Background Dilapidated dam will seriously threaten people's life and property safety, therefore, the identification and research of check dam's operation risk is particularly important.

Methods Selecting Chelugou dam system of Ningxia as the research object, a set of relatively complete evaluation index system of operation risk of both single dam and the whole dam system were extracted and established respectively from four aspects of engineering, management, economy and structure. With the method of improved AHP (Analytic Hierarchy Process) to calculate the index weight, the operation risk of single dam under seven different storm return periods and that of the whole system under the return period of 300 years were calculated and evaluated comprehensively, meanwhile the risk map of temporal and spatial distributionof single dam was made as well.

Results For the operation risk of single dam, it showed that there were three check dam including Chelugou, Qianzu and Dongzhuangwan, which operation risk grade grew from class Ⅲ(generally dangerous stae) under the occuring period of 10 years to classⅡ(dangerous state) under the occuring period of 50 years, 100 years, 300 years, which need to be taken seriously. On the whole, the project and economic risk of single dam in Chelugou dam system were generally high, which exceeded 0.8 and 0.4 perspectively, that was related to, the majority of dam in Ningxia was given priority to water storage. For the evaluation of dam system, when suffered a heavy rain of period 300 years, the operation risk of Chelugou basin from high to low were as follows:Wangzhao unit(0.51, classⅢ) > Qianzu unit(0.50, classⅢ) > the whole basin(0.44, classⅢ) > Dapin unit(0.39, classⅣ) > Panluwan unit(0.35, classⅣ), meaning that all dam unit were in the generally dangerous state or generally safe state. And from the view of whether dam system unit or the whole basin, the basin were all in a safe state of operation. It could also been seen from the results that the key dam unit was the Wangzhao unit and Qianzu unit which influenced the operation safety of the whole dam system. In addition to building spillway, it was necessary to deal with the damaged parts of dam body as well as water release works as soon as possible to eliminate hidden dangers.

Conclusions The paper realized the evaluation work of operation risk of single dam, check dam unit as well as the dam system on the whole. These results would provide certain reference to the safety forecast warning of check dam in the region and help the administrative department of rapid decision-making, so as to ensure the safe and stable operation of check dam and lay the foundation for establishing the safety emergency response mechanism and operation measures.