The energy balance of ground water (groundwater) flow developed by Oosterbaan, Boonstra
and Rao (1994) (see reference), and used for the groundwater flow in unconfined aquifers, is
applied to subsurface drainage by pipes or ditches with the possibility to introduce
entrance resistance and/or (layered) soils with anisotropic hydraulic conductivities.
Owing to the energy associated with the recharge by downward percolating water, it is found
that use of the energy balance leads to lower water table elevations than when it is ignored.
The energy balance cannot be solved analytically and a computerized numerical method is
needed. An advantage of the numerical method is that the shape of the water table can be
described, which was possible with the traditional methods only in particular situations,
like drains without entrance resistance, resting on an impermeable layer in isotropic soils.
Examples are given of effects of varying drainage and soil conditions on the drain spacing
and the level/depth of the water table.
& case studies
Shape of the water table in anisotropic soil
The energy balance equation can be solved numerically for quifers consisting of several layers with anisotropic hydraulic conductivity.
In addition the presence of pipe drains or open ditches can be accounted for.
The water table is flat midway between the drains (at half the distance of the drain spacing), elsewhere it is curved.