Dinâmica do uso dos recursos hídricos nas bacias do ribeirão Entre Ribeiros e do rio Preto, afluentes do rio Paracatu / Water resources use dynamics in watersheds of Ribeirão Entre Ribeiros and Rio Preto, tributaries of the Paracatu River

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

From times past, humanity confronts problems of environmental degradation. The environment, which always performed efficiently its function of filtration, today finds itself excessively overburdened by human activities: it suffers the risk of its resources exhausting, not being able in certain situations to recuperate itself and needing the help of man. However, considering the present models of production and development that prioritize economic maximization, finding definitive solutions for these matters seems distant. Recently this concern has won supporters in the entire world, and there is effectively a greater consciousness for environmental causes, including successful cases in recovery procedures and viable proposals for sustainable development. Nowadays, to reach this aim, a modern model of managing a certain region must take the hydrographic basin which is implanted as a basic unit of planning. It has to be considered the increase in demand for water use that has been evidenced over the course of time, particularly in the last decades, is causing serious conflicts among users in many regions of the earth, inclusively in Brazil, as in São Francisco basin. This hydrographic basin has a total demand of 224 m3 s-1 of water, with irrigation being the main consumer, accounting for 71,4% of the demand. Paracatu river, located in Middle San Francisco river, is its biggest tributary, contributing with about 40% of the river flow in its discharge section. Although, in the last decades, irrigation has presented expressive growth in Paracatu basin, mainly after the incentives from the governmental programs that had its begin in the 1970s, such as the Integrated Development Plan of the Minas Gerais Northwest (PLANOROESTE). As consequence of the great expansion of irrigated agriculture, serious conflicts has been arising in several parts of the basin, mainly in the sub-basins of Entre Ribeiros stream and Preto Rivers, tributaries of Paracatu river, that drain an area of 14,149km2, which 74,87% (10,621km2) are in Minas Gerais State, 15,71% (2,212km2) in Goiás State and 9,42% (1,316km2) in Federal District. Thus, discuss and propose solutions for the problems related with the basin hydrographic, looking for the sustainable water use in the urban and rural areas and its relation with the sustained development are purposes that the planning and management of water resources must assure to future generations. However, the relation between soil use and watersheds has been marked by the failure, with environment significant damages, what have been transformed in losses for all collectivity. Thus, modifications on the outflow regime of a hydrographic basin can be caused by changes in the land use, climatic variability, storage dams construction or by the irrigation increase. When the land cover is changed for another one, the components of the hydrologic cycle on watersheds could be modified, changing the outflow regime: in this context are the watersheds Entre Ribeiros Stream and Preto River. It has to be considered, to aggravate the situation even more, that the occurrence of extreme meteorological and climatologic phenomenon has become a fact. In spite of the adoption of emergent providences, some problems intensified: increment of the concentration of gases of heating effects; decrease of ozone layer; reduction of the grounds for agriculture, increasing contamination of the aquatic ecosystems and progressive decrease of the resources of softer water. Nevertheless, a serious problem has been perceived - the absence of evaluation of the questions about prediction in the implantation of projects. In this study, it was searched to represent the existent interrelations of the changes of the kinds of oil use and its influences over climatic factors and the aquatic ecosystems, in the hydrographic basin of Entre Ribeiros Stream and Preto River. In these basins, where the medium annual outflow retired by the Irrigation have had an increase of 62 times in the period of 1970-1996, producing a regional series of conflicts, it has happened the replacement of the native vegetation Cerrado for Cultivation, mainly. The situation is worry when it is verified by analysis of the water offered in the period of 1985-2000, that the precipitation in the basin and the medium and minimum outflows has had significant reductions. For these questions, the proposal of this search was develop a model of offering and requesting of the water use, based in the origins of Dynamic of Systems with the support of STELLA SOFTWARE. To this, it had been used data from the monitoring of soil use in the period from 1985 to 2000; associated the hydrological behavior of the maximum, minimum and medium outflows observed in the basins with the variations happened in the use of the soil of themselves; simulated sceneries of increase and reduction in the water offer and calculated the Sustained Index, having as a base the data from the fluviometric stations Barra da Égua Farm and Porto dos Poções, located, respectively, in the basins of Entre Ribeiros Stream and Preto Rivers. The called Water Model was developed to approach a variety of sceneries of offering and demand of water in the studied area. By means of a system analysis of the water resources of the related basins had been determined the main variable and its respective inter- relations, in accordance with the structure of the model of offering and demand water. This structure was represented in the causal diagram, which served of base to the elaboration of the diagram of supply and flow, by means of which was established the mathematical model that allowed to effect the numerical simulation. Tests for the validation of the model had been applied whose the gotten results allowed to verify that the model is conformed and it behaves in coherent form to the existing data in the reality, what changes it adequate for simulation.As horizon of planning for the present study, it was chosen a period of 65 years. Eight sceneries were examined that include future increases in the water demand and restrictions in the offer of this resource, with the objective of evaluating the sustentability of the offer of available water in the related basins. To evaluate the sustentability it was constructed an index that discloses if the system, under the assumptions incorporated in the related scenery, it meets or not, in happening of the period in study, in a situation of stresses. In the basin of Entre Ribeiros Stream, for instance, it has occurred the substitution of savannah (-47,65%) for cultivation (+198,09%) which reduces the interception of the rainy water, increases the superficial flowage and reduces the infiltration of the water in the soil, causing reduction of the medium and minimum outflow. Herein by the based modeling in principles of Dynamic of the Systems and with the use STELLA software, it was simulated possible effects of climatologic changes in the referred basin, considering, in one of proposed sceneries, increases of 1C in the temperature and of 6,9% in the precipitation in the period 1995-2060. It was verified the tendency of a reduction of -18,70% in the Direct Precipitation and significant alterations in the evapotranspirometric taxes for Grass (+33,34%), Cultivation (+23,77%), Savannah (+8,54%) and Forest (-9,49%). In the basin of Preto River, for the period of 1995- 2006, it was verified the tendency of reduction of -23,08% in the Precipitation in Actual Agronomic trade scenery. It has to be considered that in the eight (8) evaluated sceneries, the simulation pointed to the reduction of the direct precipitation in the basins: it was verified, in all the considered scenes, that the system would be unsustainable in the medium and long terms. The developed model in the present study allowed to increase the understanding in relation to the form of functioning of the water resources system of the basins Entre Ribeiros stream and Preto river, what converts it into a valuable computational instrument of assistance to the managements of the politics for the planning of the water resources - in the related basins, as well as in other hydrographic basins.

ASSUNTO(S)

recursos hídricos dinâmica de sistemas engenharia de agua e solo water resources planejamento ambiental dynamic systems environmental planning

ACESSO AO ARTIGO

Documentos Relacionados