Urbanization and runoff in the Tucunduba hydrographic basin, Belém, PA, Brazil

The present work investigated the runoff resulting from urban sprawl in the area of Tucunduba basin, in Belem, in the period between 1972 and 2006, which is characterized by a urbanization process started in the 1960s by low income population without adequate infrastructure services. Urbanization modifies the soil surface interfering on the ground phase of the hydrological cycle, inasmuch as it reduces the area of infiltration, increases runoff, and the runoff coefficient. A geographic database with land use and land cover map layers extracted from orthophotos acquired in 1972, 1977, and 1998 and a SPOT satellite image acquired in 2006 were used. Digital maps and analysis of the urbanization processes were supported by tools available in ArcGIS™ software package. To estimate the infiltration potential (S) and effective rainfall (Pe), as a function of rainfall duration equal to the maximum time of concentration of the water in the basin, Curve Number methodology proposed by the Natural Resources Conservation Service (NRCS) was applied. Rainfall estimates were calculated using the maximum rain equation for the city of Belém, with return times specified at 2, 5, 10, 15, 20, 25, 50, 100, and 200 years. The results showed an increase in areas of high and medium population density (urban) and reduced area of low population density (secondary forest growth) for the years of 1972, 1977, 1998, and 2006, that generated a higher effective precipitation value and, therefore, a higher effective runoff coefficient value (C).