Geoscience Reference
In-Depth Information
TABLE 19.1
Typical Reaeration Constants ( k 2 ) for Water Bodies
Water Body
Ranges of k 2 @ 20°C
Backwaters
0.10-0.23
Sluggish streams
0.23-0.35
Large streams (low velocity)
0.35-0.46
Large streams (normal velocity)
0.46-0.69
Swift streams
0.69-1.15
Rapids
>1.15
Source: Spellman, F.R., Stream Ecology and Self-Purification, ,
Technomic, Lancaster, PA, 1996.
The reaeration constant, k 2 , is the reaction characteristic of the stream and varies from stretch
to stretch, depending on the velocity of the water, the depth, the surface area exposed to the atmo-
sphere, and the amount of biodegradable organic matter in the stream. Reaeration constants are
given in Table 19.1. The reaeration constant for a fast-moving, shallow stream is higher than for a
sluggish stream or a lake. The reaeration constant for shallow streams, where vertical gradient and
shear stress exist, is commonly found using the following formulation:
48 6
.
1/4
5/4
S
k
(20°C)
=
(19.13)
2
H
where
k 2 = Reaeration constant.
S = Slope of stream bed (ft/ft).
H = Stream depth (ft).
The reaeration constant for turbulence that is typical in deep streams can be found by using the
following equation:
= .
130
V
1/2
3/2
k
(20°C)
(19.14)
2
H
where:
k 2 = Reaeration constant.
V = Velocity of stream (ft/sec).
H = Stream depth (ft).
The Streeter-Phelps equation should be used with caution. It should be remembered that the
Streeter-Phelps equation assumes that conditions (flow, BOD removal and oxygen demand rate,
depth, and temperature throughout the stream) are constant. In other words, their equation assumes
that all conditions are the same or constant for every stream. However, this is seldom true; a stream,
from reach to reach, changes. Additionally, because rivers and streams are usually longer than they
are wide, organic pollution mixes rapidly in these surface waters. Further, some rivers and streams
are wider than others are. Thus, the mixing of organic pollutants with river or stream water does not
occur at the same rate in different rivers and streams.
 
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