Basic terms and definitions
Accounting unit - this is a set of instruments and devices that provide recording of the amount of flowing liquid.
Measuring instrument (metering device, flow meter) - technical means, intended for measurements. Has standardized metrological characteristics, can store and/or reproduce certain measured data physical quantity within the established error. In this case, the main measurement value is the volume of flowing liquid.
Primary flow transducer (sensor) - a device that provides direct measurement of the parameters of the flowing liquid and transmits them to the secondary converter.
Secondary flow transducer (recorder) - a device that converts data received from the primary transducer (sensor) and calculates the flow rate of the flowing liquid using a certain algorithm. Typically, the secondary converter is equipped with a display module and a data storage device.

Methods for measuring pressure flows

To determine the flow rate in pressure flows It is enough to measure one parameter of the flowing liquid - speed. The cross-sectional area is always known and limited by the walls of the conduit. Flow is determined by multiplying the fluid flow rate by the flow area.

Tachometer method- so-called mechanical flow meters, among them we can distinguish vane, turbine and screw ones. The operating principle is based on measuring the speed of a moving element that rotates under the influence of flowing liquid. The most affordable equipment, but has whole line restrictions on use.

Variable pressure differential method- depending on the design and operating principle of the primary transducer, there are several types of measuring instruments, but each of them is based on the dependence of the pressure drop that is created by the primary transducer on the flow rate of the flowing liquid. Most widespread received measuring instruments called "diaphragms".

Ultrasonic time-pulse method- often called simply “ultrasonic”, although this is not entirely true, since there are several ultrasonic methods for measuring flow. As a rule, at least two piezoelectric transducers are mounted in a water pipeline opposite each other at an angle of 30 to 60°, which alternately work as an emitter and receiver. The principle of operation of this method is based on measuring the speed of passage of an ultrasonic signal from the emitter to the receiver, while the speed of passage of the signal along the liquid flow is higher than against the flow. It is possible to design both with sensors embedded in the walls of the water conduit and with surface-mounted sensors.

Advantages	Flaws	Error
relative versatility: installed in water pipes diameter from 15mm to 5000mm	high requirements for servicing mortise sensors: periodic cleaning required	±0.5% ... ±2%
measurement possible aggressive environments when using overhead sensors	high requirements for servicing overhead sensors: periodic replacement required acoustic gel and cleaning the internal section water pipeline from sediments in the area of ​​the measuring section
possible high accuracy when measuring a homogeneous medium without suspensions and bubbles	low stability of measurements at saturation measured medium with suspensions and bubbles up to complete unreliability

The most universal method for measuring pressure flows at the moment. The principle of operation is based on measuring the electromotive force (EMF) arising in a fluid flow flowing through an artificially created magnetic field, while the EMF is directly proportional to the speed of the fluid flow. This method was proposed by Michael Faraday back in early XIX century. The primary transducer, as a rule, is a full-bore measuring section with electromagnets (to create magnetic field) and a pair of electrodes located diametrically opposite in the measuring section to measure the EMF.

Advantages	Flaws	Error
versatility: measurable	always full bore	±0.25% ... ±2%
	when inducing strong electromagnetic interference
low requirements for the quality of the measured environment;

Based on the experience of organizing pressure flow metering units, it can be argued that the electromagnetic measurement method is the most universal and in demand. Depending on the metrological task, it is possible to use various measurement methods, but it is always necessary to take into account the available technical specifications at the measurement object and think through measures for further maintenance and operation of measuring instruments.

Methods for measuring free-flow flows

Acoustic (non-contact) method- the most common due to its relatively low cost, measuring equipment of this type has long been produced in Russia and is widely known. Determination of flow rate when using this method is carried out by measuring the water level and recalculating the obtained value using the “level-flow rate” function using calibration tables. The level is calculated by measuring the travel time of the ultrasonic signal from the primary transducer located above the flow to the surface of the flow and the reflected echo signal to the sensor. It should be noted that the speed with this method of determining flow is not measured explicitly, which leads to unreliable results in the event of deposits at the bottom of the conduit and/or backwater. This method has a number of advantages and disadvantages.

Advantages	Flaws	Error
non-contact method allows you to take into account streams from aggressive environment	high requirements for the lengths of straight sections: 20 maximum water line fill levels before the primary converter and 10 after	from ±3% up to full unreliability of testimony
even very small volumes can be measured	high requirements for the gas environment between primary converter and the surface of the measured medium (vapor formation affects on the quality of signal transmission) and to the very surface of the measured medium (foaming makes a big contribution in measurement error)
	the need to maintain a constant slope the entire measuring section
	in case of backup (stream stops or goes in the opposite direction) the equipment always considers the flow rate as a plus
	usually for equipment installation organization required additional measuring chamber (well)

Ultrasound Doppler method- the name of the method is due to the simultaneous measurement of both the flow level and its speed. Primary speed and level transducers are installed in the flow itself, usually at the bottom of the conduit. The speed is determined using the Doppler method - an ultrasonic signal is emitted into the flow, which is reflected from suspended particles in the flow. The velocity sensor then receives the reflected signal and determines the speed of the particles by the displacement of the oscillation frequency relative to the emitted signal. The level is determined either by the hydrostatic method (by the pressure of a liquid column on a sensitive membrane) or by the ultrasonic method (it is possible to use an acoustic level gauge or a submersible ultrasonic level sensor - the ultrasonic signal is emitted vertically upward and the speed of its passage to the media interface and back is measured). Knowing the geometry of the conduit and measuring the flow level, the flow area is calculated. The flow rate is determined by multiplying the flow velocity by the cross-sectional area.
There is also a more progressive method based on the Doppler method - cross-correlation. The essence remains the same, but the speed measurement is carried out in several planes and is averaged by the cross-correlation method, which increases the measurement accuracy relative to traditional method Doppler

Electromagnetic (magnetic induction) method- V Lately This method is increasingly being used to measure free-flow flows. The essence of the method is to convert a free-flow flow into a pressure flow, i.e. a conventional flow meter is used electromagnetic flow meter For pressure systems. The special design of the inlet and outlet pipes of the flowmeter makes it possible to increase the level of water flow in the measuring section.

Advantages	Flaws	Error
versatility: subject to measurement any conductive liquids	the cost depends on the diameter of the water pipeline; primary converter version always full bore	±0.25% ... ±2%
high accuracy and stability of measurements (if there is a self-cleaning system for electrodes)	Possible measurement instability on hover strong electromagnetic interference
low requirements to the quality of the measured environment; This method is also used for measuring the volume of unrefined Wastewater
full bore section determines no pressure loss in the water pipeline

Our company measures water flow, both pressure and non-pressure flows. Depending on the measurement method, appropriate equipment is used.

Why us?

• Moderate prices at high quality
• Same day departure
• We work all over Russia
• Full cycle works from searching and determining the location of the leak to restoration and installation work on a turnkey basis
• Use of advanced technologies and equipment
• Experts have more than 10 years of experience

The pressure flow is limited on all sides by the walls of the conduit, which is why the pressure at any point differs significantly from atmospheric pressure. A free-flow flow, in turn, has a free surface under the influence of atmospheric pressure.

Methods for measuring pressure flows

Water flow in pressure flows directly depends on the speed of the flowing liquid and the flow area. In this case, the cross-sectional area is limited by the walls of the water conduit and is therefore always known. To determine the flow rate, you need to multiply the cross-sectional area by the flow velocity.

Tachometer method. It is used by mechanical flow meters and is based on determining the rotation speed of a moving element under the influence of liquid flowing in a conduit.

Variable pressure differential method. Regardless of the measuring instrument, this method is based on the dependence of the pressure drop, which is formed using a primary converter, on the liquid flow rate.

Ultrasonic time-pulse method. It is based on measuring the speed of passage of an ultrasonic signal between two sensors installed on a water pipeline, alternately working as an emitter and a receiver.

Magnetic induction method. It is based on determining the magnitude of the electromotive force that occurs in a stream of water when it flows through a magnetic field artificially created by electromagnets.

Contact us if you needexamination and analysis of utility networks

We carry outmajor or partial repair of pipelines according to your order

We deal with urgent matterseliminating water leaks in pipes . Details on our website.

Methods for measuring free-flow flows

Currently, the two most widely used methods for measuring free-flow flows are acoustic and two-channel Doppler.

Acoustic method. It is based on the acoustic determination of the liquid level, the indicators of which are recalculated using calibration tables using the “level-flow” function.

Two-channel Doppler method. It is based on the simultaneous measurement of not only the flow speed, but also its level. In this case, the Doppler method is used only to determine the flow velocity.

Businesses and residential buildings consume a large number of water. These digital indicators become not only evidence of a specific value indicating consumption.

In addition, they help determine the diameter of the pipe assortment. Many people believe that calculating water flow based on pipe diameter and pressure is impossible, since these concepts are completely unrelated.

But practice has shown that this is not so. The throughput capabilities of the water supply network depend on many indicators, and the first in this list will be the diameter of the pipe assortment and the pressure in the main.

It is recommended to calculate the pipe capacity depending on its diameter at the design stage of pipeline construction. The data obtained determines key parameters not only domestic, but also industrial highways. All this will be discussed further.

Calculate the pipe capacity using an online calculator

ATTENTION! To calculate correctly, you need to note that 1 kgf/cm2 = 1 atmosphere; 10 meters of water column = 1 kgf/cm2 = 1 atm; 5 meters of water column = 0.5 kgf/cm2 and = 0.5 atm, etc. Fractional numbers are entered into the online calculator through a dot (For example: 3.5 and not 3.5)

Enter parameters for calculation:

What factors influence the permeability of liquid through a pipeline?

The criteria that influence the described indicator make up a large list. Here are some of them.

1. Inner diameter, which has a pipeline.
2. The speed of flow, which depends on the pressure in the line.
3. Material taken for the production of pipe assortment.

The water flow rate at the outlet of the main is determined by the diameter of the pipe, because this characteristic, together with others, affects the throughput of the system. Also, when calculating the amount of liquid consumed, one cannot discount the wall thickness, which is determined based on the expected internal pressure.

One could even argue that the definition of “pipe geometry” is not affected by the length of the network alone. And the cross section, pressure and other factors play a very important role.

In addition, some system parameters have an indirect rather than a direct effect on the flow rate. This includes the viscosity and temperature of the pumped medium.

To summarize, we can say that determining the throughput allows you to accurately determine optimal type material for the construction of the system and make a choice of technology used for its assembly. Otherwise, the network will not function effectively and will require frequent emergency repairs.

Calculation of water consumption by diameter round pipe, depends on it size. Consequently, over a larger cross section, a significant amount of liquid will move within a certain period of time. But when performing calculations and taking into account the diameter, one cannot discount the pressure.

If we consider this calculation for specific example, it turns out that less liquid will pass through a meter-long pipe product through a 1 cm hole over a certain time period than through a pipeline reaching a height of a couple of tens of meters. This is natural, because the most high level water consumption in the area will reach its highest values ​​at maximum pressure in the network and at the highest values ​​of its volume.

Watch the video

Section calculations according to SNIP 2.04.01-85

First of all, you need to understand that calculating the diameter culvert is a complex engineering process. This will require special knowledge. But when carrying out the domestic construction of a culvert, hydraulic calculations of the cross-section are often carried out independently.

This type The design calculation of the flow velocity for a culvert can be carried out in two ways. The first is tabular data. But when referring to tables you need to know not only exact amount taps, but also containers for collecting water (bathtubs, sinks) and other things.

Only if you have this information about the culvert system, you can use the tables provided by SNIP 2.04.01-85. They are used to determine the volume of water based on the girth of the pipe. Here is one such table:

External volume of pipe assortment (mm)

Approximate quantity water received in liters per minute

Approximate amount of water, calculated in m3 per hour

If you focus on SNIP standards, you can see the following in them - the daily volume of water consumed by one person does not exceed 60 liters. This is provided that the house is not equipped with running water, and in a situation with comfortable housing, this volume increases to 200 liters.

Clearly, these volume data showing consumption are interesting as information, but a pipeline specialist will need to determine completely different data - this is the volume (in mm) and the internal pressure in the line. This cannot always be found in the table. And formulas help you find out this information more accurately.

Watch the video

It is already clear that the cross-sectional dimensions of the system affect the hydraulic calculation of consumption. For home calculations, a water flow formula is used, which helps to obtain the result given the pressure and diameter of the pipe product. Here is the formula:

Formula for calculation based on pressure and pipe diameter: q = π×d²/4 ×V

In the formula: q shows the water consumption. It is calculated in liters. d is the size of the pipe section, it is shown in centimeters. And V in the formula is a designation for the speed of movement of the flow, it is shown in meters per second.

If the water supply network is powered by a water tower, without the additional influence of a pressure pump, then the flow speed is approximately 0.7 - 1.9 m/s. If any pumping device is connected, then the passport for it contains information about the coefficient of pressure created and the speed of movement of the water flow.

This formula is not the only one. There are many more. They can be easily found on the Internet.

In addition to the presented formula, it should be noted that great value The functionality of the system is influenced by the internal walls of pipe products. For example, plastic products They have a smoother surface than their steel counterparts.

For these reasons, the resistance coefficient of plastic is significantly lower. Plus, these materials are not affected by corrosive formations, which also has a positive action on the capacity of the water supply network.

Determination of head loss

The water passage is calculated not only by the diameter of the pipe, it is calculated by pressure drop. Losses can be calculated using special formulas. Which formulas to use, everyone will decide for themselves. To calculate the required values, you can use various options. The only one universal solution this question does not exist.

But first of all, it is necessary to remember that the internal lumen of the passage of plastic and metal-plastic construction will not change after twenty years of service. And the internal lumen of the passage metal structure will become less over time.

And this will entail the loss of some parameters. Accordingly, the speed of water in the pipe in such structures is different, because in some situations the diameter of the new and old network will be noticeably different. The resistance value in the line will also differ.

Also, before calculating the necessary parameters for the passage of liquid, you need to take into account that the loss of water supply flow rate is associated with the number of turns, fittings, volume transitions, and the presence shut-off valves and friction force. Moreover, all this when calculating the flow rate should be carried out after careful preparation and measurements.

Calculation of water consumption simple methods not easy to carry out. But, if you have the slightest difficulty, you can always turn to specialists for help or use online calculator. Then you can count on the fact that the installed water supply or heating network will work with maximum efficiency.

Video - how to calculate water consumption

Watch the video

3.1 Instruments and equipment.

To measure flow, in practice, a hydrometric turntable GR-21M is used; the number of the turntable is indicated on the blade propeller. Blade propellers are No. 1 main - with a diameter of 12 cm and a geometric pitch of 20 cm, No. 2 - non-component, with a diameter of 12 cm, a geometric pitch of 50 cm. It is imperative to indicate what the spinner is lowered into the water on (rod, cable). Main parts of turntables:

1) The bladed propeller or rotor is brought into a rotating state as a result of the force action of the oncoming flow.

2)The axis on which the bladed propeller or murmur rotates. The axis serves to strengthen the blade propeller; it can be movable and connected directly to the blade propeller.

3) Turntable body. It serves as the basis for strengthening and placing individual parts of the turntable, for strengthening the turntable on a rod or cable. The appropriate body shape is streamlined, creating the least resistance to flow.

4) Counting and contact mechanism. It is used to count the revolutions of the blade propellers.

5) Tail or rudder. The tail unit or rudder serves to position the turntable in the flow direction, which is especially important when working with a cable.

Fig.2. Fig.3.

Floats are also used to measure water flow. Hydrometric floats are considered the most inaccurate way to measure water flow. For our river, surface floats were used, which were made in the form of circles, sawed off from a dry log with a diameter of 5-15 cm and a thickness of 2-3 cm. No more than 4 pieces.

3.2. Methods for measuring water flow.

Water flow is the volume of water passing through a given cross-section of a river flow in 1 s. For large watercourses - rivers, canals, spillways of hydraulic structures, etc. – water consumption is expressed in cubic meters per second. The water flow of small watercourses - springs, streams, wells, as well as laboratory flumes is expressed in liters per second.

There are the following methods for calculating water consumption; they can be divided into two main groups:

1. Direct flow measurement.

2. Indirect flow measurement.

The direct measurement of flow rate includes the so-called volumetric method, which is based on measuring flow rate using measuring vessels placed under a stream of water. The filling time of the measuring vessel is also measured. Consumption is determined by dividing the volume of water in the vessel by the duration of filling.

Indirect measurement of water flow can be performed various methods, common feature which is that they measure not the water flow itself, but individual elements of the flow, and the flow rate is obtained by calculation. These methods include:

A). Determination of flow using measuring devices: hydrometric flumes, weirs.

b). A mixing method that has several varieties (thermal, electrical and colorimetric).

V). Determination of flow rate from measured flow velocities and cross-sectional area of ​​the flow is called the “velocity-area” method. We used this method in practice. The cross-sectional area of ​​the flow is determined from the results of depth measurements, and the velocity at individual points of the live cross-section.

3.3. Measuring the flow rate of the hydrometric vertical.

Determination of water flow rates using hydrometric meters is carried out using the “velocity-area” method. To ensure sufficient accuracy of flow measurement, it is necessary that a smoothly changing movement of water be observed in the selected area; the flow of water both in the main channel and on the floodplain must have a general direction across the entire width of the river. The flow speed during low water should be at least 0.15-0.25 m/sec, so that it can be changed with a turntable. It is advisable that during periods of high water and floods, speeds do not exceed 3.0-4.0 m/sec. In winter, the river section should be covered with a continuous ice cover. There should be no areas with standing water or reverse currents on the site. When choosing a site for temporary work, it is enough to take into account the convenience of the location during a given period of the year.

A hydrometric cross-section across a river at which water flows are measured. The position of the hydrometric alignment is fixed on the plane with strong pillars - benchmarks.

The hydrometric alignment is divided perpendicularly general direction rivers, focusing on the direction of the banks, since to correctly determine the flow rates, it is necessary that the cross section of the river along the target line be located normal to the average direction of the flow. As a rule, one gauging station is installed at the measurement site, coinciding with the station of the water gauging station or located close to it. However, in some cases it is necessary to have two, and sometimes three, alignments. This is due to the fact that in different periods of the year the conditions for water flow can change significantly.

Determination of the direction of the hydrological section using a turntable that measures the direction of the flow.

Work to determine the alignment direction is carried out in the following sequence:

1) depth measurements are taken at a pre-selected and fixed alignment, after which, in accordance with the width of the river and the outlines of the alignment profile, high-speed verticals are assigned in an amount of no more than 10-12;

2) on all speed verticals, current velocities and directions are measured at one point at a depth of 0.6 h from the surface; the resulting velocity value on the vertical is taken as average speed on the vertical.

3) water consumption is calculated (we multiply the speed of the river by the water cross-sectional area)* see KG-3 Water consumption for the turntable GMCM-1

When measuring water flow rates with turntables, three methods are used - detailed, composite and abbreviated, which differ in the degree of detail of velocity measurements in the live section.

Before measuring water flows, it is necessary to check the serviceability of the hydrometric instrument, as well as the condition of all equipment at the hydrometric station. When measuring water flow, the following steps are performed: following works:

1) description of the state of the river, weather, aquatic vegetation, state of the river bed, timber rafting indicating the type of rafting, wind strength and direction, waves, water turbidity, presence of ice phenomena.

2) observation of the water level.

3) depth measurements at the hydraulic station.

4)measurement of flow velocities on turntables.

When measuring speeds along each vertical, the following work is performed:

1) The weather and river conditions are different.

2) The water level is determined (in case of significant changes) based on observations at the water gauging station for the beginning and end of work on the turntables.

3) Vertical depth is measured; In winter, the thickness of snow, ice, submerged ice and slush is additionally measured.

4) The working depth on the vertical is calculated and the depths are calculated, the turntable is immersed in the speed measurement points.

5) Current velocities are measured at individual points.

To measure water consumption with a GR21-M turntable, you need to lower it to 0.6 depths in the central measuring vertical and count the number of calls. The first 2-3 signals are skipped without recording. This is necessary so that the bladed propeller acquires a rotation speed corresponding to the speed of water flow. Next, the stopwatch starts and after ≈ 100 seconds. Calls are counted (one call – 20 turns). The number of calls is multiplied by 20 and this result is divided by the number of seconds, we get the number of revolutions per second:

Using the calibration table we determine the speed:

V= 0.0408+0.3233*(0.2405) 2 = 0.1185 m/s

Q= 0.1185*2.2775= 0.27 m 3 /s

3.4 Measuring water flow using surface floats.

In addition to the hydrometric turntable, current speed can be determined using hydrometric floats. The method is based on recording the speed of a floating body-float. When determining speed with floats, it is assumed that the flow speed is equal to the speed of the float. To measure the water flow with surface floats above and below the hydrometric alignment, two additional alignments are set up at equal distances so that the duration of the floats' travel between the upper and lower alignments is at least 20 seconds. At current speeds of more than 2 m.s., the duration of the floats may be less, but not less than 10 seconds. The distance between the upper and lower sashes should be measured with greater accuracy - twice with a steel tape. In windy weather the use of surface floats is limited. When measuring velocities with floats, the result obtained in each case is the highest current speed along the float's trajectory; that speed is taken as the local speed at the point of intersection of the target line and the float's trajectory. Thin cords are pulled along the broken sections under water. One of the team members with a stopwatch stands at the top target, and the other two team members stand at the bottom and below. The student launches the float slightly higher than the upper target, throwing it onto the river core from the bank. At the moment the float passes through the upper gate, he starts the stopwatch and monitors the float. At the moment the float passes through the hydraulic gate, the observer monitors whether the float is on the river stem. At the moment the float passes the lower gate, the observer makes a signal (voice) and the student starts the stopwatch. From all the floats launched on the switch, three floats are selected, showing the shortest duration of travel between the flaps. The extreme value of the stroke duration of these three floats should not differ from each other by no more than 10%. The calculation of the flow rate measured by surface floats is given only based on the highest flow velocity according to the formula.

In river hydrometry, the most common method for measuring water flow is speed method-square". It lies in defining water section area by measuring depths along the hydraulic channel and measuring with a hydrometric measuring instrument at individual points of the water section flow speed.

When measuring water flow you must:

1) record the work environment;

2) monitor the water level;

3) measure depths at the hydrometric site;

4) measure the speed of water flow at individual points of the live section on high-speed verticals.

All records of observation data and measurements of water flow are made with a simple black pencil in the “Book for recording water flow measurements” KG-ZM *.

Before starting work, it is necessary to check the serviceability of the hydrometric turntable and its accessories, the stopwatch, as well as the presence and serviceability of life-saving equipment to ensure the safety of work, the condition of all equipment of the hydrometric station (Appendix 1). To prevent accidents, students are required to study and strictly follow the safety instructions (Appendix 2).

To measure water flow, a section of the river is selected that meets, if possible, the following requirements:

1) the banks are smooth (not winding), parallel;

2) the channel is level, stable and not overgrown with vegetation;

4) absence of dead space (part of the water section where there is no flow).

For educational practice, the selected section of the river must have depths of more than 1 m so that patterns of changes in flow speeds can be identified.

In the selected area, a hydrometric gauge (hydraulic gauge) is marked, at which water flow is measured. On small rivers, the waterworks are laid out by eye perpendicular to the direction of the river flow and secured on both banks with signs - stakes. A sign on one of the banks is taken to be constant start from which distances are measured before each measuring (speed) vertical. A cable (cord) marked every 1 m is stretched in the hydraulic channel. If measurements are made from a boat, a riding cable is stretched parallel to the marking cable (under it), which serves to move the boat along the channel and position it vertically.

Observations and measurements are carried out in the following order.

1. Information about the work environment (state of the river, weather, instruments and equipment) is recorded in the “Work Environment” section of the expense book. All phenomena that may affect the direction and magnitude of the flow velocity or affect the accuracy of determining water flow are noted. For example, the width of the mowed strip of the hydraulic drain is indicated and it is noted in what condition it is: “cleanly mowed”, “at the bottom there are remains of aquatic vegetation ... cm high.” In addition, the degree of overgrowth of aquatic vegetation in the river bed below the hydraulic station is indicated (near the banks, completely, sparsely, densely). Shoals, spits, straits, structures (dams, cofferdams, dams, bridges) are noted: it is necessary to indicate at what distance from the hydraulic station they are located.

2. Observations of the water level are carried out at the main hydrological station before and after depth measurements, as well as before and after

measuring current velocities. Recording of observation data on the height of the water level during measurements and flow measurements is carried out in the corresponding tables of the flow book.

3. Depth measurements at the hydraulic gauge are made to calculate the water cross-sectional area, as described in the section “Surveying and processing of measurement results.” Depths are measured once before measuring current velocities and are recorded in. consumption book in the “Measurements” section (in column 11). In the first and last lines, corresponding to the first: and last measuring verticals at the water's edge, c. column 0 is written “Ur.l.b.” or “Lv. p.b." (edge ​​of the left or right bank), and in column I - depth at the edge. With steep banks, this depth may not be zero. Columns 3 and 4 are filled in only in cases where the depth is measured in an unstable channel twice: forward and backward.

4. Measurements of current velocities on verticals are usually carried out with one hydrometric turntable, sequentially moved to different points of the vertical.

Number high-speed verticals, at which current velocities are measured, with a river width of up to 50 m it is taken equal to five. When choosing locations for high-speed verticals, you should strive to ensure that they are as evenly distributed as possible across the width of the river and at the same time fall at the sharp turning points of the bottom and at the deepest point of the target. The extreme high-speed verticals should be as close to the shore as possible (as far as current speed and depth allow).

The number of points at which the flow velocity on the vertical is measured is set depending on the working depth of the high-speed vertical (Table 4).

Working depth The speed vertical, as well as on the measuring verticals, calculates the vertical distance from the bottom to the surface of the water. At a constant water level, the difference in vertical depths according to the sounding and at the time of measuring the speed in conditions of a stable channel should not exceed 2-3 cm at depths up to 1 m, 5 cm at depths from 1 to 3 m. If the difference is greater, the measurement should be repeat.

Table 4

Dependence of the number and location of vertical current velocity measurements on the working depth