Overflow risk analysis on the Presidente Dutra highway using the quota-volume curve in the Una River Basin in Taubaté, SP, Brazil

Anthropic interventions and vectors of urban occupation have caused changes in the infiltration and runoff regime that can cause or accelerate erosion processes, silting and flooding in river basins. Flooding, as a stochastic phenomenon, can occur at any time and in any place, influenced by climatic factors, physical characteristics of the basin and mainly by human interference in the use and occupation of the land, which affects the type, quality and quantity of vegetation and increases soil impermeability. The aspects of regional urbanization led the State in 2012 to create the Metropolitan Region of Vale do Paraiba and the North Coast (RMVPLN), attracting large real estate investors. In the hydrographic basin of the river Una in the municipality of Taubate, there has been an increase in flooding episodes and the possibility of worsening due to changes in land use and occupation. In this study, we sought to determine runoff as a function of changes in land use and occupation expressed by the variation in runoff coefficient (C) recommended by the Department of Water and Electricity of the State of Sao Paulo, (DAEE-SP) for licensing and intervention projects in water resources. The lower limits C = 0.35 and upper C = 0.70 were used admitting variations of 0.05 points in this interval to calculate the water flow (QE) and Intake Volumes (VE) in the basin from an intense precipitation of 100 years of recurrence time, from the use of the UEHARA Method (DAEE, 2006), to the control point located at the intersection of the Una River and the Presidente Eurico Gaspar Dutra Highway (BR 116-SP) and from this the Quota-Volume curve was drawn. The flood shares were obtained by hitting the reserve volumes found on the quota-volume curve.The current runoff coefficient of the basin is C = 0.35, which allows water to pass through the Dutra highway bridge. However, the modification of C = 0.50 due to the advance of urbanization, the level of flooding would reach 557.40 m. That exceeds the level of the lower base of the bridge (556.72 m) and, with C = 0.60, would reach the quota of 558.90 m, which would cover the asphalt surface of the highway. Given the real estate pressures in the metropolitan region, special care is recommended in the conservation, preservation and expansion of native forest vegetation with actions for Payments for Environmental Services (PSAs), de-silting actions of the main gutter and Una's tributaries, to contain the identified advance of urbanization in the basin, as well as the definition and installation of detention and retention basins.