少雪寒冷地流域の土壌特性が融雪流出に及ぼす影響に関する実証的研究

在北海道，我们经常在冬季经历像加拿大、北美亚北极地区一样的地面冻结。结果表明，冻土对融雪径流量的影响比降雨径流量的影响百分比大，即与流域城市化相似。位于北海道东部北上市的富里托大坝实验盆地是为了阐明冻土对融雪径流的影响而建立的。主要结果和备注如下。(1)在融雪季节初期，随着冻土深度的增加，水文线长波出现膨胀；另一方面，在冻土深度较小的情况下，这种现象很少被发现。此外，除最大融雪季节外，该流域融雪径流量的日变化在一般流域经常观测到，但很少被认识到。(2)通过多元回归分析，霜冻深度与冻结指数、雪深和融化指数之间存在良好的关系，霜冻深度最大值与秋季累积降雨量有关。(3)为明确冻土对融雪径流的影响，通过纳入上述霜深预测模型，构建了考虑该站点霜深和雪深空间分布的4×3分区槽模型。因此，在融雪季节，由于土壤冻结降低了地表的入渗能力，有可能在山坡上发生坡面流。(4)在估算融雪量时，提出了考虑雪面层融雪再冻结的度-时法。通过考虑融雪-再冻结，可以估计融雪开始的延迟时间。

In Hokkaido, we have often experienced ground surface freezing during the winter like as Canada, North America in the subarctic zone. It shows that the effects of frozen soil on the snowmelt runoff got the runoff percentage larger than one of the rainfall runoff, that is, it was similar phenomenon as the urbanizing the basin. The Tomisato dam experimental basin, located in the eastern part of Hokkaido, Kitami City, was set up to clarify the effects of frozen soil on the snowmelt runoff.The main results and remarks are indicated as follows.(1) It was pointed out that the swell of long wavelength of hydrograph occurred in the beginning snowmelt season with the more frozen soil depth increasing. On the other hand, this phenomenon Was rarely recognized in the case of few frozen soil depth. Moreover, in this basin the diurnal change of snowmelt runoff, which has often observed in generally basin, was rarely recognized except in the maximum snowmelt season.(2) By multiple regression analysis, the frost depth is good relationship between freezing index, snow depth and melting index, and the max value of frost depth is dependent upon the accumulate rainfall at autumn season.(3) To make clear the effects of frozen soil on the snowmelt runoff, we construct 4×3 zoned tank model, which can consider the spatially distributed frost depth and snow depth at this site, by including the above frost dept prediction model. As a result, it is possible in snowmelt season to occur overland flow at the hillslopes because of reducing infiltration capacity of ground surface by soil freezing.(4) For estimating the snowmelt, we proposed the Degree-Hour method with considering the snowmelt-refreezing at the snow surface layer. By considering the snowmelt-refreezing, it is possible to estimate the delay of snowmelt start.