Seleção de modelos para o traçado de curvas granulométricas de sedimentos em suspensão em rios

Abstract

RESUMOO conhecimento da distribuição granulométrica dos sedimentos em suspensão em cursos d'água é fundamental para a realização de estudos hidrossedimentológicos. As técnicas geralmente utilizadas para a avaliação da distribuição granulométrica de amostras de sedimentos resultam em valores pontuais, dependendo de posterior interpolação para o traçado da curva granulométrica e para a obtenção de diâmetros característicos específicos. A transformação de valores pontuais em funções contínuas pode ser realizada por meio de modelos matemáticos; entretanto, são poucos os estudos desenvolvidos com a finalidade de determinar o melhor modelo para o ajuste de curvas granulométricas. Neste trabalho, objetivou-se a seleção de modelos para o traçado de curvas granulométricas de sedimentos em suspensão em rios; utilizando-se 30 amostras contendo de 8 a 10 pontos medidos, testaram-se 14 diferentes modelos. A comparação entre os modelos foi baseada na diferença da soma do quadrado dos erros entre os valores observados e os ajustados, cujos resultados indicaram que os modelos Haverkamp & Parlange (1986) e Skaggs et al. (2001), ambos com 3 parâmetros de ajuste, são os melhores para o traçado das curvas granulométricas de amostras de sedimentos em suspensão em rios.Palavras-chave: hidrossedimentologia, hidrossedimentometria, curvas de crescimento Selection of models for adjusting particle size distribution curves of suspended sediments in river ABSTRACTThe knowledge about particle-size distribution of suspended sediments in river is fundamental for some hydrosedimentological studies. In general, the techniques used to determine the particle-size distribution of a sample results in pointwise values, demanding a subsequent interpolation to fit the complete particle-size distribution curve and to obtain specific characteristic diameters values. The transformation of discrete points into continuous functions can be made by mathematical models. However, few studies have been developed with the purpose of determining the best model for fitting particle-size distribution curves. The objective of this paper was to select models for fitting particlesize distribution curves of suspended sediments in river water. Using the particle-size distribution, results from 30 samples of suspended sediments of river with 8 to 10 measured points, with 14 different models were tested. The parameter used to compare the models was the sum of the square errors between the measured and calculated values obtained in the adjustment of each model. The results showed that the Haverkamp & Parlange (1986) and Skaggs et al. (2001) models, both with three fitting parameters, are the best for adjusting particle-size distribution curves of river suspended sediment samples.

The best mathematical models describing particle size distribution of soils

“…Tested five log-normal models for 71 soils from New Zealand Hwang et al (2002) Evaluated fitting ability at 7 models on 1387 Korean soil samples Hwang (2004) Studied the effect of soil texture of 1387 Korean soil samples on the performance of nine different PSD models Lima and Silva (2007) Conducted a study on PSD of suspended sediments in river water Bah et al (2009) Compared the fitting ability of seven PSD models to data of 55 fine-textured soil samples from New South Wales in Australia Bagarello et al (2009) Evaluated the ability of the hyperbolic and Fredlund models to fit 243 soils Shangguan (2012) Investigated ten PSD models for the conversion of soil texture classification from ISSS and Katschineski to FAO/USDA system for soils from china Botula et al (2013) Evaluated the performance of 18 PSD models for 1412 soils from Central Africa which had humid tropics Weipeng et al (2015) Studied critical evaluation of PSD models of 1013 soil samples from different regions of china Bayat et al (2015) Investigated fitting capability of PSD models on the 713 PSD experimental data of the UNSODA database…”

Sediment Morphology, Distribution, and Recent Transport Dynamics in a Reforested Fragment

“…Numerous studies have been undertaken in order to understand and quantify the erosion process (Lima and Silva, 2007;Sveistrup et al, 2008;Nunes and Cassol, 2011;Santos and Sparovek, 2011). In contrast, few studies characterize the sediment generated by erosion in terms of its macro and micromorphology.…”

Turbidimetry as an alternative method to determine the rating curve of suspended sediments

“…A technique to quantify these sediments is the determination of the solid discharge, which is characterized mostly by the estimation of the quantity of suspended sediments that pass through a transversal section per unit of time (LIMA & SILVA, 2007;LIMA, SILVA & CARVALHO, 2006). In most watercourses, this portion in suspension represents more than 90% of the total sediment discharge (CARVALHO, et al, 2000).…”