Avaliação do desempenho hidráulico de dois sistemas pilotos de drenagem subterrânea usando manilhas de barro, no perímetro irrigado de Sumé-Paraíba.

Abstract

The problems of the underground water table in irrigated áreas have demonstrated the necessity of field studies especially to obtain parameters and the establishment of drainage criterion. This present work shows the results of the experimental studies developed in two pilot systems of subsurface drainage with clay pipes (10 cm internai diameter) in field conditions. The studies were carried out in sectors 23 and 33 of the irrigated perimeter of Sumê", Para Tb a-Brazil, having as principal objectives the de termination of parameters of drainage necessary to the planning of the systems, applicable in large áreas with similar general characteristics and to evaluate the performance of the systems. The soils of both sectors are alluvial introphic, with profile sufficiently hete rogeneous , rep resentati ve standard of most of the soils of that region. The tests consisted of simultaneous measurement of the depth of the underground water table and the rate of discharge at the end of the underground drain lines. The parameters of drainage were obtained from graphic processes to the condition of permanent f low (eq uat i on of Hooghoudt) and variable flow (equation of Gover-Dumm ) having occured a significant difference in the comparative results. (KHoophoudt * 2,5 the 5 ti mes-Kq, ove r_ Dumm) . The averageof apparent hydraulic transmissivity of the purtion"A" (Sector 23) demonstrated about three times more than portion "B" (Sector 33); demonstrating considerable differences between the real' spaci ngs required. The performance of the systems was evaluated by the entrance resistance, hydraulic entrance load (as a singular vaiue and fraction of the total load) and an analysis of the process of the lowering of the underground water levei, establishing a drainagem criterion. The values obtained at the entrance resistence in terms of probabilities showed a regular performance in both systems, ( re z 2 >3 days.m ^), wh i 1 e by linear regression both had a good performance (rg m-x=l .Oday.m 1). The hydraulic entrance load (1.6 and 35cm) and the relation h /h (- 0,57) we re elevated, characterizing imperfection in the performance of the systems or a peculiarity to alluvial soils of the studied sectors. In terms of the lowering of the underground water levei, a lowering of 50cm was observed in a period of iess than three days, satisfying the established criterion. The experimental equations obtained (condition of variable flow) demonstrated that the tested spacing was overestimated in 23 and 66% while the equation of Glover-Dumm, at the beginning, overestimated the spacings in relation to the experimental (11 and 36%, respectively to systems "A" and "B") .