Abstract. We present a new conceptual scheme of the interaction
between unsaturated and saturated zones of the MOBIDIC (MOdello Bilancio
Idrologico DIstributo e Continuo) hydrological model which is applicable to
shallow water table conditions. First, MODFLOW was coupled to MOBIDIC as the
physically based alternative to the conceptual groundwater component of the
MOBIDIC–MODFLOW. Then, assuming a hydrostatic equilibrium moisture profile
in the unsaturated zone, a dynamic specific
yield that is dependent on the water table level was added to MOBIDIC–MODFLOW, and calculation of the groundwater
recharge in MOBIDIC was revisited using a power-type equation based on
the infiltration rate, soil moisture deficit, and a calibration parameter linked
to the initial water table depth, soil type, and rainfall intensity. Using
the water table fluctuation (WTF) method for a homogeneous soil column, the
parameter of the proposed groundwater recharge equation was determined for
four soil types, i.e. sand, loamy sand, sandy loam, and loam under a pulse of
rain with different intensities. The fidelity of the introduced
modifications in MOBIDIC–MODFLOW was assessed by comparison of the simulated
water tables against those of MIKE SHE, a physically based integrated
hydrological modelling system simulating surface and groundwater flow, in
two numerical experiments: a two-dimensional case of a hypothetical
watershed in a vertical plane (constant slope) under a 1 cm d−1 uniform
rainfall rate and a quasi-real three-dimensional watershed under 1 month
of a measured daily rainfall hyetograph. The comparative analysis confirmed
that the simplified approach can mimic simple and complex groundwater
systems with an acceptable level of accuracy. In addition, the computational
efficiency of the proposed approach (MIKE SHE took 180 times longer to solve
the three-dimensional case than the MOBIDIC–MODFLOW framework) demonstrates its
applicability to real catchment case studies.
Evaluation of water table fluctuations and drainage discharge of bi-level drainage system in a layered soil
