In this study, dilution characteristics of heated water discharged from the staged diffuser in shallow water were investigated. New dilution equation which was proposed by the dimensional analysis was tested using experimental data collected in this study. Experimental results of the staged diffuser in stagnant ambient show that dilution of the diffuser of which ports are arranged parallel to the diffuser axis is lower than dilution of the diffuser with port-angle of

because of the merging effect between neighboring jets. Among the existing dilution equation for the staged diffuser in stagnant water, equation by Almquist and Stolzenbach (1980) gives better fit to the measured data than equation by Jirka (1982). Experimental results of the staged diffuser in crossflow show that dimensionless near-field dilution increases as length scale,

to the power 0.5 in the discharge momentum dominated region, whereas dimensionless dilution increases as

to the power 1.0 in the ambient current dominated region. Threshold value of

between two regions is around 1. By fitting dilution equations derived by the dimensional analysis to the experimental data, constants of the proposed equation were estimated as 0.58. Comparison of the proposed equation and existing dilution equations with the measured data reveals that existing equations overestimate dilution in the ambient current dominated region, i.e., in the range where

is larger than 1, whereas the proposed equation predicts the measured dilution accurately in both discharge momentum dominated region and ambient current dominated region.