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

Evaluation of the effectiveness of mechanisms for eliminating flooding of urbanized areas with surface runoff

Summary

Flooding of urbanized areas happens quite often, while, during periods of heavy rains, water rises to the surface flooding streets and basements. Flooding occurs for different reasons or due to their combination. The list of measures to reduce the flooding rate has been worked out in the world practice. These include measures aimed at reducing the runoff coefficient of drainage areas, as well as increasing the spare regulating capacities of the networks and sewers, etc. However, evaluating their effectiveness in the Russian Federation is complicated by the fact that the standard method of hydraulic calculation provides for taking into account the values of the periods of one-time excess of the calculated rainfall rates p that indicates the overflow rate in the networks. However, this method does not determine the rate pp of area flooding that results from the water spills. Through the example of St. Petersburg, a calculation method is presented for determining the average annual number of floods, as well as the results of evaluating the effectiveness of measures aimed at reducing them.

Key words

drainage area , surface runoff disposal system , climatic parameters , force of rain , rainfall duration , travel time , flooding

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