Civil Engineering Reference
In-Depth Information
in the reservoir moves downward. The farther the center of gravity moves from the
isothermal center of gravity, the more stable is the stratification, and the more energy
is required to overcome the stratification.
The use of either the OC or DE in design of lake destratification is precarious
without prior experience. Table 8-3 shows experienced power requirements and time
required to acquire destratification, using pumps and diffused air mechanical devices.
CHEMICAL TREATMENT OF RESERVOIRS
When sufficient nutrients are available and warm, sunny conditions prevail, algal
growths occur in reservoirs, and can cause taste and odor problems. Copper sulfate
and / or potassium permanganate is used as an algicide in reservoirs to reduce the
number of organisms. Chlorine has also been used in some situations, but its usage
must be carefully controlled because it combines with certain odor-forming compounds
to cause a more intense odor and may result in trihalomethane production.
Copper sulfate is considered to be effective in controlling algal growths. There is
some difference of opinion over whether copper sulfate is algistatic or algicidal; how-
ever, continuing programs in which copper sulfate is added regularly to keep growths
from occurring are more effective than programs depending on copper sulfate to de-
stroy an existing growth. In a typical situation, copper sulfate would be added to a
reservoir in a concentration of about 0.1 to 0.5 mg / L. Many times it is only necessary
to add the copper sulfate around the shoreline where the water is quiescent and the
algal growths are heaviest. The copper will eventually precipitate from solution. The
alkalinity of the water is important in determining the dosage. If the methyl orange
alkalinity is less than 50 mg / L, copper sulfate has been shown to be effective at an
application rate of 0.33 mg / L. If the methyl orange alkalinity is greater than 50
mg / L, the dosage rate will be 5.4 pounds / acre (606 kg / Mm
2
). Depth is not a factor
in high alkalinity water because precipitation of copper will occur rapidly.
Care must be exercised to prevent overdosing of copper sulfate and killing fish.
Safe dosages for most fish are about 0.5 mg / L, but for trout the safe dosage is
0.14 mg / L.
TABLE 8-3. Experienced Power Requirements for Destratification
Surface
Area
(acres)
Mechanical
Mixing
Device
Time Rq'd for
Destratification
(hr)
Volume
(acre feet)
Average
Depth (ft)
Power
(HP)
Lake
Steward Hollow
120
8
15
Pump
37.5
12
Caldwell
100
10
10
Pump
8
12
Vesuvius
1,260
105
12
Pump
208
12
Pine
98
14
7
Pump
35
12
Indian Brook
316
18
—
Diffused Air
168
8
Wohl Ford
2,510
130
—
Diffused Air
78
50
Blelham Tarn
575
27
—
Diffused Air
335
1
Source:
Adapted from References 20 and 23.
Conversion factors may be found in Appendix A.
