  GRB030329 displays one clear and, possibly, multiple less intense fast-rising
($\Delta t / t \sim 0.3$) jumps in its optical afterglow light curve. The decay
rate of the optical light curve remains the same before and after the photon
flux jumps. This may be the signature of energy injection into the forward and
reverse shocked material at the front of the jet. In this study, we model the
Gamma-Ray Burst (GRB) ejecta as a series of shells of material. We follow the
dynamical evolution of the ejecta as it interacts with itself (i.e., internal
shocks) and with the circumburst medium (i.e., external forward and reverse
shocks), and we calculate the emission from each shock event assuming
synchrotron emission. We confirm the viability of the model proposed by
\citet{2003Natur.426..138G} in which the jumps in the optical afterglow light
curve of GRB030329 are produced via refreshed shocks. The refreshed shocks may
be the signatures of the collisions between earlier ejected material with an
average Lorentz factor $\bar{\Gamma}\gtrsim 100$ and later ejected material
with $\bar{\Gamma} \sim 10$ once the early material has decelerated due to
interaction with the circumburst medium. We show that even if the late material
is ejected with a spread of Lorentz factors, internal shocks naturally produce
a narrow distribution of Lorentz factors ($\Delta\Gamma/\Gamma\lesssim0.1$),
which is a necessary condition to produce the observed quick rise times of the
jumps. These results imply a phase of internal shocks at some point in the
dynamical evolution of the ejecta, which requires a low magnetization in the
outflow.
