Sedimentation of reservoirs has its negative impacts on dams,
first by reducing useful storage, altering the benefit/cost ratio originally
calculated for the dam, and second by reducing the damsí capacity for flood
routing; increasing flooding hazards on the dam itself and for the downstream.
More problems can be created by sediments and floating debris during floods on
outlet structures by clogging them and thus creating dangerous situations, or
damage trash screens leading to even more problems. If these debris and coarse
sediments are allowed in, then they may damage dam structures such as gates,
spillways intakes in addition to chutes, stilling basins and power penstocks by
the mechanical abrasion impacts of such sediments on them. Frequent
inspections, especially after floods must be made to ensure proper functioning
of such structure and take actions for reducing the damage. In small
reservoirs, dredging; although it adds to maintenance cost, may ease the
problem, but in very large reservoirs, this may prove unpractical. Designers,
therefore, have a duty to consider sedimentation problem seriously in the
initial stages of design by: checking the anticipated accumulation of
sediments, allowing enough storage free from siltation, foreseeing their
negative impacts on intakes and outlet structures and taking design measures to
reduce these impacts. At the same time, dam stability calculations shall have
to provision for the anticipated new conditions of silting up at the face of
the dam. Operators of dams, on the other hand, shall have to keep open eyes for
all the negative issues created by sediments and floating debris, repairing
damages caused by them and take measures to reduce their impacts in the future.
siltation, benefit/cost ratio, flood routing, debris, trash screens, penstocks.