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Natural flows obtained from a simplified model and the influence of rice irrigation in these flows

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  21st Century Watershed Technology: Improving Water Quality and Environment Conference Proceedings, 21-24 February 2010, Universidad EARTH, Costa Rica  701P0210cd.(doi:10.13031/2013.29409)
Authors:   Ana Lúcia Denardin Da Rosa, Eloiza Maria Cauduro Dias De Paiva
Keywords:   Key words: natural flow, rice irrigation, basin of Vacacaí River

This study aimed to apply and assess the simplified methodology used by Paiva et al (2006 b) in a basin of the Vacaca River to obtain information about natural flows. The analyses to determine the water demands of rice farming and to sub-divide the basin were based on hydrological information and use of geoprocessing techniques. The study of use and occupation of the soil showed that the flood plains of the Vacaca River are covered by rice fields that occupy 8.06% of the basin area. Factors such as scarcity of rainfall data as well as uncertainty in the demand value adversity affected the goodness of model fit. However,it was possible to conclude that the methodology was really efficient in determining the natural flow of sub-basins with approximately 3456 km of area, and that due to factors that were not considered in the model (e.g. spreading into rivers and storage purposes) it was not possible to obtain better results for sub-basins of larger dimensions. Among the ranges of the discretized model, the ones which presented the best results were those with monthly generation and propagation of flow as well as the generation of daily flow and propagation of 7 day average flow, highlighting the monthly simulation due to the smoothing of monthly maximum flows which were not well represented. It was concluded that in areas where the number of rice fields is higher the flows in the fluviometric stations are underestimated, the knowledge about natural flows by managers becomes then relevant.

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