Modelagem hidrossedimentológica de uma bacia hidrográfica no Estado de Pernambuco utilizando o modelo SWAT

Abstract

Water resources play a fundamental role in the socioeconomic development of a region, and its disordered use has generated qualitative and quantitative problems. Erosive processes accentuated in river basins are extremely damaging to the health of water bodies. Due to the great obstacle in quantifying the sediment production in watersheds, as well as the effect of the basin scale on the hydrosedimentological processes, its estimation has been made through modeling. In general, the models are related to the physiographic, soil and climatic characteristics. The Soil and Water Assessment Tool (SWAT) integrated into the Geographic Information System (GIS) has been widely used in hydrosedimentological studies in river basins around the world, presenting good results. The choice of the hydrographic basin of the Ipojuca River was due to the fact that it is of great relevance to the State of Pernambuco, since it represents a water communication route between the backwoods and the Coast of Pernambuco and encompasses cities of great economic and tourist importance, The City of Caruaru, Bezerros, Gravatá and Ipojuca. The basin presents an environment of great complexity, evidencing in this way, climatic contractions, relief, soils, vegetation cover, as well as socioeconomic factors that require a model of water and environmental management, that meets the local peculiarities. The river Ipojuca has an extension of about 320 km crossing the physiographic regions of the wild, south woods and metropolitan. Throughout its course, largely intermittent, several problems of environmental degradation are observed, which gives it the classification of one of the most polluted in Brazil. Based on the aforementioned information, the present work seeks to estimate and analyze the spatial distribution of sediment production in the Ipojuca River basin through the SWAT model. The estimates generated by the model also allow the evaluation, besides sediment production, of deposition and transport in each sub-basin. The data of the model were compared with the data measured in the fluviometric station in the period between 1993 and 2006. The climatic data used to enter the model were obtained from the Global Weather Data for SWAT platform. Rainfall data were obtained from Agência Pernambucana de Águas e Clima (APAC) website for five stations in the basin. In the model entry, the land use and soil type maps and the digital terrain elevation model (MDE) were also used. However, the value of the Nash-Sutcliffe coefficient (NSE = - 1.4) was found to be statistically significant, indicating that there was good colinearity between the estimated and observed values (R2 = 0.74) Indicated that the means of the observed values represent better the flows than the simulated values. The value of the Agreement Index - PBIAS - (-28%) indicates that the model overestimated the field data unsatisfactorily. The sediment yield estimated by the model along the basin was quite heterogeneous, with higher values in the western portion. The spatial distribution of sediment yield simulated by SWAT, as well as its correlation with precipitation and surface runoff, was not satisfactory in several sub-basins, even when other influential parameters such as slope, elevation , Type and land use. The temporal evaluation of the sediment production was well correlated with the flow, indicating that the model presents good quantitative results, but it needs a calibration to improve the qualitative results. Therefore, it is suggested that the calibration of the model for the adequate hydrosedimentological simulation of the Ipojuca river basin be carried out.