A special method for estimating river discharges, using rainfall data in and around a catchment and water level data in a river, was applied to the Sayo River flood event in 2009, and the peak discharge and flood hydrograph were estimated. The method was designed for situations where the river’s water level was measured but the discharge not measured, as in Sayo River. A catchment runoff model was used to assist in establishing a level-discharge rating curve. As a result, the water level hydrograph at Sayo station was able to be reproduced successfully. The rating curve (H-Q curve) was well set up. The flood discharge at the embankment crest level was estimated to be about 910m3/s. By using the runoff model, the amount of rainwater storage in the basin in this flood event was estimated to be 35mm. Also the storage capacity in the surface horizon was very small (about 10% of all capacity).
