Specific features of estimating calculated rainfall rates with account

Summary

The analysis of official data resources shows that the distribution of extreme rainfall over the territory is carried out with account of the microclimatic features of the area. To estimate the degree of reliability of such patterns within megalopolises, experimental studies were carried out, where the wastewater disposal system of St. Petersburg was assumed as an experimental base; a network of 34 automatic rain gauges recording with an interval of 5 minutes was assumed as a measuring instrument, and a base was used as experimental information, i. e., a measurement data base for six years. As a result of the research, it has been established that a microclimate is formed in the urban environment that differs from the climate outside it. Besides, on a megacity scale, there are microclimatic zones where the dependences of precipitation intensities on their frequency can differ significantly. In this case, the differences begin to manifest at periods p of one-time excess of the calculated rainfall intensity from 1.5–2 years, whereas at lower values, no differences have been found. The result obtained is consistent with the research data obtained by other authors, who experimentally established that the amount of extreme rainfall increased in those areas of megacities, as a rule, historical ones, where fewer green spaces are located, and, accordingly, a higher degree of surface overheating in summer is recorded.

Key words

rainfall intensity , surface runoff disposal system , climatic parameters , rainfall duration , flooding , microclimate

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

Economic efficiency of measures to provide for the surface runoff disposal systems adaptation to changing climate conditions

Summary

The process of economic justification of measures to provide for the surface runoff disposal systems adaptation to the new operating conditions comes down to solving an optimization problem where the maximum economic effect is assumed as the optimization criterion in the form of the difference between the cost of prevented damage from flooding of territories during the periods of heavy rains and the costs of investment and operating activity. The justification of this approach is obvious, since from a stochastic point of view it is impossible to completely eliminate flooding. Accordingly, the estimation of the effectiveness of adaptation measures should be based on the comparison of costs and benefits. The key elements of such an estimation, along with the justification of effective engineering solutions for adaptation, is the determination of the number of floods for the estimated period of time and the damage expected from them, i. e., the damage function that is the sum of the products of the probabilities of damage and its cost. In the Russian Federation the approach that takes into account the probability of flooding, is unrealizable at the regulatory level, since at the stage of hydraulic calculations, the probability of exceeding the calculated rain intensity is taken into account rather than water outcrop. In addition, in domestic practice, as an engineering measure for the adaptation of wastewater disposal systems, the method of network upgrade is mainly used which is the most expensive one compared to other alternative methods. Therefore, the effectiveness of applying the method of network upgrade in combination with the introduction of elements of a «green» infrastructure and regulation of wastewater flows is analyzed using the example of a pilot wastewater drainage area.

Key words

economic efficiency , drainage area , surface runoff disposal system , flooding , adaptation measures