THEORY OF PIPE DRAINAGE ASSISTED BY MOLE DRAINAGE. DISCUSSION AND CLOSURE

A discussion of a paper with the aforementioned title by H.M. Hathoot, published in this journal (Volume 124, Number 2, March/April 1998), is presented. The discusser maintains that the author's use of the steady problem solution for calculation of water-table drawdown, the corresponding design of drain spacing, and optimization of the mole drain array step are interesting, both practically and mathematically. He questions, however, the assumption of the existence of infinitely high depth of soil above the drain arrays. He maintains that employment of sinks requires a posteriori expressions of the depth of the drain through the depth of the sink and that generally, the two depths do not coincide. In application to the flow pattern, he believes it is unclear for what stages of decrease of the water table the half-sink approximation is valid. Finally, he contends that optimization of drain spacing did not include precise formulation of the mathematical problem. Discussion is followed by closure from the author.