| The Shiyang River basin is one of three big inland river basins in Hexi Corridor, Gansu. Because of overdevelopment of water resources, vicious circle was resulted, which appear as the development on middle reaches occupies the downstream water, the downstream development occupies the ecology water, the conflict of supply and demand is severe day by day. The groundwater is over exploited seriously in Minqin, which brings about decline of water table continuously and causes water quality deterioration, the vegetation degenerates, the land desertification and the oasis shrinks. The survival of Minqin oasis has been threatened. The Shiyang River Basin has become the typical region of ecological environment degenerates in Northwest China. Therefore, it is of practical significance to analyze present situation of water resources in Shiyang River Basin, to seek the reasonable used pattern and water diversion quantity from other watersheds. At the same time, it also provides the scientific basis for the central and all levels of local authority to make strategic policy for Hexi Corridor, Gansu and for northwest China. The main conclusions and understands through analysis were obtained by the study, as follows:(1) According to the existed problems in the Shiyanghe River Basin, the Minqin Hongyashan irrigation district and Jinchang city were selected as reception area.(2) The annual runoff at mountain-pass gauging stations does not change acutely, but have remarkable reduction tendency and persistence. The rivers have the 22 year, 14 year, 10 year, and 9 years periods separately. Based on the combination forecast thought, the grey theory, self-memory model and the BP neural network were used to predict the annual runoff of the water supply system, the result is rather ideal.(3) The GM(1,1) model was established to predict the population increase.(4) The ecological water requirement in the reception region was obtained: the ecological water requirement in Minqin Hongyashan irrigation district is 1.93×108m3 and the Jinchang irrigation district is 0.068×108m3. And the total water demand and supply at different water years were sum up.(5) Based on development of higher, middle, lower level in the reception region, andaccording to the basic and intensified quota of the water saving, the balance of water supply and demand were analyzed. Based on the analysis, it was suggested that in 2010, Minqin Hongyashan irrigation district adopt the lower level of development according to intensified water saving quota, and also the Jinchang irrigation district, the urban district adopt the median level of development, and such the reception region water balance of supply and demand would be retained. In 2020, if the reception regions adopt intensified water saving quota and lower level of development, they would need the quantity of water diversion from other watersheds of 5.71×108m3, of which Minchin irrigation district 3.637×108m3, Jinchang 2.073×108m3.(6) Based on calculation of suitable scale of reception region, it was indicated that 60×104 mu irrigated farmland in Minqin Hongyashan irrigation district would be suitable. And in Jinchang irrigation district 65.36×104 mu irrigated farmland is suitable, but the proportion of forestry and grass land is too low, and it was suggested that it had better return 3.36×104 mu farmland to forestry and grass land for making the reception region in the suitable scale. If there is no water diverted into the area, it would not be maintain the existed scale and economic development level due to short of water for the Minqin Hongyashan irrigation district. The Jinchang irrigation district would return 7.6×104 of farmland into grassland, in order to keep the agro-economy maintaining the existed economic level as nowadays.
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