Ensemble rainfall forecasting was used for dam flood control. Its applicability was studied. First, an ensemble rainfall forecast with 84-hr lead time was simulated using GSM as a boundary condition. Then optimal dam flood control simulation was conducted based on the simulated ensemble rainfall forecast. Typhoons 6, 12, and 15 in 2011 were the experimental rainfall events. Although the lead time was quite long, the ensemble rainfall forecast results were good for Typhoons 6 and 15. Moreover, results showed that this ensemble rainfall forecast is extremely useful for dam flood control because the lead time is sufficiently long to ascertain the timing of the start and the end of the rainfall in advance of the start of the rain. The dam flood control simulation was conducted based on the ensemble rainfall forecast. Results show that the peak discharge in the downstream was less than that by regular control. However, the ensemble rainfall simulation result of Typhoon 12 was not good. Dam flood control by the ensemble rainfall simulation increased the downstream flood risk. Implementation of ensemble rainfall forecasts for dam flood control requires a method to avoid failure in operations because operations that increase downstream risk are strongly prohibited.

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 A preliminary experiment using storage-type rain gauges was conducted to assess changes in the interception loss ratio of Cryptomeria japonica foliage growing on logging residues after thinning. The interception loss ratio increased as the amount of C. japonica foliage increased. The interception loss ratio (%) was calculated with rainfall as a variable. When the amount of dry foliage in the area of feeding into the storage-type rain gauge was 10 t ha^-1 and 20 t ha^-1, the interception loss ratios were estimated respectively as 2.7 % and 5.4 %. Results suggest that it is important to elucidate the effects on the interception loss ratio of C. japonica foliage growing on logging residues.

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 This study developed a new automated construction method of polygonal blocks using road boundary lines with gaps. Polygonal block data are often used in studies of numerical simulation models for rainfall–runoff and flood inundation analysis. In the developed method, connected boundary lines of a street are first merged into boundary polylines. Secondly, directions of boundary polylines are aligned in a clockwise rotation. Next, gaps of boundary polylines are complemented recursively with straight lines. Finally, the areas enclosed by boundary polylines and complemented lines are output as polygonal blocks. This method was applied for the Kanda catchment. Then the shapes of polygonal blocks were validated. Results show that polygonal blocks can be created using the method outlined herein with few failures.

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