Using RVA to Determine the Feasible Draft of Main Tunnel of the Diversion Work from the Datong River to the Huangshui River

In the northwest of China, the Qinghai province intends to construct a main tunnel to divert water from the upper Datong River to the Huangshui River. In order to determine the feasible diversion of the main tunnel, a diversion dam operation model is established employing varying design diversion as one of its inputs and the Range of Variability Approach (RVA) is used. Results shows that the diversion in the upper Datong River must not exceed 377 million cubic meters that is about 23.86% of 1.58 billion cubic meters, mean annual runoff of the upper Datong River under the case not diverting water in December, January and February, which is much less than 1422 million cubic meters suggested in 1997. The mean annual diversion of the main tunnel can reach 284 million cubic meters that is about 17.97% of annual runoff of the upper Datong River.