Civil Engineering Reference
In-Depth Information
Fig. 8-12.
Microscreen installation (Courtesy of USFilter-Rex and LinkBelt Intake Products)
The hypolimnion is isolated from a source of oxygen. In aged reservoirs, or where
a reservoir has an input of organic materials, the demand for oxygen may cause a total
depletion of oxygen in all or part of the hypolimnion. The lack of oxygen may cause
anaerobic conditions, and chemical constituents in the hypolimnion and benthal de-
posits will be chemically reduced. Hydrogen sulfide may be formed, and iron and
manganese dissolved. Hydrogen sulfide imparts taste and odor to the water, and iron
and manganese form precipitates (when water is subsequently aerated) and cause the
water to be turbid and colored. Iron and manganese will also stain plumbing fixtures
and laundry, and if present in sufficiently large concentrations, will cause taste prob-
lems.
In addition, anaerobic conditions in the hypolimnion may cause reduction in pH
and an increased concentration of CO
2
, which in turn may impair the capability of the
treatment facilities.
The problem can be resolved by not drawing water from the hypolimnion, adding
more intensive water treatment, or eliminating the problem in the reservoir. In some
cases, it may be feasible to eliminate thermal stratification so as to oxygenate the
hypolimnion, or to add oxygen to the hypolimnion without thermal destratification.
These approaches may not be practical for very large reservoirs.
WINTER
SUMMER
Temp,
o
Temp,
o
15 20
0
2
4
6
8
10
12
0
5 0
25
0
0
Epilimnion
T
O
2
O
2
T
20
20
Thermocline
40
40
H
ypolimnion
60
60
0
2
4
6
8
10
12
14
Oxygen, PPM
Oxygen, PPM
Fig. 8-13.
Distribution of oxygen and temperature with lake depth (From Culp, Gordon, and
Williams, Robert,
Handbook of Public Water Systems.
Copyright
1986 by John Wiley & Sons,
Inc. Reprinted by permission of John Wiley & Sons, Inc.)
