A method and device for monitoring low flow ecological flow in small and medium-sized rivers

Abstract

The present invention relates to the field of ecological monitoring, and its purpose is to propose a method and device for monitoring the ecological flow of small and medium-sized rivers in low flow states, so as to realize ecological flow monitoring of small and medium-sized rivers in low flow states and reduce the cost of obtaining ecological flow data of rivers in data-free areas. The technical solution includes: 1. Determine the river monitoring section and select the river weir at a suitable location as the actual monitoring section of the ecological flow of small and medium-sized rivers; 2. Install flow monitoring equipment and river water level monitoring equipment to build an integrated system for monitoring the ecological flow under the free orifice outflow state of the dam body; 3. Based on the ecological flow monitoring data of representative outflow holes, combined with the relationship between the dam front water level and the number of outflow holes of the dam body free orifice obtained by on-site calibration, the ecological flow of the entire section under the free orifice outflow state of the dam body is measured in real time; 4. Based on the water level monitoring data in front of the dam, combined with the relationship between the dam front water level and the overflow outflow head of the dam body obtained by on-site calibration, the ecological flow of the entire section under the overflow state of the dam body is measured in real time.

Description

Technical Field

[0001] The present invention relates to the field of ecological monitoring, and in particular to a method and device for monitoring low-flow ecological flow in small and medium-sized rivers. Background Art

[0002] River ecological flow is a key factor in ensuring the ecological needs of aquatic organisms, such as habitat, reproduction, and migration. Through ecological flow monitoring, changes in river water volume can be monitored in real time, ensuring that rivers have sufficient water volume, maintaining their ecological functions, protecting aquatic biodiversity, and avoiding river dry-ups or ecological deterioration due to excessive water withdrawal. However, small and medium-sized rivers are often in a low-flow state; and when they are in a low-flow state, they are often accompanied by phenomena such as partially exposed riverbeds and unstable water flow patterns. Traditional monitoring methods such as flow meters have limited accuracy and are restricted by on-site river conditions. Equipment installation, commissioning, and calibration are difficult to carry out, greatly increasing the difficulty of monitoring ecological flow. Therefore, it is necessary to propose a method and device for monitoring low-flow ecological flow in small and medium-sized rivers. Summary of the Invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned background technology and propose a method and device for monitoring the ecological flow of small and medium-sized rivers in low flow conditions, so as to realize ecological flow monitoring of small and medium-sized rivers in low flow conditions and reduce the cost of obtaining ecological flow data of rivers in data-free areas.

[0004] The technical solution provided by the present invention is:

[0005] A method for monitoring low flow ecological flow in small and medium-sized rivers comprises the following steps:

[0006] Step 1: Determine the river monitoring section and select a suitable river weir as the actual monitoring section for the ecological flow of small and medium-sized rivers. The selection of the appropriate location of the river weir should take into account the following conditions:

[0007] 1. The river weir is located upstream or downstream of the river monitoring section and the distance from the river monitoring section is less than 2 km;

[0008] 2. There should be no tributaries flowing in or out between the river weir and the monitoring section, and there should be no water diversion in the river, that is, there should be no obvious water flow in or out.

[0009] 3. The selected river channel weir has a water storage capacity of less than 50,000 m 3 It cannot be a large weir or reservoir, but generally a small river weir, such as Dingbu Weir.

[0010] Step 2: Install flow monitoring equipment at the representative outflow holes of the dam body, install river water level monitoring equipment in the river channel in front of the dam, and build an integrated ecological flow monitoring system under the outflow state of the dam body free orifice. The specific steps are as follows:

[0011] S1: Install flow monitoring equipment (preferably Doppler flowmeters) at 3-5 representative outflow holes at both ends and in the middle of the river weir. Install river water level monitoring equipment (preferably radar water level gauges) at sections with stable flow patterns within 200 meters upstream of the river weir. The layout of the representative outflow hole flowmeters and the river water level monitoring equipment in front of the dam is shown in the figure. Figure 1 .

[0012] S2: Install power supply equipment, monitoring cabinets, and hydrological telemetry terminals for the flow monitoring equipment and water level monitoring equipment to form an integrated ecological flow monitoring system under the free orifice outflow condition of the dam body. The power supply equipment (preferably solar power supply equipment) should be installed in an area of ​​the river bank that is not flooded; the monitoring cabinet should be installed near the power supply equipment and connected to the power supply equipment via cables; the hydrological telemetry terminal is installed inside the monitoring cabinet and wirelessly connected to the hydrological data center to achieve real-time data transmission and monitoring; the Doppler flow meter and the radar water level meter are respectively connected to the hydrological telemetry terminal via cables. See the layout of the integrated ecological flow monitoring system for details. Figure 3 .

[0013] Step 3: Based on the ecological flow monitoring data of the representative outflow holes of the dam body and the relationship between the water level in front of the dam and the number of outflow holes of the dam body (obtained from on-site calibration), the ecological flow of the entire section under the outflow state of the dam body free orifice is calculated in real time. The steps are as follows:

[0014] S1: Based on the water level monitoring value in front of the dam The number of free outflow holes of the dam body at different water levels in the river channel was counted by manual on-site statistics. For the outflow holes that were lower or higher than the water depth of the representative outflow holes, the number of outflow holes of the current holes was converted according to the ratio of the water depth of the current holes to the water depth of the representative outflow holes. In this way, the relationship between the water level in front of the dam and the number of free outflow holes of the dam body was obtained.

[0015] S2: The ecological flow measurement method under the dam body free orifice outflow state uses the real-time water level monitoring in front of the dam. Based on the relationship between the water level in front of the dam and the number of free orifice outflow holes in the dam body, the number of free orifice outflow holes in the dam section represented by different dam body representative outflow holes under the monitored water level is obtained. Then, combined with the flow monitored by different dam body representative outflow holes, the ecological flow of the entire section under the dam body free orifice outflow state is calculated. The calculation formula is as follows:

[0016] (1)

[0017] (2)

[0018] Where, is the ecological flow of the dam section, m 3 / s; For the represents the outflow hole flow rate, m 3 / s, ; The water level of the dam body is The number of outflow holes represented by each outflow hole; For the The relationship between the water level in front of the dam represented by the outflow hole and the number of outflow holes at the free opening of the dam body; is the water level in front of the dam, m.

[0019] Step 4: Based on the dam front water level monitoring data and the relationship between the dam front water level and the dam overflow outflow head (obtained from on-site calibration), the ecological flow of the entire section under the dam overflow state is calculated in real time. The steps are as follows:

[0020] S1: Considering the uneven terrain in front of the dam, the outflow water level of different holes will be different. Therefore, according to the actual outflow of holes, the entire dam body is divided into Small sections (refer to the selection of representative outflow holes, the entire dam body is divided into 3-5 sections), the width of each small section is , the water head is The division of each segment is determined according to the actual terrain characteristics and does not necessarily require uniform distribution.

[0021] S2: Calculate the outflow rate for each section separately When the water level in front of the dam is higher than the dam body, the dam body is in an overflow state, which can be regarded as a special form of weir flow. The flow rate of each small section is calculated according to the outflow of the weir. The specific calculation formula is as follows:

[0022] (3)

[0023] (4)

[0024] Where: is the lateral contraction coefficient, ; The coefficient that takes into account the influence of downstream water level on discharge is called the flooding coefficient. , which can be determined by looking up the table; is the discharge coefficient of the weir, which can be determined by empirical formula or table; is the clear width of the weir top, m; is the acceleration due to gravity, take 9.81m / s 2 ; For the Average total water head at the weir crest, m, ; For the The relationship between the water level in front of the dam and the overflow head of the dam body.

[0025] S3: Each small segment of traffic Accumulate and get the ecological flow of the dam section .

[0026] (5).

[0027] A low-flow ecological flow monitoring device for small and medium-sized rivers is characterized in that: the device includes a plurality of flow monitoring devices arranged on the dam body of the river channel, a river water level monitoring device installed within 200 meters upstream of the dam body of the river channel, a power supply device installed in a non-flooded area on the river bank, a monitoring cabinet installed near the power supply equipment, and a hydrological telemetry terminal installed in the monitoring cabinet and wirelessly connected to the hydrological data center, wherein the flow monitoring equipment and the river water level monitoring equipment are both connected to the hydrological telemetry terminal via cables.

[0028] The power supply equipment supplies power to the monitoring cabinet and the hydrological telemetry terminal through a transmission line; the power supply equipment is a solar power supply equipment.

[0029] The flow monitoring device is a Doppler flow meter; the river water level monitoring device is a radar water level meter.

[0030] The beneficial effects of the present invention are:

[0031] 1) This invention combines a simple monitoring device with natural laws to construct an ecological flow monitoring method suitable for low flow conditions in small and medium-sized rivers;

[0032] 2) When the river water level is low and the dam is in a free-flow state, a simple monitoring device, Doppler flowmeter, is used to obtain the flow rate of the representative outflow holes of the dam in real time. Combined with the natural law of the number of outflow holes at different water levels, the ecological flow rate of the dam section in the free-flow state is calculated in real time.

[0033] 3) When the river is at low water level and the dam is overflowing, a simple monitoring device, a radar water level gauge, is used to obtain real-time water level data in front of the dam. Combining the relationship between the water level in front of the dam and the outflow head of the dam, and the calculation formula for the overflow flow of the weir, the ecological flow rate of the dam cross section under overflow is calculated in real time, thus enabling ecological flow monitoring under low flow conditions in small and medium-sized rivers.

[0034] 4) The ecological flow monitoring method of the present invention has low investment cost, reduces the cost of obtaining ecological flow data of rivers in data-free areas, reduces capital investment in instruments and devices, and increases its applicability from the perspective of method structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a diagram of the installation location of the low-flow ecological flow monitoring device for small and medium-sized rivers described in an embodiment of the present invention.

[0036] Figure 2 This is a schematic diagram of the outflow water level of the free orifice of the dam body and the overflow water level of the dam body according to an embodiment of the present invention.

[0037] Figure 3 Schematic diagram of the structure of the ecological flow monitoring integrated system in an embodiment of the present invention.

[0038] Figure 4 This is a cross-sectional photograph of the river channel upstream of the dam body in an embodiment of the present invention.

[0039] Figure 5 Schematic diagram of the installation structure of the Doppler flowmeter in an embodiment of the present invention.

[0040] Figure 6 This is a relationship diagram between the water level in front of the dam (the middle one represents the outflow hole) and the number of outflow holes at the free openings of the dam body in an embodiment of the present invention.

[0041] Figure 7 This is a relationship diagram between the water level in front of the middle section of the dam and the overflow head of the dam body in an embodiment of the invention.

[0042] Numbers in the figure:

[0043] 1—River weir, 2—Dam body outflow hole, 3—Doppler flowmeter, 4—Dam body free orifice outflow state water level, 5—Dam body overflow outflow state water level, 6—Cable, 7—Radar water level gauge, 8—Girder bridge, 9—Solar power supply equipment, 10—Hydrological telemetry terminal, 11—River flow direction, 12—River monitoring section, 1-1—Dam body. DETAILED DESCRIPTION

[0044] by Figure 1 and Figure 2 The present invention will be further described in detail by taking a specific cross section of a river in Zhejiang Province as an example.

[0045] The confirmed river monitoring section 12 is approximately 111m wide. 0.6km downstream of the section is a Dingbu Weir 1, which has a total of 185 dam bodies 1-1. Each dam body is a square concrete dam measuring 150cm×30cm×36cm. The distance between two dam bodies is 30cm, forming a dam body outflow hole 2. 0.2km upstream of the Dingbu Weir is a beam bridge 8. The river upstream of the dam section is as follows: Figure 4 shown.

[0046] Step 1: Select Dingbu Weir as the actual monitoring section for ecological flow of small and medium-sized rivers; the Dingbu Weir meets the following conditions:

[0047] 1. Dingbu Weir is 0.6 km away from the upstream river monitoring section;

[0048] 2. There is no water inflow or outflow between Dingbu Weir and the river monitoring section mentioned upstream.

[0049] 3. The Dingbu Weir has basically no water storage capacity.

[0050] Therefore, the Dingbu Weir is a river weir in a suitable location.

[0051] Step 2: Install flow monitoring equipment at the representative outflow holes of Dingbu Weir Dam and river water level monitoring equipment in the river channel in front of the dam to build an integrated ecological flow monitoring system for the free outflow state of Dingbu Weir Dam. The specific steps are as follows:

[0052] S1: According to the requirement of installing flow monitoring equipment at 3-5 representative outflow holes at both ends and in the middle of the river weir dam, according to the site survey and the cross-sectional width of the dam body, select one representative outflow hole at each end and in the middle of the Dingbu Weir dam body, and install a set of Doppler flowmeters 3 on each. The schematic diagram of the Doppler flowmeter is shown as follows: Figure 5 As shown. According to the requirement of installing river water level monitoring equipment at a section with stable flow state within 200 meters upstream of the river weir, there is a beam bridge within 200 meters upstream of Dingbu Weir. A radar water level meter is installed on the beam bridge to monitor the river water level. The layout of the flow meter at the representative outflow hole and the river water level monitoring equipment in front of the dam is shown in Figure 1 .

[0053] S2: For the flow monitoring equipment and water level monitoring equipment, power supply equipment, monitoring cabinets, and hydrological telemetry terminals are installed to form an integrated ecological flow monitoring system under the free orifice outflow state of the dam body. The power supply equipment uses solar power supply equipment 9, which is installed in an area on the river bank that is not flooded; the monitoring cabinet is installed near the power supply equipment and is connected to the power supply equipment through a cable to obtain electricity; the hydrological telemetry terminal 10 is installed inside the monitoring cabinet (for convenient power supply and equipment safety), and is wirelessly connected to the local hydrological data center through its own communication unit to achieve real-time data transmission and monitoring; the Doppler flow meter and the radar water level meter are respectively connected to the hydrological telemetry terminal through a cable 6. The structure of the integrated ecological flow monitoring system is shown in Figure 3 .

[0054] Step 3: Based on the ecological flow monitoring data of the representative outflow holes of the dam body and the relationship between the water level in front of the dam and the number of outflow holes of the dam body (obtained from on-site calibration), the ecological flow of the entire section under the outflow state of the dam body free orifice is calculated in real time. The specific steps are as follows:

[0055] S1: Based on the water level monitoring value of the water level gauge in front of the dam , the number of free orifice outflow holes of the dam body at different water levels of the river was counted by manual on-site statistics. Among them, the outflow holes that were lower or higher than the water depth of the representative outflow holes were converted into the number of outflow holes of the current hole according to the ratio of the water depth of the current hole to the water depth of the representative outflow hole. Through on-site measurement, the number of different representative outflow holes of the dam body at different water levels is shown in Table 1. The relationship between the water level in front of the dam and the number of free orifice outflow holes of the dam body is plotted as follows Figure 6 As shown, the relationship curve can be approximated by express.

[0056] Table 1 Number of outflow holes and flow rate of the dam body at different water levels in front of the dam

[0057]

[0058] Note: The water level in front of the dam is measured by a radar water level gauge, and the water level is the distance from the radar to the river surface, the same below.

[0059] S2: Method for Measuring Ecological Flow Under Free Orifice Outflow Conditions: Using the real-time water level monitored in front of the dam, the relationship between the water level in front of the dam and the number of free orifice outflow holes in the dam body is used to determine the number of free orifice outflow holes in the dam section represented by each representative orifice at the monitored water level. Combined with the flow rates monitored at each representative orifice, the ecological flow across the entire dam section is calculated. In this example, the water level monitoring data in front of the dam is substituted into the relationship between the water level in front of the dam and the number of free orifice outflow holes in the dam body for each dam section. The number of free orifice outflow holes in each dam section is then determined, combined with the flow rates at the representative orifices in each dam section. The ecological flow across the entire section is calculated according to Equation (1) and compared with the measured flow rate at the dam body. The results are shown in Table 2. The relative error between the estimated and measured dam body flow rates is within 20% on average, indicating that the estimated results of this method are consistent with the actual flow rate.

[0060] Table 2 Dam outflow at different water levels in front of the dam

[0061]

[0062] Step 4: Based on the dam front water level monitoring data and the relationship between the dam front water level and the dam overflow outflow head (obtained from on-site calibration), the ecological flow of the entire cross-section under the dam overflow state is calculated in real time. The specific steps are as follows:

[0063] S1: Considering the uneven terrain in front of the dam, the outflow water level of different holes will be different. Therefore, according to the actual outflow of the holes, refer to the selection of representative outflow holes, and divide the entire dam body into three small sections. The width of the left section is 36.9m, the width of the middle section is 35.7m, and the width of the right section is 37.5m. According to the on-site measurement, the average outflow head of each section is shown in Table 3. The relationship between the water level in front of the dam and the overflow outflow head of the dam body is obtained. The relationship between the water level in front of the dam and the overflow outflow head of the dam body is shown in Table 3. Figure 7 The relationship curve can be approximated by express.

[0064] Table 3 Average outflow head of each section of the dam body at different water levels in front of the dam

[0065]

[0066] S2: Calculate the outflow flow rate of each section separately. When the water level in front of the dam is higher than the dam body, the dam body is in a free overflow state, which can be regarded as a special form of weir flow. The flow rate of each section is calculated according to the weir outflow. The dam body has free outflow and no lateral contraction. Therefore, its lateral contraction coefficient is , flooding coefficient Then, based on the monitored water level in front of the dam, the average head of different dam sections was obtained from the relationship between the water level in front of the dam section and the overflow head of the dam body. The outflow flow of each section of the dam body was calculated according to formula (3). The outflow flow of each section was then accumulated to obtain the ecological flow of the entire dam section. The results are shown in Table 4.

[0067] Table 4 Average outflow head of each section of the dam body at different water levels in front of the dam

[0068]

Claims

1. A method for monitoring low flow ecological flow in small and medium-sized rivers, comprising the following steps: Step (1) determining a river monitoring section (12), selecting a river weir (1) at a suitable location as an actual monitoring section for the ecological flow of small and medium rivers; Step (2) Install flow monitoring equipment at representative outflow holes of the river channel weir, install river water level monitoring equipment in the river channel in front of the dam, and build an integrated ecological flow monitoring system under the outflow state of the dam body free orifice; Step (3) based on the ecological flow monitoring data of the representative outflow holes and the relationship between the water level in front of the dam and the number of outflow holes of the dam body obtained by on-site calibration, the ecological flow of the entire cross section under the outflow state of the free orifice of the dam body is calculated in real time; Step (4) based on the dam front water level monitoring data and the relationship between the dam front water level and the dam body overflow outflow head obtained by on-site calibration, real-time calculation of the ecological flow of the entire cross section under the dam body overflow state; The calibration method for the relationship between the water level in front of the dam and the number of free orifice outflow holes in the dam body in step (3) is as follows: based on the water level monitoring value Z in front of the dam, the number of free orifice outflow holes in the dam body at different water levels in the river channel is counted by manual on-site statistics. Among them, the outflow holes below or above the water depth of the representative outflow hole are converted into the number of outflow holes according to the ratio of the water depth of the current hole to the water depth of the representative outflow hole, thereby obtaining the relationship between the water level in front of the dam and the number of free orifice outflow holes in the dam body; The method for calculating the ecological flow of the entire section under the free orifice outflow state of the dam body described in step (3) is as follows: through the real-time monitoring of the water level in front of the dam, the relationship between the water level in front of the dam and the number of free orifice outflow holes of the dam body is used to obtain the number of free orifice outflow holes of the dam section represented by the representative outflow holes of the dam body under the monitored water level, and then combined with the flow monitored by the representative outflow holes of the dam body, the calculation is carried out: specifically: n i =f i (Z) (2) Where Q is the ecological flow of the dam section, m 3 / s;q i is the flow rate of the ith representative orifice, m 3 / s, i=1,2,…k; n i is the number of outflow holes represented by the ith representative outflow hole at a certain water level of the dam body; f i is the relationship between the water level in front of the dam represented by the i-th representative outflow hole and the number of free outflow holes in the dam body; Z is the water level in front of the dam, in m.

2. The method for monitoring low flow regime ecological flow in small and medium-sized rivers according to claim 1, characterized in that: The selection conditions for the appropriate location of the river channel weir in step (1) are: (1) The river weir is located upstream or downstream of the river monitoring section, and the distance from the river monitoring section is less than 2 km; (2) There should be no tributaries or diversions between the river weir and the monitoring section, and no water diversion should be carried out to avoid significant water inflow or outflow; (3) The selected river channel weir is a small hydraulic structure of Dingbu Weir, and the water storage capacity is less than 50,000 m 3 .

3. The method for monitoring low flow regime ecological flow in small and medium-sized rivers according to claim 2, characterized in that: The specific steps of step (2) are as follows: S1: Install flow monitoring equipment at 3-5 representative outflow holes at both ends and in the middle of the river weir. Install river water level monitoring equipment at sections within 200 meters upstream of the river weir where the flow pattern is stable. S2: Install power supply equipment, monitoring cabinets, and hydrological telemetry terminals for the flow monitoring equipment and water level monitoring equipment to form an integrated ecological flow monitoring system under the free orifice outflow state of the dam body.

4. The method for monitoring low flow regime ecological flow in small and medium-sized rivers according to claim 3, characterized in that: In step (4), based on the dam front water level monitoring data and the relationship between the dam front water level and the dam overflow outflow head obtained by on-site calibration, the ecological flow of the entire cross section under the dam overflow state is calculated in real time. The steps are as follows: S1: According to the actual hole outflow situation, the entire dam body is divided into N small sections, and the width of each section is B j , the water head is H j ; S2: For each small section, calculate its outflow flow Q separately j When the water level in front of the dam is higher than the dam body, the flow of each small section is calculated according to the outflow of the weir; The calculation formula is as follows: H j =φ j (Z) (4) Where: ε is the lateral contraction coefficient, ε≤1; σ is the coefficient that considers the effect of downstream water level on discharge, called the submergence coefficient, σ≤1, determined by looking up the table; m is the discharge coefficient of the weir, determined by empirical formula or table; B is the clear width of the weir top, m; g is the acceleration of gravity, taken as 9.81 m / s 2 ;H j is the average total head at the weir crest of the jth section, m, j = 1, 2, ... N; φ j The relationship between the water level in front of the dam and the overflow head of the dam body in the jth section; S3: The flow rate of each small segment Q j Accumulate and obtain the ecological flow Q of the dam section; 5. The method for monitoring low flow regime ecological flow in small and medium-sized rivers according to claim 4, characterized in that: In step (ii), the power supply equipment is installed in a non-flooded area on the river bank, the monitoring cabinet is installed near the power supply equipment, and the hydrological telemetry terminal is installed inside the monitoring cabinet and wirelessly connected to the hydrological data center.

6. A low-flow ecological flow monitoring device for small and medium-sized rivers, using the low-flow ecological flow monitoring method for small and medium-sized rivers according to any one of claims 1 to 5, characterized in that: The device includes several flow monitoring devices arranged on the dam body of the river channel, river water level monitoring equipment installed within 200 meters upstream of the dam body, power supply equipment installed in the non-flooded area of ​​the river bank, a monitoring cabinet installed near the power supply equipment, and a hydrological telemetry terminal installed in the monitoring cabinet and wirelessly connected to the hydrological data center. The flow monitoring equipment and the river water level monitoring equipment are both connected to the hydrological telemetry terminal via cables.

7. The low flow ecological flow monitoring device for small and medium-sized rivers according to claim 6 is characterized by: The power supply equipment supplies power to the monitoring cabinet and the hydrological telemetry terminal through a transmission line; the power supply equipment is a solar power supply equipment.

8. The low flow ecological flow monitoring device for small and medium-sized rivers according to claim 7 is characterized by: The flow monitoring device is a Doppler flow meter; the river water level monitoring device is a radar water level meter.

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