Estimated runoff coefficients for Atuba river hydrographic basin: Curitiba and metropolitan region - Parana/Brazil

This paper presents results from the Soil Conservation Service method (SCS), including data treatment and thematically maps done under GIS environment applied. Its aiming is evaluate the temporal and spatial variation of the runoff coefficient (C) caused by impermeable surfaces in the river basin Atuba. The temporal and spatial evaluation was done studying three different periods of urbanization: (a) beginner of 60 years, when the basin could be considered in its natural state; (b) in 1980, during the initial process of urbanization and (c) in 2000, when some areas of the basin remains close to the natural state but is easy to observe a fast increasing in urbanization process. In the methodology developed by SCS, the C coefficient for a hydrographic basin was calculated from different percentages of impermeable surface covering and previous physical and humidity characteristics for a specific soil type. So that, impermeable surfaces could be quantified and cartographic bases and surface covering these three periods were analyzed and treated digitally. In the digital photointerpretation technique the software Erdas Imagine 8.6 (R) was used to obtain surface cover maps. As a final result, it was possible to determinate quantitative parameters for maximum retention of the soils (S) and runoff indexes (C). Besides, the interpolation under a GIS environment and coverage maps of the land surface with the soil map were used to build a map for multitemporal analysis of the runoff coefficients.