Previous issues of “Our Water Our Future” have assessed why dredging was not included
in the water supply plan and how this community is already among the most efficient users
of water on a per capita basis in all of Virginia. What about the Norris Plan’s suggestion
that we can build onto the
existing dam and adjust the
size of the pipeline to shrink the
height of the dam we build?
Since Norris outlined his proposal
in February, a national panel of dam
experts has expressed “significant
concerns” about any effort to build
a new spillway or to repair the 1908
Lower Ragged Mountain Dam if it
would disturb the existing abutment
with new construction.
One of the dam experts said
that while construction could be
done on the existing dam, there would have to be significant draining of the reservoir to
safely facilitate the work. Lowering the water level at Ragged Mountain would shrink the
community’s existing storage capacity dramatically and put the water supply at significant
risk in the event of another drought. The consulting firm HydroLogics reported in July 2009
that the reservoir’s water level should not be lowered by more than ten feet during any
construction to avoid a water supply “system failure” in a severe drought.
The RWSA also agreed, as requested by City Council, to seek a study of the pipeline
size to see if that could impact the height of the new Ragged Mountain Dam. In the same
HydroLogics report, it was revealed that the size of the pipeline has no bearing on the
amount of storage needed at Ragged Mountain. The firm concluded that the full height of the
proposed Ragged Mountain Dam was required to meet water demand in 2055. It turns out
not to be a question of how fast you can fill Ragged Mountain, but rather how much
storage is available to fill.
Given that the Ragged Mountain Dam design is going to be reassessed by a new engineering
firm, there does seem to be a consensus that we have some time to re-evaluate certain aspects
of the water supply plan. For example, revisiting the cost and practicality of dredging with the
new feasibility study may provide the community data that could lead to recommendations for
construction of a somewhat smaller dam (by 5 to 15 feet) at Ragged Mountain.
The next and final issue of “Our Water Our Future” will summarize where we go next as a
community to build a safe and sufficient water supply.
This illustration shows the impact of different dam heights at Ragged Mountain. Alternatives that would
lower the dam height by 15 feet would save an estimated 46 foot strip of land along the shoreline (the
area of darkest blue, the outer band, in illustration above).
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