Abstract The use of water for several human needs, associated with climate change, indicates how important it is to understand the response of watersheds, in order to provide adequate planning and management of water resources. 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 environmental attributes, and anthropic environmental data. To support the analysis, Surface Runoff Potential Charts (SRPC) were made. 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 justifyies 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. As for pair 2, the low runoff potential was mainly due to the predominance of flat relief in the sub-basins. Their soils 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). The physical properties of these soils do not provide a low flow rate, but when associated with the low slope of the land, 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 justifyies 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.

RESUMO: A adoção da bacia hidrográfica como unidade de planejamento desencadeou providências em estudos fundamentais para estruturação dos Comitês de Bacias, tendo em vista a carência de informações que pudessem dar suporte técnico e de conhecimento da área de abrangência destes Comitês. Visando a ela boração do Plano Diretor das sub-bacias do Médio Rio Grande utilizou-se do Zoneamento Ambiental como instrumento para realizar o estudo da área. A pesquisa é parte desse projeto de Zoneamento Am biental intitulado "Grande Minas União pelas Águas" e envolve intervenções antrópicas consolidadas que foram analisadas por limites geográficos. Os dados foram integrados e processados em um sistema de informações geográficas. O produto final resultou em uma Carta com a "Classificação das Unidades Ambientais quanto ao nível de intervenções antrópicas" no Médio Rio Grande, envolvendo as classes: alta relevância, média relevância e baixa relevância. As análises foram realizadas nas 34 macrounidades da área de estudo, que foram fragmentadas em 1607 Unidades Ambientais. Dez macrounidades se des tacam com zonas de alta relevância com relação às intervenções antrópicas.

ABSTRACT: The adoption of the watershed as a planning unit brought measures in fundamental studies to structure the watershed Committee, taking into consideration the need for information which could support it technically and the need for knowledge about those Committees. Aiming at the elaboration of the Master Plan for the sub-watersheds of Middle Rio Grande, the environmental zoning was used as an instrument to perform the study in the area. The research is part of this project entitled "Grande Minas União Pelas Águas" (Large Minas Union through water) and involves finished anthropic interventions which were analyzed through geographic limitations. Data were integrated and processed in a geographic information system. The final outcome was exposed in a Map with the "Classification of Environmental Units regarding the level of anthropic interventions" in the Middle Rio Grande, involving the levels: high, medium, and low relevance. The analyses were performed in 34 macro-units of the study area, which were fragmented in 1607 Environmental Units. Ten macro-units are highlighted with zones of high relevance regarding the anthropic interventions.