Storm sewer calculation: example with calculation of pipe diameter and slope

Storm sewer calculation

Creating a truly effective rainwater collection and drainage system is no easy task. And, of course, requiring careful design taking into account the specifics of the site on which it is being created. As a rule, this is done by specialists, especially when it comes to large areas, storm drains in populated areas, large facilities, etc. But in a small suburban area, you can try to carry out an independent calculation of storm drainage. And then, based on the obtained indicators, plan the placement of all elements of the system and turn the plan into reality.

But let’s not get ahead of ourselves for now – let’s focus specifically on calculating the storm drain.

Calculation of external rainwater drainage

An example of storm sewer calculation (Moscow region, Noginsk district). The calculation was carried out according to SP 32.13330.2012.

The average annual volume of surface wastewater Wg is determined by:

Where: Wd, Wt, Wm – average annual volume of rain, melt and irrigation water, respectively, m 3

Wd = 10hdΨdF=10*465*0.261*7.75=9,406.95 m3 (formula 5, clause 7.2.2, SP 32.13330.2012)

Wt = 10hтΨтKуF=10*225*0.5*1*7.75=8,718.75 m3 (formula 6, clause 7.2.2, SP 32.13330.2012)

Wм = 10mkΨмFм=10*0.5*150*0.5*7.75=521.25 m3 (formula 7, clause 7.2.6, SP 32.13330.2012)

Wg=9,406.95 +8,718.75 +521.25 =18,646.95 m 3

Where: F is the drainage area of ​​the collector, ha;

Kу is the coefficient taking into account snow removal (see 7.3.5, SP 32.13330.2012), in the calculation it is assumed = 1;

hd—layer of precipitation, mm, for the warm period of the year, determined according to SP131.13330 (for Moscow = 465 mm);

ht - layer of precipitation, mm, for the cold period of the year (determines the total annual amount of meltwater) or the water reserve in the snow cover at the beginning of snowmelt, determined according to SP131.13330; (for Moscow = 225mm)

Ψд, Ψт - total coefficient of runoff of rain and melt water, respectively

The total runoff coefficient Ψd for the total runoff area is calculated as a weighted average of the partial values ​​for runoff areas with different surface types according to Table 7.

Table 7 SP 32.13330.2012: - Runoff coefficient values ​​for different types of surfaces

When determining the average annual volume of melt water, the total runoff coefficient Ψt from residential areas and enterprise sites, taking into account snow removal and water losses due to partial absorption by permeable surfaces during the thaw period, can be taken within the range of 0.5-0.7 (accepted in the calculation is 0.5 ).

m is the specific water consumption for washing road surfaces (assumed 0.5 for manual washing and 1.2-1.5 l/m for one mechanized washing);

K is the average number of car washes per year (for central Russia it is 100-150); Fm—area of ​​hard surfaces subjected to washing, hectares;

Ψm—runoff coefficient for irrigation water (assumed equal to 0.5)

Volume of rainwater runoff from design rain discharged to treatment facilities:

Woch = 10haΨm >3 (formula 8, SP32.13330.2012)

— ha — the maximum layer of precipitation during rain, the runoff from which is subjected to full purification, mm (we accept from 5-10 mm, see Vodgeo);

— Ψmid — average runoff coefficient for the calculated rain (defined as a weighted average value depending on the constant values ​​of the runoff coefficient Ψi for different types of surfaces according to Table 14, SP 32.13330.2012:

Table 14 SP 32.13330.2012:

The maximum daily volume of melt water, in the middle of the snowmelt period, discharged to treatment facilities:

Wт,cyt = 10hсFаΨтКy=10*25*7.75*0.8*0.5*0.9=697.5 m3 (formula 9, SP 32.13330.2012)

Where: 10 is the conversion factor;

hс— layer of melt water for 10 daytime hours at a given supply, we take 25 mm (see Appendix 1, formula 10, Vodgeo);

F- runoff area, ha;

a- coefficient taking into account the unevenness of snow melting can be taken as 0.8;

Ψt is the total coefficient of melt water runoff (assumed 0.5-0.8), 0.5 is assumed in the calculation;

Ku is a coefficient that takes into account partial removal and removal of snow, determined by the formula:

Ku= 1 - Fy /F=1-0.775/7.75=0.9 (formula 10, SP 32.13330.2012)

Fy = 0.15* F=0.1*7.75=0.775

The flow rate of rainwater in rainwater sewer collectors, l/s, will be:

Qr=(Ψmid*A*F)/tnr =0.349*384.32*7.75/(12.1) 0.59 =327.3 l/s (formula 1, section 7.4, SP 32.13330.2012)

Where A, n are parameters characterizing, respectively, the intensity and duration of rain for a specific area. A is determined by formula 13, SP 32.13330.2012. n – determined according to Table 9 SP 32.13330.2012.

Ψmid – average runoff coefficient (previously calculated)

tnr is the estimated duration of rain, determined by the formula:

tr = tcon + tsap + tr =3+0+4.1=7.1 min (formula 14, section 7.4.5, SP 32.13330.2012)

where tcon is the duration of rainwater flow to the storm water inlet (surface concentration time), (determined according to SP 32.13330.2012 clause 7.4.6: The time of surface concentration of rainwater runoff should be calculated or taken in populated areas in the absence of intra-block closed rainwater networks equal to 5-10 min, and if available - equal to 3-5 minutes. When calculating the intra-quarter sewer network, the surface concentration time should be taken equal to 2-3 minutes). The calculation took tcon=3min;

tsap - the same, for street gutters to the storm water inlet (if there are none within the block), determined by formula (15) SP 32.13330.2012. In the calculation it is taken equal to 0, because no street stalls;

tp – the same, along pipes up to the calculated cross-section, determined by:

=0.017*410/1.7=7.1, min (formula 16, section 7.4.6, SP 32.13330.2012).

Where: lp—length of design sections of the collector, m (according to the general plan);

Vp – estimated current speed in the area, m/s.

=80*20 0.59 *(1+lg(0.5)/lg(150)) 1.33 =384.32 (formula 13, SP 32.13330.2012)

Where: q20—rain intensity, l/s per 1 hectare, for a given area for a duration of 20 minutes at P=1 year (determined from Figure B.1 SP 32.13330.2012). From Figure B.1 q20=80;

mr—average amount of rain per year (according to Table 9, SP 32.13330.2012). For the flat region of the west and center of the European part of Russia mr=150.;

P-period of a one-time excess of the calculated rain intensity (determined according to clause 7.4.3., table 10,11,12, SP32.13330.2012). In calculation P=0.5;

γ-exponent (determined according to Table 9, SP 32.13330.2012). For the flat region of the west and center of the European part of Russia γ =1.33.

Rainwater flow for hydraulic calculation of rainwater networks:

Qсal = βQr = 0.71*327.3=232.38 l/s

The flow rate of wastewater sent for treatment is determined by formula 167, manual to SNiP 2.04.03-85:

Where: The values ​​of the coefficients K1 and K2 depending on the value of C and n for various conditions for calculating treatment facilities and storm drainage networks are given in Table. 55 and 56 manual to SNiP 2.04.0-85), and the values ​​of the parameter “n” and coefficient “C” in Fig. 26, 27 (manual to SNiP 2.04.0-85). For Moscow: C=0.85, n=0.65. We accept Poch = 0.1. From table 55 (manual for SNiP 2.04.0-85): K1=0.26.

P=0.5, C=0.85. From table 56 (manual for SNiP 2.04.0-85): K2=1.51

Calculation of melt water

The maximum daily volume of melt water Wt.day, m3, in the middle of the snowmelt period, discharged to treatment facilities from residential areas and industrial enterprises, is determined by the formula:

Wt.day =10 ΨtKу F hc = 69.1 m3/day

where Ψт is the total coefficient of melt water runoff (assumed 0.5-0.7);

F – drainage area, 6.91 ha;

Ku - coefficient taking into account partial removal and removal of snow, is determined by the formula:

Ku=1 - Fu/F = 0.10

Fу - area cleared of snow (including the area of ​​roofs equipped with internal drains) 6.21 hectares;

hc—melt water layer for 10 daytime hours, mm, is taken depending on the location of the object. The boundaries of climatic regions are determined by the snow runoff zoning map given in clause 5.2.6 (1) and Appendix 1 (1), as well as Fig. B.1 (3), 20 mm;

Useful information and interesting articles:

• Treatment facilities for a cottage community;
• Biological treatment facilities;
• Storm drains;
• Drainage.

Photos of drainage and sewerage:

• Water disposal and sewerage facilities.

As part of the design contract, we always stipulate warranty obligations and financial liability for failure to meet deadlines.

Region LLC specialists are ready to provide assistance at all stages of decision-making, both at the stage of considering the project concept and when considering options for the reconstruction of existing buildings and structures. At the design preparation stage - prepare technical specifications for design and the necessary research. And also prepare estimates for design and surveys based on collections of basic prices (price justification for holding a competition).

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Storm sewer calculation

Engineering communications must not only be well constructed, but also correctly calculated and designed. By calculating storm drainage, you can accurately determine what missing parameters, structural elements and solutions need to be implemented for the full functioning of the entire utility network. For mathematical calculation methods, the slope of the storm sewer is used according to SNIP 2.04.03-85. But since the calculation can be done independently, in any case, the intervention of specialists will be required to help correctly design a system that will meet the high requirements of the set of rules SP 32.13330.2012.

How to calculate project parameters

The contractor needs to have information about the geological features of the area, landscape characteristics, construction specifics of the facility, and the location of engineering systems. When performing storm drainage at an industrial enterprise, the number of access ramps, the total area of ​​the site, and its trafficability are additionally calculated.

Before developing a hydraulic project, the following points are determined:

• drawing up a work estimate;
• purchase of material;
• installation of sensors, alarms;
• number of wells, their location;
• type of sewerage (external or internal drain);
• pipe length;
• carrying out hydraulic calculations.

The above parameters depend on the norm of precipitation and its maximum possible amount, the proximity of reservoirs, the speed of water flow, and the area of ​​water intake. When laying a storm drain, a calculation is made based on water consumption, that is, the sewerage capacity during the drainage process.

The main purpose of the calculation

Let’s take, for example, the calculation of rainwater drainage, which will show us how calculation operations are carried out by specialists directly involved in the installation and design of utilities. Hydraulic calculation is the main one, which determines the following parameters and structural features of engineering communications:

• In the example of a hydraulic calculation of a storm sewer, components of household waste and wastewater should not be present, that is, they should not fall into this section of the calculation.
• All common drainage into reservoirs and other sewers should be carried out only in agreement with sanitary and epidemiological services.
• For the private sector, all surface groundwater can be sent to a common sewer system without any prior treatment. For industrial and production sites, auxiliary units are needed for surface water purification.
• Atmospheric precipitation from private territory or industrial facilities must enter each drainage unit exactly as much as the central treatment station of the facilities can withstand.
• If possible, all surface wastewater should ideally be transported by gravity.
• For large production areas, as well as for large populated areas, a closed type of storm sewer would be an ideal option. For small cities, as well as small private households, the use of a closed version of storm sewer is allowed.

Where are they used?

Such products are used only in combination with hard coatings , since drainage systems are designed to remove moisture from ground surfaces.

Concrete drainage tray covered with grating

Concrete storm drainage trays are used in the following places:

Thanks to concrete drainage gutters, the wear resistance and durability of road and other hard surfaces increases.

Tip: Do not try to install a concrete drainage system near the house by laying trays directly into the dug ditch. The earth is prone to heaving, especially in winter. The result will be displacement of the trays, disruption of the flow direction, and the structure losing its appearance.

Basic formulas used according to SNiP

How to correctly calculate the regulating capacity for storm sewers; for these purposes, we recommend using the regulatory regulations, which provide a standard mathematical calculation formula. To calculate we use this formula:

Now let’s look in detail at the meaning of each position of the formula for a storm sewer slope of 1 meter according to SNIP.

• q20 is a calculated parameter that determines the intensity of rain within 20 minutes of the appearance of natural precipitation.
• Ψ is the coefficient value of the influence of moisture for a certain category of coating.
• F is fixed surface area. The measurement is made in square meters, or hectares.

In this calculation, it should be taken into account that the value of Ψ is not constant.

• For any roof of a building, the coefficient K = 1.0 is used.
• For asphalt pavement, we use the indicator K = 0.95.
• For the concrete material we use the data K = 0.85.
• For crushed stone and other bulk materials, as well as for soil, we use the coefficient K = 0.4.

Further, in the calculation combination, an amendment is necessarily applied, which indicates certain characteristics.

The coefficient parameter β is determined according to a special table, which is indicated in the current SNiP.

Further in the table there is the value n-, which also has a number of characteristics. Below is a table of application of the specified coefficient by region

In order to calculate the cross-section of a storm drainage channel, an area with a slope of 1-3 cm per 1 linear meter of measured length, then the coefficient β, which is used in the table, will need to be slightly increased by 15%. If all facts have a large terrain slope, then this parameter is taken equal to 1 for all current calculations.

Calculation option

Let's try to give a specific example of calculating storm drainage. Let’s take, for example, a private house located somewhere in the Moscow region, with a total roof area of ​​100 m2 (0.01 hectares). We calculate the parameters of the drainpipe.

• A region-specific rainfall intensity map indicates that q20 is approximately 80 hp. Now we take for calculation the indicator of moisture absorption by the roof, which is equal to 1. Having these data, we obtain an approximate calculation of the primary type: Qr = 80 0.01 = 0.8 l/s.
• Now we take the calculation of the roof slope in this house. It exceeds the value of 0.03 (3 cm per 1 m), in this case the general fill factor parameter will be 1, and in this case the calculation will look like this: Q = Qr = 0.8 l/s
• Next, we know the fluid consumption rate for a specific object. We calculate the total diameter of the storm drain, and we can also calculate the required slope for the entire sieve system. In this case, we will need one official reference book authored by Y. Dobromyslov “Tables for hydraulic calculations of pipelines made of polymer materials. Non-pressure pipelines". We look in this reference book for the required value of 0.8 l/s.

As a result, we can safely say that the following technological elements for storm drainage are suitable for us:

• The driven diameter is 50mm, the slope is 0.03.
• The known diameter is 63mm, we use a slope of 0.02.
• We take a diameter of 75mm and above - use a slope parameter of 0.01.

Using the data, you can accurately make the required calculation for the entire storm drain. Remember that each region uses its own indicator for calculating precipitation intensity, and this is an important point when calculating an effective storm sewer system.

Conclusion

During the calculation process, it is also necessary to take into account additional factors that affect the operational characteristics of the entire drainage system. Such factors are taken into account: the material of the system, the depth used for laying the system, the installation of common risers, the location of the security zone. All work must be carried out in strict accordance with sanitary standards and requirements of supervisory authorities.

How to determine the cross-section of a pipeline

The choice of pipe diameter depends on the total flow rates of the incoming flow.
The limit indicator is calculated using the following example: Qr = Ψ *q20 * F. In this formula, Ψ is represented by the parameter of moisture absorption by the surface of the material, q20 by the value of the abundance of precipitation for a specific period of time, F by the area of ​​space for water drainage. When calculating storm drainage, pay attention to the location of the pipeline slope. This figure is approximately equal to 0.007 m with a cross-section of the product up to 0.2 m

To construct a drainage system from an industrial area, it is better to use pipes with a cross-section of 0.15 m and install them with a slope of 0.008 m.

There are situations where it is impossible to adhere to the above standard due to subjective circumstances. In this case, the use of lower standards is allowed - the cross-section of the product is 200 mm up to a slope of 0.005 m.

On a short section of pipe, you can do without a slope only if, with a certain type of terrain, it is impossible to carry out a minimum decrease in level.

We know that, in accordance with the standards, the installation of an open-type water drainage structure corresponds to a slope value of 0.003 m. For a sewer ditch, this size is considered ideal. When covering with paving stones or crushed stone, this value will increase to 0.004 m.

The regulatory evaluation results indicate that surface roughness affects the slope, so it is advisable to design a wider angle. And, conversely, the larger the cross-section of the pipe, the smaller the slope will have to be made.

Stormwater volume calculator

Storm drainage is one of the most important equipment systems in a residential area, which, unfortunately, many owners simply forget about or take it too lightly. And it is completely in vain - hopes that rain or melt water will go away by itself often lead to gradual waterlogging of the territory, destruction or failure of laid paths and platforms, erosion and erosion of the foundation structures of erected buildings, waterlogging of their walls and other negative consequences.

Stormwater volume calculator

Storm sewerage includes many different elements that are responsible for a specific water collection area, for several such areas, or for the entire system as a whole - these are storm inlets, pipes, wells, and collectors. In order for them to be able to cope with their task, their parameters must correspond to the expected volumes of water. And when planning the system, the calculator for calculating the volume of storm drains, which is offered to the reader, may be useful.

Below, under the calculator, a brief explanation of how it works will be given.

Stormwater volume calculator

Explanations for calculations

So, to plan each individual section of a storm drain, you need to know how much water can fall on it. Further, individual areas are connected through stormwater inlets and pipes to wells that already serve several such zones - and so on, up to the “top of the hierarchy,” that is, a storm sewer or main storage well. Naturally, the indicators of individual sections or groups are summed up. But the basis of the calculation, one way or another, is each individual collection site.

The volume of water to be collected from a single area can be expressed by a simplified formula:

Qsb= q20 × F× ϒ

Qsb is the total volume of storm water collection from the site.

q20 is a tabular coefficient showing the average statistical intensity of precipitation in a given region, depending on climatic conditions. All local construction, design, and meteorological organizations necessarily operate with similar values ​​- it is not difficult to recognize it. Another option is to use the map diagram below. This indicator is expressed in liters per second per hectare.

Schematic map for determining the precipitation intensity coefficient q20

F is the area of ​​the water collection area, expressed in hectares. The area is taken in plan, that is, if, for example, the calculation is carried out for a pitched roof, then only its horizontal projection is considered.

Prices for drainage channels

For the convenience of calculations, the calculator allows you to enter values ​​in square meters - the program will convert to hectares independently.

ϒ is a coefficient that takes into account the fact that a certain part of the water can be absorbed into the coating. This is a tabular value, the values ​​of which for coatings typical for private construction are already included in the calculator.

For greater user convenience, the result will be presented in three quantities: liters per second, liters per minute and cubic meters per hour.

Storm drainage system

Prices for drainage channels

Designing a storm drain is a rather difficult task, and does not end with determining the volume of wastewater. More details about the design and procedure for creating storm sewers can be found in the corresponding article on our portal.

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Video: How to use collected rainwater

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In this order, slowly and thinking through every nuance, an independent design of a storm sewer system is carried out.

Finally, there is one very important caveat. By and large, stormwater and drainage systems do similar work, just at slightly different levels. But all the same, they can be combined to a certain extent, for example, by combining them in one collector. But in no case are any, even the slightest, “intersections” with the domestic sewage system ever carried out. Such a unification is fraught with catastrophic consequences, which will be very difficult to correct later.

Storm sewer calculation: examples

Typical projects for individual residential construction or industrial sites require the availability of design documentation for storm sewer calculations. The set of rules SP 32.13330.2012 contains all the formulas, table values ​​and coefficients necessary for calculation. Since a non-professional holding a plan in his hands for the first time cannot figure it out without help, here is basic information on how to carry out calculations and not confuse himself even more when reading the features of the hydraulic calculation of a storm drain.

Drainage Product Standards

Concrete drainage products must comply with the existing European standard EN 1433, which defines their type, operating conditions, marking and maximum load. All products are assigned a specific class corresponding to the maximum weight affecting the product:

Precast concrete drainage trays are produced in two categories:

You can find out what plastic drainage trays with grates are from another article.

The drainage system is important for protecting the walls of the building and the blind area from moisture. Read about how to make gutters from sewer pipes with your own hands on our website.

Read about where a plastic drainage well is used at https://okanalizacii.ru/drenazh/plastikovyj-drenazhnyj-kolodec.html

Rules and recommendations for arranging storm drains

The main goal pursued in the process of studying sewerage arrangement is to accurately calculate the diameter and slope of the pipe, depending on the volume of precipitation falling in a particular area.

Important! Insufficient water supply capacity leads to a significant decrease in the efficiency of the sewer line as a whole. And this threatens to flood the area adjacent to the house during periods of heavy rain.

The construction of storm sewers is strictly regulated and regulated by SNiP. Remember that the drainage system is the most important element, regardless of the purpose of the building.

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 construct inspection and rotary wells, it is recommended to use ready-made industrial plastic containers or make cast ones 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 the trenches or a line of polymer pipes is installed.

If you are making a simple tray drainage system with outlet to a nearby lawn, it is advisable to consider 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.

Expert advice on sewerage installation

It is not enough to comply with the hydraulic calculation of storm drainage for the system to function properly; listen to some recommendations:

1. A separate drainage system is installed for domestic wastewater and industrial waste.
2. The place of discharge of wastewater into natural reservoirs is agreed upon with the sanitary and epidemiological service and water bodies protection authorities.
3. It is legally permitted to direct surface water from private farms directly to the central sewer system, without pre-treatment.
4. For industrial enterprises, wastewater must be passed through treatment facilities.
5. The productivity of centralized treatment facilities and its throughput determine the possibility of draining atmospheric precipitation from areas adjacent to private and industrial facilities.
6. Whenever possible, try to organize a gravity drainage mode for surface water.
7. If it is necessary to provide a large production site or an entire settlement with a water supply system, then this is, as a rule, a closed branch.
8. Low-rise and suburban properties are equipped with open sewer networks.
9. Combinations of open and closed drainage systems in private individual residential construction have received practical application.

Types of stormwater

Sewage systems designed to drain melt and rainwater are of two types:

Point collection of water from the roofs of buildings. Its main elements are rainwater inlets located directly under the drainpipes. All catchment points are provided with special sedimentation tanks for sand (sand traps) and are connected to each other by a single pipeline. Such a sewer system is a relatively inexpensive engineering structure that can cope with drainage from roofs and courtyards.

Linear is a more complex type of sewer system designed to collect water from the entire site. The system includes a network of above-ground and underground drains located along the perimeter of the site, along walkways and the yard. Typically, water from drainage systems located along the foundation or protecting the garden and vegetable beds is discharged into a common linear stormwater collector. The system is extremely sensitive to slope towards the collectors. If it is not followed, water will stagnate in the pipes and the drainage system will not be able to fulfill its functions.

Based on the method of water drainage, storm drains are divided into:

Open systems that collect water through trays and deliver it to collectors. The trays are covered with shaped gratings on top, which perfectly complement the landscape design and provide protection from debris. Such systems are installed in small private areas.

Such a 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.

For mixed type drainage systems - hybrid systems that include elements of closed and open systems. They are most often built to save the family budget. External elements are easier to install and cost less.

For closed systems consisting of rain inlets, trays, pipelines and a collector that opens into a ravine or reservoir. This is an ideal solution for draining streets, industrial areas and suburban areas with a large area.

In the photo: Open type storm drainage system in industrial design. The main structural elements are concrete trays, on top of which lattice metal sheets are laid. The same principle is used to build open stormwater drainage systems for private housing construction.

The collected water is discharged through networks of pipelines laid and hidden underground. As a rule, the collected products of atmospheric precipitation are discharged to treatment facilities and then into the waters of natural reservoirs.

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. It is also an economical construction option 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 formulas to use to calculate storm sewerage

To determine the cross-section of drainage pipes, calculate the flow of rainfall in your region of residence. This factor depends on climatic and weather conditions.

• q20 denotes the estimated intensity of precipitation over 20 minutes;
• Y is the coefficient of moisture absorption by the coating (1.0 - for roofing, 0.95 - for soil, 0.85 - for concrete, 0.4 - for crushed stone).

Hydraulic calculation of drainage systems. Water disposal in numbers and formulas

S – runoff value per 1 ha or single flow rate in l/s per ha; F – catchment area in hectares.

φ – runoff coefficient: 0.95 – for asphalt concrete pavements; 0.85 – for cement concrete pavements; 0.60 – for crushed stone materials treated with organic binders (bitumen); 0.40 – for crushed stone and gravel materials not treated with binders; Δ – rain intensity, mm/min; t – estimated duration of rain, min; n – hydraulic regional exponent (according to Table 4 SNiP 2.04.03-85).

q20 – rain intensity, l/s per 1 ha, for a given area for a duration of 20 minutes at P = 1 year (according to drawing 1 SNiP 2.04.03-85); P – period of one-time excess of the calculated rain intensity (according to clause 2.13 of SNiP 2.04.03-85);

According to the design scheme, the number of design sections for which the value of the design flow rate is determined is determined. For each calculated section, the catchment area in hectares is determined.

Practical calculation of water supply capacity

Very often, the reason for the non-functionality of storm sewers is the neglect of calculation details by designers. Relying on the general instructions of SNiP, repairmen and installers often make mistakes.

When calculating the diameter of a storm sewer, pipes with a cross section of 200-250 mm are often used. This is the optimal indicator for the unhindered movement of wastewater through pipes. Even if precipitation falls with greater intensity.

Important! Pre-calculation and procurement of necessary parts in accordance with standards and requirements helps reduce costs without compromising the functionality of the network.

Placement and size of wells

Referring to the SNiP rules, inspection wells must be installed:

1. In areas of pipe connections.
2. In sections where there is a change in speed and direction or a drop in water level, as well as a change in pipe diameter.
3. On straight sections - at equal distances, depending directly on the size of the collector:

• DN 150 – 35 m;
• DN200–450 – 50 m;
• DN500-600 – 75 m.

The diameter and depth of the well also depend on the size of the pipeline entering it.

• When private construction is underway and pipes of large diameters (over 600 mm) are not used, wells should be made with a size of 1000? 1000 mm (if round – d=1000).
• With pipelines up to DN150 it is allowed to use 700 mm, but then the depth of such a well should not exceed 1.2 m.
• But if the depth still exceeds 3 m, the size of the well must be at least 1500 mm.

Example of calculating system throughput

Let’s take 100 m2 as the area of ​​the local area, which is 0.01 of 1 hectare of land. Presumably we will drain water from this area. Let's assume that the object is in MO.

Based on the calculation table, it is determined that q20 for Moscow and microdistricts is 80 l/s. The moisture absorption coefficient for the roof is 1.

Based on certain indicators, the calculation of rainwater is as follows: Qr = 80 × 0.01 = 0.8 l/s.

In 90% of cases, the roof slope exceeds 0.03 (>3 cm per 1 m), then the filling factor of the free tank during pressure mode is taken as 1. From this it follows that: Q = Qr = 0.8 l/s.

Important! After determining the indicators for calculating rainwater, you will have the opportunity not only to calculate the diameter of the pipe for the storm sewer, but also to determine the required drainage slope.

Good recommendations are given in the reference book by A. Ya. Dobromyslov “Tables for hydraulic calculations of pipelines made of polymer materials. Non-pressure pipelines." Here the novice master will find calculated data presented in the form of tables. It is definitely clear that for a flow rate of 0.8 l/s, a pipe with the following diameter and slope is suitable:

Important! Remember that the slope of the pipes is inversely proportional to the diameter.

How water is consumed in pressure mode

When hydraulically calculating storm sewers, an adjustment is made for the filling factor of the free drainage in the event of a pressure regime (b):

Q = Qrb, where b is taken from the table:

Important! The value of n depends on the geographical location of the object.

Important! with a terrain slope of 1-3 cm per 1 m, coefficient b increases to 15%. If the slope is greater, then the indicator is considered to be 1.

Take a look at the example of storm sewer calculations.

What material is suitable for the pipeline

According to SNiP, the use of asbestos-cement, steel and plastic (PVC) pipes is permissible.

Although asbestos-cement pipes are used, they are very rare. This is an economical option, but the material is fragile and heavy (1 m of pipe with a cross-section of 100 mm weighs at least 25 kg).

Steel water supply will be easier, but there is a problem here too! Metal is prone to corrosion.

Therefore, products made from PVC plastic are preferable. Combining light weight, the ability to operate for a long time, and ease of installation.

Practical tips for installing storm drains

1. Selection of pipeline material. SNiP allows the installation of products made of asbestos cement, plastic, and steel. The most economical option, which we rarely work with, is asbestos cement. The material is characterized by a large mass (the weight of one meter is about 4 kg) and increased fragility. Steel pipes are lighter in weight than their previous counterpart, but quickly become covered with a corrosive coating. For this reason, PVC is used more often; it combines convenient and quick installation, prolonged service life, and low weight.
2. Backfill depth. We place the pipes optimally, below the soil freezing level, but above the groundwater level. The choice of this parameter depends on the type of terrain: installation of the pipeline is allowed at a distance of up to 70 cm from the surface.
3. Assembling the riser. The process of water drainage itself occurs due to the riser. Under it there are rain receivers of linear or point type. The water outlet is attached to the wall vertically. We use construction clamps for reliable adhesion of the product to the wall surface. Fastening is carried out at a certain interval. It can be determined taking into account the pipeline material. Clamps for plastic products are installed every 2 m. For steel pipes, the interval is smaller - 1.5 m.
4. Security territory. The arrangement of the security area is carried out in accordance with SNiP. This area lies close to the storm drain. According to state standards, it is prohibited to build buildings, organize a waste storage site, or plant trees at a distance of at least 3 meters from the pipeline.

Features of laying depth

When designing and calculating storm sewer treatment facilities, soil characteristics are also taken into account, including the level of soil freezing. The optimal location of the pipe is below the soil freezing line, but above the underground groundwater. These conditions are not easy to comply with due to the uneven terrain of the area, so it was determined that the pipe must be located at least 70 cm to the surface of the earth.

Channel depth

Another 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 of the construction company. This parameter also depends on the diameter of the pipes that will be laid.

Storm sewer channels

It is desirable that storm drainage channels be laid above the groundwater level, 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.

Purpose and specifics of the storm drainage device

Storm sewerage is a complex of devices and channels that collect, filter and drain atmospheric moisture into filtration fields, special reservoirs, and reservoirs. Its task is to eliminate excess moisture, which creates discomfort, destroys structures and shortens the life cycle of plants.

The storm drain is a linear network that includes such standard elements as:

• storm water inlets, represented by funnels, pallets, linear trays that collect water;
• gutters, pipes, trays transporting water to sand traps - filtration devices, and further to collectors, ditches, reservoirs, and unloading fields;
• inspection wells required to control the stormwater system;

filters, sand traps that retain soil particles, plant fibers and debris, protecting the network from contamination.

Storm drainage is a complex of channels and devices that collect excess atmospheric moisture, filter it and discharge it first into a collector well, then to unloading points

Options for rainwater inlets for storm drainage: on the left there is a door pan, in the middle there is a funnel receiving water from the drain, on the right there is a gutter with a sand catcher

All elements are combined into an integral system operating using linear or point technology. If storm sewer channels are laid in the ground, pipes are used for their construction. In surface ditches, gutters and trays made of plastic, asbestos or concrete are installed.

Classification according to wastewater collection method

Depending on the collection principle according to which the storm drainage system is installed, all existing storm drains are divided into two types.

Point systems, which include rainwater inlets installed under the gutters of internal and external drains. Each device receiving atmospheric water is connected to a common main line. According to the technical specifications, storm water inlets are equipped with special gratings and sand traps that prevent the penetration of suspended soil particles, plant residues, and debris into the system.

Point type of storm drain: a storm inlet is installed under a drain; the funnel receiving water is equipped with a mesh for filtration and an internal basket for collecting debris

A linear type of storm drain, which is a network of channels laid underground or in slightly buried trenches. Trays that collect and move water, laid in an open way, are also equipped with sand traps and equipped with gratings. Only gratings are installed along the entire line. In contrast to the point scheme, linear sewerage collects water not only from roof drains, but also from paths, from areas covered with concrete, paved with paving bricks. This type of sewer "covers" and processes more objects.

A linear storm drainage scheme can cover a large area, draining runoff not only from the roof, but also from landscaped areas, sidewalks, and from those sides of the house where, due to the specifics of the pitched structure, there are no drains

Based on design differences and extent of territory coverage, the type of system is selected. However, these are not fundamental selection criteria. Basically, storm sewerage in a dacha is arranged according to the experience available in a particular area in the organization and operation of storm sewer systems. Based on it, the type of channel laying and their depth are determined.

How to avoid mistakes

Even if the drainage pipe has been sloped correctly, the system may not function properly. Sometimes this is caused by a violation of technology or the sequence of work. If you first poured crushed stone and then sand, the result may be clogging of the holes in the pipe. If the backfill was not done at all, then this can also lead to problems.

If you do not provide a slope, then water cannot flow by gravity into a storm drain or well. Even if the work was carried out correctly and the drainage system works flawlessly, it must be remembered that such a device requires periodic maintenance and inspection. These manipulations consist of measuring the water level in the wells and cleaning the system of accumulated dirt and debris. Once the drainage pipes are installed, the system must be inspected four times a year.

Calculation of septic tank volume

The required capacity of a simple autonomous 2-chamber wastewater collector is calculated as follows:
Vseptic tank = 0.2 × Kzh × 3 × 1.2, where:

• Vseptic tank – volume of the septic tank, l;
• Kzh – number of residents in the house, people;
• 0.2 – average daily water consumption per person (200 l or 0.2 m3);
• 3 – coefficient determining that the septic tank must accommodate three days of sewage flow from all residents;
• 1.2 – correction factor used to increase the capacity of the septic tank by 20%, which is occupied by solid sediment falling to the bottom.

Calculation example:

For a family of three people, the volume of the septic tank is Vseptic tank =0.2×3×3×1.2=2.16 cubic meters

What is taken into account when calculating?

For each private construction site (exploited area of ​​the territory), designing an individual storm drainage scheme is commonplace. However, the basis is always taken to be solutions typical for standard stormwater construction projects.

Typical solutions by default 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 geodesy 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.

Mathematical form of the formula:

M = (A * 20) * S * k

Respectively:

M – mass of discharged water

A – intensity of precipitation for 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).

What values ​​must be adhered to?

The slope should be maintained within 3° along one branch of the drainage system. Sometimes the installation diagram looks like a herringbone. In this case, branches of perforated pipes should be connected to the main drainage pipe, similar to the branches that extend from the tree trunk.

The inspection wells are located 50 m from each other. They should be at bends in the drainage system or changes in pipe slope

It is important to remember that if the slope has not been provided, then the water will not be able to flow by gravity into the storm drain or drainage well

If you are constructing a closed system, then the trench is located in the ground with a recess ranging from 70 to 150 cm. The width of the hole can be 25-40 cm. The slope should be directed towards a natural or artificial water intake. It is provided taking into account sanitary standards and regulations.

For each linear meter, the slope should be 3 cm if you have to work in clayey soil. When the area has sandy soils, the slope is 3 cm per linear meter. The slope is ensured by the gravel bed on which the drains are located. The latter are corrugated perforated pipes. They are wrapped in geotextiles, which will protect the system from soil and debris.

After laying the pipe, the slope must be checked again. To do this, you can use a regular cord that is stretched along the pipeline system. When carrying out work, SNiP must be observed. According to them, the slope of the drainage pipe per 1 meter is 3 cm.

Classification of the system according to the method of waste collection

Trays for storm drainage: how to choose the right one
Based on the principle of collecting storm drainage, two types of storm drainage can be distinguished:

1. Spot
   . This type of system works as follows: all installed gutters transfer water to rainwater inlets installed below. Each of these devices is connected to a common main pipeline. All rainwater inlets are equipped with protective grilles and sand traps, as a result of which the rainwater collection system does not become clogged, since various waste such as leaves, sand, soil and other debris do not fall into it.
2. Linear
   . This design is an extensive network of drainage systems installed underground or almost at the same level with it in equipped trenches. In this case, water collection is carried out by trays installed using the open method. Their upper part is completely covered with gratings. The advantage of such a system over the previous type is the ability to collect liquid not only from the roof, but also from other surfaces on the site: paths, car areas or blind areas. This design is capable of working in almost any conditions and is a good replacement for point storm drainage where it would be impossible to install it. Linear sewerage is the best option for removing precipitation from large areas.