Lake Hickory, North Carolina-- Analysis of ambient conditions and simulation of
hydrodynamics, constituent transport, and water-quality characteristics, 1993-94
Water-Resources Investigations Report 98-4149
By J.D. Bales and M.J. Giorgino
Full Report (PDF, 71 pages, 20 Mb)
From January 1993 through March 1994, circulation patterns and water-
quality characteristics in Lake Hickory varied seasonally and were
strongly influenced by inflows from Rhodhiss Dam. The upper, riverine
portion of Lake Hickory was unstratified during much of the study
period. Downstream from the headwaters to Oxford Dam, Lake Hickory
thermally stratified during the summer of 1993. During stratification,
releases from Rhodhiss Dam plunged beneath the warmer surface waters
of Lake Hickory and moved through the reservoir as interflow. During
fall and winter, Lake Hickory was characterized by alternating periods
of mixing and weak stratification.
Water-quality conditions in the headwaters of Lake Hickory were
largely driven by conditions in water being released from Rhodhiss
Dam. In general, water clarity increased, and concentrations of
suspended solids, phosphorus, and summertime chlorophyll a decreased
in a downstream direction from the headwaters of Lake Hickory to
Oxford Dam. Two chlorophyll a samples from the upper portion of Lake
Hickory exceeded the North Carolina water-quality standard of 40
micrograms per liter during the investigation. Downstream from the
headwaters, dissolved oxygen was rapidly depleted from Lake Hickory
bottom waters beginning in May 1993, and anoxic conditions persisted
in the hypolimnion throughout the summer. During summer stratification,
concentrations of nitrite plus nitrate, ammonia, and orthophosphate
were low in the epilimnion, but concentrations of ammonia near the
bottom of the reservoir increased as the hypolimnion became anoxic.
Concentrations of fecal coliform bacteria exceeded 200 colonies per
100 milliliters in only one of 60 samples collected from Lake Hickory.
In contrast, concentrations of fecal coliform bacteria exceeded 200
colonies per 100 milliliters in 40 percent of samples collected from
the Upper Little River, and in 60 percent of samples collected from
the Middle Little River, two tributaries to Lake Hickory.
Load estimates for the period April 1993 through March 1994 indicated
that releases from Rhodhiss Dam accounted for most of the suspended
solids, nitrogen, and phosphorus entering the headwaters of Lake
Hickory. Loads of nitrogen and phosphorus from point-source discharges
were potentially important, but loads of suspended solids from these
discharges were insignificant relative to other sources.
The CE-QUAL-W2 model was applied to Lake Hickory from the U.S. Highway
321 bridge to Oxford Dam-a distance of 22 kilometers-and was calibrated
by using data collected from April 1993 through March 1994. During the
simulation period, measured water levels varied a total of 1.14 meters,
and water temperatures ranged from 4 to 31 degrees Celsius. The
calibrated model provided good agreement between measured and simulated
water levels at Oxford Dam. Likewise, simulated water temperatures
were generally within 1 degree Celsius of measured values; however,
water temperatures were oversimulated for the fall of 1993. Simulated
dissolved oxygen concentrations generally agreed with measurements;
however, the model tended to oversimulate dissolved oxygen
concentrations during the late summer and early fall. There was good
agreement between simulated and measured frequency of occurrence of
dissolved oxygen concentrations less than 4 milligrams per liter.
Simulations of tracer dye releases demonstrated the effects of
stratification on dilution and rate of transport in Lake Hickory.
Simulations were made of the effects of changes in nutrient loads
from inflows and from bottom sediments. A simulated 30-percent
reduction in inflow concentrations of orthophosphate, ammonia, and
nitrate at the U.S. Highway 321 bridge delayed the initial springtime
pulse of algal growth by about 2 weeks, but had little effect on
dissolved oxygen concentrations. Likewise, a reduction in the release
rate of orthophosphate and ammonia from bottom sediments had very
little effect on simulated algae and dissolved oxygen concentrations.
To simulate the effects of shoreline development on Lake Hickory water
quality, concentrations of orthophosphate, ammonia, and nitrate in
Snow Creek were increased to levels representative of streams
draining developed areas in Charlotte, N.C. Maximum simulated algae
concentrations increased about 100 percent relative to current
conditions, indicating that Lake Hickory may be sensitive to increased
nutrient loads into the middle reaches of the reservoir.
Bales, J.D., and Giorgino, M.J., 1998, Lake Hickory, North Carolina-Analysis of ambient conditions and simulation of hydrodynamics, constituent transport, and water-quality characteristics, 1993-94: U.S. Geological Survey Water-Resources Investigations Report 98-4149, 62 p.
For more information, contact
|North Carolina Water Science Center
U.S. Geological Survey
3916 Sunset Ridge Road
Raleigh, North Carolina 27607