  This study presents a method for approximating the multidimensional effects
of Rayleigh-Taylor instability as a modification of the one-dimensional hydro
equations. This modification is similar to the Shakura-Sunyaev {\alpha}
prescription for modeling the coarse-grained effects of turbulence in
astrophysical disks. The model introduces several dimensionless tunable
parameters that are calibrated by comparing with high-resolution
two-dimensional axisymmetric numerical calculations of Rayleigh-Taylor unstable
flows. A complete description of the model is presented, along with a handful
of test problems that demonstrate the extent to which the one-dimensional model
is able to reproduce multidimensional effects.
