Cost–Benefit Analysis of Soil Degradation and Restoration - Principles of Sustainable Soil Management in Agroecosystems - page 241

watershed was divided into 10-ha cells, each of which was placed into one of the four
slope classes. By contrasting existing land use based on the CRIES (1980) results
with recommended land use, it was found that 57% of the catchment area would not
be affected by project implementation, while 11% would have to undergo a change in
land use. In the remaining 32%, soil conservation goals would be met by mulching,
contour farming, and range renovation.
Reductions in soil loss resulting from compliance with project guidelines were
estimated by applying the USLE (see Veloz 1982) using soil survey data and the esti-
mates of slope that were used to categorize land into the four slope classes. In gen-
eral, this approach yields conservative estimates of erosion inasmuch as the USLE
explains only gross sheet and rill erosion and not gullying, stream bank scour, and
other types of soil loss.
Average sedimentation rates were calculated by multiplying an estimated sediment
delivery ratio from Onstad et al. (1977) by estimated erosion rates. Given current land
use and land management practices and evidence from Espinal (1981), it was estimated
that average yearly accumulation of sediment in the reservoir is 921 × 10 3 metric tons,
which is 59% of the rate obtained by dividing total sediment in the reservoir by the res-
ervoir's age. However, the latter rate includes the silt deposit by Hurricane David in 1979
as well as the bed load of sediment. Thus, the observed rate probably overstates the long-
term sedimentation rate. Implementation of the project throughout the watershed would
reduce sedimentation by an estimated 86%, to 130 × 10 3 metric tons a year.

10.4.2.2 Results and Implications of Analysis
Sedimentation was assumed to have a negligible impact on electricity production as
long as it remains possible to operate the hydroplant. However, without any change
in land resource management, it was estimated that the generator intake would be
clogged with silt after 19 years. As little as a 25% reduction in erosion, though,
would extend the hydroplant's lifetime by about 6 years. The group affected most
by project implementation would be hillside farmers. Researchers familiar with the
study area supplied information about farm income without the project. Budgets for
soil conserving activities were obtained from United States Agency for International
Development (USAID) and other sources (see Veloz 1982).
Economic evaluation of the watershed management project outlined above
strongly suggests that the net benefits associated with soil conservation depend on
the accounting stance. The results of private-level analysis reported in Table 10.1

TABLE 10.1
Results of Private Level Analysis

Slope Class Hectares PNPVi PNPVi/Hectare

A 7640 DR$12,500,000 DR$1635

B 17,800 -550,000 -30

C 8600 -1,925,000 -225

D 2350 -1,100,000 -470

Total 36,390 DR$8,925,000 DR$245