The complex nature of the wave structure of the oscillations is the reason for the variability of Baltic sea level. It was determined by the method of statistical data analysis. Surge wave and wind influence the local shape of the wave field which is a superposition of standing oscillations with random phases. Overlaying and mutual strengthening of these factors leads to the occurrence of such extreme events as flooding in the Eastern part of the Gulf of Finland. The article discusses the solutions to this problem – the complex of protective structures, bypass channels, and a different mathematical model for the dynamics of surface water, to detect the occurrence of surge. Considered are the main protective structures of St. Petersburg from floods and proposed new solutions to the problem.