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waters. Ponds are small lakes in which rooted plants on the top layer reach to the bottom. Reservoirs
are usually manmade impoundments of potable water. Lakes, ponds, and reservoirs are sensitive to
pollution inputs because they flush out their contents relatively slowly. Lakes undergo eutrophica-
tion, an aging process caused by the inputs of organic matters and siltation. Simply, we can state that
lakes, ponds, and reservoirs—that is, all still waters—are temporary holding basins.
20.2 STILL WATER SYSTEM CALCULATIONS
Environmental professionals involved with still water system management are generally concerned
with determining and measuring lake, pond, or reservoir morphometric data, which are commonly
recorded on pre-impoundment topographic maps. Determining and maintaining water quality
in still water systems is also a major area of concern for environmental engineers. Water quality
involves the physical, chemical, and biological integrity of water resources. The USEPA and other
regulatory agencies promulgate water quality goals for protection of water resources in watershed
management. Again, most still water data are directly related to the morphological features of the
water basin.
Mapping the water basin should be the centerpiece of any comprehensive study of a still water
body. Calculations made from the map allow the investigator to accumulate and relate a lot of data
concerning the still water body system. When determining and measuring the water quality of a still
water body, several different models are used. The purpose of modeling is to help the environmental
engineer organize an extended project. Modeling is a direct measurement method, intended for a
smaller body of water (e.g., lake, pond, reservoir); for example, water budget models and energy
budget (lake evaporation) models can be used.
20.2.1 s
till
W
ater
b
ody
m
orphometry
C
alCulations
20.2.1.1 Volume
The volume (
V
) of a still water body can be calculated when the area circumscribed by each iso-
bath (i.e., each subsurface contour line) is known. The formula for water body volume is as follows
( Wetzel, 1975):
n
h
(
)
∑
3
0
V
=
AA
+ +×
AA
(20.1)
i
i
+
1
i
i
+
1
i
=
where
V
= Volume (ft
3
, acre-ft, m
3
).
h
= Depth of the stratum (ft, m).
i
= Number of depth stratum.
A
i
= Area at depth
i
(ft
2
, acre, m
2
).
The formula for the volume of water between the shoreline contour (
z
0
) and the first subsurface
contour (
z
1
) is as follows (Cole, 1994):
(
)
1
3
(
)
(
)
V
−
=
A
+
A
+
A
+
Azz
−
(20.2)
zz
z
z
z
z
1
0
10
0
1
0
1
where
z
0
= Shoreline contour.
z
1
= First subsurface contour.
Az
0
= Total area of the water body.
Az
1
= Area limited by the
z
1
line.
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