A Schematic Representation of Runoff Collection from Paved and Unpaved Roads, Using Underground Galleries for Storage.
Source: Everaldo Rocha Porto, EMBRAPA-CPATSA.
Level of Involvement
Government involvement is necessary since the water collected with this technology is normally used to aid in the reforestation of public areas and lands. Generally, construction and maintenance is managed by the roads department, which is also responsible for road construction and maintenance. In cases where the impounded water is used by the community, private participation in constructing the water distribution system is desirable.
In Argentina, a forestation project on both sides of a 1 km stretch of paved road cost about $2 000. Costs will vary as a function of the length of roadway treated and the characteristics of the pavement. Provision of a distribution system, if required, could increase the cost per kilometer substantially.
Effectiveness of the Technology
The application of this technology as a means of supplying moisture for plantings along roadsides in the Province of Mendoza, Argentina, was very successful. During the period from 1985 through 1995, carob trees grew an average of 30.7 cm/year and pepper trees an average of 35 cm/year during the same period.
The technique is suitable for use in arid and semi-arid rural areas where runoff from paved and unpaved roads can be collected and stored.
· Runoff collection and storage enhance the flora and fauna of a region.
· Runoff collection can enable cultivation in arid and semi-arid regions.
· The technology has a low operating cost; the capital cost can be subsumed in the cost of constructing the road.
· It is easy to operate and maintain.
· It reduces erosion and controls sedimentation.
· Plants may require supplemental irrigation during dry periods.
· Animals must be kept away from the plantings to avoid plant damage.
· It requires appropriate soil conditions.
· Water collected from roadways may be contaminated by litter and debris and in the urbanized areas by chemical pollutants from vehicles.
This technology is well accepted by public works departments in arid and semi-arid areas. Communities in those areas also support the technology.
Further Development of the Technology
This technology should be combined with some of the in situ or regional impoundment techniques to improve the efficiency and utilization of runoff capture and storage. Since it is a simple and low-cost technology, its use should be encouraged.
Armando R Pedrani, Coordinador del Programa de Investigación y Desarrollo, and Alberto I. J. Vich, Investigador Adjunto del Programa de Investigación y Desarrollo: Manejo Ecológico del Piedemonte (Mendoza), Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, Unidad Ecología y Manejo de Cuencas Hídricas, Casilla de Correo N° 330, 5500 Mendoza, Argentina. Tel. (64-61)28-7029. Fax (64-61)28-7029/28-7370. E-mail: email@example.com.
Everaldo Rocha Porto, Luiza Teixeira de Lima Brito, and José Barbosa dos Anjos, Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA), Centro de Pesquisa Agropecuaria do Tropico Semi-Árido (CPATSA), BR-428 km 52, Zona Rural, Caixa Postal 23, 56300-000 Petrolina, Pernambuco, Brasil, Tel. (55-81)862-1711. Fax (55-81)862-1744. E-mail: firstname.lastname@example.org, email@example.com, and firstname.lastname@example.org.
Aderaldo de Souza Silva, Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA), Centro Nacional de Pesquisa de Monitoramento e Avaliacao de Impacto Ambiental (CNPMA), Rodovia SP-340 km 127.5, Bairro Tanquinho Velho, Caixa Postal 69,13820-000 Jaguariuna, Sao Paulo, Brasil. Tel. (55-0198) 67-5633. Fax (55-0198) 67-5225.
Carmen Fermín, Dirección de Hidrología y Meteorología, Esquina Camejo, Edificio Camejo, 5° piso, Caracas, Venezuela. Tel. (58-02)408-1952. Fax (58-2)5450607. E-mail: email@example.com.
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