A hydrologic study was performed for ungauged river basin of Sri Lanka to examine synthetic discharge relations. Rainfall-runoff relationships were used for identifying hydrological conditions of the Gin River basin. The peak discharge achieves within 4.74 hours from the onset of the rainstorm and 11.95 hours take to reach its normal discharge conditions. Stream frequency of the Gin River is 4.56 junctions/km
while the channel slope gradient is 7.90 m/km. The regional coefficient of the catchment is 0.00296. Higher stream frequency and gentle channel slope were identified as flood triggering factors of the basin. Mini-hydropower systems were recognised as the most applicable and economical flood controlling hydraulic structures. Also, it can be utilised as a reliable energy source (8,630.0 kW).
Keywords: ungauged basin, flood studies report, flood, triangular irregular network model, geographic information system, GIS, disaster mitigation, mini-hydro power, Gin River, Sri Lanka, national environmental research council