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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.
==Design, suitable conditions and design limitations==
==Costs, operation & maintenance==
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 '''costs''' of in situ rainwater collection systems are minimal. The main cost of this technology is in the equipment and labor required to build the fences and furrows. Table 1 shows representative costs reported for different methods of site preparation in cultivated areas of Brazil. Further, the construction cost of a tajamar in Paraguay has been reported at $4,500. This cost includes not only the cost of soil preparation, but also the cost of ancillary equipment such as the storage tank and windmill shown in the set up in Figure 1. '''Table 1.'''{|border="1" cellspacing="0" cellpadding="5"|-! Method! Basic Equipment! Animal Traction! Total! Hourly Cost of Implementation|-|Flat terrain trenches|150.00|300.00|450.00|0.96|-|Post-planting furrows|80.00|300.00|380.00|0.90|-|Pre-planting furrows|180.00|70.00|250.00|0.90|-|Furrows with barriers|180.00|70.00|250.00|0.90|-|Inclined raised beds|1,500.00|1,000.00|2,500.00|12-15|-|Furrows in partial areas|100.00|80.00|180.00|0.70|-|Guimarães Duque method| ...| ...| ...|12-15|}
