  In a draining rotating fluid flow background, surface perturbations behave as
a scalar field on a rotating effective black hole spacetime. We propose a new
model for the background flow which takes into account the varying depth of the
water. Numerical integration of the associated Klein-Gordon equation using
accessible experimental parameters shows that gravity waves in an appropriate
frequency range are amplified through the mechanism of superradiance. Our
numerical results suggest that the observation of this phenomenon in a common
fluid mechanical system is within experimental reach. Unlike the case of wave
scattering around Kerr black holes, which depends only on one dimensionless
background parameter (the ratio $a/M$ between the specific angular momentum and
the mass of the black hole), our system depends on two dimensionless background
parameters, namely the normalized angular velocity and surface gravity at the
effective black hole horizon.
