Type III stilling basin, according to U.S.B.R. classification, is conventionally designed like other basins for a single discharge which is usually the design discharge and its performance at other discharges is tested in a hydraulic model. This paper presents a new method of design for a modified type 111 basin over a major range of discharges passing the spillway structure. The modified basin has two rows of friction blocks in contrast to one row in the U.S.B.R. basin, to improve velocity distribution of post-jump subcritical flow in the basin. The design is accomplished by developing a dimensionless semi-theoretical relationship for forced jump height curves (FRJHCS) of the spillway-stilling basin combination and matching the dimensionless tailwater rating curve (TWRC) of the river site with one of the FRJHCS, translating the TWRC verticaly if necessary. So as to avoid preparation of a large family of FRJHCS for the purpose of matching, an alternative method of matching has been developed based on the assumption that both the FRJHCS and TWRCS may be represented by simpler equations of power law form.