The control of reservoir sedimentation through hydraulic flushing has
been employed in several parts of the world to sustain the useful stor
age capacity of the reservoirs. However, no comprehensive analysis has
been conducted to understand the sediment flushing processes. In this
study, laboratory experiments were performed to investigate the flush
ing processes during drawdown flushing, including outflow sediment dis
charge, characteristics of the flushing channel and flushing effective
ness. From both laboratory and field data, it is found that outflow se
diment discharge can be well related to a hydrauic parameter which is
a function of outlet discharge, water-surface gradient and flushing ch
annel width. It is also found that flushing efficiency increases drama
tically when retrogressive erosion emerges. A geomorphic relationship
is used to estimate the equilibrium width of the flushing channel. A 1
-D diffusion model presented herein is employed only to simulate the g
eneral trend of bed profile evolution and the amount of reservoir sedi
ment removal during flushing in order to evaluate the applicabilities
and limitations of this model. Simulated results of this diffusion mod
el agree well with laboratory data in a narrow flume (with essentially
1-D flow) with nearly uniform flow condition after rapid drawdown ope
ration. However, there is a 15% average error if this diffusion model
is applied to a wide reservoir (relative to the width of the flushing
outlet) as performed in our laboratory. A two-dimensional or three-dim
ensional model is needed to study flushing processes involving strong
lateral erosion in a wide reservoir.