ESTIMATIVA DO ESCOAMENTO SUPERFICIAL A PARTIR DE TESTES DE INFILTRAÃÃO NA BACIA HIDROGRÃFICA DO RIBEIRÃO ITAIM

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The Itaim Watershed lacks planning for land use, reflecting typical conditions frequently seen in the area of the valley of ParaÃba. This has been causing increase of runoff, increase in soil erosion, sedimentation of the water channels, inundations and floods in those watersheds that form the ParaÃba do Sul Basin. This study carried out in the Itaim watershed, municipal district of TaubatÃ, SP, aimed to estimate surface runoff based on the Curve- Number (CN) method in area with vegetation cover of grassland (Brachiaria Decumbens), that prevails in this watershed. The values of the number of the curve CN were defined as a function of land use type and vegetation cover of the soil, soil surface condition, of the hydrological condition of the soil and of the soil group that the area has been classified. The estimate of the surface runoff was made based on three different ways: in the 1st, values of accumulated Infiltration (Iac) obtained in the field were used, considered as the Potential Infiltration (S), which varied from 15.37 mm to 51.88 mm with a medium value of 23.46 mm. With those measured infiltration rates and using the maximum precipitation values for TaubatÃ, SP, with duration time of 3 hours: P = 54.4; 70.3; 80.8; 86.7; 90.9; 94.1 and 103.9 mm, respectively, for the return times, Tr = 2, 5, 10, 15, 25 e, 50 years, the following values of surface runoff were generated: 34.83, 49.33; 59.14; 64.71; 68.69; 71.73 and 81.10 mm, respectively; In the 2nd, way it was considered that the prevailing vegetation cover of the watershed was Dirty Pasture (Pasture with regrowth of natural vegetation) and therefore, a value of CN = 75 was used and generated a potential infiltration, S = 84,7 mm and resulted in surface runoff values that varied from 11 to 44 mm, which were lower than the values generated by the method Curve-Number, especially for greater return times. In the 3rd, way, the value of CN was considered equal to 66.57. This value was calculated weighting the contribution of all land use cover classes of the watershed, and as a result a higher value of potential infiltration, S = 127 mm, was obtained. Consequently, the surface runoff values were 5.33; 11.,64; 16.72; 19.83; 22.16; 23,98 and 29.83 mm. Therefore, lower than the values obtained in the first way. The comparison of results obtained by the two Curve-Number methods (conventional and weighted) allowed to be concluded that the Curve-Number method applied in a conventional way underestimated the surface runoff in the studied area. However, results indicate that is possible to use this method for surface runoff estimates as long as adjustments based on potential Infiltration obtained in field be used for local situations.

ASSUNTO(S)

infiltration curve-number curva-nÃmero infiltraÃÃo ribeirÃo itaim surface runoff infiltrometer rings conservacao de bacias hidrograficas infiltrÃmetro de anÃis hydrographic basin escoamento superficial bacia hidrogrÃfica itaim stream

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