1. Researcher, Dept. of Hydrology, Faculty of Global Environmental Science, Kim Il Sung Univ., Pyongyang 999093, DPR of Korea (corresponding author).
2. Professor, Director of Dept. of Hydrology, Faculty of Global Environmental Science, Kim Il Sung Univ., Pyongyang 999093, DPR of Korea.
3. Researcher, Faculty of Geology, Kim Il Sung Univ., Pyongyang 999093, DPR of Korea.
4. Researcher, Dept. of Hydrology, Faculty of Global Environmental Science, Kim Il Sung Univ., Pyongyang 999093, DPR of Korea.