RESUMO:A evapotranspiração de referência (ETo) é um importante parâmetro agrometeorológico, principalmente para planejamento e manejo de irrigação, mas, também, é considerada elemento climático de demanda hídrica, daí sua aplicação em estudos O método de Radiação Solar apresentou (r2=0,44; r=0,67; d=0,97 e c=0,65). O método de 42; r=0,65; d=0,97 e c=0,63). O método de Radiação solar apresentou os melhores parâmetros estatísticos, sendo o indicado em substituição ao método padrão para a região e período de estudo. PALAVRAS -CHAVE: manejo de irrigação, Penman-Monteith, demanda hídrica.

In this paper an experimental work was conducted to study the effect of a weir height and location in a main channel on the head and discharge of branching channel connected upstream the weir, with three differe a le a d he ed lo e of the main and branch channel was kept constant and it was equal to 0.0002 and 0.0005, respectively. A variable height weir was fixed in the main channel at different distance (60, 90 and 120 cm) downstream the branching point. For each location, seven different discharges were used, and for each discharge, the height of the weir was changed from 2 to 10 cm. The results of the research showed an existence branching and main discharges, and a similar relation between branch discharge and the weir height. It is also found that the ratio of discharge (the branch discharge divided by main discharge) increases with increasing weir height, and the magnitude of this decreases as the discharge increases. The result also ho ed ha he a le o a h ha el a e highest values for discharge ratio. The depth of water in the branch channel varies directly with the height of weir, and a maximum percentage of increases of depth observed in all experiments were 194%.