Study of the storm runoff mechanism (for discussion)

Summary

For the hydraulic calculation of surface runoff disposal networks in SP 32.13330.2018 «Sewerage. External Networks and Structures», a technique is applied that implements the method of «limiting intensities». Despite its notability and widespread use in practice, a number of authors point to a limited area of its use. However, there are no results of a quantitative assessment of the errors of this method in the technical literature. For this reason, the analysis of the degree of influence of the accepted assumptions on the results of hydraulic calculations was carried out. It has been established that with certain ratios of other factors, the use of the «limiting intensities» method can result in an underestimation (from 1.2 to 1.7 times) of the calculated wastewater flow rates. Taking into account the results obtained, two directions of work are formulated to eliminate the consequences of flooding in sewer basins. The first direction provides for the introduction of engineering measures aimed at increasing the reliability and efficiency of the sewer system operation, the second – the improvement of the construction regulations that exclude the creation of problem situations in the future.

Key words

drainage area , method of limiting intensities , climatic parameters , force of rain , rainfall duration , surface runoff disposal systems , travel time

Substantiation of the method for estimating the climatic parameters of rain showers by the data of the precipitation gauge system (for the discussion)

Summary

The standard procedure of the hydraulic calculation of surface runoff disposal systems, given in CP 32.13330.2018 «Sewerage. External networks and structures», is implemented within the framework of the method of limiting intensities developed about 100 years ago by Professor P. F. Gorbachev, based on the «theory of rain showers», that was subsequently improved. Herewith the rated parameters of rains determined by the results of many years of observations several years ago were used as initial data. Due to climate change, the need for updating local climate constants is obvious; however, this cannot be implemented in each region due to the lack of self-recording rain gauges or due to the small amount of information accumulated. Using the example of St. Petersburg, an experimental substantiation of the method for accelerated estimation of the climatic parameters of rain showers according by the data of a system of 34 precipitation gauges was carried out. It is established that the revealed rainfall patterns over 5 years do not contradict the classical theory. Moreover, in the interval of periods of a single excess of p > 10 years, their validity is the highest compared to other methods due to a more representative sample.

Key words

surface runoff disposal system , method of limiting intensities , climatic parameters , force of rain , rainfall duration

Systems for the removal of surface runoff: problems and solutions (for discussion)

Summary

For the hydraulic calculation of storm sewer networks removing surface runoff in our country, the concept of immediate removal of runoff formed as a result of rainfall has been used for more than 60 years. With this aim, the method of «limiting intensities» has been used up nowadays, implemented with the help of the methods laid down in Norms and Technical Conditions for Design 141-56, SNiP II-G.6-62, SNiP II-32-74, SNiP 2.04.03-85, SP 32.13330. 2012, CP 32.13330.2018. If we continue to be guided by this concept, then in order to adapt the operated systems to the current conditions, in most cases relaying all the networks with larger pipe diameters would be required, which is practically impossible not only from the economic, but also from the technical and social point of view. In the current situation, introducing alternative solutions for adapting storm sewer networks is needed, which, in comparison with relaying all the networks, are more economically justifiable. Among them, noteworthy are the solutions that provide for the detention and retention of water in sewers, and for reducing runoff coefficients. The effectiveness of these solutions is estimated using numerical modeling and analytical calculations.

Key words

drainage area , method of limiting intensities , climatic parameters , force of rain , rainfall duration , surface runoff disposal systems , travel time