  The dynamics of the avalanche width in the evolution model is described using
a random walk picture. In this approach the critical exponents for avalanche
distribution, $\tau$, and avalanche average time, $\gamma$, are found to be the
same as in the previous mean field approximation but SOC appear at
$\lambda_{critical}=2/3$, which is very close to numerical value. A continuous
time random walk is studied numerically as a possible way to reconstruct in
simpler concepts the evolution model.
