Storm Drains

Storm drains are artificial structures serving for the removal of contaminated waters—fecal, domestic, industrial, atmospheric, and groundwater. Usually, storm drains represent a system of pipelines of various forms and sizes, depending on the quantity of liquid to be drained, through which water is removed by gravity. In the USSR, storm drains are classified according to their purpose, namely: 1. Sanitary sewerage—a network for the removal of fecal, domestic, and industrial waters, i.e., such waters that require preliminary treatment and disinfection before being discharged into natural bodies of water. 2. Proper storm drains—for the removal of atmospheric waters (rain and meltwater), which in essence can be discharged into natural bodies of water without preliminary treatment. 3. Drainage storm drains—for lowering and removing groundwater for the purpose of drying out the area. Thus, proper storm drains are those pipelines that remove only atmospheric waters (rain and meltwater). Sometimes the removal of domestic and industrial waters is combined in one common network with the removal of atmospheric waters; such a system is called combined, as opposed to separate, when two independent pipeline networks are built for both types of waters (an example of a separate system—Moscow). In combined systems, to facilitate the operation of treatment facilities (irrigation fields, filtration fields, etc.) and to avoid overloading these expensive structures, storm overflows are installed at certain points in the network for the direct discharge into natural bodies of water of that large excess of water which enters the network during rains and which, due to significant dilution of fecal and domestic waters in the common network, does not require preliminary treatment and disinfection and can be discharged into bodies of water without harm. - The storm drain network, like sewerage, must be laid along all city streets for the rapid and proper removal of upper waters from streets and building blocks. Unlike sewerage, the construction of which in cities is possible only under certain conditions, such as: sufficient population density, uniform distribution of population over the city area, presence of a water supply, etc., the construction of a storm drain network is possible with any development of the city and its improvement. The laying of the storm drain network is oriented to the terrain and begins from natural bodies of water in the lower parts of the city, gradually rising, following the slope of the terrain, and reaches the watershed divides. The depth of laying storm drain pipes and channels depends on local conditions, the terrain, and the size of the channels, but in any case, it should not be less than 1¹/2 meters for the northern and middle zones of the USSR; in areas with less prolonged and severe winters, pipes can be laid at a shallower depth. For the calculation of the storm drain network and for the proper selection of pipe sizes, it is necessary to determine what quantity of rainwater the network should be designed for. Of all types of atmospheric precipitation (rain, snow, frost, and hail), heavy rains and, to some extent, moderate downpours that give a large amount of water in a very short period of time are important for channel calculation. It is not feasible to design storm drains for the heaviest downpours, because, on the one hand, with this method of calculation, channels receive very large dimensions and the construction of the network becomes extremely expensive, and on the other hand, heavy downpours occur relatively rarely and there is no need to design the network for them, consciously accepting the possibility of flooding the area during exceptionally heavy downpours. Therefore, meteorological data based on many years (at least 20 years) of observations obtained from records of self-recording rain gauges should be the basis for selecting the design rainfall. Further, for the proper calculation of the network, it is necessary to take into account the circumstance that not all water falling on a certain area (basin) enters the storm drain network; part of the water is delayed by conditions of its runoff over the surface, part evaporates, part is absorbed into the ground, etc., i.e., it is necessary to establish the runoff coefficient for a given city and its individual parts, which depends on the density of development, the type of street and yard coverings, the size of green plantings, etc., and is determined empirically. Thus, for example, for Moscow, it is accepted to divide it into 3 zones: 1) central, with a runoff coefficient of 0.85, 2) middle—0.70 and 3) peripheral—from 0.50 to 0.25. Finally, the third factor affecting the amount of water to be drained is the retardation of runoff, which consists in the fact that with large basins and not too prolonged downpours, there is a delay of liquid from remote parts of the basin to certain sections of the network. In such cases, discharges from remote parts of the basin begin to flow to the outlet sections already after the end of the rain, which gives a reduction in calculated discharges. The shapes of the cross-sections of pipes and channels are extremely diverse; the most common are circular and egg-shaped (see Figure 1 and 2). The latter have the property that in them, with small water discharges, a greater velocity is obtained than in circular ones. In these two types of channels, the requirement from a hydraulic point of view is met, i.e., that the ratio of the cross-sectional area to the wetted perimeter is the greatest (hydraulic radius). In case of heavy loads on the collector, it is given a shape advantageous from the point of view of static calculation (see Figure 3). Often, depending on local conditions, when the collector has to be laid close to the street surface, it is given the form of a compressed trough section (see Figure 4). The material for pipes and channels of the storm drain network is ceramic (glazed pottery pipes), concrete, brickwork, and reinforced concrete; in rare cases and exceptional conditions—cast iron and iron. Circular pipes, with a diameter from 13 to 76 cm, are manufactured by the factory in the form of glazed pottery pipes, about 1 m long with sockets; other types of channels, except metal ones, are laid in trenches in place during construction. For monitoring the operation of the pipe network and for the possibility of cleaning them, brick or concrete inspection wells of sufficient size for the descent of one worker are built over them.

Figure 1.

Figure 2.

The wells are brought to the surface of the street and are covered with heavy cast iron covers or manholes that withstand the pressure of heavy carts (see Figure 5). For receiving rainwater from city streets, brick intake wells with iron gratings are built, which should be opened to allow for cleaning the wells from accumulating dirt in them (see Fig. 6). A well-constructed storm drain network from non-rotting materials requires almost no expenses for its operation, except for repairs when necessary. The speed of water in the pipes is chosen with such a calculation that during rains self-cleaning of the pipes occurs and only small branches from the manholes and the manholes themselves from accumulating street sweepings and other foreign objects thrown into them need to be cleaned. In winter, storm drains do not operate, but in spring, during general thawing, they remove a very large amount of water; therefore, to prevent freezing, the network has to be insulated, i.e., the manholes are covered in winter so that there is no draft of cold air in the network. Due to the extraordinary variety of pipe diameters, from 45 cm to 4-5 m (and more), different depths of their laying and degree of network development, it is quite difficult to determine the total cost of installing a storm drain network in a city; however, according to experimental data, it can be tentatively accepted that the complete installation of a storm drain network in a separate sewerage system of a city costs about 1.5-2 rubles per square meter of territory area with full network development. For small territories, this cost increases. The installation of storm drain networks has very great significance in the matter of improving and improving cities: thanks to properly constructed storm drain networks, upper waters are quickly removed both from streets and from built-up areas, which, besides the possibility of keeping populated areas clean, prevents the waterlogging of the soil.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

the only possibility for drying out areas with high groundwater levels, since they themselves contribute to this lowering and, in addition, drainage systems specifically designed for diverting groundwater can be discharged into them; the presence of a storm drain network makes it possible to wash away ordinary street pollution of city thoroughfares and public places, especially when cities have improved pavements; finally, storm drain networks greatly contribute to the installation, preservation, and proper functioning of other underground and above-ground structures that serve the improvement of populated centers, such as street and off-street railways, gas networks, networks of all kinds of cables, and so on. All this together places storm drain networks in the category of structures necessary for any well-organized city, along with water supply systems, sewerage systems, and others; however, in practice it is otherwise, and proper storm drain networks in many cities are usually built only after water supply and sewerage systems, since due to lack of funds, cities have to first construct those structures that have the greatest sanitary significance, and these are, first, the water supply system that provides the population with good drinking water, and second, the sewerage system that diverts and neutralizes polluted urban waters. Lit.: Ivanov V., Sewerage of Populated Areas, Odessa, 1926; Ushakov N., Sewerage of Populated Areas, M.-P., 1923; Gorbachevy F., On the Calculation of Storm Water («Report of the XII All-Russian Water Supply and Sanitary Engineering Congress in Moscow in 1922», L., 1925).