New experimental results at the onset of turbulence in a gravity-drive
n pipe flow are presented, and a simple phenomenological model is intr
oduced to describe the intermittent behavior observed. In this model s
lugs are stochastically produced at the pipe inlet, and the decrease i
n velocity due to turbulent friction is taken into account. The presen
t approach shows that stochastic arguments account well for several ex
perimental observations at low intermittency factors. In particular, i
t is shown that special intermittency routes to chaos are not needed t
o explain the exponentially decaying inverse cumulative distribution o
f laminar times.