Comparative analysis of the performance of mixed terraces and level and graded terraces

Abstract

ABSTRACT. The terracing of agricultural land is the most widespread mechanical practice used among farmers in the control of water erosion. The objective of this paper was to carry out a comparative analysis between mixed terraces and level and graded terraces. The dimensioning of level terraces was carried out based on the surface runoff volume, while the graded terrace dimensions were based on the maximum runoff flow rate. For the mixed terraces, the dimensioning was carried by considering two surface runoff hydrographs, one for the determination of the terrace channel capacity and another to estimate the flow rate at the extremity of the terrace channel. Therefore, in order to contain and transport the excess volume, an additional value was calculated and added to the depth of the channel. A case study was performed for the Uberaba, Minas Gerais State (Brazil) rainfall conditions, considering events with return periods of 10, 30, and 50 years. The obtained results provided quantitative evidence that mixed terraces have a lower height than level terraces and a higher level than the graded terraces, resulting in direct consequences for the soil movement for the terrace construction.Keywords: terraces, soil and water conservation, control of water erosion.Análise comparativa do desempenho de terraços mistos com terraços em nível e com gradiente RESUMO. O terraceamento de terras agrícolas consiste na prática mecânica mais difundida entre os agricultores no controle da erosão hídrica. O objetivo deste trabalho foi proceder a análise comparativa do desempenho de terraços mistos com terraços em nível e com gradiente. O dimensionamento de terraços em nível foi feito com base no volume de escoamento superficial, enquanto o de terraços com gradiente foi baseado na vazão máxima de escoamento superficial. Para o dimensionamento de terraços mistos são utilizados dois hidrogramas de escoamento superficial, sendo um para a determinação da capacidade de armazenamento do terraço e o outro para a estimativa da vazão que escoa na extremidade do canal do terraço. Assim, de maneira a conter e transportar o excesso de volume escoado, um valor adicional foi calculado e somado à altura do canal. Um estudo de caso foi realizado para condições de precipitação de Uberaba, Estado de Minas Gerais (Brasil), considerando eventos de precipitação com período de retorno de 10, 30 e 50 anos. Os resultados obtidos permitiram evidenciar, quantitativamente, que terraços mistos requerem menor altura do que os terraços em nível e maior que os com gradiente, o que traz consequências diretas na movimentação de terra para a construção dos terraços.Palavras-chave: terraços, conservação de água e solo, controle da erosão hídrica.

Effects of terracing practices on water erosion control in China: A meta-analysis

“…The dimensions of level terraces are determined based on the surface runoff volume, and the sizes of sloped and zig terraces are based on the maximum runoff flow rate. The dimensions of slope-separated terraces are determined by considering two surface runoff hydrographs; one hydrograph is used to determine the terrace capacity, and the other hydrograph is used to estimate the flow rate at the extremity of the terraces (de Oliveira et al, 2012). Maintained embankments of terraces in northern China are vital for water erosion control and have been reported to reduce runoff and sediment yield by 20%-45% and 31.5%-71.2%, respectively (Cai, 2004;He et al, 2008).…”

“…The GeoWEPP model when applied to forest and orchard lands in southeastern China, predicted that terracing would decrease runoff by 44.7% and 61.1%, respectively, and sediment yield would decrease by 43.7% and 68.6%, respectively . The terracing of croplands is the most widespread engineering practice used by farmers for controlling erosion (de Oliveira et al, 2012). Generally, agricultural terracing systems are efficient for controlling water erosion when proper cultivation and management are used (Liu et al, 2011b;Mai et al, 2013).…”

Viabilidade Econômica Do Uso De Trator/Implementos Agrícolas Na Construção De Terraços

“…Terracing is a mechanical practice used to control water erosion that, according to Oliveira et al (2012), is the most widespread practice among farmers.…”