Irrigation Drainage System Problem

Background:

The irrigation system for the Spartan valley is to control the water table at a minimum of 3.5 ft below the ground surface.  This is done to prevent flooding in agricultural fields which can damage or completely destroy crops. The proposed solution is to create a system of 6ft. deep parallel ditches that ‘remove’ groundwater through surface seepage, such that the water table does not rise to a depth less than the minimum allowable depth (see below).   

It is known from a recent study that the transmissivity, T, of the alluvium deposits is 10⁴ ft²/day and the downward infiltration (return flow), ε, to the water table during the irrigation season is 0.01 ft/day. Borehole logs suggest that the aquifer is approximately 100 ft thick.

Problem 1

Using an analytical approach, estimate the maximum drain spacing that be used for the parallel ditch system. 

Problem 2

Develop a simple MAGNET numerical model to verify the analytical results. Consider the land elevation to be 0 ft.