The application snowmelt runoff model considered the characteristics of snow distribution outside of forests to the dam located in high elevation zone in Japan

Thursday, 18 December 2014
Terumasa Nishihara, Civil Engneering Research Institute for Cold region, Sapporo, Japan, Makoto Nakatsugawa, Muroran Institute of Technology, Muroran, Japan and Tomohide Usutani, Japan Weather Association, Hokkaido Branch, Sapporo, Japan
In snowy cold regions, snow-melt water can cause a snowmelt floods. For this reason, many snowmelt runoff models have been proposed for predicting the volume of runoff into dams. Given that snow distributions differ between inside of forests versus outside of forests, we developed a snowmelt runoff model that is able to correct the snow distribution by using observation data from snow surveys. This paper reports the results obtained when the model was applied to Chubetsu Dam, Japan, which is at a high elevation and about 40% of whose basin area is higher than the forest limit.

The Model consists of three sub-models, first, a snowmelt model and a snow permeation model are applied to meshes of about 1 km2; then, water supply to the ground is estimated for each mesh. After that, water supply to the ground for each mesh in the entire basin are lumped together, and the lumped value is applied to the runoff model to obtain dam inflow. With regard to the correction of snow water equivalent distribution, a correction method that considers topography is applied to meshes inside of forests, a correction method using overground openness as a parameter is applied to meshes outside of forests, and the parameters for the correction formula are determined based on the results of the annual snow survey.

Calculation was performed using the data of the five snow-melting seasons from 2008 to 2012. The accuracy is higher when this method is employed than when no correction is made; thus, the correction of snow distribution was found to be effective. Since there is no significant difference between when no correction was made and when this method was employed in the early snow-melt season, it is considered that the correction of snow distribution is very effective at high elevations, where snow-melting peaks in the late snow-melting season. At high altitudes above the forest limit, fallen snow tends to be redistributed by wind. The snow distribution corrected by means of overground openness gives consideration to the characteristics of snow distribution after redeposition, i.e., after the wind has redistributed the snow. From this, it is assumed that the snow distribution in the high-altitude range was properly corrected, thus contributing to improved accuracy of dam inflow calculation.