JPS6253059B2 - - Google Patents

Description

[Detailed Description of the Invention] Recently, there has been a strong demand for more sophisticated river water management such as flood forecasting and water use adjustment, and there is an increasing need for improved accuracy and automation of river flow measurement.

Methods using current meters and floats are generally used to measure the flow rate in open waterways such as rivers, but these methods both require human labor and cannot continuously measure flow rates. Ultrasonic current meters have been experimentally used as automatic flow rate measurement devices in open channels, but in actual rivers, the results have not been very good due to irregular cross-sectional shapes and the effects of turbid water during floods. It hasn't been done yet.

Therefore, in order to continuously measure the flow rate, the method of continuously measuring the water level and converting it to the flow rate using the water level-flow curve is widely adopted. Under conditions where the flow rate is changing, it takes several months to a year to create a water level-flow curve through flow rate observation, making it impossible to satisfy the demands of management problems that require immediate flow rate. Furthermore, the water level-flow rate curve itself does not hold at points where the water surface gradient changes independently of the water level, such as upstream points of tidal areas, movable weirs, and upstream points of confluence points.

On the other hand, gauging weirs and persial fliers can be used for small waterways, but this method is often not available for rivers and large waterways because it is difficult to install such facilities.

By the way, the flow rate Q is the product of the flow rate υ and the cross-sectional area A, Q=A・υ...(1), and the flow rate υ is expressed by the Manning formula υ=1/nR〓I〓...(2) , the roughness coefficient n, which is a constant, the diameter depth R and the water surface slope I, which are determined as a function of the water level.
Therefore, by continuously measuring the water surface gradient in addition to the water level, the flow velocity and flow rate can be continuously calculated.

Water surface slope I is the water level difference ΔH between two points upstream and downstream of an open channel divided by section length L ^* , so I=ΔH/L...(3) Mathematically, there are All you have to do is install a water level gauge, measure the water level, calculate the difference, and divide it by the section length, but from a measurement perspective, this method has a wider measurement range than the water level difference, so it is relatively Effective results cannot be obtained because large errors in water level measurement and difficulty in maintaining the relative positional relationship between two points upstream and downstream greatly affect the accuracy of measuring water level differences.

*The section length L varies depending on the accuracy of setting ΔH and the maximum value of the water surface slope to be measured, but is actually 30 to 200 m.

This invention is a water surface gradient method that ensures high measurement accuracy by detecting the water level difference between two water surfaces formed at one place by introducing water from two points upstream and downstream using a single detector. The aim is to provide a measurement plan.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

In the attached drawings, reference numerals 1 and 2 are sand settling tanks, which are water intake parts, installed at two points, upstream and downstream, separated by a water level measurement section length L, and a pressure tank 5, which is a water level difference detection part, is connected by water guide pipes 3 and 4. is connected to. The pressure tank 5 forms a reverse siphon, and when the air inside is depressurized by the operation of the suction pump 6, the water from the sand settling tanks 1 and 2 installed at the upstream and downstream points is transferred to the The water guide pipes 3 and 4 are connected to two water tanks which are constructed so that water can be sucked up through the water guide pipes 3 and 4, and which are partitioned by a partition plate inside the tank. Further, the pressure tank 5 is provided with a detection mechanism for measuring and detecting the difference in water levels in each of the water tanks. The detection mechanism includes floats 7 and 8 floating on the water surface of the two water tanks.
, a differential gear mechanism 9 connected to the floats 7 and 8 by pulleys, and a potentiometer (not shown) that converts the difference in position between the floats 7 and 8 into a rotation angle of the differential gear. Or a detection member configured to detect the water level difference using an encoder (not shown).

Here, if the change in flow in the open channel is slow enough, hydrostatics can be applied to the water in the sedimentation tank, water guide pipe, and pressure tank, so atmospheric pressure P ₀ , air pressure in the tank P, and upstream water level H ₁ , the downstream water level H ₂ , the upstream water level in the tank H ₁ ', and the downstream water level in the tank H ₂ ', the following relationship holds true.

P ₀ +H ₁ =P+H ₁ ′ ...(4) P ₀ +H ₂ =P+H ₂ ′ ...(5) From equations (4) and (5), H ₁ −H ₂ =H ₁ ′−H ₂ ′= ΔH...(6) In other words, regardless of the atmospheric pressure P ₀ and the tank air pressure P, the water level difference between the two water levels in the tank is
Equal to the water level difference between points.

Regarding the detection of the water level difference in the tank, a high accuracy of 0.1% is achieved using the double float method shown in the figure, but an accuracy of 0.5% can also be easily achieved using the differential pressure gauge method.

A problem with water level measurements in large waterways such as rivers is the elimination of short-period waves such as wind waves and dynamic water pressure, but with the device of the present invention, these can be easily eliminated by the friction of the pipe. In addition, removal of earth, sand, garbage, sludge, etc. that cause difficulties in maintenance and management can be dealt with by rationally designing the structure of the settling tank and by conducting periodic inspections and cleaning.

The features of the device of this invention are as follows.

(1) Flow rate can be measured without affecting the flowing water of an open channel, such as by raising the dam by a weir or throttling by a frium.

(2) Since it is based on hydraulic formulas, flow velocity and flow rate can be calculated using roughness coefficients for which empirical values have been accumulated and cross-sectional characteristics such as cross-sectional area and diameter depth.

(3) Hydraulic knowledge such as roughness coefficients can be accumulated through calibration work such as flow rate observation.

(4) High accuracy can be ensured because the maximum value of the water level difference can be set to the full scale, and maintenance is easy because there is no need to pay special attention to maintaining the reference height of the upstream and downstream water inlets.

(5) Because the facilities are civil and mechanical, they are easy to maintain by river engineers and have high operational reliability.

(6) Can be used for the entire range of river flow from low to high water.

(7) It can also be used in locations where forward or reverse currents occur, such as tidal areas.

(8) If the suction method is used as a water conveyance method, it will be easier to install and maintain pressure tanks and water conveyance pipes, it will be easier to prevent and remove sediment, and water will be conveyed more reliably in times of low water. effective.

If the water surface gradient meter of this invention is used in conjunction with a water level meter and the recently advanced microcomputer is used, it is possible to automatically and continuously measure, record, and display the flow rate at river sites, etc. This will have a tremendous effect on water use adjustment and flood forecasting, which require the flow of water, and will enable total automation of river water management systems for the first time. Furthermore, it is expected that significant labor savings will be achieved in flow rate observation work for survey purposes, which has traditionally required a large amount of manpower on each river.

The device of this invention is absolutely necessary at points where the water level and water surface gradient change independently, such as tidal areas, upstream points of movable weirs, and upstream points of confluence points, but it can also be used in general rivers and irrigation channels. In reality, there are many cases where the water surface slope changes with the water level, so the use of the device of this invention can be expected to improve flow measurement accuracy and save labor, and is particularly effective in measuring flood peak flow in small rivers with rapid flow. is very large.

[Brief explanation of the drawing]

The figure shows the basic mechanism of the present invention, which pumps up water using pipes from two points up and down an open channel and generates a water level difference to be measured in a pressure tank installed at a central point.

Claims (1)

[Claims] 1. A water intake part that is submerged at two points upstream and downstream along the water flow direction of an open channel, and two still water surfaces that are placed at the midpoint of both water intake parts and are obtained by conducting water from both water intake parts with water conveyance pipes. a water level difference detection unit capable of measuring and detecting a water level difference between the two points, and determining a water surface gradient of the flowing water by dividing the water level difference detected by the water level difference detection unit by the distance between the two upstream and downstream points. A water surface gradient meter featuring: