WATER POLLUTION CONTROL RESEARCH SERIES • 16080 —10/70
INDUCED HYPOLIMNION AERATION FOR WATER QUALITY
IMPROVEMENT OF POWER RELEASES
ENVIRONMENTAL PROTECTION AGENCY
WATER QUALITY OFFICE
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about our cover
The cover illustration depicts a city in which rnan t s activities coexist
in hannony with the natural environment. The Water Quality Control
Research Program has as its objective the development of the water
quality control technology that will Irmke such cities possible. Previously
issued reports on the Water Quality Control Research Program include:
Report Number Title/Author
16O8ODRX 1O/69 Stratified Reservoir Currents; by Oregon State Univ.,
Corvallis, Ore.
16080—06/69 Hydraulic and Mixing Characteristics of Suction Mani-
folds; by Univ. of Wash., Seattle, Wash.
16080-——lO/69 Nutrient Removal from Enriched Waste Effluent by
the Hydroponic Culture of Cool Season Grasses; by
Jas. P. Law. Robt. S. Kerr Water Res. Ctr., Ada, C)kla.
16O8O—u/69 Nutrient Removal from Cannery Wastes by Spray Irriga-
tion of Grassland; by Robt. S. Kerr Water Res. Ctr.,
Ada, Okia.
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INDUCED HYPOLIMNION AERATION FOR WATER QUALITY
IMPROVEMENT OF POWER RELEASES
by
Lowell E. Leach, Research Hydraulic Engineer
William R. Duffer, Ph. D., Research Aquatic Biologist
Curtis C. Harlin, Jr., Sc. D., Chief
Water Quality Control Research Program
Robert S. Kerr Water Research Center
South Central Region
Ada, Oklahoma
for the
WATER QUALITY OFFICE
ENVIRONMENTAL PROTECTION AGENCY
Program #16080
October 1970
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402 - Price 50 cents
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EPA REVIEW NOTICE
This report has been reviewed by the Environmental
Protection Agency and approved for publication. Ap-
proval does not signify that the contents necessarily
reflect the views and policies of the Environmental
Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or
recommendation for use.
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ABSTRACT
Summer stratification in reservoirs creates large volumes of poor quality
water below the thermocline. Conventional hydraulic structures in most
dams withdraw low—flow releases and power releases from the hypolimnion
resulting in serious degradation in long reaches of streams below these
dams. A technique for improving the quality of power releases without
costly modification of existing outlet works is presented. Induced aeration
of the hypolimnion was tested in Eufaula Reservoir during the summer of
1968. Dissolved oxygen transfer efficiency of the aeration system ranged
from 1.8 to 3.0 pounds of dissolved oxygen per horsepower—hour of expended
energy resulting in an operating cost of 4.10 to 6.25 dollars per thousand
pounds of oxygen incorporated in the power releases. Research needs for
development of the induced aeration system are discussed.
1
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TABLE OF CONTENTS
Section Page
I. Introduction • i
II. Procedures and Equipment 5
III. Evaluation 11
IV. Discussion 15
V. Acknowledgments 29
VI. References 31
111
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LIST OF FIGURES
Figure Page
1. Eufaula Reservoir——Vicinity Map 3
2. Project Location Map 6
3. Temperature Distribution, August 2, 1968 8
4. Dissolved Oxygen Stratification, August 2, 1968 9
5. Comparison of Stratification and Induced Aeration Effects at
Station 1 12
6. Eufaula Dam Power Discharge Schedule 14
7. Comparison of Natural Aeration and Maximum Induced Effect on
the Central Pool 16
8. Effect of Aeration on Power Release 17
9. Effect of Aeration Without Power Release 18
10. Effect of Aeration During 4,000 cfs Power Release 19
11. Effect of Aeration During 8,000 cfs Power Release 20
12. Effect of Aeration During 12,000 cfs Power Release 21
13. Increase of Dissolved Oxygen in 4,000 cfs Power Release
Periods During Reservoir Induced Aeration 23
14. Increase of Dissolved Oxygen in 8,000 cfs Power Release
Periods During Reservoir Induced Aeration 24
15. Increase of Dissolved Oxygen in 12,000 cfs Power Release
Periods During Reservoir Induced Aeration 25
V
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LIST OF TABLES
Table Page
1. Background Monitoring Data 5
2. Oxygenation Capacity for Various Aeration Systems . . . . 28
vii
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SU 1NARY
During the summers of 1967 and 1968, induced aeration research was
conducted in Eufaula Reservoir in eastern Oklahoma. The first summer’s
work was the pilot study of aeration research by the Robert S. Kerr Water
Research Center and was the first destratification research conducted in
a very large reservoir. The pilot—study research was the first attempt to
determine the limiting effects of a particular sized aeration—distribution
system centrally located in a large body of water where effects are un—
confined. The details of the 1967 researcl) are reported in Pilot Study
of Dynamics of Reservoir Destratification.’ 7 The second year’s research,
which this report details, was a follow—up study of the 1967 pilot study.
The design of the aeration system used in the 1968 study was based
on the results of the 1967 study. The compressor was located on Eufaula
Dam because of its size and weight and the availability of an adequate
power supply. Confpressed air was piped to the distribution system located
on the reservoir bottom about 750 feet upstream. Advantage was taken of
the location of the distribution system to measure not only the outward
expansion of aeration effects in the hypolimnion and upstream limits of
aeration effects but also the effects of hypolimnion aeration on downstream
power releases.
Since the study of hypolimnion effects on power releases was con-
ducted during a period of unaltered normal power release schedules, previously
established by the U. S. Army Corps of Engineers and the Southwest Power
Administration, the most ideal aeration test conditions were not possible.
However, care was taken to coordinate the time of the aeration test and
monitoring periods with periods of stable power discharge in order to collect
the most reliable data possible.
It was found that induced aeration of the hypolirnnion immediately
upstream of power penstock intakes is a very effective, low—cost method
of increasing dissolved oxygen in downstream releases. Without supplemental
aeration, dissolved oxygen is slightly increased in downstream releases
during normal power operation by the entrainment of waters of higher dis-
solved oxygen concentrations in the upstream flow net from the epilimnion.
However, dissolved oxygen was greatly increased in the upstream flow net for
each incremental increase In power discharge by upstream hypolimnion aeration.
Statistical analysis of data collected during aeration test showed that
dissolved oxygen was increased in downstream releases between 55 and 80
percent (depending on the discharge rate) above the concentration during
static stratified conditions.
In comparison with other methods tested in recent years, this technique
had equal or greater oxygenation efficiencies (expressed in poun of oxygen
added per horsepower—hour of energy used) than most other systems. Since
an electrically driven compressor can be used in this type of aeration
ix
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system and electrical power is usually available at each dam, there is an
opportunity to utilize this technique in most power—producing reservoirs
at minimal cost. Installation of an aeration system similar to the one
studied would require no modification of outlet works or loss in efficiency
of the existing power equipment.
x
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RECONNENDATIONS
It is recommended that induced aeration of hypolimnion waters be
further studied in reservoirs of various depths during extreme stratification.
Further research should be planned in detail and conducted at reservoirs
where the power discharge schedule can be modified in such a way that each
discharge rate of an array of power discharge rates could be held constant
for several days during continuous induced aeration. Rigid control of
power discharge conditions will allow the stability necessary for very
accurate measurements of aeration effects for each rate of power discharge.
Tests should be conducted in a number of reservoirs, each with different
physical conditions. Study situations should be varied with respect to
depth of stratification, depth of reservoir, and chemical concentrations
in the hypolimnion. The aeration system should be placed at different
points upstream of the dam and tested with a range of air volumes at each
placement. In this manner, the most efficient placement distances from
the power penstocks with respect to the air input can be determined. The
distribution system should be tested at various depths below the thermocline
at the position of optimum upstream placement. Other chemical parameters
in addition to dissolved oxygen should be measured in the power releases
immediately below the dam. Specifically, the nitrogen series, hydrogen
sulfide, biochemical oxygen demand (BUD), chemical oxygen demand (COD),
and phosphates should be measured throughout the aeration test periods.
When the system has been fully evaluated by this technique, it can
then be installed and demonstrated in any reservoir where water quality
problems exist in downstream releases.
xi
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SECTION I
INTRODUCTION
Nan in his quest to harness water by constructing dams behind which
water is impounded for power production, irrigation, flood control, navi-
gation, and other purposes has produced unanticipated results, some of
which are detrimental to his environment. As the movement of water is
retarded and streams are allowed to deepen, the natural reoxygenation
capability is reduced. The reduction of this capability becomes even
greater where waters have been allowed to become stilled as in lakes and
impoundments.
During summer months, deep lakes and impoundments develop the classic
“sandwich” of epilimnion—thermocline—hypolimnion, commonly known as thermal
stratification. (1 ) During early summer, the surface waters begin to warm,
as atmospheric temperatures increase, and a strata of less dense water is
formed above the cold bottom waters. As the surface strata pilimnion)
warms and is wind circulated, the thermocline or middle strata is developed
and acts much as a diaphragm preventing surface—induced circulation below
that depth. Since waters below the thermocline (hypolimnion) cannot be
reoxygenated, they soon become void of oxygen by chemical reduction proc-
esses and biological respiration, forming a stagnant mass. As dissolved
oxygen becomes depleted in hypolimnion waters, many deteriorating chemical
reactions also occur leaving the water mass high in hydrogen sulfide,
phosphates, nitrates, and various toxic metals.(l,2,3) Often, these changes
go unnoticed through the months of summer stratification, unless the water
is being used for public water supplies or is being released downstream
through low—level power generating outlet works or low-flow release gates.
Hypolimnion releases often cause downstream fish kills and are
hazardous to people in the area breathing the toxic hydrogen sulfide gases
released. Since the water is void or very low in dissolved oxygen it is
not useful for stream flow augmentation and high concentrations of undesirable
chemical compounds may be released into the streams.
In recent years, the increased public awareness of environmental
problems, the national demand for improved water quality, and requirements
for greater volumes of potable water have encouraged researchers to attack
the water quality problems arising from impoundment stratification.
Research in eliminating stratification has been primarily directed
toward testing various devices for circulation of the entire water mass in
small lakes. These devices range from mechanical pumps ( 4 ’ to various
types of diffused air releases and pure oxygen These
systems have primarily been evaluated by determining the rate of induced
oxygenation of the entire water mass in which they were installed, effi-
ciency of oxygen transfer in the entire water mass per unit of power input,
and observation of changes in various chemical parameters. Other research
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has been directed toward improving power and low—flow releases. Research
in this are inclkldes studies of multilevel outlet works for selective
withdrawal, 2 13) vented and forced air injection into power turbines,( - 4 )
submerged weirs upstream of power turbines, J 5,16) and various spray devices
attached to low—flow release structures such as the Howell—Bunger valve
tested by the Tennessee Valley Authority. Aeration effects of various
configurations and designs of stilling basin energy dissipaters have also
been studied. While it is true that a measure of correction of the down-
stream problems is possible with multilevel outlet works, submerged weirs,
vented power turbines and various other devices, the initial cost of in-
stallation is usually great. As a result, they have not been fully evalu-
ated to determine if they are economically justifiable when compared with
other methods of aeration. These structures are few and are not being
constructed extensively in problem reservoirs because of their cost, loss
of generating efficiency, and the uncertainty in achieving the desired
water quality effects.
In past years, most reservoirs constructed throughout the United
States were economically justified on the basis of benefits derived from
flood control, hydroelectric power, water supply, navigation, and more
recently recreation without regard for water quality either in the impound-
ment or its release. As a result, the present operation of many reservoirs
is dictated by the design of outlet works such that power releases and
flows withdrawn during summer stratification cause serious downstream
quality problems. Outlet works are located in some dams at levels where
it is virtually impossible to release anything but poor quality water during
the summer season. This has resulted in design and construction agencies
giving high priority to water quality considerations in their planning and
design phases of all new dams. However, the problem of poor quality releases
from existing structures must be corrected if streams and reservoirs in
river systems are to be significantly improved.
Little research has been conducted to determine the feasibility
of improving water quality by induced aeration immediately upstream of
existing power intake structures. The research described in this report
was an evaluation of the diffused aeration technique in storage reservoirs
to aerate hypolimnion waters withdrawn during power generation. The project
was conducted in 1968 at Eufaula Reservoir, a Corps of Engineers Reservoir
located in eastern Oklahoma.
Eufaula Reservoir, the largest reservoir in which aeration research
has been conducted, has a surface area of 102,500 acres and a storage of
2,800,000 acre—feet at power pool elevation 585 ft (Figure 1). The central
pool, where the major portion of the research was conducted, has a surface
area of 10,800 acres and a volume of abait 570,000 acre—feet at 585 feet
elevation.
2
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C hecotoh
foula
canadian
Enterprise
EUFAULA
RESERVOIR
d
p
Quinton
- — Featherston
210 2 4
Scale of Miles
MC Ales ter
CONTROL STATIONS —.
FIGURE I - EUFAULA
RESERVOIR VICINITY
MAP
3
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SECTION II
PROCEDURES AND EQUIPMENT
In January 1968, 17 sampling stations were located in the central
pool of Eufaula Reservoir by triangulation surveys (Figure 2). Vertical
profiles of temperature and dissolved oxygen were taken at 5—foot intervals
every two weeks during winter and spring to establish antecedent conditions
and to determine the progress of stratification. Two upstream stations
(Stations land 2 on Figure 1) which were outside the influence of the
aeration system were also monitored and used as control stations.
In addition to monitoring of the 17 reservoir stations, dissolved
oxygen and temperature of downstream power releases were also measured to
determine the influence of normal reservoir stratification on power releases.
Table 1 illustrates how the dissolved oxygen continued to be reduced in
the power releases while the temperature continued to increase during
development of stratification conditions.
TABLE 1
BACKGROUND MONITORING DATA
Date
Discharge
cfs
Dissolved Oxygen
mg/i
Temp— C
D.O. %
Saturation
July
5,1968
12,000
5.0
21.7
58.1
July
10,1968
12,000
3.8
23.0
44.9
July
18, 1968
8,000
3.4
23.5
40.8
July
25, 1968
8,000
3.0
24.0
35.7
August 2, 1968
8,000
3.0
24.0
35.7
Stratification was hampered during the spring months by unusually
heavy rainfall and unseasonably cool weather. During May and June, high
inflows resulted in the reservoir rising to a record elevation of 590.5
feet. At this elevation, it was necessary to release stored water through
the tainter gates, as well as through the power penstocks, for about 10
days. During these high releases, work on installation of the air distri—
bution system on the reservoir bottom, a short distance upstream of the dam,
had to be suspended for safety reasons, resulting in considerable delay.
These tremendous discharges, together with the large inflow, caused the
upstream turbid waters to move downstream from the upper reaches of the
reservoir, engulfing the central pool. This movement of water through
the reservoir mixed the central pool and slowed stratification.
5
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Texanna
Scale of Miles
FIGURE 2 — PROJECT LOCATION
EUFAULA RESERVOIR
CENTRAL POOL
•l0
-x-
Engineers
Project
Office
Enterprise
•—BUOY STATIONS
MAP
6
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Stratification finally began in mid—July, and a weak thermal
stratification pattern became stable by the end of July. Figure 3 shows
temperature profiles for stations in the central pool on August 2, just
prior to initiation of aeration. Because of the unusually large flow
through the reservoir, the “classical” temperature profiles did not develop.
There was, however, an identifiable thermocline between the 30— and 40—foot
depths. This compared with a thermocline depth in 1967 of about 25 feet
which was well established at the end of June when the first measurements
were made.
The dissolved oxygen profiles for the central pool on August 2 are
shown on Figure 4. Stratification is more evident from the dissolved oxygen
profiles than from the temperature profiles. Oxygen concentrations varied
from 7.3 to 8.3 mg/l on the surface and were fairly constant to a depth of
about 30 feet. Below 30 feet, oxygen concentration was reduced rapidly to
zero at 60— to 70—foot depths.
The design of the air distribution system used in this research was
based on the performance of the system used in the 1967 pilot study and the
volume of effect desired. The system consisted of six 40—foot arms of
4—inch diameter pipe, each arm having eight equally spaced microporus
diffusers. One end of each of the six arms was attached to a central header
of 10—inch pipe to which the air supply hoses were coupled. The arms were
equally spaced around the central header, 600 apart in a horizontal plane.
The diffusers were co imnercially fabricated, microporus porcelain, hollow
candles, having a length of 8—3/16 inches and an interior diameter of 1—1/2
inches. Th bubble—forming microporus capillaries had an average radius
of 25 x 10 cm resulting in 27 percent porosity for each candle.
Air was supplied to the distribution system through two 900—foot
lengths of 2—1/2 inch flexible hose. The air distribution system was
located approximately 750 feet upstream of the power penstock intakes where
the water depth was 95 feet. The distribution system was supported 2.5 feet
above the bottom.
The air compressor was a 1,200 cubic feet per minute (cfm) electrically
powered, rota—screw—type machine capable of supplying this volume at 125
pounds per square inch gauge (psig) pressure. The compressor was placed on
the top of Eufaula Dam near the roadway above t.he power penstocks due to
its size and weight and for convenience to a high—voltage power source.
Air delivered from the compressor was filtered through a “scrubber” to
remove oil and water vapor before it passed through the air—metering equip-
ment. Instrumentation was installed to continuously record air volume,
temperature, pressure, and power utilization. Air temperature, air pressure,
and power utilization were measured directly. Volume of air flow was
calculated from a record of pressure differential and inlet pressure for
air at 60°F and corrected to actual air temperatures.
7
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10 20
TEMP. -
4
5TAT10t
I0
2
8 — 100 0’S FEET
0
8
L i i
L ii
I
L i i
2
6
6
8
20
FIGURE 3 - TEMPERATURE DISTRIBUTION
— AUGUST 2, 1968
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FIGURE 4 - DISSOLVED OXYGEN STR ATIFlCATION - IAUGUST 2, 1968
STATIONS
4
5
7
H
8
w
w
U.
I
I-
0
6
2
4
12
10 , FEET
6 0 /STANCE /000 S
‘4
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SECTION III
EVALUAT ION
Aeration started on August 2, with a constant flow of compressed
air being delivered at the rate of 1,200 cfm to the air distribution system.
The air pressure was 55 psig and the temperature was 150°F at the air re-
cording meter on top of Eufaula Dam. The air pressure was reduced to about
45 psig at the submerged distribution system as a result of friction losses
and the hydrostatic head of the water above the system. Air was measured
in the distribution system by a remote thermistor which had a connector at
the lake surface. The air temperature was reduced from 150°F on the dam
to 75°F as it was released in the reservoir bottom. The compressed air
was cooled in the hose in transit to the distribution system as a result
of heat lost to the cooler surrounding water mass.
Reservoir stations were monitored twice weekly after aeration
began. Drimediately before the start of aeration on August 2, vertical
profiles of dissovled oxygen and temperature characterized the stratifi-
cation conditions of the reservoir at Station 1, located approximately
200 feet east of the distribution system (Figure 5). These antecedent
profiles were similar to the average of the 17 stations, but the temperature
at Station 1 was slightly warmer throughout the depth as a result of the
sheltering effect near the dam. Antecedent conditions are compared with
conditions on August 27 after 26 days of aeration. During this period,
aeration was continuous except for interruptions to service equipment and
to correct operating problems.
A period of intense monitoring of the water being drawn into the
power penstocks was conducted beginning on August 29 and lasting until
September 15. Dissolved oxygen concentrations of the power discharges
were measured for each discharge rate to characterize the dissolved oxygen
concentration with respect to flow rate. Eight monitoring stations (des-
ignated A through H) were located at intervals of 100 feet between Eufaula
Dam and the air distribution system for collection of vertical profiles
of temperature and dissolved oxygen. These profiles allow an accurate
characterization of the behavior of the flow net temperature and dissolved
oxygen layers entrained into the penstocks during power release periods.
The work schedule was coordinated with the power plant operators in order
that flow net profiles and downstream discharges could be monitored during
the most stable portion of each release period. For example, during flow
net monitoring, the hourly power release schedule for the following day
was reviewed in order to schedule monitoring of the flow net for flow rates
of 4,000 cfs, 8,000 cfs, and 12,000 cfs which corresponded to operating one,
two, and three turbines. Downstream temperature and dissolved oxygen data
were collected simultaneously with each flow net profile monitoring period.
11
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DISSOLVED OXYGEN -mg/I
FIGURE 5 - COMPARISON OF STRATIFICATION AND
INDUCED AERATION EFFECTS AT STATION I
4
5
6
7
MAXIMUM AERATION
Effects on D.O.
Aug. 27, 1968
I
MAXIMUM AERATION
Effects on Temp.
Aug. 27,1968
ANTECEDENT TEMP.
Aug. 2, 1968
I .-
U i
Ui
U-
z
I
I-
a-
Ui
ANTECEDENT 0.0.
Aug. 2,1968
I
I
I
I
I
)
,
/
/
/
/
/
/
/
/
/
I
18 20 22 24 26 28 30
TEMP. -
12
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The power release schedule could not be modified during the aeration
study to allow long—term testing of power release rates. The power discharge
schedule and periods of aeration are shown in Figure 6. The duration of
constant flow periods was not sufficient for determination of downstream
dissolved oxygen change rates with respect to time from the start of aeration.
A modified operating schedule to allow these test measurements would have
been ideal for statistical comparison of actual operational dissolved oxygen
and temperature changes with respect to duration of aeration and power dis-
charge rates.
During monitoring periods for each of the three power discharge
rates tested, downstream temperature and dissolved oxygen were measured
after the flow had stabilized. Measurements were conducted both prior to
and during the period of aeration for each change in power discharge. In
analyzing the data and correlating it with the actual power release schedule,
it was found that some of the downstream measurements would have to be
discarded since they were taken during times when power releases were being
changed in the power house. Therefore, only dissolved oxygen values of
power releases that were collected in the most stable power release periods
were selected for detailed analysis.
13
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i’’n’’’v —AERATION IN PROGRESS
‘—AERATION NOT IN PROGRESS
U
0
8
U i
C ,
z
C
I
C - ,
CC )
0
U i
0
a.
k\\N i\\\\\\\\\\\Ni\\\\\\\\\\\\\\\\\Vj K\\\\\\\\\\\\\\\\\\1 _ Jx \X\\\\\\Nk\\N
AUGUST 1968
SEPTEMBER 1968
I\\\\\\v’cx\ \\\\I
FIGURE 6 — EUFAULA DAM POWER DISCHARGE SCHEDULE COINCIDENT WITH INDUCED AERATION TEST
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SECTION IV
DISCUSSION
Aeration was begun on August 2, and maximum aeration effects in
the reservoir were achieved on August 27. The greatest effects were re-
alized at Station 1, located near the distribution system, although the
influence of aeration was detectable as far as 11,000 feet upstream. Dis-
solved oxygen profiles for the two dates show that oxygen was added between
the 40— and 70—foot depths at Station 1 (Figure 5). However, there was a
reduction in oxygen from the surface to a depth of 40 feet. These lower
dissolved oxygen concentrations resulted from the upward movement of
hypolimnion water. By comparing temperature profiles, representing the
period of aeration (Figure 5), it is evident that a reverse effect occur-
red in the temperature relationships. The temperature profiles indicated
that bottom waters were warmed and surface waters cooled by the pumping
action of the air distribution system.
The aeration effect upstream of Station 1 formed a horizontal cone
or wedge of oxygenated water with detectable limits reaching upstream
between Stations 4 and 5, (Figures 2 and 7). The maximum horizontal wedge
of aerated hypolimnion water, illustrated by the intersection of the dashed
and solid lines in Figure 7, was approximately 29,400 acre—feet. This is
less than half that reported in the pilot study of 1967.0-7) This hori-
zontal wedge of aerated water did not expand at the rate anticipated.
Apparently, the volume of aerated hypolimnion water in the reservoir was
not diffusing upstream at the rate anticipated because the aerated water
was being discharged through the dam during power generation. Power dis-
charge volumes exceeded the maximum volume aerated in the hypolimnion;
therefore, only during periods when power generation was not in progress
was any appreciable volume of oxygenated water accumulated in the hypolimnion.
It was observed during the course of aeration that dissolved oxygen
concentrations of water released during power generation increased from
3 mg/i immediately before aeration began to a range of 4.0 to 5.3 mg/i,
depending on the volume of power releases and the time of observation after
the start of aeration (Figure 8). The intensive study conducted between
August 29 and September 15 was for the purpose of defining the aeration
effects on the flow net entering the power penstocks and to relate these
effects to water quality changes in the power releases.
Results of flow net changes are illustrated in Figures 9, 10, 11,
and 12. Figure 9 illustrates both the effect of normal stratification and
the aeration operation on the dissolved oxygen layers between Eufaula Dam
and the air distribution system after a normal weekend of no power releases.
Conditions presented are averages of all periods having no power releases.
It should be noted that aeration during the periods of no power release
resulted in the 4.0 mg/i strata of dissolved oxygen being developed approx-
imately eight feet deeper than under stratification conditions with no
aeration.
15
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EUFAULA DAM
DO-mg/I (ANTECEDENT-AUG 2, 1968)
— — — — — — DO. - mgi I (MAXIMUM AERATION - AUG.27, 968)
-8UOY STATIONS
3
4 -WATER SURFACE ELEV. —585.0 mel
4
6——-.-
..... ........ .T
5 —— —
4 —
4—— — — — — — — —
I I
I I
2 3 4 5 6 7
DISTANCE FROM EUFAULA DAM — l000s FEET
8 9 10 II
L.
0
10
20
3
40
50
I
/
I-
0.
5
0
1c
a
0
12
FIGURE 7 — COMPARISON OF NATURAL AERATION AND MAXIMUM INDUCED EFFECT ON THE CENTRAL POOL
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28- ‘I
• £___-
— U
26-
,
,
24 \\ /
- / TEMP. °C
I
I ——-—%D.0.SAT.
\ I
22 I
10 15 20 2530 5
JULY 1968 - I -
10 15 20 25 30
AUGUST
5 10
SE PT.
70
2
60o
I—
4
F-
4
50cr
o
I-
4 0Z
w
U
l x
U i
a-
30
FIGURE 8- EFFECT OF AERATION ON POWER
RELEASE
6
STRATIFICATION
AERATION
4
3
2
— . - —
Power Discharge
•—I2000cfs
E
z
U i
0
0
Ui
0
U)
U)
0
0
Ui
F-
U— 8000 cfs
Ø 4000 cfs
17
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Compressor
Dam
Air Hose
B
LEGEND
__________ — Compressor On
—— — ——— Compressor Off
Buoy Stations
(Water Surface)
E F G H
C
D
-J
(I)
z
00
I-.
4
>
w
U i
Penstoc k
Air Hose
D.O. —5.0 mg/I
DISTANCE - FEET
500
600
700
800
FIGURE 9 — EFFECT OF AERATION WITHOUT POWER
RELEASE
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6
Compressor
LEGEND
Dam
Air Hose
Compressor On
Compressor Off
Buoy Stations
-J
U)
4
>
w
-j
w
I’
I’
Intake
Air Hose
52
I
H - - -
51
D.O.-4.O mg/I
D.O.-O.O mg/I -
0 100 200 300 400 500
DISTANCE — FEET
600
700
800
FIGURE 10 — EFFECT OF AERATION
DURING 4000 cfs
POWER RELEASE
-------
ompressor
LEGEND
Dam
Air Hose
Compressor On
—— ————CompressorOff
Buoy Stations
(Water Surface)
-J
‘I )
z
01-
4
>
w
-J
w
F
5
Penstock
Intake
Air Hose
D.0. - 5.0
mg/I
DISTANCE — FEET
FIGURE II - EFFECT OF AERATION DURING 8000 cfs
POWER RELEASE
-------
620
$ SO r
LEGEND
Dam
5:
Compressor On
5’
Air Hose
570
—— — — — — Compressor Of f
Buoy Stations
(Water Surface)
E F G H
D
560
-J
U,
z
0
I-
>
w
-J
U i
550
Penstock Intake
Air Hose
51
D.O. - 5.0mg/I
4
0
100
400
DISTANCE — FEET
FIGURE 12 -EFFECT OF AERATION DURING 12000 cfs POWER RELEASE
-------
Flow net conditions between the aeration unit and the turbine
intakes were influenced by both the intake velocities of the three power
discharge rates and the induced aeration operation (compare Figures 10,
11, and 12). Power releases under normal operating conditions suppressed
the dissolved oxygen strata in the vicinity of penstock intake structures.
The effect of continuous aeration at a constant rate was to further suppress
the dissolved oxygen strata for the same flow conditions. It should be
pointed out that conditions illustrated in Figures 10, 11, and 12 for periods
in which there was no induced aeration are averages for one—week periods.
Flow nets for each discharge rate were very stable, however, and exhibited
only a slight variation from the average conditions.
Flow nets shown under conditions of induced aeration illustrate
effects on the dissolved oxygen strata for three separate power discharge
rates. They characterized the maximum condition during the total operating
period. The dissolved oxygen concentration of 4.0 mg/i was suppressed
completely to the reservoir bottom, immediately in front of the dam during
aeration at peak power release (Figure 12). Data from the final days of
aeration show that the oxygen levels of the flow net had reached near
stable conditions. It is obvious from these profiles that the induced
aeration unit increased the dissolved oxygen content of the hypolimnion
upstream from the power intakes causing increases in the dissolved oxygen
content of all power discharges. The actual volume of aerated water for
each power release rate is represented by the area between the initial and
changed dissolved oxygen levels upstream of the dam.
Following stratification, dissolved oxygen concentrations in the
power discharges became stable for each discharge rate (2.9, 3.0, and
3.5 mg/i for 4,000, 8,000, and 12,000 cfs, respectively). These values
were observed for a period of about a week prior to the strat of aeration
on August 2 and were used as the base for analyzing the effect of power
release aeration. A least squares regression analysis was performed using
the expression C a+b t in which C = the concentration of dissolved oxygen
in mg/i; t = time after the start of aeration in days; a = the intercept
at time zero calculated from the standard least squares equation; and b =
the regression coefficient or the slope of the least squares line. The
least squares lines calculated from data collected during each release
rate are shown in Figures 13, 14, and 15. At the beginning of aeration
(intercept “a” at aeration time zero), the calculated dissolved oxygen
concentrations were similar to the stable measured dissolved oxygen values
for each of the discharge rates discussed above. The intercepts (a) are
2.88, 3.50, and 3.57 for 4,000, 8,000, and 12,000 cfs, respectively.
The regression analysis resulted in correlation coefficients
of 0.961, 0.872, and 0.945 with standard errors of 0.192, 0.290, and 0.229
while the standard errors of regression coefficients were0.029, 0.021, and
0.033 within 95% confidence for power discharge rates of 4,000, 8,000, and
12,000 cfs, respectively. With this information, it was possible to cal-
culate a 95% confidence belt for any value of C for a given time t after
the start of aeration for each of the three power discharge rates. The
confidence belts are shown as curved lines about the least squares regression
22
-------
FIGURE 13- INCREASE OF DISSOLVED OXYGEN IN 4000 cfs POWER
PERIODS DURING RESERVOIR INDUCED AERATION
RELEASE
C:2.88-f O.0565t
z
U i
0
0
Ui
0
(I)
U)
0
L ) Z
0
4
z
Ui
C -,
z
0
0
C)
.
95 % Confidence Belt
I 1 I
2 4 6 8 10 12 14 16 18 20 22 24 26 28
t -TIME FROM START OF AERATION — DAYS
30 32 34 36 38 40
-------
C: 3.50 +0.04541
E
z
0
>.
‘C
0
0
w
>
—I
0
C l )
Cl)
0
0
N
‘ 0
I—
4
I-
z
U i
C .)
z
0
C.-)
C-)
S
95% Confidence Belt
-.-——----
.
0 2 4 6 8 IC 12
1— TIME FROM START OF AERATION - DAYS
FIGURE 14 - INCREASE OF DISSOLVED OXYGEN
14 16 18 20 22 24 26 28 30 32 34 36 38 40
IN 8000cfs POWER RELEASE
PERIODS DURING RESERVOIR INDUCED
AERATION
-------
c = 3.57 + 0.0489 t
E
z
U i
C,
>-
x
0
U i
>
-J
0
U)
(I)
Ni
Li
0
z
0
I—
4
z
U i
0
z
0
0
.
95%
Confidence
Belt
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
t - TIME FROM START OF AERATION — DAYS
FIGURE 15- INCREASE OF DISSOLVED OXYGEN IN I2000cfs POWER
PERIODS DURING RESERVOIR INDUCED AERATION
RELEASE
-------
lines. From the regression analysis, it was possible to calculate the
most probable rate of oxygen increase in each of the power release rates
resulting from upstream hypolimnion aeration. The estimated oxygen increase
resulting from the 40—day study for 4,000 cfs release periods was from 2.88
to 5.14 mg/l, for 8,000 cfs release from 3.50 to 5.32 mg/l, and for 12,000
cfs release from 3.57 to 5.53 mg/l. It should be realized that dissolved
oxygen concentrations for each power generation rate would eventually be-
come static. Static conditions would be reached when the water mass reaches
saturation or the aeration system had reached its maximum aeration capacity
for the flow release condition.
Temperature of the release water at the beginning of aeration was
24°C with a corresponding dissolved oxygen saturation of 35 percent (Figure 8).
The temperature of the release rose from 240C to a maximum of 27.2°C during
the intensive study followed by cooling due to lower atmospheric temperatures.
The oxygen saturation of the releases during peak temperatures reached about
61 percent. The saturation after that time was partially influenced by
the lower atmospheric temperatures.
During the 40—day study period, the compressor was operated 750
hours, pumping a total of 49.73 million cubic feet of air equivalent to
931 thousand pounds of oxygen through the distribution system. By cal-
culating the increased oxygen content from the three regression analysis
and applying these increased oxygen concentrations to the volumes of power
release at the specific time of release, it was found that 69 percent of
the oxygen pumped into the reservoir passed through the dam. The fate of
the remaining 31 percent of the oxygen pumped into the reservoir could not
be determined. However, the data show that a portion was absorbed in the
water mass upstream of the dam while the remainder was probably vented
to the atmosphere.
As mentioned previously, only the dissolved oxygen values of power
releases that were collected during the most stable power release periods
were selected for detailed regression analysis. Total calculated dissolved
oxygen added to the release was based on flow volume during each specific
power generation period during the 40—day study and the oxygen increase
at specific times of power generation. These calculations, when compared
to the Kilowatt hours of power required for air delivery, resulted in an
efficiency of 3.0 pounds of dissolved oxygen added to the power releases
per horsepower—hour of energy expended. However, when results of regression
analysis of all dissolved oxygen values measured in the power release——
regardless of the stability of discharge-—were used for comparison, eff i—
ciency was found to be 1.8 pounds of dissolved oxygen added per horsepower—hour
of expended energy. Electrical installation and power costs for 750 hours
of aeration was $2,625, resulting in an operation cost between $4.10 and
$6.25 per thousand pounds of oxygen added to the releases.
Research conducted on releases at Eufaula Reservoir illustrates
a feasible, economic way of managing the quality of power releases at dams
where hydraulic features have not been designed for maximal quality purposes.
The level of oxygen saturation in power releases was increased by the
aeration unit at the three discharge rates studied. The oxygenation
26
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efficiency of this system (1.8 to 3.0 pounds of oxygen transferred per
horsepower—hour) compares favorably with other systems recently reported
(Table 2). Values in Table 2 are referenced and include efficiency of
oxygen transfer for aeration systems including turbine aeration. Eff i—
ciency range of the present study is considered conservative since Increased
dissolved oxygen concentrations in the reservoir for periods of no release
were not used in the calculations. Further development of induced aeration
systems may indicate they should be considered in design of outlet works
of future dams. Additional research is necessary to develop this induced
aeration system and optimize its design characteristics. Induced aeration
research should take two separate avenues: first, the system should be
developed to optimize the quality of releases, and second, it should be
developed for water quality control in impoundments. In developing the
aeration system to optimize the quality of release waters, a detailed study
should be conducted in which selected chemical parameters——in addition to
temperature and dissolved oxygen——are evaluated in the discharge, particularly
nitrogen and hydrogen sulfide. Additional research is necessary to define
optimum upstream placement and depth of air release for maximum dissolved
oxygen retention in the flow net. The research should include additional
testing of size and geometry of the distribution system with respect to
volumes and pressures of compressed air. In conducting the study, every
effort should be made to test the effects of aeration during several days
of uninterrupted discharge for each of the normal power operating rates.
The development of aeration systems for water quality management
of the entire impoundment by seasonal destratification should be accomplished
through an economic evaluation based on a mathematical model. The model
should be developed utilizing data from several recent studies. Development
would include location of the optimum number and size of distribution
systems based on the radiating effect of the air plume, depth and volume
of air release, and pressure of induced air as well as physical shape and
dimensions of the impoundment. After the model has been satisfactorily
tested on available data, a reservoir should be selected and predicitions
made with the model as to number, size, and spacing of distribution units
required for specific aeration effects. The reservoir should then be field
tested and the mathematical predictions verified.
27
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TABLE 2
OXYGENATION CAPACITY FOR VARIOUS AERATION SYSTEMS
1. Present Study
2. Diffused Air
Wahnback Reservoir (7)
3. Hypolimnion Mixing
Wahnbach Reservoir (7)
4. Diffused air
Baldency Lake (7)
5. Lake Pfaf faker (7)
6. Turbine Aeration (7)
7. Turbine Aeration (7)
8. Activated Sludge (7)
9. Aero—Hydraulic Gun (8,18)
10. Boltz Lake
Mechanical Pump (4,19)
11. U—Tube Stream Aerators (20)
12. Stream Spray Aerators (21)
13. Vented Power Turbines (21)
14. Mechanical Stream Aerators (21)
15. Stream Surface Aerators (21)
16. Diffusor Stream Aerators (21)
2.4 — 4.0 1.8 — 3.0
1.2 0.9
2.1 1.6
0.33
4.3
1.3 — 5.6 (range)
2.4 average
4.3 — 5.6 (02 Saturation
below 10 percent)
3.1 (Coarse bubble)
1.4
1.0 0.75
3.3
2.5
1.1 — 2.1
0.8 — 1.6
2.4 — 2.8
1.8 — 2.1
2.1 — 2.5
1.6 — 1.9
1.1 — 2.3
0.8 — 1.7
0.8 — 1.9
0.6 — 1.4
OXYGENATION
Method lb. 02 transferred/Kw—Hr.
EFFICIENCY
lb.
09
transferred/Hp—Hr.
Go
0.25
3.2
1.0 —
1.8
3.2 —
2.3
1.0
4.2 (range)
4.2
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SECTION V
ACKNOWLEDGMENTS
The authors express their sincere appreciation to the U. S. Army
Corps of Engineers, Tulsa District, Tulsa, Oklahoma, especially the
Operations and Engineering Divisions, without whose cooperation access to
an adequate power supply and suitable compressor site would not have been
possible. The authors are also grateful to the Southwestern Power Admini-
stration, Tulsa, Oklahoma, for cooperation in making provisions for a high
voltage electrical power source on Eufaula Dam.
This research study was conducted in cooperation with the Oklahoma
Cooperative Fishery Unit, Bureau of Sport Fisheries and Wildlife, Oklahoma
State University, Stiliwater, Oklahoma, under direction of Dr. Robert C.
Summerfelt. The Oklahoma Cooperative Fishery Unit conducted extensive fish
distribution and productivity studies in connection with destratification
effects in the central pooi of Eufaula Reservoir.
A study to establish the vertical distribution of fish in Eufaula
Reservoir was conducted under the direction of Mr. Robert M. Jenkins,
Director, National Reservoir Research Program of the Bureau of Sport
Fisheries and Wildlife, U. S. Department of the Interior. Its contribution
to this research is greatly appreciated.
29
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SECTION VI
REFERENCES
1. Kittreil, F. W., “Effects of Impoundments on Dissolved Oxygen Resources. tt
Sewage and Industrial Waste. , 31, 7, 1065 (Sept. 1959).
2. Churchill, M. A., “Effect of Storage Impoundments on Water Quality.”
Jour., San. Eng. Div., ASCE, 83:SA—l, Paper 1171 (1957).
3. Symons, J. M., Weikel, S. R., and Robeck, G. C., “Impoundment Influences
on Water Quality.” Jour . AWWA, 57:51 (Jan. 1965).
4. Symons, J. M., Irwin, W. H., Robinson, E. L., and Robeck, C. C.,
“Impoundment Destratification for Water Quality Controi:Mechanical Pumping
and Diffused Air.” Presented at the 87th Annual Conference of AWWA, Atlantic
City, New Jersey (June 4—9, 1967).
5. Hooper, F. F., Bali, R. C., and Tanmer, H. A., “An Experiment in the
Artificial Circulation of a Small Michigan Lake.” Trans. i\mer. Fish Soc.,
82 (1952).
6. Ford, M. E. Jr., “Air Injection for Control of Reservoir Limnology.”
Jour . AWWA, 55:3 (March 1963).
7. Bernhardt, H., “Aeration of Wahnbach Reservoir Without Changing the
Temperature Profile.” Jour . AWWA, 55:8 (August 1967).
8. Laurie, A. H., “The Application of the ‘Bubble—Gun’ Low Lift Pump, A
Remedy for Stratification Probeims.” Water and Waste Treatment , Vol. 8 (1961).
9. Thackston, E. L., and Speece, R. E., “Supplemental Reaeration of Lakes
and Reservoirs.” Jour . AWWA, 58:10 (October 1966).
10. Speece, R. E., “U—Tube Stream Reaeration.” Presented at the Seventh
Annual Sanitary and Water Resources Engineering Conference, Vanderbilt
University, Nashville, Tenn. (May 1968).
11. Speece, R. E., “The Use of Pure Oxygen in River and Impoundment Aeration.”
Presented at the 24th Purdue Industrial Waste Conference (May 8, 1969).
12. Stratified Flow in Reserovir and Its Use in Preventing Siltation .
B—li, H. S., Misc. Pub. No. 491, U. S. Dept. Agricultural, Soil Conservation
Service (Sept. 1942).
13. Austin, G. H., Gray, D. A., and Swain, D. G., “Report on Multilevel Outlet
Works at Four Existing Reservoirs.” Office of Chief Engineer, Bureau of R&C,
USD1, Denver, Colorado (1968).
31
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14. Cooperative State—Industry Studies of the Flambeau and Fox Rivers in
1957. I. Turbine Reaeration on the Flambeau River . Wisconsin Committee on
Water Pollution and the Sulfite Pulp Manufacturers Research League (March 1958).
15. Powell, S. T., Pritchard, D. W., and Hooper, 0. L., “Effects of Sub-
merged Weir Upon Quality of Water Discharged From Gaston Reservoir.” Eng.
Rept. to Virginia Electric and Power Company, Roanoke Rapids, N. C. (June 1955).
16. Special Report Number 1, Roanoke River Studies. A Study of the Effects
of a Submerged Weir in the Roanoke Rapids Reservoir Upon Downstream Water
Quality . Committee Report to the Subcommittee for Operations, Roanoke River
Studies, Raleigh, N. C. (Feb. 1958).
17. Leach, L. E., Duff er, W. R., Ph. D., and Harlin, C. C., Jr., “Pilot
Study of Dynamics of Reservoir Destratification.” Robert S. Kerr Water
Research Center, Federal Water Pollution Control Administration, USD1,
Ada, Oklahoma.
18. Bryan, J. G., “Physical Control of Water Quality.” Jour . of the
British Waterworks Association, XLVI, p. 546 (1964).
19. Symons, J. M., Irwin, W. H., Clark, W. M., and Robeck, G. C., “Management
and Measurement of ‘DO’ in Impoundments.” Jour . San. Engr. Div. Proc. of
the ASCE (In Press).
20. Speece, R. E., “U—Tube Oxygenation for Economical Saturation of Fish
Hatchery Water.” Presented at the American Fisheries Society Meeting, Tucson,
Arizona (Sept. 1968).
21. Cleary, E. J., “The Reaeration of Rivers.” Industrial Water Engineering ,
pp. 16—21 (June 1966).
32
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1 A ’essionNurnber 2 Subject Field & Group
I SELECTED WATER RESOURCES ABSTRACTS
05 G INPUT TRANSACTION FORM
5 Ordaniza(ion
Environmental Protection Agency
Robert S. Kerr Water Research Center
Ada, Oklahoma
JT tle
INDUCED HYPOLIMNION AERATION FOR WATER QUALITY IMPROVEMENT OF POWER RELEASES,
10 Author(s)
Leach, Lowell E.
Duffer, William R.
Harlin, Curtis C., Jr.
161 Project Designation
1608O———l0/70
JN0te
22 Citation
23 Descriptors (Starred First)
*Aeration, *Thermal stratification, *Impoundments, *Hypolimnion,
Dissolved oxygen, Mixing, Oxygenation, Air entrainment, Thermocline,
Epilimnion
25 Identifiers (Starred First)
*Water quality control, *Induced aeration, destratification,
*Hypolimnion aeration, Air distribution system, Oxygenation efficiency,
Power release aeration
27 Abstract
____ Conventional hydraulic structures in most dams withdraw low flow and power releases
from the poor quality hypolimnion waters during suimner stratification resulting in
serious degradation of long reaches of streams below dams. Induced aeration of
hypolimnion waters during summer stratification has great potential in water quality
management of power releases, low flow releases, and limited volumes of impoundments
without costly modification of existing outlet works. Hypolimnion aeration research
on power discharge quality improvement was conducted at Eufaula Reservoir in south-
eastern Oklahoma during the summer of 1968. Dissolved oxygen transfer efficiency of
the aeration system ranged from 1.8 to 3.0 pounds of dissolved oxygen per horsepower—
hour of expended energy resulting in an operating cost of 4.10 to 6.25 dollars per
1,000 pounds of oxygen incorporated into the power releases. Additional research
for development and optimization of the induced aeration system is discussed.
SEND TO WATER RiSOURCES SCIENT!FIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 20240
WR’02 REV IULY 1969)
WRSI C
AbstractOr Lowell E. Leach
Research Hydraulic Engineer
ht tittitbon Robert
P. 0.
S.
Box
Kerr
l19R
Water Research Center
Ar a, Oklahoma
* c” 0 1S6S—559 33
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WATER EOILtJTION CONThOL RESEARCH SERIES
The Water Pollution Control Research Reports describe the
results and progress in the control and abotement of poi—
lution in our Nationt s waters. They provic e a central
source of inforiaation on the research, dove locment, arid
demonstration activities in the Water Quality Office,
Environmental Protection Agency, through inhouse research
and grants and contracts with Federal, State, and local
agencies, research institutions, and industrial organizations.
Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Head, Froj ect Reports
System, Planning and Resources Office, Office of Research
and Development, Water Quality Office, Envirormental
Protection Agency, Room 1108, Washington, I). C. 202Lt2.
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