Hydrological surveys and construction of irrigation facilities in inland arid regions of the Republic of Chile: A case study of cost-sharing construction of hydraulic structures by public participation

Summary The results of estimating the probable rainfall in Ninhue Village and its vicinity in the Republic of Chile revealed that the annual precipitation in 1998 was equivalent to a record-low level which occurs once in 50 to 200 years. In the San Jose District, which is designated as the model project site, the permeability of the soil in the upland areas was extremely poor at a saturated hydraulic conductivity of the order of 10E-8 cm/s and a basic intake rate of 0.1 mm/h attributable to the densely grained soil texture with few macro pores, whereas the permeability of the soil in the lowland areas was classified as medium to low level. The rainwater runoff was shown to differ conspicuously between the rainy and dry seasons, and the monthly and annual rainwater runoff rates were obtained. The amount of annual recharge in the shallow groundwater was estimated by the water balance method and the porosity method, based on which the amount of water stored in the shallow groundwater and reservoirs available as water resources for irrigation was estimated. These results will provide useful fundamental data for drawing up plans and designs when constructing new irrigation facilities in the future. Meanwhile, fruit trees and greenhouse vegetables were cultivated in the model fields where drip irrigation facilities were installed, based on which the amount of irrigation water required, the state of crop growth, and the yields of crop production were identified. Eight farming households in the San Jose District constructed drip irrigation facilities in their orchards with financial support from the Instituto de Desarrollo Agropecuario (INDAP: Institute of Agricultural Development) which provided the farmers with advance loans for construction. The breakdown and the ratios of construction expense items incurred were identified, and a method for mitigating the burden on farming households in return for their labor was established. These results will provide farming households with a strong incentive for constructing irrigation facilities in the future. To follow the model case of the San Jose District for promoting agriculture in the inland arid regions, the Ministerio de Agricultura (MINAGRI: Ministry of Agriculture) of Chile needs to take the following actions.l) To implement an agricultural development project covering the entire San Jose District, plans for land use, irrigation farming, and the construction of irrigation facilities for the respective groups of 10 to 20 farming households, each group sharing the same single watershed, should be drawn up jointly with the departments in charge of farming and cultivation systems and soil management. 2) A comprehensive method for exploiting water resources, including the surface runoff water, shallow groundwater, and deep (bedrock) groundwater, should be developed.3) The precision of estimating the water storage at source should be improved by prospecting the deep groundwater and conducting hydrological surveys on a routine basis. 4) An irrigation management method for producing high quality crops should be developed.