Abstract: Water level is one of the most important hydrological indicators of lake, which reflects effectively not only the variations of lake water volume, but also the evolution of eco-environmental conditions of the surrounding lake wetlands. This study investigated the minimum ecological water area and the lowest ecological water level of the East Juyanhai, the rump lake of the downstream of Heihe River, using lake morphology method. The ecological water demand under different scenarios was estimated based on the principle of water balance and the existing researches. We evaluated the discharging water volumes at the hydrologic section under different scenarios(hydrological frequency), considering the water consumption law of Heihe River channel. The results show as follows:(1)the minimum ecological water area and the lowest ecological water level of the east Juyanhai are 11.11 km² and 998.78 m, respectively;(2)the minimum ecological water demand is 0.28×10⁸ m³;(3)in dry years(hydrological frequency=75%), the runoff at Yingluoxia and Zhengyixia hydrological stations should be no less than 10.93×10⁸ m³ and 6.27×10⁸ m³, respectively. In flat and abundant water years(hydrological frequency=25% and=50%), they should be no less than 21.46×10⁸ m³ and 12.32×10⁸ m³;(4)these results are reasonable and consistent with previous studies. The research method developed in this study can be applied practically and universally to other regions for the estimation of the minimum ecological water demand. This study is of great significance for the protection of lake wetlands and the rational utilization of water resources in arid area. At the same time, it provides a scientific basis for the implementation of Ecological Water Transfer Project in Heihe River Basin.

Key words: scenarios, rump lake, ecological water level, water demand, East Juyanhai