Review of selected documents related to flooding at city of Salisbury facilities on the Yadkin River upstream from High Rock Dam, North Carolina
Open-File Report 2007-1314
By Jerad D. Bales
Abstract
This report documents a review of the hydraulic and
sediment-transport models developed by the City of Salisbury,
Alcoa Power Generating, Inc., and the Federal Energy Regulatory
Commission to address issues of flooding and sedimentation in the
vicinity of Salisbury.s water-supply intake 19.4 miles upstream from
High Rock Dam. The objective of the review was to determine if the
modeling results submitted by Salisbury clearly demonstrate that the
presence of High Rock Dam has led to an increase in water levels at
Salisbury facilities or, conversely, if the documents of Alcoa Power
Generating, Inc., demonstrate that High Rock Dam has not had an effect
on water levels at Salisbury facilities. No new data were collected as
a part of the review, and the models developed by involved parties were
not tested during the review. Some historical discharge-measurement
notes and previously published reports were checked as part of the
review.
The one-dimensional hydraulic modeling results submitted by Alcoa
Power Generating, Inc., did not assess the effects of changes in
bathymetry on changes in flood levels at Salisbury.s facilities because
pre-impoundment conditions were not simulated. Hydraulic modeling
performed by consultants for the City of Salisbury seems to indicate
that both the presence of the dam in the absence of any post-impoundment
sedimentation and changes in bathymetry between pre-impoundment and 1997
conditions have resulted in increased water levels relative to
pre-impoundment conditions at Salisbury facilities on the Yadkin River
for a fairly wide range of flows. The degree to which the dam and the
changes in bathymetry have affected flood levels at the Salisbury
facilities relative to pre-impoundment conditions is open to discussion
because of uncertainty in topographic/bathymetric data and the absence
of calibration and sensitivity testing of the hydraulic models. None of
the three hydraulic models appears to have been calibrated to or tested
against measurements, and no sensitivity testing was reported.
Sediment-transport modeling results submitted by the City of Salisbury
were calibrated, well documented, and provide a good understanding of
the expected growth of the sediment delta in the upper end of High Rock
Lake. Simulations made using this model seem to have demonstrated that
the presence of the dam and the growth of the delta have resulted in
increases in water-surface elevations at Salisbury.s facilities over a
range of flows and that these increases are expected to increase through
time if current conditions remain unchanged.
Citation:
Bales, J.D., Review of selected documents related to flooding at city of Salisbury facilities on the Yadkin River upstream from High Rock Dam, North Carolina, September 2007: U.S. Geological Survey Open-File Report 2007-1314, 9 p.
For more information, contact |
|
North Carolina Water Science Center
U.S. Geological Survey
3916 Sunset Ridge Road
Raleigh, North Carolina 27607
(919) 571-4000
E-mail
|
|
|