  We describe a simulation for the distribution of galaxies focusing on the
atomic Hydrogen content. We aim to make predictions for surveys of galaxies
using the redshifted 21 cm line emission. We take the expected distribution of
HI masses, circular velocities, sizes of galaxies and orientations into account
for this simulation. We use the sensitivity of ASKAP and MeeKAT radio
telescopes to estimate the number of detections of HI galaxies in upcoming
surveys. We validate our simulation with earlier estimates carried out by using
some of these considerations. We show that unlike earlier simulations that take
some of the factors into account, the predicted number of galaxies and their
distribution across masses changes significantly when all of these are
accounted for. We describe our predictions for the MIGHTEE-HI and WALLABY
surveys for blind detection of galaxies using the redshifted 21 cm radiation.
We study the dependence of the predicted number of detections on the HI mass
function. We also describe our future plans for improving the simulation.
