🚀 go-pugleaf

In <rpenny-ya023580001402971517370001@nntp.ix.netcom.com>
rpenny@ix.netcom.com (Richard Penny) writes: 
>
>
>I would also reference an article by Nancy Vogel in the January 29th
>Sacramento Bee, titled "Storm Debris Shrinks Folsom Lake Space." The
>article points out that silt introduced in the 1986 high water event
shrank
>Folsom reservoir's capacity from 1.01 million acre-feet to 9.77
million
>acre-feet.

I presume you mean shrunk to 977,000 acre-feet.

I do not have the data to either confirm or dispute this, but such
deposition is within what is possible.  In any case, so what?

Multipurpose projects are usually designed with a certain amount of
"dead storage" below the lowest outlets, sized to contain the sediment
expected sediment over the project lifetime, often considered to be 100
years.  If Folsom is behaving in the designed manner, I say again, so
what? and also What is the problem?. (I am not in a position to state
that Folsom is indeed behaving in the designed manner, since I do not
have that data.)  It does not matter to the operation of a project
whether water or sediment occupies dead storage.  There are no
facilities to extract either water or sediment from the dead storage at
any reservoir. 

At the end of the design life of a water project (again, usually 100
years), major rehabilition costs are expected to be incurred.  Such
costs and rehabilitation can include sediment dredging and disposal (in
a manner that meets then current environmental requirements for such
disposal).  Dams can also be designed with low level sluices to pass
sediment (It is too bad that the Russians did not design the High Aswan
Dam this way.)  Such sluices have been successfully used throughout the
world for many years.  A good recent U.S. example is the Cowlitz Falls
Project in Washington State.  A good technical reference on the design
and performance of sediment management facilities is:

"Sediment Management and Erosion Control on Water Resources Projects",
the syllabus for the 15th Annual USCOLD Lecture Series, which was held
in San Francisco in 1995.  Copies can be purchased from the USCOLD
office in Denver.  USCOLD = U.S. Committee on Large Dams

Many of the examples of silted California reservoirs cited by various
authors in this thread are small reservoirs behind diversion dams. 
These dams maintain head for diverting portions of flow into power
tunnels and/or penstocks for hydroelectric plants, our only large
scale, non-polluting source of electricity.  The siltation of such a
reservoirs is not a problem relative to its purpose.

As the above should demonstrate, the fact of siltation is real, but is
not necessarily a problem from the point of view of operations. 
"Problem" is here defined as something that causes a project to be
outside of its design parameters.  Mr. Powell was indeed correct when
he stated that siltation is not a problem in large Sierra reservoirs. 
He did not deny, as I recall, that siltation occurs.

Warren J. Paul, P.E.
Dam Engineer and Proud of it!