Abstract: This paper describes a simple method for the definition and verification of seasonal freeboards taking advantage of elements that make up a risk model, focusing on hydrological safety, and provided that hydrological data and reasonably long incoming flow series are available.
Definition of seasonal freeboards can be a complex problem involving many variables, such as safety, hydrological analysis, dam user requirements, applicable safety regulations and economic analysis, with safety priorities often being at odds with an efficient operation. Thus, a dam-reservoir risk model, which encompasses most safety related aspects, becomes an efficient way to integrate this wide range of variables.
The first step in the evaluation of the seasonal freeboards is a characterization of the seasonal hydrology. Often, lack of sufficient data, such as historic pool levels or incoming water flow adds uncertainty to this analysis, so simplified methods have to be adopted. A flood routing model must then be used, establishing a relationship between incoming seasonal floods, freeboards and peak outflow. The possibility of overtopping must also be addressed.
A downstream consequences model, which links dam outflows and possible damages, including loss of human life may then be applied.
The final goal is to obtain, for any given flood, its seasonal probability (and its return period), the dam-reservoir response (as an outflow, or even overtopping), and then its downstream consequences, so that a sensibility analysis can be made. Minimal seasonal freeboards for any safety condition can then be directly found.
A case study will be provided, in which seasonal freeboards are analyzed and verified for a large Spanish dam, taking into account data availability, operating rules, downstream flood consequences and legal requirements.

Key words: risk analysis model, flood, seasonal freeboard

摘要： 重点关注水文安全方面，在水文数据和合理的长期入流系列资料可获取的前提下，利用组成风险模型的各要素，使用一种简单的方法来确定和验证季节性的安全超高。
确定季节性的安全超高是一个包含了众多变量的复杂问题，比如安全、水文分析、大坝用户的要求、可应用的安全规章和经济分析，而安全优先通常与高效运营相抵触。因此，考虑了大多数安全因素相关方面的大坝-水库风险模型是综合这众多变量的有效方法。
评估季节性安全超高的第一步是对季节性水文条件进行定性。通常，数据不足（如历史库水位或入库流量等）将增加分析的不确定性，因此，只能采用简化的方法。再使用洪水演进模型，建立季节性入库洪水、安全超高和峰值出流量之间的关系。漫顶的概率问题也必须加以说明。
然后，再使用将大坝出流量与可能的损失联系起来的下游后果模型，其中包括居民生命损失。
其最终目标是，对于任意给定洪水，都能获得其季节可能性（和其重现期）、大坝-水库响应（比如出流量或甚至是漫顶）以及下游的后果，然后才能进行敏感性分析。这样，对任意安全条件，都能直接找到最小季节性安全超高。
笔者列举了一座西班牙大坝作为案例分析和验证季节性安全超高，其间考虑了数据可获取性、运行规则、下游洪水后果和法律要求等。

关键词: 风险分析模型, 洪水, 季节性安全超高