1. The basin boundary of the Heihe River Basin was obtained based on a high-precision digital elevation model (DEM) and analysed using the GIS hydrological analysis function, with reference to remote sensing images, topographic maps, ground surveys and previous research results. The surface catchment area of the Black River Basin extends over an area of approximately 255,000km2, from the middle Qilian Mountains in the south, with the Gobi Altai Mountains in Mongolia on the northern boundary, from the Mahair Mountains in the west to the Yabuli Mountains in the east. Compared to the traditional extent of the Black River Basin, the new basin adds the Badangilin Desert, the Kuanzi Lake, the northern region of the Mahair Mountains and the southern foothills of the Gobi Altai Mountains in Outer Mongolia.

Note: The Nan Shi and Bei Shi rivers are rivers formed by seepage from the alluvial fan of the Shule River, and form a separate hydrological unit (the Huahai Basin hydrological systems) with the Petroleum, Baiyang and Broken Pass rivers, with the Ganhaizi as the caudal lake. This hydrological unit is more related to the Heihe River Basin than to the Shule River, both in terms of surface catchment conditions and historical hydrological changes, and should be considered part of the Heihe River Basin. Considering the current state of modern water use, the Beishi River has been artificially modified to be directly connected to the main stream of the Shule River and is an important channel for the Shule River to deliver water to Ganhaizi, which has become a de facto important tributary of the Shule River. Under the influence of a series of water conservancy projects, the Shiyou and Baiyang rivers also have a much greater surface hydraulic connection with the Shule River than they do with the Zhurai River.

2. Black River Basin Yellow Committee amended boundary

The revised boundary of the Yellow Committee of the Heihe River Basin was obtained on the basis of the boundary of the Heihe River Basin prepared by the Yellow River Conservancy Committee of the Ministry of Water Resources in 2005, using a high-precision digital elevation model (DEM), with reference to remote sensing images, 1:100,000 topographic maps, ground surveys and other information. The basin boundary covers an area of about 76,000km2, of which the upstream boundary of the middle Qilian Mountains is extracted in strict accordance with the ridgeline using the DEM based on the GIS hydrological analysis function, while the downstream northern boundary is divided in accordance with the national boundary according to international conventions.

3. Boundaries of the Black River Basin Study Area

Extended study area generated from the Black River Basin basin boundary, primarily for model data input needs.

The above three boundaries are to provide a unified study area boundary for the Black River Basin Plan project, and it is recommended that the revised boundary of the Black River Basin Yellow Committee be used as the core study area boundary.