Hydrological response of hydrographic sub-basins in the Piracicaba River Basin - Southeast Region of Brazil

Abstract

Use of water for several human needs, associated with climate change, indicates the need understand the response of watersheds, in order to provide adequate water resources planning and management. This study was carried out in two pairs of hydrographic watersheds, in the Piracicaba River Basin, southeast of Brazil, analyzing water response, integrating in-situ collected precipitation and flow data, natural environment attributes, and anthropic environmental data. To support the analysis, Surface Runoff Potential Charts (SRPC). The evaluation of the physical characteristics of the sub watersheds (SW(A) and SW(B)) shows that these areas present very low to low potential, indicating greater infiltration capacity. The use and coverage of the soil partially justifies the flow changes in pair 1, since SW(A) has a larger extent of agricultural areas that can use irrigation. SW(B), even with a greater variety of crops, has a smaller cultivated area and tends to demand less water. At pair 2, the low runoff potential is mainly due to the predominance of flat relief in the sub-basins. The soils that compose them present a higher fraction of silt and clay, with thicknesses > 5m in SW(C) and varying from 0.5m, reaching depths above 5m in SW(D), however, the physical properties of these soils do not provide a low flow rate, but associated with the low slope of the land, the geological characteristics and low drainage density are configured in regions where the flow flows more slowly, contributing to the evaporation and infiltration process. The use and coverage of the soil also partially justifies the flow oscillations, due to anthropic activities in SW(C) and SW(D), such as irrigation and spraying of citrus, fertirrigation of sugarcane, irrigation of seedling nurseries, directly interfering with the availability of surface water.