Hydraulic calculation of storm sewers example. Calculation of storm sewers
Storm (rain) sewerage - a system designed to collect and drain storm atmospheric and melt water through grooves or using sewer pipes. Water drainage is carried out behind the site or into a storm well. A stormwater drainage system is necessary to maintain the strength of the foundation and walls of the building, in order to protect them from flooding by rain and melt water when filtering them through the ground.
For drainage of water, a pressure or gravity pipeline can be used. The pressure pipeline is used much less often, due to its unreliability, high cost and great complexity in execution. For the movement of water through gravity pipes without delay, a slope of 0.5-1 cm is arranged, which depends on the type of drainage system, its diameter or on the coating of its surface.
To complete a storm sewer project, you need:
Topographic plan of the territory on a scale of 1: 500;
Results of geological survey of the site;
- Technical conclusion on the hydrogeological conditions of construction;
Relief organization project;
Territory development plan;
TU for connection to centralized systems (if such connections are implied);
Plans and elevations of the floors of the basements and subfields of the building;
Plans, sections and unfolded building foundations;
Plans, longitudinal profiles and sections of underground channels;
Desired methods of organizing the collection and disposal of water, determined by the Customer.
The storm sewer project is carried out on the basis of the following regulatory documents:
- "Internal water supply and sewerage of buildings" (SNiP 2.04.01-85 *);
The storm sewer project includes:
1. Storm drainage plan with indication of the location of the system elements;
2. Sections along the storm pipeline, taking into account the geological structure of the site;
3. Explanatory note with detailed description;
4. Specification of materials for sewerage.
Storm sewage can be carried out according to 2 schemes: point and linear.
Also, for the installation of storm sewers, it is necessary to calculate the required diameter of the drain, which in turn depends on the amount of precipitation in the construction region (SNiP 2.04.03-85).
The storm sewer scheme includes, as a rule, the following elements that can be combined in one case or another:
Storm water inlets;
Trays (gutters);
Sand catchers;
Inspection wells.
The specialists of our company can develop a storm sewer project of any complexity. We guarantee high-quality and fast execution of project documentation.
This type of sewage system is a complex engineering device, therefore, an accurate calculation of a storm sewer 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, by the authorities for the protection of fish stocks and the protection and regulation of waters.
Stormwater drainage design
Stages of drawing up 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 in all the necessary instances.
- Direct implementation on the site.
At the first design stage, the project documentation is developed. The basis for such work is the terms of reference, 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 in in accordance with GOST 19.201-78. The terms of reference reflect the timing of the work, the purpose of the device, technical and economic requirements, and the control procedure. Applications are allowed if necessary.
Calculation of the parameters included in the project
The method for calculating storm sewers includes the following key points:
- determination of what type of this sewage system needs to be applied: internal or external;
- finding out the location of storm sewer wells, what will be their number;
- 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 water bodies (natural or artificial) in the immediate vicinity, the maximum amount of precipitation and the average rate of precipitation, the speed with which the runoff water moves and other factors that may characterize this object.
The calculation of the water flow and the cross-section of the stormwater pipes are described in the article "".
In order to have an idea of \ u200b \ u200bthe monetary investments invested in the organization of this system, an estimate for the storm sewer is drawn up. It includes the cost of all components, namely:
- Point type water collectors.
- Water drainage piping systems.
- Stormwater drainage wells for different purposes.
- Filters that purify drains.
If necessary, the estimate can be supplemented with other elements at the request of the customer.
One of the important parts that the storm sewer scheme includes is a well. Depending on its type, it can collect wastewater, distribute it for purification, water sampling, erosion of sediments, measurement of flow parameters, inspection and maintenance of underground utilities.
The design process of a rainwater drainage system has its own characteristics, which include:
- tracing;
- calculation of hydraulic parameters;
- design of system elements, their linking.
Tracing is necessary in order to collect rain and melt water from a specific area and take them to the place of release or treatment.
At what depth to place storm sewers
Despite the fact that this issue is vigorously discussed at construction forums, a clear answer to it is given by SNiP 2.04.03-85, which states that the depth based on the experience of operating networks in the region is taken as the smallest depth.
Pro tip:
If the data is insufficient, then the minimum depth of laying the stormwater pipeline for pipes up to half a meter in diameter is taken - by 30 centimeters, and pipes with a diameter of more than half a meter - not less than 70 centimeters from the surface.
To determine the minimum depth, heat engineering and statistical calculations are carried out.
For practical purposes, the depth of the stormwater drainage is such a value that it is possible to minimize the amount of work performed when digging a trench, as well as to ensure the pipes are safe from external damage and to prevent freezing of waste water in the pipeline.
Storm drain slope
Pro tip:
To determine the minimum slope of a storm sewer, it is necessary to take into account the type of drainage, the diameter of the section and the surface coverage.
With an inner diameter of 0.2 meters, the slope should be 0.007, and if the inner 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 drainage systems, the values of the minimum slope for stormwater pipes are:
- for the drainage ditch - 0.003;
- roadway tray, covering - asphalt concrete - 0.003;
- carriageway tray, which is 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, it can be seen that the slope depends on the roughness: the larger it is, the greater the slope is 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:
When self-erecting a drainage system, it is best to use a "slope along the surface". The other two methods are applicable only in the case of using ready-made factory drainage channels.
The numbers given in the 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 you need to build a reliable system. If you adhere to these norms, then with the right one, 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 sewers, the correct calculation of the drainage of rainwater that will avoid the threat of erosion and collapse of the foundation, waterlogging of the soil and other troubles. Water balance control includes the equipment of a system of wells, pipes, storm water inlets, flumes and other elements. Thanks to the presence of the system, the user will be able not only to extend the service time of the structure, but also of all road surfaces on the site. Moreover, the drainage of rainwater from the territory, the roof into the storage tank is an excellent opportunity to use thawed accumulations for watering the garden, which is economically profitable and convenient.
The calculation of storm sewers does not always require the help of professionals, everything can be done by hand, especially if a drainage system for rainwater is not required on an industrial, but on a domestic scale. Having considered an example of calculation, it is permissible to construct structures for an enterprise, its own private buildings, as well as the creation of storm drains in other territories.
The calculation technique affects:
- data of landscape, geological features of the site,
- construction specifics of structures,
- location of utilities,
- average rainfall;
- materials to be used for the construction of structures.
Thinking over the storm drain for the enterprise, it is also necessary to take into account the traffic, the 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 required stormwater parameters.
Basic aspects of calculations, example
The first stage of the construction of a sewage system for the outflow of rainwater from the territory of the enterprise, areas includes the determination of the largest volume of water with which the structure will have to cope.
Important! It is calculated by the formula: V = g20 * S * D in which V is the highest 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 facilitate the calculations, it is worth using the table below, where the types of materials and water absorption indicators are indicated:
- 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 absorption of rainwater can be found in SNiP, but it is worth taking into account the values for a particular area.
After the example calculation shows the exact characteristics that are required for the system, you have to view and select the cross-section of the pipes. Again, it all 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 of the total costs of all flows.
Storm runoff calculation 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 the drainage system of rain, melt water from the territory of an enterprise or a country house, 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 for implementation, then the standards are reduced to 0.007 for a section of 150 mm, and to 0.005 for a section of a pipeline of 200 mm.
As the example of the calculation formula shows, the slope will not be too uneven, and in short sections of the pipeline it is possible not to slope if the terrain does not allow even a minimal decrease in the level.
Important! Arrangement of an open drainage structure requires a slope of 0.003 m. This is the ideal size for a drainage ditch, as well as highway trays where asphalt concrete is covered. In the case of crushed stone or paving stones, the slope rate increases to 0.004. Cobblestone pavements or plant grounds also increase the rate to 0.005. The same goes for the separately placed trays.
Analysis of these requirements suggests that the roughness affects the slope, therefore, with a serious level of this indicator, you will have to equip a sufficient angle. The size of the cross-section of the pipes also affects (they must be selected according to the indicator of the volume of falling rainwater): the larger the cross-section, the smaller the slope needs to be done.
And to make all the formulas as clear as possible, look at the example calculations. The default parameters are:
- a plot of 15 acres (1500 m2);
- location on a plot of lawns and flower beds, occupying 300 m2.
So, the lawn and flower beds will already absorb streams of rainwater only if the site does not have a serious slope. The calculations of the drainage structure take into account the water absorption coefficient: the roof has a more impressive indicator than the ground, therefore 300 m2 are not included in the calculations.
Determination of the volume of water supplied to 1200 m2 will also be according to standard indicators - a maximum of 25l / 1m2 hour. It turns out that about 30m3 falls on 1200 m2. The figure in the example determines the amount of rainwater that will have to be diverted, so a pipe with a cross section of 110 mm and a slope of 10 mm per 100 cm is not quite suitable. The throughput of the pipe will be no more than 6.19 l / s or 22,200 l / h, but a pipe with a diameter of 160 mm with the same slope calculation will be ideal.
A simple example of calculating the drainage of rain flows from the territory, the roof shows that everything can be done independently. But do not forget about a number of stormwater trays. Also, for the arrangement of the drainage pipeline on flat areas, a hydraulic pump is sometimes required, which provides a quick diversion of flows from the trays, as well as the transportation of water through the pipeline.
First and foremost: The key to the development of an economically profitable and technically competent storm sewer project (as, by the way, of any other project) is a correctly drawn up Terms of Reference. An unaccounted for nuance or an error made in the preparation of the technical assignment usually leads to additional costs and loss of time for both the contractor and the customer of the project. Be careful and do not hesitate to use expert advice even at this initial stage. The specialists of the "Flotenk" company will be happy to advise you on all issues.
Next, it is necessary to calculate the amount of wastewater for which networks will be designed and the parameters of surface runoff treatment facilities and sewage pumping stations are calculated. In this case, you will need to refer to tabular and "local" geodetic and meteorological characteristics. Calculation is the foundation of a typical project storm sewer.
In outline, A typical storm sewer project can be imagined as:
Drawing up a structural diagram - the basis of the project.
Calculation of the number and type of water collectors: storm wells or collectors. Also, depending on the location of these elements, their construct is selected.
Based on the drawn up structural diagram, tied to the plan, the footage of the drainage pipeline and / or storm trays is calculated. This takes into account the depth of the pipeline, the distance from the catchment point to the drainage well and the slope.
The needs for shut-off, control and connecting fittings, the number and location of inspection wells, and, of course, storm water treatment facilities are taken into account.
The equipment is placed on plans, profiles of sewerage networks, equipment specifications, wiring diagrams are drawn up.
A few examples of our projects:
The development of a storm sewer project in full is a serious work, in which specialists with sufficient experience in the field of design should be involved.
A competent storm sewer project will allow you to easily go through the approval of project documentation in supervisory authorities, carry out construction on time, save you from penalties from regulatory authorities and, in the future, close the issue of collecting and discharging surface wastewater for many years.
Storm sewage is a rather complex engineering structure, which includes storm water inlets, distribution wells, pipes and other necessary elements. Installation of such a system can be done independently. But the drafting of a storm shower can only be done by specialists with the appropriate specialized education.
There are several important points to consider in the project. such as uninterrupted and long-term service of the entire system, the safety of footpaths and access roads, ensuring high-quality drainage from the foundations of buildings. A well-designed downpour will help to collect and remove the entire volume of atmospheric precipitation from the site, that is, it will save the owners from problems with rainwater and melting snow.
Sewerage, designed to drain melt and rainwater, is of two types:
- Spot provides collection of water from the roofs of buildings. Its main elements are storm inlets located directly under the downpipes. All catchment points are equipped with special sedimentation tanks for sand (sand traps) and are interconnected by a single line. Such a sewage system is a relatively inexpensive engineering structure that can cope with the drainage of water from roofs and courtyards.
- Linear - a more complex type of sewage system designed to collect water from the entire site. The system includes a network of surface and underground drains located along the perimeter of the site, along the footpaths and the courtyard. Typically, a common linear rainfall collector is drained from drainage systems placed along the foundation or protecting the garden and garden beds.
According to the method of water drainage, storm showers are divided:
- On closed systems, consisting of storm water inlets, trays, pipelines and a collector that goes into a ravine or reservoir. It is the ideal solution for draining streets, industrial sites and large suburban areas.
- On open systems that collect water through trays and deliver it to collectors. The trays are covered from above with curly lattices, which perfectly complement the landscape design and provide protection from debris. Such systems are installed in small private areas.
- For mixed drainage systems - hybrid systems that include elements of closed and open systems. Most often they are built to save the family budget. Outdoor elements are easier to install and cheaper.
When you need a shower
The arrangement of storm sewers is directly related to climatic features and the state of the soil in a particular area. The more the area is moistened, the more acute is the need to install a rain shower.
Factors indicating the need for water drainage:
- regularly falling heavy precipitation (torrential rains, heavy snow);
- high groundwater level;
- heating basements and cellars in the spring;
- the appearance of dampness on the walls and foundation (the appearance of mold, cracks);
- damage to paths and yard cover due to rain and snow melting;
- slow drying of the soil (stagnation of water in puddles).
Design features
Any sewerage system must comply with the technical requirements shown in a special document - SNiP. This also applies to the storm. The project is drawn up taking into account all the technical requirements of SNiP. In the future, it is necessary to strictly adhere to the design documentation, which will indicate the slope angles of the trays and the pipeline, the length of the communication, building materials, equipment and tools necessary for the work.
For an accurate calculation you will need:
- Get data on the average annual rainfall. The local meteorological service will provide the necessary information.
- Clarify the drainage area. For this, the area of the roof and the entire territory is calculated (if not only the yard is drained).
- Determine the quality of the soil. Sand and sandy loam perfectly absorb moisture, which cannot be said about loam and stony soils. Absorption also slows down the presence of plants on the site - the root system facilitates the drainage of water, but prevents its rapid absorption.
- Find out the location of other communications (main sewerage, water supply, drains).
- An important indicator is the freezing point of the soil. If the pipes are laid below this point, the sewage system will function without interruption even in winter.
The problem of soil freezing can be solved in a more modern way. For this, the pipes are not digged deeply, but under them is laid electric cable for heating. However, such a system will cost the owners a fairly substantial amount - having saved on earthworks, they will have to pay increased amounts of electricity bills in winter.
It should be noted that the SNiP contains all the formulas necessary for carrying out calculations, taking into account the type of drainage system, the diameter and material of the pipes. The finished project must be approved by the supervisory authorities!
It is preferable to contact a licensed design organization, which will quickly and efficiently prepare all the necessary documentation, as well as agree on the project in all instances without the participation of the owners.
Installation process
A rain shower device from scratch includes the following steps:
- Holders for gutters are fixed on the roof at a distance of 80-90 centimeters from each other. A slope of two millimeters is observed for each running meter of the gutter.
- Places for funnels are marked in the gutters. The finished hole is 10 centimeters. A funnel is inserted into it. The open ends of the gutters are closed with plugs.
- Then the gutters are placed in the holders, joining the segments with the help of connecting elements and sealant.
- Angle elbows are attached to the funnels, which ensure the outflow of water into the drains, placed vertically on the walls of the building.
- Downpipes are attached to the walls with clamps. The distance from the drain to the wall should not be less than 10 centimeters!
- Drain elbows are mounted to the lower edges of the drains. The distance from the knee to the ground is 30 centimeters. A separate gully is placed under each drain elbow.
- The stormwater mains are laid in already prepared trenches with a sand cushion at the bottom with a thickness of 10-15 centimeters. Shallow ditches are dug for trays and storm water inlets. Collectors and inspection wells are being built at the same time.
- All trays and gutters are provided with sand traps. Then they are connected with the help of knees to the main drain located below the freezing point of the soil. The tightness of all joints is strictly observed.
- The general is displayed in the collector (in front of it you can install additional filters, for example, sorption filters).
- From the collector, water enters a storage well, from which an emergency drain is provided through a special pipe led into a ravine, a nearby reservoir or city sewer. Also, water can be pumped out manually using a pump. In this case, a water discharge pipe is not needed.
After installation, the system is checked for operability. For this, water is poured into the stormwater inlet. After that, the trays are closed with protective gratings, and the pipes are covered with soil.
Necessary tools
To carry out the work you will need:
- bayonet and shovel for excavation of soil from trenches and pits for wells and collectors;
- hacksaw for cutting plastic pipes;
- wrenches (adjustable and wrenches);
- screwdriver;
- file for polishing pipe sections.
Materials used:
- plastic pipes;
- trays, funnels and gratings (required for the installation of an open drainage system);
- inspection chambers made of plastic or concrete rings for their construction;
- storm water inlets, sand traps and filters (if the water will be used for watering the garden and contains harmful impurities).
- cleaning of protective gratings of ground elements from large debris (branches, leaves, etc.);
- removal of sediment from sand traps;
- cleaning of gutters around the perimeter of the roof.
It is also necessary to pay special attention to the efficiency of the storm shower. If stagnant water or poor-quality drainage is noted, the reason lies in the blockage of the pipeline located underground. To solve the problem is required.
Sewerage flushing is carried out through inspection wells or collectors. Specialists use special water pumps equipped with a long hose with a nozzle attachment. High pressure water flushes out debris and looses the pipeline.
Such an emergency flushing is required only if the basic operating rules are not followed:
- in case of untimely cleaning of grids and sand traps;
- or in the absence of filters and sand traps in the system.
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