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Summary and Conclusions
Comparative SCS CN and
L-THIA based Estimation
Changes in estimated runoff depths
due to land use changes between 1920 and 1990 for design rainfall events
ranging from 24 hour/1 year return period to 24 hour/100 year return period
ranged from about 7-17% for the KSC area and 22-55% for the IRLB area. The
changes in average annual runoff due to land use changes were much greater
for both study areas. Between 1920 and 1943, estimated average annual runoff
for the KSC area increased less than 10% while that for IRLB increased by
nearly 26%. Between 1943 and 1990, estimated average annual runoff for the
KSC area increased by 37% while runoff for IRLB increased by 69%. Between
1920 and 1990, estimated average annual runoff for the KSC area increased
about 49% while that for IRLB increased nearly 113%. For both the KSC area
and the IRLB, most of the increase came from the "urbanization" of land
uses. Urbanized land uses in the KSC area made up only 20.5% of the total
land area, but contributed 47% of the estimated average annual runoff volume
for 1990 land uses. The striking differences in runoff changes between KSC
and the IRLB from 1920 to 1990 are due to differences in rates of land use
changes. The IRLB has experienced far greater "urbanization" of land uses
than the KSC area (urban land uses in IRLB are 35% versus 21% in KSC in
1990).
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