# Screen theory for wells and soil drainpipes

## Abstract

A theoretical solution is given for steady flow in a confined aquifer to a well tube having equally distributed screens. It is shown, quantitatively, by use of Darcy's law and Laplace's equation, that more flow results if a given total length of screen is utilized in a number of sections over the full length of the well tube than if the given length of well screen is all used at the bottom of the tube. For a pumped well of 0.25-ft radius, 200-ft radius of influence, 50-ft thickness of aquifer, and 25-ft length of screen the use of the screen in five 5-ft-long sections equally distributed over the well tube results in 25% more well how than if the 25-ft length of screen is all in one piece at the lower 25 ft of the aquifer. If the screen is used in ten 2.5-ft sections rather than in the single 25-ft length, the increase will be 33%; and for an ‘infinite’ number of sections (the 25 ft of the 50-ft well pipe still being impervious) the flow increase will be 45%. It is shown that the basic theory also applies to seepage flow to the joints between individual lengths of drainpipes used in land drainage. The results are presented in tables and graphs having dimensionless parameters so that the flow for a particular flow system may be found in any units. Mathematically, the problem is of the mixed boundary value type.