Analysis of efficiency of retention terraces in sub-basins of the São Francisco River

Although being an old practice, the terracing still presents relative difficulties to its use, being its efficiency dependent on the correct sizing of the space between terraces, the depth of superficial draining, its transversal section and mainly the constructive uniformity. Terraces of holding, type Nichols were studied, constructed in two distinct areas in sub-basins in the North of Minas Gerais state in Icaraí de Minas, Pintópolis and Ubaí cities, in the scope of the Program of Revitalization of Watersheds of the São Francisco River. By means of the section in the lowest quota of the crest of the ridge, combined with the lowest quota of its extremity, its volume of effective storage was determined. Through the relation between the effective and necessary volume, it was possible to observe that for Icaraí de Minas areas 01 and 02, the efficiency varied from 76.40 to 44.80%; for Pintópolis, from 9.00 to 63.50% of the volumetric potential of water holding in the terraces, not being possible to evaluate the efficiency for the terraces of Ubaí city. These results evidence efficiency problems of terraces built by the Program of Revitalization, for the North of Minas Gerais conditions.

terrace; efficiency; soil and water conservation