Effects of Perforation Geometry on Pipe Drainage in Agricultural Lands

Abstract

Corrugated high density polyethylene pipes, where groundwater enters through perforations on the pipe wall, are widely used in subsurface drainage systems on agricultural lands. There has been a growing interest in using circular holes in the valleys of corrugated pipes to improve the hydraulic performance of subsurface drains. However, the effects of these circular perforations on the entrance resistance (αe), delivery ratio (Q/Q0), drain spacing, and water table drawdown have not been adequately investigated for corrugated pipes. This study uses a numerical model, calibrated with datasets from sand tank experiments, to simulate the effects of perforation shape, size, and configuration on αe and Q/Q0. The results show that Q/Q0 in corrugated pipes with circular holes is 20% lower than that for plain wall pipes with the same perforation configuration. Perforations shaped as rectangular slots have half the αe of circular holes with the same surface area. It is concluded that the use of rectangular slots is hydraulically more advantageous than circular holes in the valleys of corrugated pipes.