Method for determining ecological flow of seasonal river in northern cold region considering river water loss

Abstract

The present application is directed to the northeast cold region seasonal river, and provides a method for determining the ecological flow of the seasonal river in the cold region in the north considering the water loss of the river channel, comprising: collecting basic data; dividing the river section into several leakage characteristic sections according to the lithology of the river bed and the hydraulic relationship; calculating the monthly river channel water loss coefficient based on the water balance principle, and determining it according to the hydrological classification and the water frequency; using the coefficient to calculate the ecological flow target from the upstream approved ecological flow section to the downstream section by section, and using the Q90 method to determine the target when the loss coefficient is 1; according to the natural measured data statistics section of the section before the high-intensity development of human beings, the characteristics of the section, the perennial river section and the seasonal dry section are controlled by the ecological flow and the basic ecological water quantity respectively; the rationality of the target is verified through consistency checking, natural runoff series backtracking checking and measured data verification; monitoring and early warning and scheduling guarantee measures are formulated, and the scientificity and accessibility of the determination and guarantee of the ecological flow target are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of ecological flow target calculation and protection, and in particular to a method for determining the ecological flow of seasonal rivers in northern cold regions that takes into account river water conveyance losses. Background Technology

[0002] Currently, there are over 200 methods for calculating ecological flow both domestically and internationally, which can be broadly categorized into several types, including hydrological methods, hydraulic methods, habitat methods, and holistic analysis methods. Among these, hydrological methods, such as the Tennant method, Qp method, and wetted perimeter method, are widely used due to their simplicity in data types and ease of calculation. Based on current regulations and standards such as the "Specification for Calculation of Water Demand for River and Lake Ecological Environment" and the "Specification for Calculation and Design of Ecological Flow for Water Conservancy and Hydropower Projects," the determination of ecological flow typically employs methods such as monthly allocation using the Tennant method and calculating flow during extreme dry seasons using the Q90 method, with independent calculations performed for individual control sections.

[0003] However, current methods for determining ecological flow have significant technical shortcomings when applied to seasonally interrupted rivers in cold northern regions, especially those flowing through the middle and lower reaches. First, existing methods generally ignore the objective physical laws governing river water loss. When a river flows through a highly permeable gravel or pebble bed, there is a close hydraulic connection between river water and groundwater; surface water seeps along the river to replenish groundwater, resulting in significant water loss. Ignoring this physical process and directly using the ecological flow target value of the upstream section or independently calculating the downstream section using the same method will lead to a severely inflated target value for the downstream section, making it impossible to achieve in actual scheduling. Second, existing methods fail to differentiate the management needs between normally flowing river sections and seasonally interrupted river sections. Current regulations lack a targeted technical approach for determining the ecological flow of interrupted rivers and do not set differentiated management target types based on the natural interruption characteristics of different river sections, resulting in management measures lacking specificity and operability. Secondly, existing methods do not fully consider the differences in river channel water conveyance losses across different horizontal years. River channel seepage losses are comprehensively affected by factors such as inflow volume, water level, and groundwater depth. The water conveyance loss coefficients vary significantly under different horizontal year conditions. The lack of a systematic consideration of these differences makes the calculation results difficult to adapt to the ecological scheduling needs under different inflow conditions. Finally, existing methods lack a systematic technical framework. The objectives are not coordinated across different cross-sections, making it impossible to form a complete technical closed loop from objective determination to verification and validation to the formulation of safeguard plans. This makes it difficult to achieve unified ecological flow scheduling and management at the watershed level.

[0004] Therefore, there is an urgent need in this field for a complete method for constructing ecological flow targets that can fully consider the physical laws of river water loss, differentiate the management needs of river sections with constant flow and those with seasonal flow interruption, and systematically establish a multi-level annual river water loss coefficient system. This method would solve the technical problems of existing methods in determining ecological flow in seasonally interrupted rivers in northern cold regions, such as targets that are too large to achieve, single management types that lack specificity, and inconsistencies between targets at different cross sections. This would provide scientific and reliable technical support for the unified scheduling and management of water resources in the basin and the restoration of the Mother River. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the ecological flow of seasonal rivers in cold northern regions, taking into account water transport losses, in order to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: This invention provides a method for determining the seasonal ecological flow of rivers in cold northern regions, taking into account water transport losses, comprising the following steps: Step 1: Collect basic data of the target river basin. The basic data includes the natural monthly runoff restoration series and measured daily average flow series of each control section, river hydrogeological parameters, operation data of existing water conservancy and hydropower projects, water intake data of the interval, and water requirements of ecological protection objects. Step 2: Based on the riverbed lithology, permeability coefficient, and hydraulic relationship between groundwater and surface water, the target river section is divided into several seepage characteristic sections. The hydrological station is used as the segment node to determine the surface water-groundwater conversion relationship in each river section. Step 3: Based on the principle of water balance, using the measured runoff data of adjacent hydrological stations at the same time, combined with the water intake of the interval, calculate the monthly river water conveyance loss coefficient of each seepage characteristic section, and statistically analyze it separately according to the three hydrological periods of freezing period, non-flood period and flood period. At the same time, the river water conveyance loss coefficient of each period is determined according to different water inflow frequency conditions. Step 4: Obtain the phased ecological flow target values ​​of the approved ecological flow control sections in the upstream of the target river. Using the river water conveyance loss coefficient determined in Step 3, calculate the phased ecological flow target of each downstream control section from upstream to downstream. When the river water conveyance loss coefficient of a certain phase is 1 under the set water inflow frequency, the ecological flow target of that phase is determined by the Q90 method. Step 5: Using the measured daily average flow data of the target cross-section before high-intensity human development, statistically analyze the flow interruption characteristics of each target cross-section. If a cross-section has never experienced flow interruption under natural conditions, it is determined to be a control cross-section of a perennial river section, and the control target is ecological flow. If a cross-section experiences periodic flow interruption under natural conditions, it is determined to be a control cross-section of a seasonal flow interruption river section, and the control target is basic ecological water volume. Step 6: Convert the ecological flow of each section determined in Step 4 into basic ecological water volume, back-calculate the actual river transport loss coefficient used in each river section, check the consistency with the river transport loss coefficient under the same inflow frequency condition in Step 3, and conduct a retrospective check on the degree of satisfaction of the natural runoff series from 1956 to 2000, and verify it using recent measured data. Step 7: Based on the verified ecological flow or basic ecological water volume targets, formulate monitoring and early warning plans and ecological scheduling and protection measures for each control section.

[0007] Preferably, the Q90 method described in step 4 for determining the ecological flow target specifically involves: based on the natural monthly average flow or runoff of the river control section over a long series (n≥30 years), using the frequency of the driest month each year, selecting the average flow or runoff of the driest month at 90% frequency as the ecological base flow of the river control section.

[0008] Preferably, the daily average flow data measured in nature before high-intensity human development mentioned in step 5; the criterion for determining the flow interruption is that the daily average flow is 0.

[0009] Preferably, the retrospective verification of the satisfaction level of the 1956-2000 natural runoff series in step 6 specifically involves: using the natural monthly runoff series from 1956-2000 to reconstruct the series, statistically analyzing the satisfaction level of the ecological flow or basic ecological water volume of the target section in each period. The satisfaction level is the ratio of the number of periods in each period that reach or exceed the ecological flow target value to the total number of periods in each period. If the satisfaction level of each period is not less than 90%, the ecological flow target is deemed reasonable; if the satisfaction level of a certain period is less than 90%, the ecological flow target value for that period is lowered to the level that meets the 90% guarantee rate requirement.

[0010] Preferably, the verification using recent measured data in step 6 specifically involves: obtaining measured daily average flow data after the implementation of ecological scheduling, statistically analyzing the actual satisfaction level of ecological flow or basic ecological water volume at each stage of the target section, and if the measured satisfaction level is lower than 90% due to the influence of continuous extremely dry water conditions, then the rationality of the target is comprehensively judged in conjunction with the water inflow frequency analysis.

[0011] Preferably, the monitoring and early warning scheme in step 7 is as follows: For control sections of perennial river sections using ecological flow control, two early warning levels are set: blue and red. The threshold for blue early warning is 100%-110% of the ecological flow target value, and the threshold for red early warning is below the ecological flow target value. For control sections of seasonally interrupted river sections using basic ecological water volume control, early warnings are issued at a set frequency after the flood season. The threshold for blue early warning is 70%-80% of the basic ecological water volume target value, and the threshold for red early warning is below 70% of the basic ecological water volume target value.

[0012] Preferably, the method is applicable to the determination of ecological flow in seasonally interrupted rivers in the north; the freezing period is from December to March of the following year, the non-flood season is from April to May and from October to November, and the flood season is from June to September.

[0013] The present invention achieves the following beneficial technical effects compared to the prior art: This invention provides a method for determining the ecological flow of seasonal rivers in northern cold regions, considering channel water conveyance losses. This method is characterized by its strong scientific basis, good operability, and high adaptability to specific types of rivers. By collecting basic data and dividing the river into seepage characteristic sections, based on the principle of water balance, and classifying and determining the monthly channel water conveyance loss coefficient according to hydrological periods and inflow frequency, this invention uses this coefficient to extrapolate the ecological flow target segment by segment downstream from the approved upstream cross-section. Simultaneously, it uses the Q90 method to determine the target for extremely dry periods, effectively avoiding the drawback of excessively large downstream ecological flow targets due to neglecting channel seepage losses. Furthermore, by utilizing pre-intensive human development data to statistically analyze the flow interruption characteristics of the river segments where each target cross-section is located, and by considering the differences between normally flowing river segments and seasonally interrupted river segments... This invention employs two control target types—ecological flow and basic ecological water volume—to overcome the technical deficiency of existing methods that uniformly apply flow control to all cross-sections, leading to unattainable targets in seasonally dry river sections. By retrospectively verifying the satisfaction level of natural runoff series from 1956 to 2000 and setting a qualification standard of no less than 90%, and by using recent measured data to verify the actual attainability of the targets, a systematic multi-dimensional verification process is constructed. This compensates for the shortcomings of existing methods in the complete "determination-verification-verification" technical chain, forming a relatively systematic closed-loop process. This invention can significantly improve the scientific validity and attainability of ecological flow targets, coordinating control measures with the natural hydrological rhythms of rivers. It can provide a standardized technical solution for the ecological flow determination of similar seasonal rivers in northern China and has good prospects for widespread application. Attached Figure Description

[0014] To more clearly illustrate the embodiments of the present invention or the prior art, the accompanying drawings required in the embodiments are briefly described below. It should be noted that the drawings described below are only some embodiments of the present invention, and those skilled in the art can obtain other drawings based on them without creative effort.

[0015] Figure 1 The flowchart of the method for determining the seasonal ecological flow of rivers in cold northern regions, taking into account water transport losses, provided by the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The purpose of this invention is to provide a method for determining the ecological flow of seasonal rivers in cold northern regions, taking into account river channel water transport losses. This method addresses prominent issues in existing technologies, such as neglecting river channel seepage losses leading to unrealizable downstream ecological flow targets, failing to distinguish between perennial and seasonally interrupted river sections resulting in a lack of targeted management, and lacking a systematic verification framework leading to inconsistencies in targets across different sections. This method makes the determination of ecological flow targets more scientific and reasonable, providing reliable technical support for the unified scheduling and management of water resources in the basin and the restoration of the Mother River.

[0018] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Example 1: like Figure 1 As shown, this invention provides a method for determining the ecological flow of intermittent rivers considering channel water transport losses. The following section uses the ecological flow determination at two control sections on the main stream of the Tao'er River—Taonan Station and Heidi Temple Station—as examples to detail the process of determining the ecological flow target for seasonally intermittent rivers in northern alluvial fan topography using the method of this invention. The Tao'er River is a right-hand tributary of the lower reaches of the Nenjiang River, with a main stream length of 563 km, flowing through Hinggan League in Inner Mongolia Autonomous Region and Baicheng City in Jilin Province, before emptying into the Nenjiang River at Yueliangpao. The Charshen Reservoir is the only key control project on the main stream of the Tao'er River, located in the middle reaches, controlling a drainage area of ​​7780 km². 2 It is a large-scale water conservancy project that integrates flood control and irrigation with power generation, water supply, aquaculture, and aquatic ecological environment utilization. The ecological flow targets for the Charsun Reservoir section and the Zhenxi section (provincial boundary section of the main stream) have already been approved by the Ministry of Water Resources. This project requires the addition of ecological flow control requirements for the downstream Taonan Station and Heidi Temple Station. The middle and lower reaches of the Taoer River flow through the Taoer River alluvial fan. The riverbed sediments are coarse-grained and highly permeable, with a close hydraulic connection between river water and groundwater. Surface water seeps into the groundwater along the river, exhibiting significant characteristics of seasonal flow interruption, making it a typical alluvial fan river in northern China.

[0020] Step 1: Collect basic data for the target river basin. Specifically, in this embodiment, precipitation and runoff data were collected from the Zhenxi, Taonan, and Heidi Temple hydrological stations in the Tao'er River basin. The Zhenxi station has a catchment area of ​​18,462 km². 2The catchment area of ​​Taonan Station is 27,200 km². 2 The catchment area of ​​Heidi Temple Station is 30,150 km². 2 The flow data includes a natural monthly runoff reduction series from 1956 to 2016 and a measured daily average flow series from January 2010 to July 2024. Monthly water intake data for major water diversion projects in the region were also collected, including agricultural irrigation water intake and ecological replenishment from April to September 2021 to 2024 for the Taobei Irrigation District, Zhenxi Irrigation District, Manzhoudai Irrigation District, and Qingyou Irrigation District in Baicheng City. Hydrogeological survey results of the Taoer River basin were also collected, including parameters such as riverbed lithology, permeability coefficient, aquifer thickness, and groundwater depth for each river section, as well as previous research results such as the river channel water conveyance loss assessment report for the two provinces downstream of the Charsun Reservoir. These basic data are the fundamental basis for subsequent calculations of river channel water conveyance loss coefficients and determination of ecological flow targets. Data quality directly affects the reliability of the final results; therefore, long-term, multi-source data should be used as much as possible, and cross-validation should be performed.

[0021] Step two involves dividing the target river section into several seepage characteristic segments based on riverbed lithology, permeability coefficient, and the hydraulic relationship between groundwater and surface water. Using hydrological stations as segmentation nodes, the surface water-groundwater conversion relationship is determined for each seepage characteristic segment. In this embodiment, based on field investigations and hydrogeological surveys, and combined with the distribution of hydrological stations in the river channel downstream of the Charsun Reservoir, the 227 km long river section between the Charsun Reservoir and the Heidi Temple hydrological station is divided into three seepage characteristic segments. The first section is the river section from Charsun Station to Zhenxi Station. This section is located in the mountain valley area of ​​Xing'an League. The topography on both sides of the river changes greatly. Loose porous aquifers are widely distributed in the floodplain and first terrace. The lithology of the aquifer is gravel, with particles larger than 2 mm accounting for 70%-80%. The thickness of the aquifer is generally 6-7 m, and can reach more than 9 m in the thickest part. The permeability coefficient is relatively high, which is conducive to the hydraulic connection between river water and groundwater. However, due to the relatively small thickness of the aquifer, the storage space and consumption pathways of groundwater are limited, and the leakage of the river is not very large. It is judged to be a medium leakage section. The second section is the section from Zhenxi Station to Taonan Station. This section is mainly located in the upper part of the Taoer River fan-shaped landform. The aquifer in this section has fine particles, good roundness, and good sorting. The aquifer is relatively thick and the lithology is loose. The upper part is gravelly sandy soil, and the lower part is sandy gravel and gravel. Some sections are exposed. Most of the time, the surface water level is higher than the groundwater level, and surface water is more likely to be converted into groundwater. The leakage of the river channel is relatively large, and it is judged to be a strong leakage section, which is the main section of river channel water conveyance loss. The third section is the river segment from Taonan Station to Heidi Temple Station. This segment is located on the outer edge of the Taoer River fan-shaped landmass, i.e., the alluvial plain area. Compared to the section from Zhenxi Station to Taonan Station, the aquifer particles are finer and the thickness is reduced. A layer of weakly permeable loess of varying thickness covers the surface, and the groundwater depth increases to 6-11 m. The connection between surface water and groundwater is relatively weakened, resulting in less seepage in the river channel. This segment is classified as a weakly seeping segment. By dividing the river into these characteristic seepage segments, the river transport loss coefficient can be determined for different hydrogeological conditions, improving the accuracy of subsequent calculations.

[0022] Step 3: Based on the principle of water balance, using the concurrent measured runoff data from adjacent hydrological stations and the water intake in the interval, calculate the monthly river transport loss coefficient for each seepage characteristic section. Statistics are compiled separately for three hydrological periods: the freezing period, the non-flood season, and the flood season. Furthermore, the river transport loss coefficient for each period is determined according to different inflow frequencies. Evaporation loss from the river surface is relatively small and can be ignored when the river width is small and the flow rate is large. Taking the seepage section from Zhenxi Station to Taonan Station as an example, the river transport loss coefficient is calculated monthly using measured data from a complete hydrological year from June 2023 to May 2024, and then the average value is taken according to the three hydrological periods. The freezing period is from December to March of the following year. During this period, the temperature is below 0℃, the river is frozen, and evaporation loss is negligible. The calculated freezing period loss coefficient for the Zhenxi to Taonan section is 0.724. The non-flood season is from April to May and October to November, which is the ice-melting period and autumn / winter season, with relatively small runoff. The calculated non-flood season loss coefficient is 0.483. The flood season is from June to September, which is the main rainfall period with larger runoff. The calculated flood season loss coefficient is 0.294. The calculated results for the seepage section from Taonan Station to Heidi Temple Station show a freezing period loss coefficient of 0.162, a non-flood season loss coefficient of 0, and a flood season loss coefficient of 0, indicating that the baseflow of the river in this section can reach the downstream area during both the non-flood and flood seasons. Simultaneously, based on four inflow frequency conditions (P=50%, P=75%, P=90%, and P=25%), the river transport loss coefficients for each period under normal, dry, extremely dry, and abundant water years were statistically analyzed, forming a loss coefficient index system under different level year conditions. This provides a basis for subsequent ecological flow estimation under different inflow conditions.

[0023] Step four involves obtaining the phased ecological flow target values ​​for the approved ecological flow control sections upstream of the target river. Using the river channel loss coefficient determined in step three, the phased ecological flow target for each downstream control section is calculated section by section from upstream to downstream. When the river channel loss coefficient for a certain phase is 1 under a set inflow frequency condition, the ecological flow target for that phase is determined using the Q90 method. In this embodiment, the upstreammost approved control section is the Zhenxi Hydrological Station, which is also the provincial boundary section of the main stream. Its approved ecological baseflow target is 2.53 m during the freezing period. 3 / s, 5.00 m during non-flood season 3 / s, 7.50 m during the flood season 3 / s. Because the annual average natural runoff of the hydrological series from 1980 to 2016 varied by more than 10% compared to the 1956-2000 hydrological series, with a 16.22% decrease in natural runoff at the Taonan section and a 14.50% decrease at the Heidi Temple section, the ecological flow at both Taonan and Heidi Temple stations was calculated using natural runoff data from 1980 to 2016. Considering various factors, for Taonan station, the Q90 method was used for calculations during the freezing period, while the water transport loss coefficient between Zhenxi Station and Taonan Station was used for calculations during the non-flood season and flood season, based on 90% inflow conditions. The calculation results were converted to Tennant method values, i.e., 2% and 8% of the annual average flow. For the Heidi Temple station, considering the constraints of the water-carrying capacity during the freezing period and non-flood season under the condition of 90% inflow (P=90%), only the ecological flow of the Heidi Temple station during the flood season is subject to control requirements. For the non-flood season and flood season, the water conveyance loss coefficient of the Taonan-Heidi Temple channel under the 90% inflow condition is used for calculation, and the ecological flow is converted into basic ecological water volume. The calculation result is converted to 3% of the multi-year average flow using the Tennant method. The final verified result is an ecological flow of 0.33 m³ during the freezing period at Taonan station. 3 / s, non-flood season ecological flow 0.9 m 3 / s, ecological flow during the flood season: 3.62 m³ 3 / s, the basic ecological water volume at Heidi Temple Station during the flood season is 13.6 million m³. 3 .

[0024] Step 5: Using the measured daily average flow data of the target cross-sections before intensive human development, statistically analyze the flow interruption characteristics of each cross-section. If a cross-section has never experienced flow interruption under natural conditions, it is identified as a control cross-section of a normal-flowing river section, and the control target is ecological flow. If a cross-section experiences periodic flow interruption under natural conditions, it is identified as a control cross-section of a seasonally interrupted river section, and the control target is basic ecological water volume. In this embodiment, measured daily average flow data from various hydrological stations during the period of 1959-1985 were selected for flow interruption characteristic statistics. This period was before the construction of the Charsun Reservoir and can reflect the flow interruption situation of the river section under natural conditions. The criterion for determining flow interruption is a daily average flow of 0. Statistical results show that the Taonan station did not experience any flow interruption during the period of 1959-1985, and belongs to the control cross-section of a normal-flowing river section. Therefore, the control target is ecological flow. The Heidi Temple Station experienced varying degrees of flow interruption between 1959 and 1970, with the longest period of interruption reaching 244 days. As it is a seasonally interrupted river section, the basic ecological water volume was adopted as the control target.

[0025] Step six involves converting the ecological flow at each cross-section determined in step four into basic ecological water volume, back-calculating the actual river transport loss coefficient used in each river section, and verifying its consistency with the river transport loss coefficient under the same inflow frequency conditions in step three. A retrospective verification of the satisfaction level of the natural runoff series from 1980 to 2016 is also performed, along with validation using recent measured data. In this embodiment, to fully verify the rationality of the ecological flow target, the ecological flow targets for Taonan Station and Heidi Temple Station are calculated and verified for each scheme based on the river transport loss coefficients for three different levels of years: normal water year, dry year, and wet year. Based on the river transport loss coefficient for a normal water year, the ecological flow at Taonan Station during the freezing period is determined to be 1.35 m³. 3 / s, 3.69 m during non-flood season 3 / s, 6.16 m during the flood season 3 / s, freezing period at Heidi Temple Station: 1.00 m 3 / s, 3.08 m during non-flood season 3 / s, 5.53m during flood season 3 / s. A satisfaction analysis of the proposed scheme was conducted. Using measured data from June 2023 to May 2024, the satisfaction rate at Taonan Station was 100.00% during the freezing period, 94.74% during the non-flood season, and 83.61% during the flood season. At Heidi Temple Station, the satisfaction rate was 100.00% during the freezing period, 93.24% during the non-flood season, and 79.51% during the flood season. However, using long-term measured data from 1980 to 2016, the satisfaction rate at Taonan Station was only 50.68% to 68.24% for each period, and at Heidi Temple Station, only 31.08% to 64.19%, indicating a significantly low satisfaction rate. Based on the river channel water transport loss coefficient during dry years, the ecological flow at Taonan Station during the freezing period was determined to be 0.00 m³. 3 / s, 0.88 m during non-flood season 3 / s, 3.27 m during the flood season 3 / s, freezing period at Heidi Temple Station: 0.00 m 3 / s, 0.00 m during non-flood season 3 / s, 0.91 m during flood season 3 / s, where periods with a target value of 0 are not included in the satisfaction analysis. Using measured data from June 2023 to May 2024, the satisfaction rate at Taonan Station was 97.37% during the non-flood season and 95.90% during the flood season, while at Heidi Temple Station it was 94.26% during the flood season, with all participating periods exceeding 90%. However, using long-term measured data from 1980 to 2016, the satisfaction rate at Taonan Station was only 68.24% during the non-flood season and 74.32% during the flood season, while at Heidi Temple Station it was only 72.30% during the flood season, still significantly low. Based on the river channel water conveyance loss coefficient during high-water years, the ecological flow at Taonan Station during the freezing period was determined to be 0.70 m³ / s. 3 / s, 2.58 m during non-flood season 3 / s, 5.29 m during the flood season3 / s, freezing period at Heidi Temple Station: 0.59 m 3 / s, 2.58 m during non-flood season 3 / s, 5.29 m during the flood season 3 Using measured data from June 2023 to May 2024, the satisfaction rate of Taonan Station during the freezing period was 100.00%, 94.74% during the non-flood season, and 85.25% during the flood season. For Heidi Temple Station, the satisfaction rate was 100.00% during the freezing period, 93.24% during the non-flood season, and 81.15% during the flood season. Using long-term measured data from 1980 to 2016, the satisfaction rate for each period at Taonan Station ranged from 52.03% to 70.27%, and at Heidi Temple Station from 35.14% to 64.19%, both showing relatively low satisfaction rates.

[0026] The verification results of the three schemes revealed that the ecological flow requirements for Taonan Station and Heidi Temple Station, calculated after considering river seepage losses, were relatively low. This was mainly due to two reasons. First, the Taoer River basin experienced a continuous 12-year period of extremely low water levels after 1999, with the average annual runoff at the Charsun Reservoir Station being only 255 million cubic meters per second. 3The discharge volume is less than 28% of the reservoir's average annual runoff. Secondly, the original design of the Charsun Reservoir did not include requirements for downstream river ecological water use. From its construction and operation in 1991 until the completion of its reinforcement in 2018, the reservoir's discharge volume was combined with irrigation water supply, resulting in phased water supply. No discharge occurred during the reservoir's freezing period after December. Therefore, the Charsun Reservoir began ecological discharge on April 11, 2019. A specific verification was conducted only for the period from April 11, 2019 to December 31, 2023, based on the downstream river's water transport loss coefficient at P=90% inflow. Statistical results show that during this period, the satisfaction rate at Taonan station was 68.33% during the non-flood season and 84.92% during the flood season, while the satisfaction rate at Heidi Temple station was 68.52% during the flood season. The satisfaction rate for each period was still less than 90%. Further analysis of the annual satisfaction levels from 2020 to 2023 reveals that the Tao'er River experienced consecutive dry years after 2000. The average annual runoff from 2001 to 2016 was only 25% of that from 1980 to 2000. Coupled with the increasing artificial groundwater extraction leading to a continuous decline in the groundwater level, this exacerbated infiltration losses in the river channel, resulting in a low satisfaction level in 2020. From 2021 onwards, with the increase in river runoff and the gradual rise in the groundwater level, the satisfaction level in most areas reached over 90%. Using measured data from June 2023 to May 2024, during the implementation of the Mother River Restoration Action, the various schemes were validated. Under the dry year scheme, the satisfaction level at Taonan station reached 97.37% during the non-flood season and 95.90% during the flood season, while at Heidi Temple station it reached 94.26% during the flood season, all exceeding 90%. This verifies the actual achievability of the dry year scheme objectives under normal scheduling conditions. Taking into account the determination that ecological flow control is appropriate for the Taonan station section as it is a perennial flow section, and basic ecological water volume control is appropriate for the Heidi Temple station section as it is a seasonally dry section, and combining the verification and validation conclusions of various schemes, the calculated results under the river channel water transport loss coefficient in the dry year were finally adopted as the verification target, namely, the ecological flow of 0.33 m³ / h at Taonan station during the freezing period. 3 / s, 0.9 m during non-flood season 3 / s, 3.62 m during the flood season 3 / s, the basic ecological water volume at Heidi Temple Station during the flood season is 13.6 million m³. 3 By determining the types of differentiated control targets and comparing and verifying multi-level annual schemes, ecological flow control measures are coordinated with the natural hydrological rhythms of rivers, avoiding the technical problem of seasonally interrupted river sections being unattainable due to simply applying a unified control model.

[0027] Step 7: Based on the verified ecological flow or basic ecological water volume targets, formulate monitoring and early warning plans and ecological scheduling safeguards for each control section. In this embodiment, Taonan Station is a control section for a perennial river section, and ecological flow control is adopted. Two early warning levels are set: blue and red. The blue early warning threshold is 100%-110% of the ecological flow target value, i.e., 0.33-0.37 m during the freezing period. 3 / s, 0.9-1.0 m during non-flood season 3 / s, 3.62-4.01 m during the flood season 3 / s, the red alert threshold is when the flow rate is below the ecological flow target value, i.e., below 0.33 m during the freezing period. 3 / s, below 0.9 m during non-flood seasons 3 / s, below 3.62 m during the flood season 3 / s. The Heidi Temple station is a control section for the seasonally interrupted flow section of the river, and basic ecological water volume management is adopted. Due to the uneven distribution of precipitation in the Tao'er River basin throughout the year, with the main rainfall concentrated in the flood season from June to September, warnings are issued at the Heidi Temple station after the main flood season each year, with two warnings issued at the end of August and the end of September. The warning thresholds for August are set as 70% and 80% of the ecological water volume target value for blue and red warnings respectively, i.e., the blue warning threshold is 9.52 million to 10.88 million m³. 3 The red alert threshold is below 9.52 million m³. 3 In September, the warning thresholds were set as follows: blue and red warnings were set at 80% and 90% of the ecological water volume target value at the control section, respectively. Specifically, the blue warning threshold was 10.88 million to 12.24 million cubic meters per second. 3 The red alert threshold is below 10.88 million m³. 3 When the cumulative discharge at the monitoring and control section reaches different warning thresholds, corresponding ecological water volume warning information will be issued. Ecological scheduling and guarantee measures include: incorporating the ecological flow and ecological water volume guarantee of Taonan Station and Heidi Temple Station into the annual water resources scheduling plan of Taoer River; incorporating important water intake projects such as the Taoer River Irrigation Area in Baicheng City into the unified scheduling and management of water resources in the Taoer River Basin; formulating and strictly implementing the scheduling system of Manzhoudai Hub and Qingyou Hub; prohibiting the complete closure of both dam gates throughout the year and ensuring that at least one gate is open to strengthen the control of ecological flow discharge; strictly calculating the quarterly and annual water use statistics of the irrigation area and verifying the water use in a timely manner to ensure that water intake and use comply with the water allocation plan; strictly implementing the approved control conditions for normal water replenishment of important wetlands and flood diversion control conditions of the western Jilin water supply project; strengthening the scheduling of Longhua Tushui Hub, Hongqi Pumping Station, and Qingyou Water Conservancy Hub; and providing ecological water replenishment for lakes and ponds such as Xianghai Wetland and Niuxintao Wetland according to the inflow conditions. When an ecological flow warning is issued, the monitoring unit should increase the frequency of monitoring the outflow at the control section, and the responsible entity should strengthen the monitoring of water intake at river intakes and organize investigation and analysis to promptly identify the cause of the warning and formulate a solution to lift the warning as soon as possible.

[0028] By following the above seven steps, the scientific determination of ecological flow in interrupted rivers, taking into account water transport losses, can be fully realized, providing reliable technical support for the unified scheduling and management of water resources in the basin and the ecological recovery of rivers and lakes.

[0029] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0030] It should be noted that the components mentioned in the above embodiments are all general standard parts or components known to those skilled in the art. Their structures and principles can be learned by those skilled in the art through technical manuals or conventional experimental methods.

[0031] This invention has illustrated its principles and implementation methods using specific examples. The descriptions of these embodiments are merely illustrative of the method and its core ideas; furthermore, those skilled in the art will recognize that modifications may be made to the specific implementation methods and application scope based on the principles of this invention. Therefore, the content of this specification should not be construed as limiting the invention.

Claims

1. A method for determining the ecological flow of seasonal rivers in cold northern regions, considering water transport losses, characterized in that... Includes the following steps: Step 1: Collect basic data of the target river basin. The basic data includes the natural monthly runoff restoration series and measured daily average flow series of each control section, river hydrogeological parameters, operation data of existing water conservancy and hydropower projects, water intake data of the interval, and water requirements of ecological protection objects. Step 2: Based on the riverbed lithology, permeability coefficient, and hydraulic relationship between groundwater and surface water, the target river section is divided into several seepage characteristic sections. The hydrological station is used as the segment node to determine the surface water-groundwater conversion relationship in each river section. Step 3: Based on the principle of water balance, using the measured runoff data of adjacent hydrological stations at the same time, combined with the water intake of the interval, calculate the monthly river water conveyance loss coefficient of each seepage characteristic section, and statistically analyze it separately according to the three hydrological periods of freezing period, non-flood period and flood period. At the same time, the river water conveyance loss coefficient of each period is determined according to different water inflow frequency conditions. Step 4: Obtain the phased ecological flow target values ​​of the approved ecological flow control sections in the upstream of the target river. Using the river water conveyance loss coefficient determined in Step 3, calculate the phased ecological flow target of each downstream control section from upstream to downstream. When the river water conveyance loss coefficient of a certain phase is 1 under the set water inflow frequency, the ecological flow target of that phase is determined by the Q90 method. Step 5: Using the natural measured daily average flow data of the target cross-section before high-intensity human development, statistically analyze the flow interruption characteristics of each target cross-section. If a cross-section has never experienced flow interruption under natural conditions, it is determined to be a control cross-section of a perennial river section, and the control target adopts ecological flow. If a section experiences periodic flow interruption under natural conditions, it is determined to be a seasonally interrupted river section control section, and the control target is the basic ecological water volume. Step 6: Convert the ecological flow of each section determined in Step 4 into basic ecological water volume, back-calculate the actual river transport loss coefficient used in each river section, verify the consistency with the river transport loss coefficient under the same inflow frequency condition in Step 3, and conduct a retrospective verification of the satisfaction level of the natural runoff series from 1956 to 2000, as well as verify the satisfaction level using recent measured data. Step 7: Based on the verified ecological flow or basic ecological water volume targets, formulate monitoring and early warning plans and ecological scheduling and protection measures for each control section.

2. The method for determining the seasonal river ecological flow in northern cold regions considering water conveyance loss, as described in claim 1, is characterized in that... The Q90 method described in step 4 determines the ecological flow target as follows: based on the long series of natural monthly average flow or runoff at the river control section, the average flow or runoff at the driest month of each year is selected as the ecological base flow at the river control section using the frequency of the driest month.

3. The method for determining the seasonal river ecological flow in northern cold regions considering water conveyance loss, as described in claim 1, is characterized in that... The measured daily average flow data of nature before high-intensity human development mentioned in step 5; the criterion for determining the flow interruption is that the daily average flow is 0.

4. The method for determining the seasonal river ecological flow in northern cold regions considering water transport losses, as described in claim 1, is characterized in that... Step 6 involves retrospectively verifying the satisfaction level of the 1956-2000 natural runoff series. Specifically, this involves using the 1956-2000 natural monthly runoff series to statistically analyze the satisfaction level of the target section's ecological flow or basic ecological water volume in each period. The satisfaction level is the ratio of the number of periods in each period that reach or exceed the ecological flow target value to the total number of periods in each period. If the satisfaction level in each period is not less than 90%, the ecological flow target is deemed reasonable. If the satisfaction rate of a certain phase is less than 90%, the ecological flow target value for that phase will be lowered to the level that meets the 90% guarantee rate requirement.

5. The method for determining the seasonal ecological flow of rivers in northern cold regions, considering water transport losses, as described in claim 1, is characterized in that... The verification using recent measured data in step 6 specifically involves: obtaining the measured daily average flow data after the implementation of ecological scheduling, statistically analyzing the actual satisfaction level of ecological flow or basic ecological water volume at each stage of the target section, and if the measured satisfaction level is lower than 90% due to the influence of continuous extremely low water conditions, then the rationality of the target is comprehensively judged in conjunction with the water inflow frequency analysis.

6. The method for determining the seasonal river ecological flow in northern cold regions considering water conveyance loss according to claim 1, characterized in that, The monitoring and early warning scheme described in step 7 is as follows: For control sections of perennial river sections using ecological flow control, two early warning levels are set: blue and red. The threshold for blue early warning is 100%-110% of the ecological flow target value, and the threshold for red early warning is below the ecological flow target value. For control sections of seasonally interrupted river sections using basic ecological water volume control, early warnings are issued at a set frequency after the flood season. The threshold for blue early warning is 70%-80% of the basic ecological water volume target value, and the threshold for red early warning is below 70% of the basic ecological water volume target value.

7. The method for determining the seasonal river ecological flow in northern cold regions considering water conveyance loss according to claim 1, characterized in that, The method is applicable to the determination of ecological flow in seasonally interrupted rivers in high-altitude and cold regions of northern China; the freezing period is from December to March of the following year, the non-flood season is from April to May and from October to November, and the flood season is from June to September.

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