Sistema de informações geográficas aplicado à gestão da bacia do Caeté – nordeste paraense

Abstract

The northeastern of Pará state is one of primal centers of people and products convergence in this state. It contains the highest concentration of urban centers, and is a zone of intense agricultural activity with an advanced process of deforestation. The need for greater knowledge about of the watershed is evident, mostly because for they constitutes planning and implementation unites for a public policies, subsidized by studies, which transcends the scope of purely scientific. In Caeté watershed, located in the NE of the state, agricultural and livestock activities have been practiced with major intensity since the beginning of the century XX, which causes an environmental degradation. The primal objective of this study was an organization of a geographic database with focus on physical environment to add to an environmental diagnoses and the management of this watershed. Using the techniques of remote sensing and geoprocessing for the multitemporal analysis of use and cover of the land; the integration of this with different components of the physical environment (geology, geomorphology, pedology, precipitation, hydrometers and sedimentology); elaboration of maps of agricultural suitability of the lands and natural soil loss vulnerability and building a geodatabase. The morphometric analysis of the basin showed a low probability floods due to: the elongated shape of the basin; 57.6% of its area has flat topography; 50.1% of the basin have dispersive forms of the land. The analysis of the flow, in m³/s, using the Doppler effect (ADCP) showed values of 8.06 in the Arraial do Caeté station, 34.14 in the Tentugal station and 87.45 in the Nova Mocajuba station, for the month of June, while, for the month of September, the flow was 2.79 in the Arraial do Caeté station, 12.09 in the Tentugal station and 33.72 in the Nova Mocajuba station. The calculation of precipitation based on an interpolation of the stations Primavera, Capanema, Nova Timboteua, Ourém, Santa Luzia do Pará and Emboraí showed larger concentration in the mid-north portion of the basin, which presents rainfall between 400 and 450 mm/month. From the integrated analysis of the data of flow and precipitation is observed that the highest values of flow and precipitation occur in forested areas, while the lowest values are observed in areas with large amounts of exposed soil. This occurrence is because the flow tends to be less in upstream direction and in this portion of the basin is where founded a most propitious relief for agricultural practices which had been developed with major intensity during the process of occupation of the watershed. The permanent preservation areas occupy 4.6% of the basin and of these 37.8% is in disagreement with current environmental legislation. The increase identified in the vegetation index (NDVI) for the past 10 years, demonstrated a direct relationship with rainfall during the drier seasons. The watershed showed homogeneity in relation to agricultural suitability. It was observed that the main restricting factor at the management B was the fertility deficiency. In concerning of loss of soil natural vulnerability it was observed that the watershed in question is fairly stable, showing predominant values of vulnerability between 1.8 to 2.2. The generation of the database allowed the analysis of the maps produced and the concerned areas could be observed in more detail. Thus, the data will be available to the society to be used for the benefit of development of the region and with the possibility of update the data as new knowledge and technologies are acquired.