THE CHANGES OF HEI RIVER (RUOSHUI) SYSTEM IN HEXI
河西黑河(弱水)水系的变迁

The Hexi desert and oases region of Gansu Province belong to internal drainage area where all rivers originate from Qilian Mountains. From east to west, the rivers can be divided into four drainage systems; Shiyang river system, Hei river system, Shule river system and Harteng river system. Har-teng river flows into Suganhu Basin which lies in the northern margin of Caidamu Basin, while all theot her three drainage systems flow into Hexi Corridor, Hei river is the greatest and longest of all these rivers, stretching north to Alashan Plateau. This paper mainly discusses the distribution and change features of Hei river system based on the ancient and modern maps and salt content in ancient rivers and lakes and deduces how it has changed from exterior river to interior river, from integrate drainage system to many seperate drainage systems, from a river with its middle and lower reaches in the same course to a special river which changes alternately between surface water and undergronud water in the middle and lower reaches, and forming many oases of varying sizes along the bank of the river in certain regions.