A technical structure designed to collect and drain rain (melt) water is called a storm drain. This is one of those important structures for economic and technical purposes, which are among the integral elements of residential, commercial and industrial buildings.
An important factor in construction is the calculation storm sewer. The construction of the system “blindly” risks flooding or drying out landscape areas, as well as destruction of the soil structure.
In the article we presented, the types of storm drains are analyzed in detail and the methods of their construction are described. The basic principles of designing atmospheric water drainage systems are outlined. Valuable recommendations for construction are given.
The practice of constructing various types of structures shows the use of three types of systems, each of which differs in the methods of collecting and removing precipitation products:
- Based on open channels and trays (ditch).
- Based on closed wells and pipelines (closed).
- Based on a combined solution (mixed).
The first project is implemented in practice by constructing canals that connect drainage trays to each other and, ultimately, drain the collected water beyond the intended territory.
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All these elements of the storm drainage system have an open connection with environment. The construction of such structures requires a relatively small amount of resources and materials.
Storm drainage scheme closed type should be considered more advanced in design terms. Hidden drainage lines are being built here, as well as a system of storm water inlets - special intermediate storage tanks.
Storm drain open type in industrial design. The main structural elements are concrete trays, on top of which lattice metal sheets are laid. Open storm drainage schemes for private housing construction are built using the same principle.
The collected water is discharged through networks of pipelines laid and hidden underground. As a rule, the collected precipitation products are displayed on wastewater treatment plants and further in the waters of natural reservoirs.
The third option is mixed storm sewer. It is constructed on the basis of mounting components designed for both open and buried systems.
The design of mixed storm sewerage is carried out based on the rationality of operating the system in individual areas of the area. The financial side of its implementation plays an important role in the decision to choose a combined option.
Separately, a ditch (trough) system for collecting and draining rainwater should be highlighted. This storm drainage system, together with its simple manufacturing scheme, is characterized by universal operation.
Ditch storm drainage has the advantage that, together with the function of draining rainwater, it can act as a supplier of moisture for agricultural plantings. Also this economical option construction compared to other projects
Thanks to the ditch design, it is possible to organize not only quite effective drainage of precipitation products. The same system can be successfully used as an irrigation structure, for example, for the needs of a household (dacha) farm.
What is taken into account when calculating?
For each private construction project (exploited area of the territory), individual design is commonplace.
However, the basis is always taken to be solutions typical for standard stormwater construction projects. Standard solutions by default, they involve resorting to technical calculations before the construction of the system begins.
Calculations are carried out with an eye to SNiP and taking into account the following factors characteristic of a specific area and object:
- annual precipitation rate;
- soil properties;
- object area;
- mass of discharged water;
- required drainage area.
In addition to information about the mass of sediment discharged, other information can be obtained by contacting the local weather service. And the conditional amount of discharged precipitation products is calculated using the formula, where the area of the drainage area and the parameter of the intensity of this precipitation are taken as calculation data.
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Mathematical form of the formula:
M = (A * 20) * S * k,
In it accordingly:
- M– mass of discharged water;
- A– intensity of precipitation within 20 minutes;
- S– drainage area (for the roof also + 30% of the total area of the building walls);
- k– coefficient of moisture absorption by the object material.
The materials of the object are often roofing coverings (k=1); concrete and asphalt structures (k=0.9); soil (k=0.75); crushed stone, gravel (k=0.45).
System design features
Atmospheric precipitation is removed from the roof of the building through. These are external lines of riser pipelines located under the end points of the receiving gutters. In turn, receiving gutters are mounted along the perimeter of the roof area under the lower edge of the covering.
Collection of rain (melt) water from the roof area is carried out, first of all, by gutters. These structural elements are mounted along the lower edge of the roof covering and are adjacent to the riser at the lowest point of the slope. Next, the water is directed through the pipe to the rain receiver
On flat roofs, the drainage goes directly into the pipe risers. With this scheme, drain pipelines are usually mounted vertically inside buildings, and their upper sockets are brought out onto the roof and are integral with the roofing carpet. On flat roofs of private houses, the presence of one drainage funnel is permissible.
If the house uses internal risers with an open outlet, their design should provide for the possibility of draining melt water into winter time into the domestic sewer system. The drain line must be equipped with a water seal. Based on the calculated data on the consumed mass of water, the diameter of the pipes for the construction of the storm sewer riser is selected.
Table for selecting pipes for the riser:
The preferred material for internal drain pipes is plastic, asbestos cement, cast iron. Tin and plastic pipes are usually used to construct an external storm drainage system.
When installing horizontal trunk lines, it is required to maintain a standard slope (not less than 0.005 m and not more than 0.15 m per 1 m of line length).
Storm drainage projects for private housing construction usually involve the use of plastic pipes for the installation of linear mains. This is the most reliable option, but the most economical. However, frequent damage to individual areas negates all savings.
For cases maintenance it is necessary to provide for the installation of inspections and cleanings. On storm sewer risers, audits are installed within the boundaries of the lower floor of the building.
In order to calculate the throughput of linear storm drainage trays, you need to take into account the area of the treated object, towards the channels and the water absorption coefficient adopted to cover the territory. In addition to these data, you will also need to calculate the hydraulic cross-section of the tray.
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General principles for arranging a storm drain
Owners of private houses are quite capable of constructing communications for collecting and draining rain (melt) water with their own hands. After completing all the calculations and purchasing the required materials, they begin to arrange the storm drainage system.
The first step is to dig trenches for drainage lines in the local area, according to the planned plan. Trenches are brought to the locations of drain risers (drainpipes). For planning a private household system, a trench depth of 300-500 mm is sufficient.
When excavating trenches, take into account the slope of future pipelines (or trays) towards the central storage reservoir. The bottom of the finished trenches is compacted by tamping and covered with a layer of river sand (at least 200 mm high)
On sites under drainpipes, pits are dug for storm water inlets and installed. These system elements are rectangular containers of small volume (5-10 liters).
To install inspection and rotary wells, it is recommended to use ready-made industrial ones or make them cast from polymer concrete. The first option is more expensive, but easier to install and maintain.
Industrially produced storm water inlets are usually supplemented with large waste collection baskets. Natural debris inevitably ends up in storm drains with rainwater flows.
One of the many existing storm drain designs. Manufacturing material – plastic. The optimal choice for private real estate projects. Such containers are usually supplemented with filter baskets to trap large debris
Based on the chosen technology for constructing storm sewers (open or closed), trays are laid in trenches or a line of
If you are making a simple tray drainage system with outlet to a nearby lawn, it is advisable to take into account the risks of possible soil erosion in the drainage areas. Elements of closed installation at joints must be sealed.
The communications collected in this way must be connected to a common storage tank or collector of a centralized network.
You should also take care of constructing sand filters immediately before entering the common storage tank. And don’t forget to install inspection wells. Their installation is necessary on sections of highways longer than 10 meters, as well as in places in the diagram where turns in the drainage line are formed.
Methods for discharging collected water
A serious task for owners of suburban real estate is the drainage of rainwater collected from the total area of the site.
If there are no centralized communications near the house, there are two options left to solve this problem:
- Collection in a special tank and subsequent use for irrigation;
- Discharge of water from the reservoir into the ground or into natural areas.
The first option is considered rational, provided that there are watering facilities on the territory of the house. In this case, you will need a simple device (household pumping station) for pumping water from a storage tank with its subsequent supply to irrigation areas.
Scheme of drainage of collected rainwater into the ground. One of those possible schemes that are available to owners country houses. The efficiency in terms of removal speed is low, but given the use in small areas, this scheme is quite suitable
The second option is accompanied by great difficulties. Removal into the ground is a time-consuming process. How long it takes to hatch depends on the soil’s ability to absorb moisture. In different relief areas, the coefficient of soil saturation with moisture can differ significantly.
In order to divert the storm sewer product to natural areas (“to the relief” or “to the landscape”), an additional scheme will have to be implemented. This scheme includes a central reservoir and a groundwater treatment system, for example.
The “relief” or “landscape” output scheme is accompanied by difficulties in constructing treatment modules. Both options require approval from environmental authorities.
Usually, the owner of the property (plot) has to contact the following organizations with the subject of approval:
- Department of Natural Surveillance.
- Fisheries Department.
- Office of Consumer Regulation.
- Basin and water management.
- CGMS.
The subject of approval means “Draft standards characterizing the discharge procedure.” Based on such a project, a permit is issued allowing the discharge of pollution “onto the landscape” or “on the relief”, and a decision is made on the provision of a water body.
Discharge of water from storm drains “to the relief” or “to the landscape”. Such schemes are not regulated in any way by SNiP documents.
Implementing such options illegally carries the risk of high fines, and legal disposal requires approval from the authorities.
Private real estate projects traditionally include, along with storm drainage, other communication networks. Domestic sewerage is also part of household communications. The principle of their operation differs little from the functioning of storm drains, in which owners of private houses often see the possibility of using these networks.
Meanwhile, combining storm sewer with domestic sewer scheme drainage of wastewater is prohibited by SNiP. Prohibition on combination different types sewerage is caused by obvious factors.
Thus, provided that rainwater is discharged into the domestic sewer system and taking into account the high intensity of precipitation, the normal level of sewerage is increased several times.
Flooding of working wells leads to blockage of household and fecal wastewater. Mud deposits and natural debris flow into the domestic sewage system. As a result, after the next rainstorm, the organizers of the structure will have to clean the system.
Combining a storm drain with a sewer main threatens to result in disastrous results. Overflow of the drainage system due to a violation design loads leads to flooding of the building foundation.
Frequent flooding disrupts the structure of the soil, which causes displacement of foundation blocks, erosion of the foundation monolithic design, and in the future can lead to the destruction of the building.
Conclusions and useful video on the topic
Useful videos will expand your horizons about the purpose and installation of storm drains.
Video #1. Storm drainage in a private house - from design to installation:
Video #2. Industrial technologies:
The stages of design and careful calculation of storm drainage are an integral part of the construction of private houses. A carefully thought-out storm drain design and accurate calculations mean the durability of the structure and a comfortable environment for its inhabitants.
Would you like to tell us about how you installed a storm drain on your own summer cottage? Would you like to inform useful information and post a photo on the topic of the article? Please write comments in the block below.
Atmospheric precipitation brings a lot of trouble to residents of country houses if they are not provided with drainage. The most common problems that owners face are the erosion and gradual destruction of the foundation, flooding of the site, rotting of the roots of trees and bushes growing in the yard, and the formation of a swamp.
To avoid the consequences of heavy rain, you can install a simple storm drain, which will not require much effort or financial costs. Storm drainage is a system consisting of the following elements:
- manholes;
- devices intended for transporting wastewater;
- sand traps;
- storm water inlets.
There are two technologies by which storm sewers can function: point and linear.
Pay attention! A linear sewer system is more functional. It is capable of collecting wastewater from large areas and is used to drain atmospheric precipitation that flows from the roof and sidewalk.
The first thing that needs to be done when arranging a storm sewer is to draw up a design and calculations for the system. If you skip this step, you may encounter a number of troubles during operation. If you build an insufficiently efficient wastewater drainage network, water will be retained on the territory, albeit in smaller quantities. If you make a system that is too powerful, you will have to spend a lot of extra financial resources not only during construction, but also during maintenance.
- the average amount of precipitation for the area according to meteorological data;
- if you plan to use storm sewers to drain melt water, you should take into account how thick the snow cover is;
- the area of the territory from which wastewater will be collected;
- soil characteristics;
- communications laid underground.
Storm drain
When calculating the dimensions, it is necessary to determine the volume of the storm sewer, its depth, and the slope necessary for the quality functioning of the system. If you doubt that you will calculate the necessary parameters correctly, seek advice from a specialist.
Important! Exact calculation The size of the storm sewer will ensure maximum efficiency of its operation, and will also help save financial resources at the construction stage.
How to calculate volume
One of the most important parameters that must be taken into account when installing storm drainage on a site country house- this is its volume. The main criterion for calculation is the average amount of precipitation falling in a particular area. Rainwater, snow, and hail are taken into account.
The size of collectors and catch basins depends on the volume of wastewater. The volume of the sewer is determined using a special formula, which requires the following values:
- the amount of wastewater entering the system (an approximate figure can be found in the SNiP collection);
- precipitation intensity;
- the area of the territory from which wastewater will be collected;
- correction factor.
Arrangement of storm drainage on the site of a country house
All obtained values are simply multiplied. Calculating these parameters is quite simple. The only question that may arise is what the correction factor is. This is an indicator that depends on what material covers the area from which wastewater will be collected. If this is an area covered with crushed stone, the coefficient is 0.4, for areas filled with concrete - 0.85, for areas covered with asphalt - 0.95 and for roofs - 1.
Channel depth
One more important parameter is the depth of the storm drain. The trays are laid at a depth characteristic of the region. To find out the depth of the storm drain, you can ask your neighbors or representatives construction company. This parameter also depends on the diameter of the pipes that will be laid.
Pay attention! It is impossible to combine storm sewer and drainage systems, as they will work very inefficiently, which can lead to flooding of the area with precipitation.
Storm sewer channels
It is desirable that storm drainage channels be laid above the ground level groundwater, but below the soil freezing level, and this range is from 1.2 to 1.5 meters. Considering that excavation work requires a lot of effort and a lot of money, the owners decide to reduce the minimum depth of the storm drain. If the diameter of the pipe is 50 mm, then laying should be carried out at a depth of at least 0.3 m, but if the diameter is larger, then the pipe is deepened by 0.7 m. When calculating the depth, the nature of the soil on the site is also taken into account.
Storm drain slopes
Storm sewer is a non-pressure system for removing atmospheric precipitation. For its effective operation, it is necessary to correctly calculate the minimum slope of the storm drain. It is determined taking into account the speed of wastewater flow through the channels and the diameter of the pipe.
If the angle of inclination of the storm drain is too small, it will not work efficiently. A large angle of inclination means that wastewater will very quickly accumulate in the lower part of the system, without having time to be absorbed by the soil. In order not to calculate these values yourself, you can use the table located on the pages of SNiP.
Storm drain slopes
- If the diameter of the pipes is 200 mm, to calculate the slope for the storm sewer, a coefficient of 0.007 should be applied.
- When installing pipes to storm water inlets, they are laid with a slope of 0.02.
- Gravel-filled channels responsible for drainage should be laid with a slope of 0.003.
- For drainage trays, the average slope angle is 0.003-0.005.
Correctly calculated main parameters of storm drainage are the key to long-term and high-quality functioning of the atmospheric wastewater drainage system.
Accurate calculation of storm drainage is the key to optimizing the cost of such construction. After all, excessively deep bedding and overly wide channels hit the customer’s wallet no less strongly than errors in the project.
Therefore, any storm sewer project starts with approximate calculations based on average geodetic and meteorological data, and ends with optimization of estimates based on “local realities.” And in this article we will go from start to finish, touching on the topic of calculations and methods for optimizing the results obtained.
A typical project begins with the preparation of a technical specification, which stipulates all the technical nuances, declares the results and clarifies the cost of the work done. The preparation of technical specifications for stormwater drainage is regulated by GOST 3634-99 and the relevant SNiP.
The next stage of the project is the calculation of stormwater flow using tabular and “local” geodetic and meteorological characteristics.
Moreover, at this stage they calculate the following characteristics and parameters of the future water pipeline:
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- Storm drain design type. At this stage, the structural design of the storm sewer is determined (external or internal, deep or surface, and so on).
- Based on the diagram, the number and type of water collectors - storm wells or collectors (and the location of these elements relative to the foundation) are determined.
- Based on the location of the catch basins, the footage of the drainage pipeline and/or storm gutters is calculated. Moreover, the footage is influenced by the depth of the storm sewer, the slope of the drainage channel, and the distance from the catchment point to the drainage well.
- Finally, the needs for shut-off, control and connecting valves are determined, as well as the number and location of inspection wells.
Moreover, most of the parameters are influenced by the calculation of water flow and the cross-section of stormwater pipes, the slope and laying depth, and more accurate results, obtained in the process of these calculations. Therefore, we will talk specifically about such research.
Calculation of water consumption
Calculation of the flow rate (volume) of water passed through stormwater pipes is the basis for all further research. After all, it is used as a starting point when determining both the throughput capacity and the diameter and slope of the outlet pipeline. Moreover, water consumption most of all affects the expected volumes of water reservoirs and collectors. After all, the entire volume of wastewater will be accumulated in these elements of the storm drain.
Well, the consumption itself is calculated using the formula:
V=q20 x S x D
Where V- this is the expense itself, q20 is a reference value indicating the volume of precipitation (in liters) falling over an area of one hectare (10 thousand square meters), S is the roof area converted from square meters to hectares (10,000:1), and D is the coefficient of moisture absorption by the foundation soil.
Moreover, both the volume of precipitation and the moisture absorption coefficient are indicated in a special collection of building standards (SNiP 2.04.03-85). Only q20 is displayed in graphical form, linked to a map of the former USSR, and D – in tabular form, linked to soil type.
Calculation of storm sewer pipe diameter
Accurate calculation of the pipe diameter involves very complex calculations, which also take into account the roughness coefficient inner surface drainage pipeline, and the speed of fluid flow through the pipe, and the slope of the drain, and other values.
Therefore, in most cases, it is customary not to go into details, but to operate with the minimum possible diameters specified in SNiP 2.04.03-85. And this standard mentions that the minimum diameters of non-pressure drainage networks are 200-250 millimeters.
It is this diameter that guarantees the optimal flow rate of wastewater in a free-flow pipeline - 0.7 m/s, thanks to which it is possible to ensure rapid disposal of wastewater of an average daily volume.
Slope calculation
Knowing the diameter of the pipe and the speed of liquid flow, it is possible to determine the minimum slope of the storm sewer, which guarantees the flow of liquid under the influence of gravity. However, in SNiP 2.04.03-85 the indicated values are linked, first of all, to the diameter of the pipeline.
And for pipes with DN200 (nominal diameter 200 millimeters), the minimum slope is determined by a coefficient of 0.007. Moreover, pipes installed to storm water inlets (drainage trays, storm wells, etc.) are laid with a slope of 0.02 (up to 2 centimeters per linear meter of drainage).
Open drainage trenches filled with gravel (trapezoidal in shape, 30 cm wide at the bottom and 40 cm deep) have a slope of 0.003. And the slope of drainage trays ranges from 0.003 to 0.005.
Determining the depth of the bookmark
The minimum laying depth of a stormwater pipeline is determined based on several factors:
- Groundwater level.
- Soil type.
- Soil freezing depths.
Ideally, the minimum laying depth should be less than the groundwater level and greater than the soil freezing mark. That is, the storm drain will have to be deepened by 1.2-1.5 meters, if the groundwater level allows it. And this is only the “upper” edge of the drain, since the depth of immersion in the ground of the lower end is determined taking into account the difference in heights, according to the slope of the pipe.
Estimate for storm drainage: ways to optimize costs
A typical storm sewer consists of the following elements - drainage trays, drainage pipes, sand collectors, intermediate wells (inspection and drainage) and a wastewater collection tank.
1. Moreover, the best results are demonstrated only by a fully equipped sewer system, the design of which contains all of the above elements. Therefore, saving the estimate by excluding any components is far from the best solution.
However, no one is stopping us from combining some elements “in one bottle.” For example, a manhole with a difference in pipes can be turned into the same sand collector. And instead of trays - quite expensive products - use a perforated drainage pipe laid in a ditch filled with crushed stone.
2. In short, there are a lot of options for combining functions. And each promises tangible savings. In addition, it is possible to reduce the cost by optimizing the size of wastewater pipelines or drainage wells. After all, the dimensions recommended in SNiP (200-250 millimeters) are suitable for industrial buildings and for entire blocks of one-story buildings.
3. But for a separate house equipped with a non-pumpable storm well, a 100 mm pipe is sufficient (to protect against flooding, you can use a 150 mm pipe). The result is one-and-a-half or even double savings on pipes alone.
4. Another way to save money is the already mentioned non-pumped storm well, buried to the horizon with high permeability. There is no need to pump water out of such a well or connect it to the central sewer system. The drains will go away on their own, dissolving in sand that conducts moisture well.
As you can see, a creative approach to design provides a real chance for savings.
However, some self-will is permissible only when arranging a domestic storm sewer laid near small dacha or a modest country house.
Really large buildings with roofs large sizes or industrial facilities are better equipped with storm sewerage, equipped according to recommendations from GOST and SNiP. Otherwise, the owner of such objects may pay double the price for his own indiscretion (and this does not take into account the cost dismantling works unsuitable storm drain).
This type of sewerage system is a complex engineering device, so accurate calculation of storm sewerage during its design is of no small importance. In general, the installation of such a system requires an integrated approach; in the process it is necessary to comply with certain technical requirements. The project must be approved by the sanitary and epidemiological service, the fisheries protection and water protection and regulation authorities.
Storm drain design
Stages of drafting a project
The design process consists of the following stages:
- Storm sewer project: its development in relation to a specific site.
- Coordination of this project with all necessary authorities.
- Direct implementation on site.
At the first stage of design, project documentation is developed. The basis for such work is the technical specification, diagrams, drawings. When developing, it is necessary to rely on regulatory documents: SNiPs, SanPiNs, GOST 3634-99 and some others.
The main document at this stage is the terms of reference. It is compiled based on the wishes and requirements of the customer, filled out in accordance with GOST 19.201-78. IN terms of reference the timing of the work, the purpose of the device, technical and economic requirements, and the control procedure are reflected. Applications may be available if necessary.
Calculation of parameters included in the project
The storm sewer calculation method includes the following key points:
- determining what type of sewage system needs to be used: internal or external;
- finding out the location of storm sewer wells and what their number will be;
- calculation of the required pipe length;
- selection of alarms, sensors and materials.
The decision is influenced by such parameters as the catchment area, the presence of reservoirs in the immediate vicinity (natural or artificial), the maximum amount of precipitation and the average rate of precipitation, the speed at which runoff water moves and other factors that may characterize a given object.
Calculation of water flow and the cross-section of stormwater pipes are described in the article “”.
In order to have an idea about cash investments invested in the organization of this system, an estimate for storm drainage is drawn up. It includes the cost of all components, namely:
- Point type water collectors.
- Pipe systems that drain water.
- Various purposes of storm sewer wells.
- Filters that clean wastewater.
If necessary, the estimate can be supplemented with other elements at the request of the customer.
One of the important parts that a storm drainage scheme includes is a well. Depending on its type, it can collect wastewater, distribute it for treatment, take water samples, wash away sediments, measure flow parameters, and inspect and maintain underground utilities.
The design process of a rainwater sewer system has its own characteristics, which include:
- tracing;
- calculation of hydraulic parameters;
- designing system elements and connecting them.
Tracing is necessary in order to collect rain and melt water from a specific area and divert it to the place of release or purification.
At what depth should the storm drain be placed?
Even though this question is being vigorously discussed in construction forums, a clear answer to it is given by SNiP 2.04.03-85, which states that the minimum depth is taken to be the depth based on the experience of operating networks in a given region.
Pro tip:
If the data is insufficient, then the minimum laying depth of the stormwater pipeline for pipes up to half a meter in diameter is 30 centimeters, and pipes with a diameter of more than half a meter are at least 70 centimeters from the surface.
To determine the minimum depth, thermotechnical and statistical calculations are carried out.
For practical purposes, the depth of the storm sewer is such that it is possible to minimize the amount of work performed when digging a trench, as well as to ensure the pipes are protected from external damage and prevent wastewater from freezing in the pipeline.
Storm drain slope
Pro tip:
To determine the minimum slope of a storm drain, it is necessary to take into account the type of drainage system, cross-sectional diameter and surface coverage.
With an internal diameter of pipes of 0.2 meters, the slope should be 0.007, and if the internal diameter is 0.15 meters, the slope should be at least 0.008. If for objective reasons it is impossible to make such a slope, the standard is reduced to 0.007 for 150 mm pipes and to 0.005 for 200 mm pipes.
For open-type drainage systems, the minimum slope values for stormwater pipes are:
- for a drainage ditch – 0.003;
- roadway tray, the coating of which is asphalt concrete – 0.003;
- roadway tray, covered with crushed stone or paving stones – 0.004;
- when covering the roadway tray with cobblestones – 0.005;
- separately located tray – 0.005.
Based on these numbers, you can see that the slope depends on the roughness: the greater it is, the greater the slope required. The diameter of the pipes also matters: the larger it is, the less slope is required to ensure the required flow rate.
Pro tip:
At self-construction drainage system It is best to use a “surface slope”. The other two methods are applicable only if ready-made factory drainage channels are used.
The numbers given in regulatory documents, are the result of practical research in the construction of a large number of buildings, however, they are not a dogma for the developer. They provide the information needed to create a reliable system. If you adhere to these standards, then if done correctly, it will serve uninterruptedly for many years.
The construction of a suburban building requires some attention to garden drainage in the adjacent area. It is the design of storm drains and the correct calculation of rainwater drainage that will allow you to avoid the threat of erosion and collapse of the foundation, waterlogging of the soil and other troubles. Control water balance includes equipment for a system of wells, pipes, storm water inlets, trays and other elements. Thanks to the presence of the system, the user will be able not only to extend the service life of the building, but also of all road surfaces on the site. Moreover, draining rainwater from the territory and roof into a storage tank is an excellent opportunity to use melted accumulations for watering the garden, which is economically beneficial and convenient.
Calculating storm drainage does not always require the help of professionals; everything can be done with your own hands, especially if drainage for rainwater is required not on an industrial scale, but on a domestic scale. Having considered an example of a calculation, it is permissible to construct structures for an enterprise, your own private buildings, as well as the creation of storm drains in other territories.
The calculation method affects:
- data on landscape and geological features of the site,
- construction specifics of structures,
- location of utilities,
- average precipitation;
- materials that will be used to construct structures.
When thinking over a storm drain for an enterprise, it is also necessary to take into account the traffic flow, area of the territory, the presence of access ramps and other structures. The general arrangement of the drainage system is carried out immediately after determining the necessary stormwater parameters.
Basic aspects of calculations, example
The first stage of constructing a sewer system for the outflow of rainwater from the territory of the enterprise and sites includes determining the largest volume of water that the structure will have to cope with.
Important! It is calculated by the formula: V = g20*S*D in which V is the highest rate of flow rate in the drainage system, and g20 is the intensity of precipitation, S is the area of the enterprise, roof, site, and D is the water absorption coefficient.
To make calculations easier, you should use the table below, which shows the types of materials and water absorption rates:
- roof – 1.0;
- asphalt concrete – 0.95;
- cement concrete – 0.85;
- crushed stone – 0.4;
- crushed stone with bitumen – 0.6.
Other indicators of the intensity of rainwater absorption can be found in SNiP, but it is worth taking into account the values for a specific area.
After the calculation example shows the exact characteristics required for the system, you need to view and select the cross-section of the pipes. Again, everything depends on the volume of rainwater flows, however, the following tables can be taken as an example:
| Slope/diameter mm | 100 | 150 | 200 |
| 0-0,3 | 3,89 | 12,21 | 29,82 |
| 0,3-0,5 | 5,02 | 15,76 | 38,5 |
| 0,5-1,0 | 7,1 | 22,29 | 54,45 |
| 1,0-1,5 | 8,69 | 27,31 | 66,69 |
| 1,5-2,0 | 10,03 | 31,53 | 77,01 |
Important! When choosing the basis for arranging the envelope method, the parameters of the riser are determined by the sum of the volume general expenses all streams.
Calculating storm drainage requires attention to the location of the slope. If pipes are taken with a cross-section of up to 0.2 m, the indicator is approximately equivalent to 0.007 m. The diameter of pipes for a system for draining rain and melt water from the territory of an enterprise or country house, with an indicator of no more than 0.15 m, requires a slope of at least 0.008 m.
Attention! If this standard is not possible to implement, then the standards are reduced to 0.007 for a cross-section of 150 mm, and to 0.005 for a pipeline cross-section of 200 mm.
As the example calculation formula shows, the slope will not be too uneven, and on short sections of the pipeline there is no need to make a slope if the terrain does not allow even a minimal level reduction.
Important! The arrangement of an open-type drainage structure requires a slope of 0.003 m. This is the ideal size for a drainage ditch, as well as highway gutters where the coating is an asphalt concrete mixture. In the case of crushed stone or paving stones, the slope increases to 0.004. Cobblestone streets or plant areas also increase the rate to 0.005. The same goes for separately placed trays.
Analysis of these requirements suggests that the slope is affected by roughness, therefore, with a serious level of this indicator, it will be necessary to arrange a sufficient angle. The cross-sectional size of the pipes also affects (they must be selected based on the volume of rainwater falling): the larger the cross-section, the smaller the slope needs to be made.
To make all the formulas as clear as possible, look at the example calculations. The default parameters are:
- plot of 15 acres (1500 m2);
- location of lawns and flower beds on the site, occupying 300 m2.
So, the lawn and flower beds will already absorb rainwater flows only if the area does not have a serious slope. Calculations of the drainage structure take into account the water absorption coefficient: the roof has a more impressive indicator than the ground, so 300 m2 is not included in the calculations.
Determination of the volume of water supplied to 1200 m2 will also be based on standard indicators - a maximum of 25 l/1 m2 hour. It turns out that approximately 30 m3 falls per 1200 m2. The figure in the example determines the volume of rainwater that will have to be drained, so a pipe with a cross-section of 110 mm and a slope of 10 mm per 100 cm is not entirely suitable. Bandwidth pipe will be no more than 6.19 l/sec or 22200 l/hour, but a pipe with a diameter of 160 mm with the same slope calculation will be ideal.
A simple example of calculations for draining rain flows from the territory and roof shows that everything can be done independently. But do not forget about a certain number of storm drainage trays. Also, to install a drainage pipeline on flat areas, a hydraulic pump is sometimes required to quickly remove flows from the trays, as well as transport water through the pipeline.