Simplified Dynamic Reliability Models for Hydraulic Design

Two simplified dynamic reliability models for hydraulic design are developed, which consider both hydraulic and hydrologic uncertainties. To incorporate the safety factor into the reliability model properly, the actual design flood is introduced and defined as the product of the safety factor and the design flood. The reliability models represent unique relationships between actual design flood and reliability. If actual design floods are the same, regardless of changes between the safety factor and the design flood, the same reliability results are obtained by the simplified models, given that the service periods are identical. The simplified models can be reduced to the conventional reliability models when only hydrologic uncertainty is considered. The risk due to hydraulic uncertainty can be estimated from the difference of the reliability results by the conventional reliability models and those by the simplified models, i.e., the difference between single and total reliabilities. The simplified models can be used to design new hydraulic structures and to evaluate the reliability level for existing hydraulic structures.