Forecasting Water Level at a Tidal River by the Nearest-Neighbor Method

The Barato River joins the Ishikari River near the river mouth. That river basin is sometimes in danger of flood because it is low, flat and tidal area around the tributaries influenced by the backwater of the Ishikari River. Therefore the gate is provided at the confluence of Ishikari River to avoid counter flow. Flood forecasting is necessary to determine the gate operation and disaster prevention system. In tidal river, to convert forecasting discharge into water level is so hard that the rating curve is not proper. Accordingly, we investigate the applicability of the Nearest-Neighbor Method to the forecasting of water levels for six hours ahead in order to support the operation of floodgates in such an area. This report deals with water level forecast that needs to operate the floodgate installed in order to prevent the counter flow from the Ishikari River. Although this method constructed by a very simple scheme like a pattern matching, its performance much better than the ones based on the water level correlation between the concerned site and Upper observation sites.