Sérgio Monthezuma Santoianni Guerra

Relationship between bedload and suspended sediment in the sand-bed Exu River, in the semi-arid region of Brazil

Abstract Suspended sediment and bedload discharges in sand-bed rivers shape semi-arid landscapes and impact sediment delivery from these landscapes, but are still incompletely understood. Suspended sediment and bedload fluxes of the intermittent Exu River, Brazil, were sampled by direct measurements. The highest suspended sediment concentration observed was 4847.4 mg L-1 and this value was possibly associated with the entrainment of sediment that was deposited in the preceding year. The bedload flux was well related to the stream power and the river efficiently transported all available bedload with a mean rate of 0.0047 kg m-1 s-1, and the percentage of bedload to suspended sediment varied between 4 and 12.72. The bed sediment of Exu River was prone to entrainment and showed a proclivity for transport. Thus, sand-bed and gravel-bed rivers of arid environments seem to exhibit the same mobility in the absence of armour layer. Editor D. Koutsoyiannis; Associate editor B. Touaibia Citation Cantalice, J.R.B., Cunha Filho, M., Stosic, B.D., Piscoya, V.C., Guerra, S.M.S., and Singh, V.P., 2013. Relationship between bedload and suspended sediment in the sand-bed Exu River, in the semi-arid region of Brazil. Hydrological Sciences Journal, 58 (8), 1789–1802.

Topolitossequências de solos do Alto Paranaíba: atributos físicos, químicos e mineralógicos

Little is known bout the pedogenetic differentiation in Alto Paranaiba, western Minas Gerais, Brazil, when materials with such a variety of chemical compositions as tufite, alkaline-ultramafic igneous rocks and carbonatites are compared, which are all found in this region. The purpose of this study was to characterize the physical, chemical and mineralogical properties of three representative soil topolitosequences of the Alto Paranaiba region. Therefore, 11 soil profiles were described and collected in the Serra do Salitre, Patrocinio and Coromandel counties, representing the influence of mafic-ultramafic bodies along the geological interface between Bambui and Araxa groups. Soil samples were routinely analyzed for physical and chemical properties, besides determinations of Fe, Al and Si after sulfuric extraction; Fe after extraction by DCB and oxalate; Fe, Ca, Mg, K, P, Ti, and other heavy metals after total digestion (triacid attack); and determination of the different components in the clay fraction by DRX. The Latosols (Oxisols) of the Alto Paranaiba are extremely weathered and have very low Ki and Kr indexes, indicators of soils with high iron and aluminum oxides contents, with no defined relationship with the underlying parent materials, indicating intense pedoturbation and mixture with alloctonous materials. The geochemical signatures of the ultramafic nature are the unusual high content of Cr, Ni, Mn, Fe, and Mg. The clay fraction mineralogy of the Latosols shows the coexistence of VHE, kaolinite, gibbsite, and anatase, indicating a polycyclic genesis of the minerals from the finer fraction and the high weathering degree. In the Cambisols, the current rapid desilification indicates the coexistence of gibbsite and iron oxides with smectites and illite because of the fast weathering in the silicon-poor mafic or alkaline-ultramafic rock substrates.

Produção de água e sedimentos em bacia representativa do semiárido pernambucano

Water erosion is a major physical process responsible for soil degradation, particularly in semiarid areas, susceptible to high intensity rainfall and limited vegetation cover, especially during dry periods. This study aimed to experimentally evaluate the hydrossedimentological characteristics of Mimoso watershed, in the semiarid region of Pernambuco, in Pesqueira-PE. The representative Mimoso watershed presented high peak flows in a control section with intermittent hydrological regime. The suspended solid discharge production in the Mimoso Rivulet is high and the observed sediment concentrations was of 10.91 and 0.91 t ha-1 yr-1, for the years 2009 and 2010, respectively.

Morphometric characterization and assessment of water quality Hydrographic Basin of Bita, Ipojuca-PE

1 –Professor Adjunto Departamento de Tecnologia Rural/UFRPE. Recife-PE. smsguerra@hotmail.com 2 –Engenheira Química Departamento de Engenharia Química/UFPE. Recife-PE. amrbsilva@ig.com.br 3 –Engenheira Agrícola e Ambiental Departamento de Tecnologia Rural/UFRPE. Recife-PE sofia.pimentel@hotmail.com ; brunooricardoo@hotmail.com 4 –Professor Associado Departamento de Tecnologia Rural/UFRPE. Recife-PE. metri@dtr.ufrpe.br 5 – Professora Titular – Departamento de Engenharia Química/UFPE. Recife-PE. leaq_val@yahoo.com.br Artigo recebido em 10/09/2015 e aceito em 30/11/2015

Bedload and Suspended Sediment of a Watershed Impacted by Dams

Sediment transport relates to suspended sediment and bedload. The suspended sedi‐ ment plays the most important role on the land-ocen sediment flux. On the other hand, the bedload should be considered in order to assess the impacts of dams on sediment transport and sediment yield. Recent effects of dam construction have been widely reported. The sediment load has been reduced by more than 75% for major rives, such as Nilo, Orange, Volta, Indus, Ebro, Kizil Irmark, Colorado, and Rio Grande and more than 40% of its lux is trapped within large dams. In addition, the multiple trapping through sequential dams has impacted the sediment transfer from terrestrial to coastal zone, triggering the coastal erosion. In terms of sediment reten‐ tion and transport, China stands out the most impacted country by dams, followed by United States, and continents such as Europe, Africa, and South America. Based on the foregoing, the impact of dams on sediment transport and yield of an important Brazilian watershed with multiple dams will be the focus of this chapter. Thus, a three years field sampling (2009-2011) was carried out to measure the sediment yield of Capibaribe Watershed, and also its contribution to coastal erosion. The ratio between QB and SSQ ranged from 0.12% to 27.3% with 76% of all values lower than 5%. Usual‐ ly, the bedload transport rate of a river is about 5–25% of the suspended sediment transport. This ranging sheds light on the lack of bedload reaching the coastal zone and it is likely one of the reasons to yield coastal erosion. The low rates can be attrib‐ uted to the presence of dams which have been admitted to have a strong effect on sediment transport. The sediment yield was equal to 3.69, 4.36, and 6.7 t km-2 ano-1 in 2009, 2010, and 2011, respectively. In comparison with bedload yield, the suspended sediment yield was higher than 95% for all studied years. Therefore, the limited bed‐ load supply – mainly responsible for construction of coastal landform – is likely con‐ tributing to the coastal erosion along part of the northeast region, Brazil. The multiple dams along the Capibaribe River watershed produce a deficit in sediment flux to