Dinâmica fluvial na bacia hidrográfica do rio Carapá, inserida na bacia do rio Amazonas (River dynamics in the Carapá river hydrographic basin, inserted in the Amazon river basin)

O estudo teve como objetivo analisar a dinâmica fluvial na bacia hidrografica do rio Carapa, em Colider e Nova Canaa do Norte – MT. Para o monitoramento da dinâmica fluvial, foram realizadas coletas e analises de sedimentos de fundo, margem e suspensao, instalacao de pinos, estacas e afericao de batimetria. A bacia do Carapa e de sexta ordem, o rio principal possui 163,526km de extensao. A dinâmica fluvial revelou que o rio nao tem um padrao regular, podendo ser encontrados trechos sinuosos, meandrantes e retilineos. A area molhada da secao variou entre 0,248m² (secao 1 - periodo de estiagem) e 103,350m² (secao 11 - periodo chuvoso). A velocidade do fluxo foi maior no periodo chuvoso em todas as secoes e a maior vazao variou entre 2,174m³/s na secao 1 e 75,297m³/s na secao 11 no periodo chuvoso. Nos sedimentos de fundo, predominaram os grosseiros na maioria das secoes nos dois periodos. A fracao silte predominou nos sedimentos de margem na maioria das secoes. A magnitude da erosao medida por pinos variou entre 0,07cm/mes (secao 1) e 1,04cm/mes (secao 11). As secoes 1, 3 e 10 os agregados sao estaveis em agua, concentrando a maior parte das particulas entre 1 a 4 mm, enquanto as demais secoes se mostraram mais susceptiveis a erosao. A concentracao de sedimentos em suspensao variou entre 12 mg/L e 252mg/L ao longo do canal. A descarga solida em suspensao registrada ficou entre 0,135 t/d (secao 1, periodo seco) e 396,850 t/d (secao 11, periodo chuvoso). A B S T R A C T The objective of this study was to analyze river dynamics in the Carapa river hydrographic basin, in Colider and Nova Canaa do Norte - MT. In order to monitor the river dynamics, collections and analyzes of the bottom sediments, margin and suspension, installation of pins, stakes and bathymetry measurement were accomplished. The Carapa basin is of the sixth order, the main river is 163.526 km long. The river dynamics revealed that the river does not have a regular pattern, and sinuous, meandering and rectilinear stretches can be found. The wet area of the section varied between 0.248 m² (section 1 - dry season) and 103.350m² (section 11 - rainy season). The flow velocity was higher in the rainy season in all sections and the highest flow ranged between 2,174 m³/s in section 1 and 75,297 m³/s in section 11 in the rainy season. In the bottom sediments, the thicker ones were predominant in the most sections in the two periods. The silt fraction predominated in the margin sediments in the most sections. The magnitude of the erosion measured by pins ranged from 0.07 cm / month (section 1) to 1.04 cm / month (section 11). In the sections 1, 3 and 10, the aggregates are stable in water, concentrating the most of the particles between 1 and 4 mm, while the other sections are more susceptible to erosion. The concentration of the suspended sediments ranged from 12 mg / L to 252 mg / L along the canal. The registered solid discharge in suspension was between 0.135 t/d (section 1, dry season) and 396,850 t/d (section 11, rainy season). Key words: Colider, sediment, aggregate, erosion, flow