Soil Conservation Preserves Reservoir Benefits Nationwide
LeRoy
Hansen
Over 75,000 reservoirs in the 48 contiguous
States provide recreation, scenic beauty, flood
control, fish and wildlife habitat, water supplies,
hydroelectric power, and other benefits. But over
time, sediment settling to the bottom of reservoirs
reduces their water-holding capacity and the quality
of benefits they provide. Agricultural runoff is
a major source of reservoir sediment in many areas
of the country. Sediment washed from fields moves
down streams and settles in lakes and reservoirs.
Therefore, steps to reduce soil erosion on the Nation’s
farms and ranches can protect the benefits provided
by reservoirs.
A recent analysis by ERS estimates
that the value of a 1-ton reduction in agricultural
soil erosion and the subsequent reduction in reservoir
sedimentation is as high as $1.38 per ton. The analysis
provides per ton benefit values for all of the 2,111
watersheds in the 48 contiguous States. Benefit
values across the country vary because of site-specific
differences in the physical effects, that is, the
quantity of sediment deposited due to a 1-ton change
in soil erosion, and the value people place on changes
in reservoir benefits. In general, as the number
of reservoirs within a watershed increases, physical
effects increase. As the size of the population
affected in a region increases, the total value
of benefits increases. Consequently, benefit values
tend to be higher in the East.
The ERS estimates of the benefits
of soil conservation, in terms of their impact on
reservoirs, are derived from two models. The first
links changes in soil erosion to changes in reservoir
sedimentation, using data on reservoir characteristics,
sedimentation rates, and erosion rates. The second
model links changes in the value of reservoir benefits
to changes in reservoir sedimentation and is estimated
with data on reservoir characteristics and, indirectly,
dredging costs. The analysis estimates a benefit
model using cost data because it is reasonable to
assume that the benefits of dredging a reservoir
are sufficient to at least cover dredging costs.
Although estimates of the benefits
of a 1-ton reduction in erosion amount to less than
$0.20 per ton in 80 percent of the watersheds, the
total value of soil conservation with regard to
reservoir benefits is substantial. For example,
through a variety of public and private initiatives,
soil erosion in 1997 was 640 million tons less than
in 1982. The public benefit for the subsequently
lower level of reservoir sedimentation is estimated
to be $154 million. Of course, this is just one
of many soil conservation benefits.
This
finding is drawn from . . . |
| “The
Value of the Reservoir Services Gained with
Soil Conservation,” by Leroy Hansen
and Daniel Hellerstein, in Land Economics,
83(3) (August 2007): 285-301. |
|
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