Method for measuring flow in a gentle slope channel

Abstract

The present application relates to the technical field of channel water measuring, and is a gentle slope channel flow measuring method, which is performed according to the following steps: first, a flow regulating section is designed downstream of a water measuring weir groove of a gentle slope channel provided with the water measuring weir groove, and the surface of the flow regulating section is treated to reduce the surface roughness; second, after the surface roughness treatment, the submergence of the water measuring weir groove of the gentle slope channel is reduced, and the gentle slope channel is calculated according to a water measuring formula to obtain the channel flow. The present application adopts the treatment mode of reducing the surface roughness of the flow regulating section, improves the submergence of the upstream and downstream of the water measuring weir groove, and enables the water measuring weir groove to also use the flow measuring formula under high submergence to accurately calculate the channel flow. The present application effectively solves the problem that the submergence of the water measuring weir groove is too high due to the too gentle slope of the channel, and the flow cannot be accurately measured. The method of the present application is simple to implement, the materials are easy to obtain, the operation is simple, the cost is low, the applicability is strong, and the method is easy to popularize and use.

Description

Technical Field

[0001] This invention relates to the field of channel water measurement technology, and is a method for measuring flow in gently sloping channels. Background Technology

[0002] Currently, common methods for measuring water flow in irrigation canal systems include current meter measurement, standard cross-section measurement, weir measurement, and flume measurement. Among these, weir and flume measurement both belong to the water level method. The water level method involves constructing a weir or flume within the canal based on its shape and the magnitude of the water flow. By monitoring the water level passing through the weir or flume, the flow rate can be calculated using hydraulic formulas. Commonly used weirs and flumes include thin-walled weirs, measuring sills, Parshall flumes, parabolic throat flumes, straight-walled flumes, and airfoil flumes. The water level method is widely used in canal flow measurement due to its adaptability, low head loss, and high measurement accuracy. However, the water level method, which calculates flow rate based on the water level of the weir or flume, is less suitable for gently sloping channels due to the small slope and minimal drop in water level downstream. The submergence ratio (downstream water level / upstream water level) approaches 1, reducing its applicability and leading to inaccurate measurements. For example, the existing national standard GB / T 21303-2017, "Specifications for Water Measurement in Irrigation Canal Systems," specifies that the submergence ratio for sill measurement should be controlled at around 0.85, for parabolic throat flumes it should not exceed 0.88, and for straight-walled flumes it should not exceed 0.83. For gently sloping flow measurement, the high submergence ratio limits the applicability of these weirs and flumes. The Parshall flume method, which has the most lenient submergence requirements, applies to channels with a free-flow flow rate of less than 0.7 and to channels with a submerged flow rate between 0.7 and 0.95. For gently sloping channels, the submergence level still exceeds the applicable range of the Parshall flume flow rate formula. In addition, existing measuring weirs and flumes have more or less affected the water carrying capacity of the channels, reducing the water carrying capacity, and the impact is even greater on the water carrying capacity of gently sloping channels. Summary of the Invention

[0003] This invention provides a method for measuring flow in gently sloping channels, which overcomes the shortcomings of the prior art and effectively solves the problem of difficult flow measurement in existing gently sloping channels.

[0004] One of the technical solutions of the present invention is achieved through the following measures: a method for measuring flow in a gently sloping channel, performed as follows:

[0005] The first step is to design a straightening section downstream of the measuring weir in the gently sloping channel with a measuring weir, and to treat the surface roughness of the channel surface in the straightening section to reduce its surface roughness. The second step is to reduce the submergence of the measuring weir in the gently sloping channel after the surface roughness reduction treatment, and to calculate the channel flow rate of the gently sloping channel according to the measuring formula.

[0006] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions:

[0007] The aforementioned straightening section is located downstream of the measuring weir, and its length is 20 to 40 times the channel water depth.

[0008] The above-mentioned treatment to reduce surface roughness involves coating with a roughness-reducing and gloss-enhancing paint or applying a smooth film.

[0009] The aforementioned water measuring weir or water measuring trough is a water measuring weir or water measuring trough.

[0010] The coating thickness of the above-mentioned roughness-reducing and gloss-enhancing coating is 1.5 mm to 3 mm.

[0011] The thickness of the smooth film is 0.5 mm to 3 mm.

[0012] The aforementioned roughness-reducing and gloss-enhancing coating is one of the following: polyurea coating, polyester resin coating, polyurethane coating, epoxy resin coating, and silicone resin coating.

[0013] The aforementioned smooth film is one of the following: a smooth acrylic plastic sheet, a PVC plastic film, or a metal sheet.

[0014] The aforementioned measuring weir is a thin-walled weir or a measuring sill.

[0015] The aforementioned measuring tank is one of the following: Parshall flume, semi-cylindrical measuring tank, rectangular throatless measuring tank, parabolic throat measuring tank, straight-walled measuring tank, airfoil-shaped measuring tank, and long-throat measuring tank.

[0016] This invention employs a method of reducing the surface roughness of the channel surface in the rectifying section, thereby improving the submergence degree upstream and downstream of the measuring weir and flume. This allows for accurate calculation of channel flow using flow measurement formulas even under high submergence conditions. The method of this invention is simple to implement, uses readily available materials, is easy to operate, has low cost, strong applicability, and is easy to promote and use. Detailed Implementation

[0017] This invention is not limited to the following embodiments; specific implementation methods can be determined according to the technical solutions and actual conditions of this invention. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art. Unless otherwise specified, the equipment and apparatus used in this invention are all well-known and commonly used equipment and apparatus in the art.

[0018] The present invention will be further described below with reference to embodiments:

[0019] Example 1: The flow measurement method for this gently sloping channel is carried out according to the following steps:

[0020] The first step is to design a straightening section downstream of the measuring weir in the gently sloping channel with a measuring weir, and to treat the surface roughness of the channel surface in the straightening section to reduce its surface roughness. The second step is to reduce the submergence of the measuring weir in the gently sloping channel after the surface roughness reduction treatment, and to calculate the channel flow rate of the gently sloping channel according to the measuring formula.

[0021] This invention employs a method of reducing the surface roughness of the channel surface in the rectification section, thereby reducing the surface roughness of the downstream rectification section of the measuring weir. After treatment, the downstream water level of the measuring weir can be significantly reduced, thereby improving the submergence of the measuring weir in the gently sloping channel. This allows the measuring weir to accurately measure the flow rate under high submergence conditions by referring to the flow calculation formula in the existing known technology.

[0022] The water measurement formula in this invention is a well-known formula for calculating channel water flow in the field.

[0023] Example 2: As an optimization of the above example, the rectifying section is located downstream of the measuring weir, and its length is 20 to 40 times the channel water depth. In this invention, when the submergence is too high, the length of the rectifying section can be appropriately extended to meet the requirements of accurate flow measurement in the measuring weir to reduce the submergence.

[0024] Example 3: As an optimization of the above examples, the treatment to reduce surface roughness is to apply a roughness-reducing and gloss-enhancing coating or to lay a smooth film.

[0025] In this invention, the smooth film includes, but is not limited to, rigid thin-plate materials, malleable materials, and flexible materials (or films).

[0026] Example 4: As an optimization of the above examples, the thickness of the smooth film is 0.5 mm to 3 mm.

[0027] Example 5: As an optimization of the above examples, the coating thickness of the roughness-reducing and gloss-enhancing coating is 1.5 mm to 3 mm.

[0028] Example 6: As an optimization of the above examples, the roughness-reducing and gloss-enhancing coating is one of polyurea coating, polyester resin coating, polyurethane coating, epoxy resin coating, and silicone resin coating.

[0029] Example 7: As an optimization of the above embodiment, the smooth film is one of the following: a smooth acrylic plastic sheet, a PVC plastic film, or a metal sheet.

[0030] Example 8: As an optimization of the above example, the measuring weir is a measuring weir or a measuring trough.

[0031] Example 9: As an optimization of the above embodiment, the measuring weir is a thin-walled weir or a measuring sill.

[0032] Example 10: As an optimization of the above embodiment, the measuring tank is one of the following: Parshall flume, semi-cylindrical measuring tank, rectangular throatless measuring tank, parabolic throat measuring tank, straight-walled measuring tank, airfoil-shaped measuring tank, and long-throat measuring tank.

[0033] Example 11: Aigelangri Dou Canal in Weiganhe Irrigation District, Shaya County, Xinjiang

[0034] The irrigation canal is a trapezoidal, gently sloping canal with a semi-circular measuring flume inside. The canal has a water depth of 1.0 meter, a bottom width of 1.0 meter, and a top width of 4.0 meters. The canal is faced with mortar-grouted bricks. The water measuring section (i.e., the section with the measuring weir) is a rectangle with a bottom width of 2 meters and a length of 3.2 meters. It contains a semi-circular measuring flume with semi-circular side weirs on both sides with a radius of 0.4 meters. The water depth (upstream head) upstream of the measuring flume is 0.649 meters, and the water depth (downstream head) downstream is 0.619 meters, with a submersion degree of 0.954.

[0035] According to the flow calculation formula for a semi-circular flume provided in "Irrigation District Water Allocation and Measurement Technology," the critical submersion degree of a semi-circular flume is ≤0.85. The current submersion degree of this channel is 0.954, which is higher than the applicable range of the calculation formula. Therefore, the flow calculation formula for the semi-circular flume is not applicable, and flow measurement of the channel cannot be performed.

[0036] The method of this invention is used to process the channel:

[0037] The first step involved designing a 20-meter-long roughening and straightening section downstream of the measuring flume. SK polyurea coating, with a thickness of 2mm, was sprayed onto the surface of this section. After applying the SK polyurea coating, the water depth downstream of the measuring flume decreased to 0.545 meters, and the submersion degree decreased to 0.84, which falls within the applicable range of the flow calculation formula for a semi-circular measuring flume.

[0038] The second step is to calculate the flow rate of the channel according to the flow rate calculation formula of the semi-circular measuring tank (Formula 1 and Formula 2 below).

[0039]

[0040] 0 淹没 =0 自由 ×σ (critical submergence degree is 0.85)...........Equation 2

[0041] In this embodiment:

[0042] σ is a function of the submergence degree. In this embodiment, it is obtained through actual measurement and calibration. When the submergence degree is 0.84, σ = 0.54.

[0043] The upstream draft reading h is 0.649 meters;

[0044] Throat width B c It is 1.2 meters.

[0045] The channel free flow rate Q was calculated. 自由 It is 1.14m 3 / S, flood flow rate Q 淹没 It is 0.614m 3 The calculated value is within 5% of the measured value of the flow meter, which meets the flow measurement specifications.

[0046] Example 12: A gentle slope canal in the Weigan River Irrigation Area of ​​Shaya County, Xinjiang

[0047] The irrigation canal is rectangular, with a rectangular throatless measuring flume inside. The canal is 1.2 meters deep and 1.2 meters wide. The rectangular throatless measuring flume is 0.8 meters wide and 1.8 meters long. The water depth (water gauge reading) upstream of the rectangular throatless measuring flume is 0.56 meters, and the water depth (or water gauge reading) downstream is 0.51 meters, with a submersion degree of 0.91.

[0048] According to the requirements of the national standard GB / T 21303-2017, "Specification for Water Measurement in Irrigation Canal Systems," the critical submersion degree of a rectangular throatless measuring flume is 0.8. The current submersion degree of this canal is 0.91, which exceeds the applicable range of the calculation formula, rendering the flow calculation formula inapplicable.

[0049] The method of this invention is used to process the channel:

[0050] The first step is to lay a 1mm thick PVC weather-resistant, drip-free plastic film on the surface of a 30-meter-long section downstream of the rectangular throatless measuring flume. After laying the film, the water depth downstream of the rectangular throatless measuring flume is reduced to 0.44 meters, and the submersion degree is reduced to 0.78, which meets the applicable scope of the flow calculation formula for rectangular throatless measuring flumes in the national standard GB / T 21303-2017.

[0051] The second step is to calculate the flow rate of the channel according to the formula for the submerged flow rate of a rectangular throatless flume (Formula 3 below) in Chapter 11.3 of the national standard GB / T 21303-2017.

[0052]

[0053] In this embodiment:

[0054] The submergence degree S is 0.78.

[0055] The upstream water depth H in the channel is 0.56 meters.

[0056] Upstream water depth h in the channel d It is 0.44 meters.

[0057] From the table in standard GB / T 21303-2017, we know that n1 is 1.64, n2 is 1.34, and C2 is 1.57. The calculated submerged flow rate Q is 0.958 m³. 3 / S, the error between the calculated result and the measured value is less than 5%, and the accuracy meets the requirements of the flow measurement specification.

[0058] This invention employs a method of reducing the surface roughness of the channel surface in the rectification section, thereby reducing the submersion degree of the measuring weir in the gently sloping channel. After the submersion degree is reduced, the requirements of the measuring weir for submersion degree are met by the measuring weir flow measurement formula. According to the corresponding measuring weir flow measurement formula, the flow rate of the gently sloping channel can be accurately calculated, enabling the measuring weir to accurately measure the flow rate even when the submersion degree exceeds the limit, based on the flow calculation formula.

[0059] The implementation of the method of the present invention does not require the replacement of existing channel weirs and troughs, thus avoiding the waste of existing weirs and troughs. The channel is modified by simply applying a roughness-reducing and gloss-enhancing coating or laying a smooth film. The materials are readily available, the operation is simple and the cost is low, the applicability is strong, and it is easy to promote and use.

[0060] In summary, this invention reduces the surface roughness of the channel surface in the rectifying section, improving the submergence degree upstream and downstream of the measuring weir. This allows for accurate calculation of channel flow using flow measurement formulas even under high submergence conditions, effectively solving the problem of inaccurate flow measurement caused by excessively gentle channel slopes and high submergence levels. The method is simple to implement, uses readily available materials, is easy to operate, low-cost, highly applicable, and easy to promote and use.

[0061] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A method for measuring flow in a gently sloping channel, characterized in that... The procedure is as follows: First, design a straightening section downstream of the measuring weir in the gently sloping channel with a measuring weir, and treat the surface roughness of the channel surface of the straightening section to reduce its surface roughness; Second, after the surface roughness reduction treatment, the submergence of the measuring weir in the gently sloping channel is reduced, and the channel flow rate is calculated according to the measuring formula.

2. The method for measuring flow in a gently sloping channel according to claim 1, characterized in that... The straightening section is located downstream of the measuring weir, and its length is 20 to 40 times the depth of the channel.

3. The method for measuring flow in a gently sloping channel according to claim 1 or 2, characterized in that... Treatments to reduce surface roughness include coating with a roughness-reducing and gloss-enhancing paint or applying a smooth film; and / or, the measuring weir or measuring trough is a measuring weir or measuring trough.

4. The method for measuring flow in a gently sloping channel according to claim 1 or 2, characterized in that... The coating thickness for reducing roughness and enhancing gloss is 1.5 mm to 3 mm; or / and, the thickness of the smooth film is 0.5 mm to 3 mm.

5. The method for measuring flow in a gently sloping channel according to claim 3, characterized in that... The coating thickness for reducing roughness and enhancing gloss is 1.5 mm to 3 mm; or / and, the thickness of the smooth film is 0.5 mm to 3 mm.

6. The method for measuring flow in a gently sloping channel according to claim 1, 2, or 5, characterized in that... The roughness-reducing and gloss-enhancing coating is one of the following: polyurea coating, polyester resin coating, polyurethane coating, epoxy resin coating, and silicone resin coating; and / or the smooth film is one of the following: acrylic plastic sheet, PVC plastic film, and metal sheet with a smooth surface.

7. The method for measuring flow in a gently sloping channel according to claim 3, characterized in that... The roughness-reducing and gloss-enhancing coating is one of the following: polyurea coating, polyester resin coating, polyurethane coating, epoxy resin coating, and silicone resin coating; and / or the smooth film is one of the following: acrylic plastic sheet, PVC plastic film, and metal sheet with a smooth surface.

8. The method for measuring flow in a gently sloping channel according to claim 4, characterized in that... The roughness-reducing and gloss-enhancing coating is one of the following: polyurea coating, polyester resin coating, polyurethane coating, epoxy resin coating, and silicone resin coating; and / or the smooth film is one of the following: acrylic plastic sheet, PVC plastic film, and metal sheet with a smooth surface.

9. The method for measuring flow in a gently sloping channel according to any one of claims 3, 5, or 7, characterized in that... The measuring weir is a thin-walled weir or a measuring sill; or / and the measuring flume is one of the following: Parshall flume, semi-cylindrical flume, rectangular flume without throat, parabolic throat flume, straight-walled flume, airfoil flume, or long-throat flume.

Images