Abstract
The functions that a dam reservoir increases the scanty runoff were evaluated at 11 catchments in Kanto area by comparing with the discharge-duration curves that were made of discharge from a forested catchment and dam. In this report, two indexes, the duration-stabilized-transform ratio, the achievement ratio, are introduced new. These indexes are used to discuss to what degree dam reservoir stabilizes discharge. In normal years, values of these indexes in 10 dams among 11 were small relatively, in other words these dam reservoirs didn't play a roll in increasing the scanty runoff. That means these dam reservoirs didn't contribute to stabilizing discharge. In the drought year, the duration-stabilized-transform ratio became larger in 7 catchments. And 5 dams among 7 had contributed to stabilizing discharge.
