  We investigate the conditions that facilitate galactic-scale outflows using a
sample of 155 typical star-forming galaxies at $z$~2 drawn from the MOSFIRE
Deep Evolution Field (MOSDEF) survey. The sample includes deep rest-frame UV
spectroscopy from the Keck Low-Resolution Imaging Spectrometer (LRIS), which
provides spectral coverage of several low-ionisation interstellar (LIS) metal
absorption lines and Ly$\alpha$ emission. Outflow velocities are calculated
from the centroids of the LIS absorption and/or Ly$\alpha$ emission, as well as
the highest-velocity component of the outflow from the blue wings of the LIS
absorption lines. Outflow velocities are found to be marginally correlated or
independent of galaxy properties, such as star-formation rate (SFR) and
star-formation rate surface density ($\Sigma_{\rm SFR}$). Outflow velocity
scales with SFR as a power-law with index 0.24, which suggests that the
outflows may be primarily driven by mechanical energy generated by supernovae
explosions, as opposed to radiation pressure acting on dusty material. On the
other hand, outflow velocity and $\Sigma_{\rm SFR}$ are not significantly
correlated, which may be due to the limited dynamic range of $\Sigma_{\rm SFR}$
probed by our sample. The relationship between outflow velocity and
$\Sigma_{\rm SFR}$ normalised by stellar mass ($\Sigma_{\rm sSFR}$), as a proxy
for gravitational potential, suggests that strong outflows (e.g., > 200 km
s$^{-1}$) appear ubiquitous above a threshold of log($\Sigma_{\rm
sSFR}/\rm{yr}^{-1}\ \rm{kpc}^{-2}$) ~ -11.3, and that above this threshold,
outflow velocity uncouples from $\Sigma_{\rm sSFR}$. These results highlight
the need for higher resolution spectroscopic data and spatially resolved
imaging to test the driving mechanisms of outflows predicted by theory.
