What about the sediment?
When Congress approved Glen Canyon Dam it was clear
that sediment accumulation would force the decommissioning of the
dam within 200 years of its completion. The reservoir won't entirely
fill with sediment for 500 - 700 years, but because of significant
storage capacity losses and potential safety problems that will
materialize within the first 200 years, decommissioning will have
to occur much sooner.
In working to restore the Glen, the less sediment
that accumulates beforehand the better, which is why advocates are
calling for the restoration decision to be taken "now."
Although photo documentation and geomorphologic studies have indicated
that sediment will be rapidly flushed from the side canyons and
the main channel itself, some sediment will have to be removed manually.
The sooner this begins the better. Furthermore, the level of pollution
and even radioactive material contained in this sediment will require
clean-up at some point, again reinforcing the need to act quickly.