Demetrius D. da Silva

Chuvas intensas no Estado da Bahia

Series historicas de precipitacao pluvial de 19 estacoes pluviograficas localizadas no Estado da Bahia e operadas pela Agencia Nacional de Energia Eletrica (ANEEL), foram analisadas, objetivando-se ajustar modelos teoricos de distribuicao de probabilidade aos dados de chuvas intensas e estabelecer a relacao entre intensidade, duracao e frequencia da precipitacao pluvial. Para cada estacao pluviografica determinaram-se as series de intensidade maxima anual das precipitacoes com duracoes de 10, 20, 30, 40, 50, 60, 120, 180, 240, 360, 720 e 1.440 min. Os modelos probabilisticos testados foram os de Gumbel, Log-Normal a dois e tres parâmetros, Pearson e Log-Pearson III. As equacoes de intensidade-duracao-frequencia da precipitacao pluvial foram ajustadas utilizando-se o metodo de regressao nao-linear de Gauss-Newton. O teste de aderencia de Kolmogorov-Smirnov, utilizado para a verificacao do ajuste dos modelos aos dados de chuvas intensas, evidenciou que o modelo de Gumbel foi o que melhor se ajustou para a maior parte das combinacoes entre estacoes pluviograficas e duracoes estudadas. Foram evidenciadas, para uma mesma duracao, grandes variacoes nas intensidades de precipitacao entre as estacoes estudadas.

Aplicação da análise estatística multivariada no estudo da qualidade da água do Rio Pomba, MG

ABSTRACT The aim of this study was to evaluate the water quality and identify groups of pollution in the Middle Pomba River through multivariate statistical technique. There were two campaigns from Oct/2008 to Jan/2009 in nine geo-referenced points along the Middle Pomba River including the analysis of 18 variables of water quality. The multivariate statistical technique, through the application of factor analysis/principal component analysis, caused a decrease in the number of variables of water quality, since the best performance of the variables occurred with the inclusion of 15 of the 18 variables. By the use of factor analysis/principal components analysis, it was found that the best behavior of the variables of the water quality of the Middle Pomba River waters was the one composed of three factors, explaining 74.30% of the total variance. Changes in water quality of the Middle Pomba River were defined by a group of nutrients associated with sewage and diffused pollution; for an organic group, caused by untreated sewage in the water stream, and by a group of suspended solids, expressing the process of water erosion in the basin.

Índices e espacialização da erosividade das chuvas para o Estado do Rio de Janeiro

For improving the knowledge about rainfall erosivity in the state of Rio de Janeiro, Brazil, the present study aimed to calculate the erosivity indices EI30 and KE > 25 using two methodologies to estimate the kinetic energy, average monthly erosivity indices based on pluviometric data and to obtain the isoerosivity maps for the State. EI30 and KE > 25 were obtained using rain gauge data of 14 stations located in Rio de Janeiro. Index estimates were also obtained by using correlations with the average monthly precipitation or the rainfall coefficient and spatialization via maps generated by ArcView 3.2a software. The results permit to conclude that the erosivity indices, for the different studied places, present expressive differences among themselves; there were no significant differences between the results obtained by the equations proposed for the calculation of rain kinetic energy and the estimate of rainfall erosivity using the average monthly precipitation gave better results compared to based on rainfall coefficient.

Efeito da cobertura nas perdas de solo em um argissolo vermelho-amarelo utilizando simulador de chuva

The present work was carried out in the experimental area of the Agronomy Department of the Vicosa Federal University, Brazil, aiming to evaluate the effect of soil cover and kinetic energy of rainfall on soil losses. The soil management used was the contour cropping, with six experimental units (4,0 m2) with soil cover percentage of 0; 20; 40; 60; 80 and 100%. The tests were conducted with a rotative rainfall simulator and the soil in the experimental area was a Red-Yellow Podzolic, with an average slope of 9.5%. The six rainfall intensities used were 60; 80; 100 and 120 mm h-1, with periods of time of 68; 40; 24 e 14 minutes, and resulting in kinetic energy values of 1,401; 1,122; 841; e 589 J m-2, respectively. Six successive rainfall applications were made in 12 hour periods, regularly, for each rainfall intensity. It was observed a pronounced decrease in soil losses with higher soil cover percentage, and higher soil losses with lower rainfall intensities, due to the long rainfall period of application. The influence of soil cover on soil loss was more effective than rainfall intensity and that, the erosive potential of the intense rains was reduced by soil cover increase, passing the erosion process to be dominated by erosive effect of the runoff, which occurs for a larger period in the less intense rains, due to their larger duration.

Umidade do solo no semiárido pernambucano usando-se reflectometria no domínio do tempo (TDR)

Present study aimed to investigate the temporal variability of surface water content in soil by time domain reflectometry (TDR), as consequence of precipitation characteristics of Pernambuco semiarid, studying such dynamics under different types of the soil cover. The study was conducted in a slope of a representative catchment, in a Typic Hapludalf soil, where four experimental plots were installed with two TDR probes for soil moisture investigation as well as monitoring the runoff. Treatments were natural cover (CN), bare soil (SD), cactus (P) and microdams associated with mulch (B + CM). From the results obtained during a period with erosive rainfall, it was found that soil moisture observed during the experimental period showed high variability in time, related to different types of coverage and soil properties. Mulching was the most appropriate conservation practice for maintaining soil moisture.

Avaliação do desempenho dos modelos de predição da erosão hídrica USLE, RUSLE e WEPP para diferentes condições edafoclimáticas do Brasil

The objective of this study was to evaluate the performance of USLE, RUSLE, and WEPP soil loss prediction models for different Brazilian soil and climatic conditions. To achieve this objective, soil losses estimated by the mentioned models in nine locations in Brazil were compared with the losses measured in the field by the following statistical parameters: correlation coefficient, root mean square error, Wilmott concordance index, confidence index, Nash-Sutcliffe coefficient, and efficiency coefficient models. The experimental plots adopted in studies of soil losses used in this study had varied dimensions (38 to 1875 m2) and monitoring times and periods (01 to 07 years). There was a significant difference between the overall average of soil loss estimated by the models and the corresponding values measured in the field. Soil losses estimated by the WEPP model were more accurate in 46% of the cases, followed by RUSLE and USLE models with 42 and 12%, respectively. The statistical indicators showed that the WEPP model had better performance when compared with the other models. Despite the difference between the observed and the measured data for the three models, the WEPP model, which presented highest performance, angular coefficient closer to the unity in the relation between soil losses measured in the field and estimated by the model, and because it is based on physical processes, demonstrates to have higher potential to predict erosion for different Brazilian edaphoclimatic conditions.

Modelo hidrológico para estimativa do escoamento superficial em áreas agrícolas

Desenvolveu-se um modelo hidrologico para estimar o escoamento superficial em areas sob condicoes agricolas. O modelo e baseado na analise dos diversos processos associados ao balanco hidrico e nele se usa a equacao de intensidade, duracao e frequencia da precipitacao para estimar a intensidade de precipitacao e a equacao de Green-Ampt modificada por Mein-Larson, para estimar a velocidade de infiltracao permitindo, tambem, a consideracao da interceptacao pela cobertura vegetal e do armazenamento de agua sobre a superficie do solo por meio de diferentes metodologias. O escoamento superficial comeca apos a capacidade de armazenamento sobre a superficie do solo ter sido preenchida, e e calculado subtraindo-se a velocidade de infiltracao da agua no solo da intensidade de precipitacao durante o intervalo de tempo em que a intensidade da chuva e maior que a velocidade de infiltracao. Resultados de um experimento de validacao do modelo e duas aplicacoes praticas sao apresentados, sendo que os resultados obtidos com o modelo foram muito proximos daqueles observados no campo.

Estudo do comportamento hidrológico do Rio São Francisco e seus principais afluentes

The Sao Francisco Basin has 36 major tributaries, of which 19 are perennial. The areas of drainage of these tributaries, except for the Raverde Livarde, are located in the area of the basin not included in the drought region, representing 50% of the total area of the basin. In this study the hydrological behavior of the Sao Francisco River and its main tributaries was analyzed in relation to the annual data of mean precipitation, mean specific flow and outflow coefficient. The obtained results lead the following conclusions: the studied hydrological variables presented mean values in the second period superior to those of the first one; the studied tributaries that represent 46.3% of the basin area contribute 81% of its flow for the period without the influence of the reservoir accumulation; the sub-basins that present the largest contributions for the formation of the flow of Sao Francisco River are the ones of the Rivers Paracatu, Grande and Velhas.

Influência da declividade do solo e da energia cinética de chuvas simuladas no processo de erosão entre sulcos

A rainfall simulator and a soil channel were used to evaluate the effect of the soil slope and kinetic energy of simulated rainfall on the soil loss for interrill areas. The experiment consisted of a factorial arrangement, with five values of kinetic energy (495, 832, 1,151, 1,541 e 1,959 J m-2) corresponding to precipitation intensities of 30, 46, 69, 88 and 107 mm h-1, respectively, and five soil slopes (2, 6, 10, 14 and 18%). In the test, a horizon of a Red Yellow Latosol soil was used. The soil loss was determined by direct method and a regression equation was obtained relating the soil loss with the soil slope and kinetic energy. The results showed that the accumulated soil loss with time presented a tendency towards linearity providing, this way, soil loss rates constant through out the tests; and the total soil loss increased with the increase of the soil slope and of the kinetic energy, but the slope had a less expressive effect on soil loss than the precipitation kinetic energy.

Avaliação de um modelo para a estimativa da lâmina máxima de escoamento superficial

A erosao hidrica e um dos principais processos associados a degradacao ambiental, sendo a desagregacao e o transporte das particulas do solo decorrentes, principalmente, da energia cinetica proveniente do impacto das gotas da chuva sobre o solo e do escoamento superficial. Tendo em vista as perdas na producao agricola resultantes da erosao hidrica, aliadas ao alto custo de adocao e manutencao de sistemas de conservacao de solos, e fundamental que estes sejam instalados de maneira adequada. Visando otimizar o projeto e adotar sistemas de conservacao de solos, Pruski e colaboradores desenvolveram um modelo com vistas em obter a lâmina maxima de escoamento superficial em condicoes tipicas de areas agricolas. Neste trabalho, procedeu-se a avaliacao deste modelo pela comparacao dos valores calculados com os obtidos experimentalmente, tendo-se evidenciado pequenas diferencas percentuais e altos coeficientes de correlacao entre os valores obtidos experimentalmente e os calculados. Esses valores indicam que o modelo avaliado mostra-se eficiente para prever a lâmina maxima de escoamento superficial.