  The problem of determining the threshold of motion of a sediment particle
resting on the bed of an open channel has historically been dominated by an
approach based on the time-space-averaged bed shear stress (i.e. Shields
criterion). Recently, experimental studies have promoted an alternative
approach to predict the dislodgement threshold, which is based on the impulse
of the flow-induced force. Nonetheless, theoretical analyses accompanying these
studies result in complex expressions that fail to provide a direct estimate of
said impulse threshold. We employ the work-energy principle to derive a
prediction of the fundamental impulse threshold that the destabilising
hydrodynamic force must overcome in order to achieve full particle
dislodgement. For the bed configuration studied, which is composed of spheres,
the proposed expression depends on the mobile particle's size and mass, and
shows excellent agreement with experimental observations previously published.
The derivation presented in this paper may thus represent a robust theoretical
framework that aids in the re-interpretation of existing data, as well as in
the design of future experiments aimed at analysing the importance of
hydrodynamic impulse as criterion for prediction of particle dislodgement.
