Definition method of design flood water level for tidal reach mainly included in direct frequency analysis method for flood water level, indirect method getting design flood water level from design rainstorm, and frequency combination method.

Abstract: Based on the introduction of theory of frequency combination method, the paper analyzes the influence factors of drought occurrence and the features of this method,and demonstrates the feasibility of applying this method in drought analysis.

In order to calculate the actual flood control capacity of the Fushi Reservoir at present, the stochastic coupling method and frequency combination method were adopted to analyze the probability distribution of actual starting regulation level of the reservoir during the typhoon flood period and then combining with the design flood.

Based on observation data in the basin,the stage design flood at the dam site is calculated by area interpolation method,compared with the maximal value of design flood,and the quantitative relations between them are also worked out by introducing the conception of combined frequency.

This paper investigates various combined frequency interference in integrated and double-converted transceivers, and points out that the reason is the non-linearity of frequency mixer and amplifier.

In order to do a good work on flood control works and to seek for a better calculation method, this paper describes the theory and its application of frequency combination method and compares it with the traditionally used method via the practical examples.