Saturated Water Storage in Shallow Perched Aquifer With
Evapotranspiration From the Phreatic Surface and Unsaturated Lacunae:
the Saint-Venant Theory Revisited
Abstract
Two models are compared for Darcian flows in a vadose zone and shallow
unconfined aquifer with an intensive evapotranspiration, common for
hyperarid climates. An analytical 2-D Dupuit-Forchheimer approximation,
in which the vadose zone is considered as a “distributed sink”
(similar to a standard “distributed source” which models recharge to
the water table in humid climates), is collated with HYDRUS3D. In a
planar domain, a vertically-averaged flow from a constant piezometric
head contour (seepage from ditches or trenches) is studied and integral
criteria (the volume of the saturated zone and the area of unsaturated
lacuna) are either evaluated or estimated by the Pòlya and Szegö
isoperimetric inequalities. Mixed BVPs for Richards’ equation in
cylindrical domains are numerically solved and give the pressure head,
moisture content, and velocity fields, streamlines and criteria.
Implicaitons for urban hydrology and ecohydrology of water logged
drylands are discussed.