Geoscience Reference
In-Depth Information
Compute the mean depth:
V
A
2274 acre-ft
510 acres
D
==
=
4.46 ft
20.2.1.4
Bottom Slope
D
D
m
S
=
(20.5)
where
S
= Bottom slope.
D
= Mean depth (ft, m).
D
m
= Maximum depth (ft, m).
20.2.1.5 Volume Development
Another morphometric parameter is volume development (
D
v
) (Cole, 1994). This metric compares
the shape of the still water basin to an inverted cone with a height equal to
D
m
and a base equal to
the still water body's surface area:
D
D
D
=×
3
(20.6)
v
m
20.2.1.6
Water Retention Time
(
)
3
Storage capacity
acre-ft,m
RT
=
(20.7)
(
)
3
Annualrun
off
acre-ft/yr, m/yr
where
RT
is retention time (years).
20.2.1.7
Ratio of Drainage Area to Still Water Body Capacity
(
)
2
Drainage area
acre, m
R
=
(20.8)
(
)
acre-ft,m
3
Storage capacity
■
EXAMPLE 20.2
Problem
: Assume annual rainfall is 38.8 inches and watershed drainage is 10,220 acres. Using the
data provided in Example 20.1, calculate the bottom slope, volume development, water retention
time, and ratio of drainage area to lake capacity.
Solution:
First determine the bottom slope:
D
D
m
446
80
.
.
S
== =
056
.
t
Calculate volume development:
D
D
D
=× =× =
3
3
056168
.
.
ft
v
m
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