**Abstract**

Reservoir is an important part of water conservancy engineering system and an important infrastructure for economic and social development. However, with the increase of operating time, as well as the change of social demand and operating environment, the safety, function, benefit, cost, and other characteristics of the reservoir are also changing. Like living things, reservoirs also have a life cycle of "birth, old age, illness, and death." The retirement of a dam is an inevitable stage in the life cycle management, as well as a means of resource readjustment and rational utilization. Combined with dam retirement cases that caused severe impacts in history, generalized dam removal eco-environment influence factors are obtained from aspects of materializing, ecology, society, and economy. Based on economic rationality theory and flood consequence assessment, two decision-making methods of dam retirement are put forward. The flood consequence method is applied on the case of Heiwa reservoir; key evaluation indexes are compiled from the aspects of ecology, economy, and society; and the evaluation system based on single index is constructed.

**Keywords:** risk assessment, risk reduction, dam retirement decision, dam removal

### **1. Introduction**

After the dam removal, the ecosystem balance formed by the long-term storage of the reservoir will be broken, which is not a simple adverse process of the ecological environment impact of the dam construction, and may pose a new threat to the river ecosystem. Therefore, it is of great theoretical significance and practical value to establish a method to assess the impact of removal decision. In order to achieve that, key factors need to be identified first.
