Chemical and Water Quality Kinetic Characteristics and Processes - Hydro-Environmental Analysis: Freshwater Environments - page 383

Oxygen concentration (mg L -1 )
FIGURE 14.14 Vertical oxygen concentration proile for Bull Shoals Reservoir, Arkansas, on June 12, 2012.
(Based on online dissolved oxygen and temperature lake reports from the U.S. Army Corps of Engineers,
Little Rock District, Available at http://www.swl-wc.usace.army.mil/.)
Then, as the season progresses, and depending on the low and other conditions, the hypoxic zone
extends further down the reservoir toward the dam, as illustrated in Figure 14.16.
This trend is illustrated in Figure 14.17a and b using CE-QUAL-W2 model predictions for Lake
Lanier in Georgia by Martin and Hesterlee (1998). Lake Lanier is a warm monomictic reservoir,
impounded by Buford Dam on the Chattahoochee River in north-central Georgia (northeast of
Atlanta). The reservoir was initially constructed for hydropower, lood control, navigation, and for
streamlow regulation. As shown in Figure 14.17a and b, the oxygen depression in the upper portions
of the reservoir begins as early as March and then progresses down the reservoir, with much of the
deeper portions of the reservoir being anoxic during the summer months. The oxygen distribution is
impacted by inlows, wind mixing, and the operation of the hydropower facility. As cooling begins
in the late fall, the oxygen concentrations increase in the upper portions of the reservoir and the
bottom volume of the hypoxic water diminishes. The reservoir completely mixes usually in January.
Similarly, predicted for July 31, 1995, the spatial distributions of water temperature, water age,
chlorophyll-a, and DO concentrations are illustrated in Figures 14.18 through 14.21 for Lake Walter
F. George and Lake Allatoona in Georgia, both of which are warm monomictic systems. Lake Walter
F. George is located along the Georgia-Alabama border in the southern portion of both states, and is
managed for hydropower, navigation, and recreation. Lake Allatoona is one of the most frequently vis-
ited U.S. Army Corps of Engineers (“the Corps”) lakes in the nation, receiving more than 13 million
visitors each year and is located north of Atlanta. The Allatoona Dam is also operated for hydropower.
The predictions for Lake Walter F. George for this particular date demonstrate the impact of a
high-low event moving into the reservoir, so that the riverine zone extends a considerable distance
into the reservoir. This can be seen in the contours of the temperature and water quality constitu-
ents, but it is most apparent in the contours for water age. Recall that water age is a synthetic (model)
parameter that is used to estimate the residence time, which accumulates at a rate of 1.0 day -1 with
all “new” (boundary) water entering the system having an age of zero. So, by July 31, beginning
from January 1, the maximum possible age would be 212 days (365 days for the year). The event
illustrated (Figure 14.18b) that the “oldest” water for this date had been pushed to near the dam,