A method for determining ecological water volume of seasonal rivers oriented to the life cycle of key species

Abstract

The present invention discloses a method for determining the ecological water volume of seasonal rivers oriented to the life cycle of key species, comprising the following steps: determining the control section and its associated sections of the ecological water demand of seasonal rivers; identifying the key species and species parameters of the control section of seasonal rivers and its downstream sections; determining the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals at the control section; determining the ecological water volume threshold requirements for the life cycles of aquatic organisms and terrestrial animals at the control section; determining the ecological water volume threshold requirements for terrestrial plants between the control section of seasonal rivers and its upstream sections; determining the ecological water volume threshold requirements for the discharged ecological water at the control section of seasonal rivers; and determining the ecological water volume requirements for the control section of seasonal rivers. The method of the present invention can provide basic support and scientific basis for the setting of ecological water demand targets, ecological water demand allocation and management of seasonal rivers in China, and fundamentally promote the health of seasonal rivers and the recovery of the ecological environment.

Description

Technical Field

[0001] The present invention belongs to the technical field of water resource management and water ecological protection, and particularly relates to a method for determining ecological water volume of seasonal rivers oriented to the life cycle of key species. Background Art

[0002] Under the influence of climate change and strong human activities, the particularity and ecological system importance of seasonal rivers are becoming increasingly prominent. Water resources play an important supporting role in the succession of seasonal river ecosystems. Ecological water demand is an important indicator of seasonal river ecosystems. Ensuring ecological water demand is conducive to maintaining the stability, diversity and sustainability of seasonal river ecosystems. Insufficient ecological water demand will lead to problems such as degradation of seasonal rivers, shrinkage of wetlands and decline of ecological service functions, thus resulting in ecological system imbalance. Therefore, clarifying the ecological water volume target according to the characteristics of seasonal rivers has important guiding significance for maintaining the integrity of seasonal river ecosystems, giving full play to their ecological system service functions, and promoting the protection of seasonal river biodiversity.

[0003] Traditionally, the setting of ecological water volume targets for seasonal rivers mainly refers to perennial rivers and mostly uses hydrological methods, that is, selecting runoff observation data of seasonal rivers during non-dry-up periods to determine the minimum monthly ecological water volume of seasonal rivers. Usually, it lacks consideration of the growth and reproduction processes of key species in seasonal rivers, and also cannot consider the changes in ecological water demand of the groundwater system and the vegetation on the riverbank system brought about by the hydrological rhythm changes of seasonal rivers. In addition, seasonal river ecosystems have resilience, elasticity and toughness, and ecological water demand is a dynamic range. If the incoming water volume is not within this range, the normal succession of river ecosystems will be disturbed. If the ecological water volume is lower than the minimum threshold requirement, the seasonal river ecosystem will face withering and decline; if the ecological water volume is higher than the maximum threshold requirement, the seasonal river will undergo flood processes, bringing impacts and damages to the ecosystem. Only maintaining the minimum river ecological base flow, the ecological system functions of seasonal rivers cannot be fully exerted, and even lead to the loss of biodiversity and the degradation of ecosystems. Therefore, how to more scientifically and reasonably determine the ecological water volume range of seasonal rivers according to their characteristics is a technical problem that needs to be solved urgently at present. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for determining ecological water volume of seasonal rivers oriented to the life cycle of key species. According to the characteristics of seasonal river runoff, on the basis of identifying key species, fully consider the spatial distribution of key species and the requirements of the ecological water volume threshold range in the life cycle processes such as growth and reproduction, so as to reasonably determine the ecological water volume of seasonal rivers.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention discloses a method for determining the ecological water volume of seasonal rivers facing the life cycle of key species, and the method includes the following steps:

[0007] Step 1, determining the control section and its associated sections of the ecological water demand of seasonal rivers: Determine the control section of the ecological water demand of seasonal rivers according to the control section selection principle. For the i-th control section of seasonal rivers, identify and determine its associated sections, including the (i - 1)-th section upstream and the (i + 1), (i + 2),..., (i + I)-th control sections downstream, where I is the total number of downstream sections;

[0008] Step 2, identifying the key species and species parameters of the control section and downstream sections of seasonal rivers: Identify the key species and species parameters of the control section and downstream sections of seasonal rivers. The key species are the dominant populations and indicator species that affect the structure and function of the seasonal river ecosystem. The key species include aquatic organisms and terrestrial organisms. The aquatic organisms include aquatic plants and aquatic animals, and the terrestrial organisms include terrestrial plants and terrestrial animals; the species parameters include species type, spatial location, distribution area, and elevation;

[0009] Step 3, determining the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals at the control section: Determine the ecological water level requirement curves for the life cycles of aquatic plants, aquatic animals, and terrestrial animals at the control section respectively, and then determine the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial organisms at the control section, which specifically includes the following steps:

[0010] Step 31, determining the ecological water level requirement curve for the life cycle of aquatic plants: Aquatic plants include floating plants, emergent plants, and submerged plants. The calculation formula for the ecological water level requirement curve of the life cycle of floating plants is:

[0011] H1a i,t =H1a0 i,t +H1as i,t (1)

[0012] M1a i,t =H1a0 i,t +H1am i,t (2)

[0013] In the formula, H1a i,t and M1a i,t are respectively the lowest water level and the highest water level required for the life cycle of floating plants at the i-th control section of seasonal rivers in the t-th month, m; H1a0 i,t is the elevation of the growth and distribution of floating plants at the i-th control section of seasonal rivers in the t-th month, m; H1as i,t and H1am i,tThey are the minimum water depth and the maximum water depth required for the growth and reproduction of floating plants at the i-th control section of the seasonal river in the t-th month, respectively.

[0014] The calculation formula for the ecological water level requirement curve of the life cycle of emergent plants is:

[0015] H1b i,t = H1b0 i,t + H1bs i,t (3)

[0016] M1b i,t = H1a0 i,t + H1bm i,t (4)

[0017] In the formula, H1b i,t and M1b i,t are the minimum water level and the maximum water level required for the life cycle of emergent plants at the i-th control section of the seasonal river in the t-th month, respectively, in m; H1b0 i,t is the elevation of the growth and distribution of emergent plants at the i-th control section of the seasonal river in the t-th month, in m; H1bs i,t and H1bm i,t are the minimum water depth and the maximum water depth required for the growth and reproduction of emergent plants at the i-th control section of the seasonal river in the t-th month, respectively.

[0018] The calculation formula for the ecological water level requirement curve of the life cycle of submerged plants is:

[0019] H1c i,t = H1c0 i,t + H1cs i,t (5)

[0020] M1c i,t = H1c0 i,t + M1cs i,t (6)

[0021] In the formula, H1c i,t and M1c i,t are the minimum water level and the maximum water level required for the life cycle of submerged plants at the i-th control section of the seasonal river in the t-th month, respectively, in m; H1c0 i,t is the elevation of the growth and distribution of submerged plants at the i-th control section of the seasonal river in the t-th month, in m; H1cs i,t and M1cs i,t are the minimum water depth and the maximum water depth required for the growth and reproduction of submerged plants at the i-th control section of the seasonal river in the t-th month, respectively.

[0022] The formula for the ecological water level requirement curve of the life cycle of aquatic plants in the seasonal river is:

[0023] H1 i,t = Max(H1a i,t , H1b i,t , H1c i,t ) (7)

[0024] M1 i,t = Min(M1a i,t , M1b i,t , M1c i,t ) (8)

[0025] Wherein, H1 i,t and M1 i,t are respectively the minimum water level requirement and the maximum water level requirement for the aquatic plant life cycle at the i-th control section of the seasonal river in the t-th month, m;

[0026] Step 32: Determine the ecological water level requirement curves for the life cycles of aquatic animals and terrestrial animals: Aquatic animals and terrestrial animals include fish, zooplankton, benthic animals, and birds. The calculation formulas for the ecological water level requirement curves for the life cycles of aquatic animals and terrestrial animals are:

[0027] H2 i,t = Max(H2a i,t , H2b i,t , H2c i,t , H2d i,t ) (9)

[0028] M2 i,t = Min(M2a i,t , M2b i,t , M2c i,t , M2d i,t ) (10)

[0029] Wherein:

[0030] H2a i,t = H0 i + H2as i,t (11)

[0031] H2b i,t = H0 i + H2bs i,t (12)

[0032] H2c i,t = H0 i + H2cs i,t (13)

[0033] H2d i,t = H0 i + H2ds i,t (14)

[0034] M2a i,t = H0 i + H2am i,t (15)

[0035] M2b i,t = H0 i + H2bm i,t (16)

[0036] M2c i,t = H0 i + H2cm i,t (17)

[0037] M2d i,t = H0 i + H2dm i,t (18)

[0038] Wherein, H2 i,t and M2 i,t are respectively the minimum water level and the maximum water level required for the life cycles of aquatic animals and terrestrial animals at the i-th control section of the seasonal river in the t-th month, in m; H0 i is the river bottom elevation of the i-th control section of the seasonal river, in m; H2as i,t , H2bs i,t , H2cs i,t , H2ds i,t are respectively the minimum water depths required for the life cycles of fish, zooplankton, benthic animals, and birds at the i-th control section of the seasonal river in the t-th month, in m; M2am i,t , M2bm o,t , M2cm o,t , M2dm i,t are respectively the maximum water depths required for the life cycles of fish, zooplankton, benthic animals, and birds at the i-th control section of the seasonal river in the t-th month, in m;

[0039] Step 33. Determine the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals at the control section: According to the ecological water level requirement curves for the life cycles of aquatic organisms and terrestrial animals at the control section of the seasonal river, take the maximum value of the minimum water levels as the comprehensive minimum water level of the river ecosystem, and take the minimum value of the maximum water levels as the comprehensive maximum water level of the river ecosystem, and establish the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals. The calculation formula is:

[0040] H i,t = max(H1 i,t , H2 i,t ) (19)

[0041] M i,t = min(M1i,t , M2 i,t ) (20)

[0042] Wherein, H i,t and M i,t are respectively the minimum and maximum values of the comprehensive ecological water level requirements for aquatic organisms and terrestrial animals at the i-th control section of the seasonal river in the t-th month, in m;

[0043] Step 4: Determine the ecological water volume threshold requirements for the life cycles of aquatic organisms and terrestrial animals at the control section:

[0044] Based on the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals, calculate the ecological water volume threshold requirements for the life cycles of aquatic organisms and terrestrial animals. For seasonal rivers, assume it is a uniform flow in an open channel and use the Manning formula to calculate the ecological water volume threshold requirements at the control section. The calculation formula is:

[0045] QH1 i,t = max(8.64 × AH i,t × Vh i,t × T i , PH1 i,t ) (21)

[0046] QM1 i,t = max(8.64 × AM i,t × Vm i,t × T i , PM1 i,t ) (22)

[0047]

[0048] Wherein, QH1 i,t and QM1 i,t are respectively the minimum and maximum values of the ecological water volume requirements for the life cycles of aquatic organisms and terrestrial animals at the i-th control section of the seasonal river in the t-th month, in 10,000 m 3 ; AH i,t and AM i,t are respectively the minimum and maximum values of the cross-sectional area of the flowing water at the i-th control section of the seasonal river in the t-th month, in m 2 ; Vh i,t and Vm i,t are respectively the average flow velocities corresponding to the minimum and maximum values of the ecological water volume at the i-th control section of the seasonal river in the t-th month, in m / s; T i is the number of days in the i-th month; PH1 i,t and PM1 i,t are respectively the minimum and maximum ecological water volumes approved in the relevant plans or programs of the water administrative department or the ecological environment department at the i-th control section in the t-th month, in 10,000 m 3; S i is the bed slope of the i-th control section of the seasonal river, which reflects the influence brought by the change of the longitudinal section topography of the river bed, dimensionless; n is the natural roughness of the river channel, dimensionless; Rh i,t and Rm i,t are respectively the minimum and maximum hydraulic radii of the i-th control section of the seasonal river in the t-th month, m. When the width-depth ratio of the river channel is greater than 100, the cross-sectional average water depth is used to replace the hydraulic radius for calculation, and the error is within the allowable range; the cross-sectional average water depth is the difference between the comprehensive ecological water level of aquatic organisms and terrestrial animals in the control section and the river bottom elevation, that is:

[0049] Rh i,t = H i,t - H0 i (25)

[0050] Rm i,t = M i,t - H0 i (26);

[0051] Step 5. Determine the ecological water volume threshold requirements for terrestrial plants between the control section of the seasonal river and the upstream section: Terrestrial plants include herbs, shrubs and forest land, which are distributed on both sides of the seasonal river channel. The growth of terrestrial plants depends on groundwater recharge. By calculating the phreatic evaporation of terrestrial plants at a certain groundwater depth, the ecological water volume threshold requirements are deduced. The specific calculation formula is:

[0052]

[0053] In the formula, QH2 i,t and QM2 i,t are respectively the minimum and maximum ecological water volume requirements for terrestrial plants distributed on both sides of the river channel between the i-th control section and the i-1-th control section of the seasonal river in the t-th month, 10,000 m 3 ; j is the groundwater level classification at different depths, j = 1, 2,... J; EH j,t and EM j,t are respectively the minimum and maximum phreatic evaporation per unit area corresponding to the j-th groundwater depth, mm; F i,i is the plant area corresponding to the j-th groundwater depth of the i-th control section of the seasonal river, km 2 , which is obtained through actual monitoring or groundwater simulation; K j is the influence coefficient of the j-th groundwater depth, dimensionless; E0 t is the water surface evaporation in the t-th month, mm; a and b are empirical coefficients, which are obtained by fitting curves according to experimental results; ZH j and ZM jare the minimum and maximum groundwater depths at the j-th level, respectively, in m; Z max is the limiting depth of phreatic evaporation, in m, with a value range of 4.5 - 5.0 m;

[0054] Step 6: Determine the threshold requirements for the ecological water discharge at the control section of the seasonal river: The ecological water requirements at the downstream section of the control section of the seasonal river include the water requirements for the ecological protection targets of the terminal lake, estuary, wetland, and river valley section. The ecological water requirements at the downstream section are determined according to the ecological water volume approved in the plan or plan by the water administrative department or the ecological environment department. If there is no approved ecological water volume at the downstream section, the ecological water volume threshold at the downstream section is calculated using the life cycle of the key species at the downstream section. If there are multiple control sections with ecological protection targets downstream, the threshold requirements for the ecological water discharge at this control section are determined by the method of successive recursion. That is, the outer envelope line of the minimum ecological water volume required by all downstream control sections plus the loss is the maximum value of the ecological water discharge at this control section, and the inner envelope line of the maximum ecological water volume required by all downstream control sections plus the loss is the minimum value of the ecological water discharge at this control section. The specific formula is as follows:

[0055]

[0056] In the formula, QH3 i,t and QM3 i,t are the minimum and maximum values of the ecological water discharge requirements at the i-th control section of the seasonal river in the t-th month, which are recursively calculated from all downstream sections to this control section, in 10,000 m 3 ; PH1 p,t and PM1 p,t are the minimum and maximum values of the ecological water volume at the p-th section (p = i + 1, i + 2... i + I) downstream of the i-th control section, respectively; SS p,t and SM p,t are the minimum and maximum losses of the ecological water volume from the p-th section to the i-th control section of the seasonal river, respectively, in 10,000 m 3 ;

[0057] Step 7: Determine the ecological water volume requirements for the control sections of seasonal rivers: Combine the ecological water volume threshold requirements for the control sections of seasonal rivers and the ecological water volume threshold requirements for the downstream ecological water discharge of the control sections, conduct collaborative analysis, and determine the ecological water volume requirements for seasonal rivers. Specifically: The minimum value of the ecological water volume requirements for seasonal rivers is equal to the envelope of the minimum ecological water volume requirements for the life cycles of aquatic organisms and terrestrial animals at the control section and the minimum downstream ecological water discharge requirements recursively derived from the downstream section of the control section to this control section, plus the minimum ecological water volume requirements for terrestrial plants between the control section and the upstream section; The maximum value of the ecological water volume requirements for seasonal rivers is equal to the envelope of the maximum ecological water volume requirements for the life cycles of aquatic organisms and terrestrial animals at the control section and the maximum downstream ecological water discharge requirements recursively derived from the downstream section of the control section to this control section, plus the maximum ecological water volume requirements for terrestrial plants between the control section and the upstream section. The specific calculation formula is as follows:

[0058] QH i,t =Max(QH1 i,t ,QH3 i,t )+QH2 i,t (37)

[0059] QM i,t =Min(QM1 i,t ,QM3 i,t )+QM2 i,t (38)

[0060] In the formula, QH i,t and QM i,t are the minimum and maximum values of the ecological water volume requirements for the i-th control section in the downstream of the seasonal river in the t-th month, in 10,000 m 3 .

[0061] Furthermore, the principle for selecting the control sections in Step 1 is as follows: The control sections of seasonal rivers are determined based on the requirements of water administrative management, following the principles of representativeness, operability, and systematicness, including: river administrative control or cross-administrative section, the section at the mouth where the river flows into the sea, into the main stream, or into the tail channel, control sections of important ecological sensitive areas, and control sections of important control water projects; Priority is given to selecting sections that can be monitored, evaluated, and regulated; The selection of control sections is coordinated with relevant water conservancy plans, ecological environment protection plans, and water volume allocation plans in the basin or region.

[0062] Furthermore, the species parameters of aquatic organisms and terrestrial animals in Step 2 are identified and determined through on-site inspection and biological investigation, and the species parameters of terrestrial plants are identified and determined through on-site inspection, biological investigation, and satellite image data.

[0063] Further, the calculation process of the cross-sectional area of the i-th control section of the seasonal river in the t-th month in Step 4 is specifically as follows:

[0064] The cross-section of the seasonal river includes trapezoidal river channel cross-section, rectangular river channel cross-section and irregular river channel cross-section;

[0065] Among them, for the trapezoidal river channel cross-section, the calculation formula for the cross-sectional area is:

[0066] AH i,t =(a i +H i,t ×b i )×H i,t (27)

[0067] AM i,t =(a i +M i,t ×b i )×M i,t (28)

[0068] For the rectangular river channel cross-section, the calculation formula for the cross-sectional area is:

[0069] AH i,t =a i ×H i,t (29)

[0070] AM i,t =a i ×M i,t (30)

[0071] In the formula, a i is the bottom width of the i-th control section of the seasonal river, m; b i is the side slope coefficient of the i-th control section of the seasonal river, dimensionless;

[0072] For the irregular river channel cross-section, the cross-sectional area is determined by the measuring point method, numerical integration method or remote sensing and digitalization method.

[0073] The beneficial effects of the present invention are as follows: The method for determining the ecological water volume of seasonal rivers oriented to the life cycle of key species according to the present invention, in view of the characteristics of seasonal river runoff, fully considers the spatial distribution of key species and the requirements for the range of ecological water volume thresholds during the life cycle processes such as growth and reproduction, and realizes the coupling of rivers and riverbanks, the coupling of ecological requirements of river reaches themselves and downstream, the coupling of surface and underground processes, the coupling of aquatic and terrestrial organisms, and the coupling of ecological water levels and water volumes. The ecological water volume of seasonal rivers calculated by using the method of the present invention is beneficial to restoring the ecological hydrological rhythm of seasonal rivers, promoting the growth of aquatic plants and the reproduction of fish, birds, etc., and has important guiding value for maintaining the integrity of the structure, function and process of seasonal river ecosystems, and the stability and diversity of ecosystems. The method of the present invention can provide basic support and scientific basis for the setting of ecological water demand targets, the allocation and management of ecological water demand, the construction of ecological protection projects, the operation of water conservancy projects, etc. for seasonal rivers in China, and fundamentally promote the health of seasonal rivers and the recovery of the ecological environment.

[0074] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0075] Figure 1 It is a schematic flow chart of the method of the present invention;

[0076] Figure 2 It is a distribution map of river and lake systems and their control sections in Embodiment 1;

[0077] Figure 3 It is a graph of the comprehensive ecological water level requirements for the life cycles of aquatic organisms and terrestrial animals at the control section (i = 3) in Embodiment 1;

[0078] Figure 4 It is a schematic diagram of the change in the buried depth of the groundwater level at the seasonal river control section (i = 3) in Embodiment 1;

[0079] Figure 5 It is a graph of the calculation results of the minimum value of the ecological water volume requirements at the seasonal river control section (i = 3) in Embodiment 1;

[0080] Figure 6 It is a graph of the calculation results of the maximum value of the ecological water volume requirements at the seasonal river control section (i = 3) in Embodiment 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0081] The present invention discloses a method for determining the ecological water volume of seasonal rivers oriented to the life cycle of key species, as Figure 1 shown, the method includes the following steps:

[0082] Step 1: Determine the control sections of the ecological water demand of seasonal rivers and their associated sections.

[0083] In different seasonal rivers or different reaches of the same seasonal river, there are usually obvious differences in ecological protection objectives and ecological water volume requirements. To reflect the spatial differences of these ecological protection objects and their flow requirements in seasonal rivers, it is necessary to determine the control sections of the river, which is an important part of the ecological environment management of seasonal rivers. The control sections of seasonal rivers should be determined in combination with the requirements of water administration, based on the principles of representativeness, operability, and systematicness. They usually include: river administrative control (or cross-administrative region) sections, the mouth sections where the river flows into the sea, into the main stream, or into the tail channel, control sections of important ecological sensitive areas, and control sections of important controlling water projects (such as water intake facilities, hydropower projects), etc. Sections that can be monitored, evaluated, and regulated should be preferentially selected. The selection of control sections should be coordinated with existing plans and programs such as relevant water conservancy plans, ecological environment protection plans, and water volume allocation plans in the basin or region. For the i-th control section of a seasonal river, its associated sections should also be identified, including the (i - 1)-th section upstream and the (i + 1), (i + 2), …, (i + I)-th control sections downstream, where I is the total number of downstream sections.

[0084] Step 2: Identify the key species and species parameters of the control sections of the seasonal river and their downstream sections.

[0085] Key species are the dominant populations and indicator species that affect the structure and function of the seasonal river ecosystem, and are important targets for the protection of the seasonal river ecosystem to maintain the basic ecological functions of the river corridor. Usually, the key species of seasonal rivers mainly include aquatic organisms (including aquatic plants and aquatic animals) and terrestrial organisms (including terrestrial vegetation and terrestrial animals). It is very important to identify the parameters of these key species (including aquatic and terrestrial organisms) in seasonal rivers, mainly including species type, spatial location, distribution area, and elevation. Among them, for the species parameters of aquatic plants, aquatic animals, and terrestrial animals, they can be determined through on-site inspection and biological surveys. For the species parameters of terrestrial plants, in addition to on-site inspection and biological surveys, satellite image data from different periods can also be used for identification and determination. It should be noted that not only the key species and parameters of the i-th control section of the seasonal river need to be identified, but also the key species and parameters of the (i + 1), (i + 2), …, (i + I)-th control sections downstream need to be identified to provide a basic support for the calculation of the ecological water volume of the seasonal river. Here, I is the total number of downstream sections.

[0086] Step 3: Determine the comprehensive ecological water level requirement curves for the life cycles of aquatic organisms and terrestrial animals at the control sections.

[0087] Water level is an important indicator that affects the structure and function of seasonal river ecosystems. With the changes in seasonal water inflow, temperature and other factors, the water level of seasonal rivers begins to gradually rise in spring, reaches its highest value in summer, begins to fall in autumn, and reaches its lowest value in winter. Water level is an important factor in determining the water area of seasonal rivers and the living space of organisms. When the topographic conditions of the river channel remain unchanged, the height of seasonal river water levels directly affects the survival of aquatic plants and animals. Among them, too low river water levels will restrict and compress the habitats of aquatic organisms and pose a threat to their growth and reproduction; too high water levels may cause flood disasters, destroy the habitats of aquatic organisms, and affect their survival and development. It is particularly important to determine the ecological water level requirement curves for the life cycle processes of aquatic organisms and terrestrial animals in the control sections of seasonal rivers. Specifically, the following steps are included:

[0088] Step 31: Determine the ecological water level requirement curve for the life cycle of aquatic plants:

[0089] Aquatic plants are the most important primary producers in seasonal river ecosystems, which not only affect the survival of aquatic animals, but also are related to the balance of the entire seasonal river ecosystem. Aquatic plants mainly include floating plants, emergent plants and submerged plants. The life history of these plants usually includes a dormant period, germination period, growth period, seed period and the reciprocating cycle of the above periods. Since these different types of aquatic plants are distributed at different altitudes and have different water depth requirements during their life cycle, their ecological water level requirement curves are different, specifically:

[0090] 1) Floating plants: The calculation of the ecological water level requirement curve of the life cycle of floating plants in seasonal rivers needs to consider two major factors: the distribution elevation of floating plants and the water depth requirements. The suitable water depth for typical floating plants is 0.1-1.0m. Taking water lilies as an example, data from typical surveys and experiments show that the suitable water depth for its life cycle is shown in Table 1. Among them, March-April is the germination period; May-August is the growth period, and the water depth requirement continues to increase to support its growth and flowering; September-November is the seed period, and the water depth should be gradually reduced to promote the growth of rhizomes and lateral buds; the dormant period is from December to February of the following year, and the water level can be maintained high to protect the rhizomes from frost damage. The specific calculation formula for the ecological water level requirement curve of the life cycle of floating plants is as follows:

[0091] H1a i,t =H1a0 i,t +H1as i,t (1)

[0092] M1a i,t =H1a0 i,t +H1am i,t (2)

[0093] In the formula, H1a i,t and M1a i,tThey are respectively the minimum water level and the maximum water level required for the life cycle of floating plants at the i-th control section of the seasonal river in the t-th month, m; H1a0 i,t is the elevation of the growth distribution of floating plants at the i-th control section of the seasonal river in the t-th month, m; H1as i,t and H1am i,t They are respectively the minimum water depth and the maximum water depth required for the growth and reproduction of floating plants at the i-th control section of the seasonal river in the t-th month.

[0094] Table 1 Suitable Water Depths for the Life Cycles of Typical Floating Plants (Taking Water Lily as an Example)

[0095] Month Stage Suitable water depth (m) 3 Germination stage 0.1-0.25 4 Germination stage 0.1-0.25 5 Growth stage 0.25-0.4 6 Growth stage 0.25-0.4 7 Growth stage 0.25-0.4 8 Growth stage 0.25-0.4 9 Seed stage 0.2-0.35 10 Seed stage 0.2-0.35 11 Seed stage 0.2-0.35 12 Dormancy stage 0.4-1.0 The next year, January Dormancy stage 0.4-1.0 The next year, February Dormancy stage 0.4-1.0

[0096] 2) Emergent plants: Emergent plants in seasonal rivers are adapted to shallow water areas and need to be partially or fully exposed to the air during the growth process for photosynthesis and respiration. Taking reed as an example, the water depth requirements vary in different growth stages. The results of typical investigations and monitoring show that February to March is its germination period, and the suitable water depth is 0.1 - 0.25 m; April to June enters the growth period, and the suitable water depth is 0.1 - 0.30 m to promote the growth and reproduction of its roots; July to August is the booting and heading period, and the suitable water depth is 0.4 - 0.8 m to promote the increase of its biomass and plant height; September to October is the flowering and maturity period, and the suitable water depth is 0.4 - 0.8 m to promote its flowering, fruiting and seed maturity; November to January of the following year is the dormant period, and the suitable water depth is 0.2 - 0.5 m to reduce the hypoxia and rot of its roots. For details, see Table 2. Similar to floating plants, when calculating the ecological water level requirement curve for the life cycle of emergent plants, two factors, namely the distribution elevation of emergent plants and the water depth requirements, need to be considered. The calculation formula is:

[0097] H1b i,t = H1b0 i,t + H1bs i,t (3)

[0098] M1b i,t = H1a0 i,t + H1bm i,t (4)

[0099] In the formula, H1b i,t and M1b i,t are respectively the minimum water level and the maximum water level required for the life cycle of emergent plants at the i-th control section of the seasonal river in the t-th month, m; H1b0 i,t is the elevation of the growth distribution of emergent plants at the i-th control section of the seasonal river in the t-th month, m; H1bs i,t and H1bm i,tThey are the minimum water depth and the maximum water depth required for the growth and reproduction of emergent plants at the i-th control section of the seasonal river in the t-th month, respectively.

[0100] Table 2 Suitable water depths for the life cycles of typical emergent plants (taking Phragmites australis as an example)

[0101] Month Stage Suitable water depth (m) 2 Germination stage 0.1-0.25 3 Germination stage 0.1-0.25 4 Growth stage 0.1-0.3 5 Growth stage 0.1-0.3 6 Growth stage 0.1-0.3 7 Booting stage 0.4-0.8 8 Heading stage 0.4-0.8 9 Flowering stage 0.4-0.8 10 Maturity stage 0.4-0.8 11 Dormancy stage 0.2-0.5 12 Dormancy stage 0.2-0.5 The next year, January Dormancy stage 0.2-0.5

[0102] 3) Submerged plants: Submerged plants are completely living in water, with their stems, leaves and flowers all immersed in water. They can effectively absorb nutrients such as nitrogen and phosphorus in water and play an important role in purifying the water quality of rivers. Submerged plants are also an important food source and habitat for aquatic animals. If they overgrow, it may lead to "water blooms" in the water body. The suitable water depth for submerged plants in seasonal rivers is usually 0.5 - 2.0 m. Taking Ceratophyllum demersum as an example, typical investigation and experimental results show that February to March is its germination period, April to September is the growth period, October to November is the seed period, and then it is in the dormant period. Taking Ceratophyllum demersum as an example, the suitable water depths for typical submerged plants are shown in Table 3. Similar to floating plants and emergent plants, when calculating the ecological water level requirement curve for the life cycle of submerged plants, two factors, namely the elevation of their distribution and the water depth requirement, need to be considered. The specific calculation formula is as follows:

[0103] H1c i,t = H1c0 i,t + H1cs i,t (5)

[0104] M1c i,t = H1c0 i,t + M1cs i,t (6)

[0105] In the formula, H1c i,t and M1c i,t are the minimum water level and the maximum water level required for the life cycle of submerged plants at the i-th control section of the seasonal river in the t-th month, respectively, in m; H1c0 i,t is the elevation of the growth distribution of submerged plants at the i-th control section of the seasonal river in the t-th month, in m; H1cs i,t and M1cs i,t are the minimum water depth and the maximum water depth required for the growth and reproduction of submerged plants at the i-th control section of the seasonal river in the t-th month, respectively.

[0106] Table 3 Suitable water depths for the life cycles of typical submerged plants (taking Ceratophyllum demersum as an example)

[0107] Month Stage Suitable water depth (m) 2 Germination stage 0.2-0.5 3 Germination stage 0.6-0.8 4 Growth stage 0.5-1.5 5 Growth stage 0.5-1.5 6 Growth stage 0.5-1.5 7 Growth stage 0.5-1.5 8 Growth stage 0.5-1.5 9 Growth stage 0.5-1.5 10 Seed stage 0.3-0.8 11 Seed stage 0.3-0.8 12 Dormancy stage 0.2-0.5 The next year, January Dormancy stage 0.2-0.5

[0108] To sum up, the calculation formula for the ecological water level requirement curve of the life cycle of aquatic plants in seasonal rivers is:

[0109] H1 i,t = Max(H1a i,t , H1b i,t , H1c i,t ) (7)

[0110] M1 i,t = Min(M1a i,t , M1b i,t , M1c i,t ) (8)

[0111] wherein, H1 i,t and M1 i,t are respectively the minimum water level requirement and the maximum water level requirement for the aquatic plant life cycle at the i-th control section of the seasonal river in the t-th month, in m.

[0112] Step 32. Determine the ecological water level requirement curves for the life cycles of aquatic animals and terrestrial animals:

[0113] Aquatic animals and terrestrial animals in seasonal rivers usually include fish, zooplankton, benthic animals, birds, etc. Among them, fish belong to the top community in the seasonal river aquatic ecosystem and play an important role in the existence and abundance of other groups. The fish population is very sensitive to changes in the river hydrological regime. Select fish as the indicator organism of the lake and analyze its dynamic demand for water level. Generally, the minimum depth required for fish survival is about 2 - 3 times the average body length of the fish. The spawning period of fish is the most sensitive stage in the life cycle, including four types of fish eggs, floating, semi-floating, sinking, and sticky. Among them, drift eggs have higher requirements for flow velocity. When the flow velocity is lower than a certain flow velocity threshold, they start to sink, resulting in a low hatching rate of fish eggs and having an adverse impact on their reproduction. Some fish (such as Yellow River carp, etc.) usually require the generation of pulsed flow with peak value and duration requirements during the breeding period and growth period. Flood pulses have a profound impact on biodiversity and ecosystem functions in the river ecosystem. High-flow flood pulses bring strong life rhythm signals and have functions such as triggering development, migration, and reproduction. Pulsed floods of a certain magnitude during the fish breeding period can promote fish reproduction and shorten the spawning and fertilization time; pulsed floods of a certain flow level during the growth period can provide rich food for fish.

[0114] Different from aquatic plants, the calculation of the ecological water level requirement curves for the life cycles of aquatic animals such as fish and terrestrial animals needs to consider two major factors: river bottom elevation and water depth requirements. The specific calculation formula is:

[0115] H2 i,t = Max(H2a i,t , H2b i,t , H2c i,t , H2d i,t ) (9)

[0116] M2 i,t = Min(M2a i,t , M2b i,t , M2c i,t , M2d i,t ) (10)

[0117] Wherein:

[0118] H2a i,t = H0 i + H2as i,t (11)

[0119] H2b i,t = H0 i + H2bs i,t (12)

[0120] H2c i,t = H0 i + H2cs i,t (13)

[0121] H2d i,t = H0 i + H2ds i,t (14)

[0122] M2a i,t = H0 i + H2am i,t (15)

[0123] M2b i,t = H0 i + H2bm i,t (16)

[0124] M2c i,t = H0 i + H2cm i,t (17)

[0125] M2d i,t = H0 i + H2dm i,t (18)

[0126] In the formula, H2 i,t and M2 i,t are respectively the minimum water level and the maximum water level required for the life cycles of aquatic animals and terrestrial animals in the i-th control section of the seasonal river in the t-th month, m; H0 i is the river bottom elevation of the i-th control section of the seasonal river, m; H2as i,t , H2bs i,t , H2cs i,t , H2ds i,tThey are the minimum water depths required for the life cycles of fish, zooplankton, benthic animals, and birds at the i-th control section of the seasonal river in the t-th month, in m; M2am i,t , M2bm i,t , M2cm i,t , M2dm i,t They are the maximum water depths required for the life cycles of fish, zooplankton, benthic animals, and birds at the i-th control section of the seasonal river in the t-th month, in m.

[0127] Step 33: Determine the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals at the control section:

[0128] Based on the ecological water level requirements for the life cycles of aquatic organisms and terrestrial animals at the control section of the seasonal river, take the maximum value of the lowest water levels as the comprehensive lowest water level of the river ecosystem, and take the minimum value of the highest water levels as the comprehensive highest water level of the river ecosystem, and establish a comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals. Usually, the lowest and highest water level requirements of various species are the limit conditions for maintaining the diversity and stability of the seasonal river ecosystem. The specific calculation formulas are as follows:

[0129] H i,t = max(H1 i,t , H2 i,t ) (19)

[0130] M i,t = min(M1 i,t , M2 i,t ) (20)

[0131] In the formula, H i,t and M i,t are respectively the minimum and maximum values of the comprehensive ecological water level requirements for aquatic organisms and terrestrial animals at the i-th control section of the seasonal river in the t-th month, in m.

[0132] Step 4: Determine the ecological water volume threshold requirements for the life cycles of aquatic organisms and terrestrial animals at the control section.

[0133] Based on the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals, derive the ecological water volume threshold requirements for the life cycles of aquatic organisms and terrestrial animals. For seasonal rivers, assume it is a uniform open-channel flow, and use the Manning formula to calculate the ecological water volume threshold requirements at the control section. The specific formula is as follows:

[0134] QH1 i,t = max(8.64 × AH i,t × Vh i,t × T i , PH1 i,t ) (21)

[0135] QM1 i,t = max(8.64 × AM i,t × Vm i,t × T i , PM1 i,t ) (22)

[0136]

[0137] Wherein, QH1 i,t and QM1 i,t are respectively the minimum and maximum ecological water volume requirements for the life cycles of aquatic organisms and terrestrial animals at the i-th control section of the seasonal river in the t-th month, in 10,000 m 3 ; AH i,t and AM i,t are respectively the minimum and maximum cross-sectional areas of the seasonal river at the i-th control section in the t-th month, in m 2 ; Vh i,t and Vm i,t are respectively the average flow velocities corresponding to the minimum and maximum ecological water volumes at the i-th control section of the seasonal river in the t-th month, in m / s; T i is the number of days in the i-th month; PH1 i,t and PM1 i,t are respectively the minimum and maximum ecological water volumes approved in the relevant plans or programs of the water administrative department or the ecological environment department at the i-th control section in the t-th month, in 10,000 m 3 ; S i is the riverbed slope of the i-th control section of the seasonal river, which reflects the influence brought by the longitudinal section topography of the riverbed, dimensionless; n is the natural roughness of the river channel, dimensionless; Rh i,t and Rm i,t are respectively the minimum and maximum hydraulic radii of the seasonal river at the i-th control section in the t-th month, in m, which is equal to the cross-sectional area divided by the wetted perimeter and usually requires complex calculations to obtain; when the width-depth ratio of the river channel (i.e., the ratio of width to water depth) is large, the difference between the hydraulic radius and the cross-sectional average water depth will shrink. When the width-depth ratio is greater than 100, the cross-sectional average water depth can be approximately used to replace the hydraulic radius for calculation, and the error is within the allowable range (usually ≤ 2%); the cross-sectional average water depth is the difference between the comprehensive ecological water level for the life cycles of aquatic organisms and terrestrial animals at the control section and the riverbed elevation, that is:

[0138] Rh i,t = H i,t - H0 i (25)

[0139] Rm i,t = M i,t - H0 i (26)

[0140] The cross-sections of seasonal rivers include trapezoidal river channel cross-sections, rectangular river channel cross-sections, and irregular river channel cross-sections, etc.

[0141] Among them, for the trapezoidal river channel cross-section, the calculation formula for the cross-sectional area of water flow is as follows:

[0142] AH i,t =(a i +H i,t ×b i )×H i,t (27)

[0143] AM i,t =(a i +M i,t ×b i )×M i,t (28)

[0144] For the rectangular river channel cross-section, the cross-sectional area of water flow can be simplified to the following formula:

[0145] AH i,t =a i ×H i,t (29)

[0146] AM i,t =a i ×M i,t (30)

[0147] In the formula, a i is the bottom width of the i-th control cross-section of the seasonal river, in m; b i is the slope coefficient of the i-th control cross-section of the seasonal river, dimensionless.

[0148] For the cross-sectional area of water flow of the irregular river channel cross-section, methods such as the measuring point method, numerical integration method, or remote sensing and digitization can be used to determine it. Among them, the numerical integration method is more commonly used, that is, the river cross-section is divided into several small trapezoids or triangles, the areas of each small trapezoid or triangle are calculated respectively, and all these small areas are summarized to obtain the total cross-sectional area of water flow. With the development of information technology, methods such as using drones to take images of the river channel and combining GPS-RTK technology measurement can be used to obtain high-precision cross-sectional area data of the seasonal river channel.

[0149] Step 5: Determine the ecological water volume threshold requirements for terrestrial plants between the control cross-section of the seasonal river and the upstream cross-section.

[0150] Terrestrial plants (including herbs, shrubs, and woodlands, etc.) are mainly distributed on both sides of the seasonal river channels. The growth of terrestrial plants along both sides of the seasonal river mainly depends on groundwater recharge. The terrestrial plant system on both sides of the seasonal river channels has formed a unique mechanism to adapt to atmospheric drought and soil drought, that is, the state of relying on capillary rise of groundwater to supplement water sources. According to the ecological suitability theory, when the groundwater level is too high, the salts dissolved in the groundwater will accumulate on the soil surface to form salinization under the influence of evaporation, which is not conducive to plant growth; when the groundwater level is too low, the groundwater cannot rise to the extent that plants can absorb and utilize through capillaries, resulting in soil drying, vegetation decline, and land desertification. Therefore, the growth of terrestrial plants in seasonal rivers requires a reasonable groundwater burial depth. The ecological water volume threshold requirements can be calculated by calculating the phreatic evaporation of plants at a certain groundwater burial depth, and the specific calculation formula is as follows:

[0151]

[0152]

[0153] In the formula, QH2 i,t and QM2 i,t respectively represent the minimum and maximum ecological water volume requirements of terrestrial plants distributed on both sides of the seasonal river between the i-th control section and the (i - 1)-th control section in the t-th month of the seasonal river, in 10,000 m 3 ; j is the groundwater level classification at different burial depths, j = 1, 2,... J; EH j,t and EM j,t respectively represent the phreatic evaporation per unit area corresponding to the minimum and maximum values of the j-th groundwater burial depth, in mm; F i,j represents the plant area corresponding to the j-th groundwater burial depth at the i-th control section of the seasonal river, in km 2 ; K j is the influence coefficient of the j-th groundwater burial depth, dimensionless; E0 t is the water surface evaporation in the t-th month, in mm; a and b are empirical coefficients, which are obtained by fitting curves according to experimental results; ZH j and ZM j respectively represent the minimum and maximum values of the j-th groundwater burial depth, in m; Z max is the limit burial depth of phreatic evaporation, in m, with a value of 4.5 - 5.0 m.

[0154] Generally, the plant areas corresponding to different groundwater burial depths can be obtained through actual monitoring or through groundwater simulation (such as models like MODFLOW, MODCYCLE, MT3D, etc. and self-programming). The required input information usually includes data and parameters in aspects such as DEM, hydrogeology, soil distribution, and groundwater level monitoring.

[0155] Step 6: Determine the threshold requirements for the ecological water discharge of the control section of the seasonal river.

[0156] The ecological water requirements for the downstream section of the seasonal river include the water requirements for the ecological protection objectives of the tail lakes, river mouths, wetlands, river valleys and other sections. The ecological water requirements for these downstream sections are usually determined according to the ecological water volume approved by the water administrative department or the ecological environment department in relevant plans or programs. If there is no approved ecological water volume for these downstream sections, the threshold requirements for the ecological water volume of the downstream section are calculated according to the life cycle of the key species in the downstream section described in the previous steps. If there are multiple control sections with ecological protection objectives downstream, the threshold requirements for the ecological water discharge of the control section are determined by a step-by-step recursive method, that is, the minimum ecological water volume required by all downstream control sections plus the outer envelope of the loss volume is the maximum value of the ecological water discharge of the control section, and the maximum ecological water volume required by all downstream control sections plus the inner envelope of the loss volume is the minimum value of the ecological water discharge of the control section. The specific formula is as follows:

[0157]

[0158] In the formula, QH3 i,t and QM3 i,t are respectively the minimum and maximum values of the ecological water discharge requirements for all downstream sections of the i-th control section of the seasonal river in the t-th month, in 10,000 m 3 ; PH1 p,t and PM1 p,t are respectively the minimum and maximum values of the ecological water volume of the p-th section (p = i + 1, i + 2... i + I) downstream of the i-th control section; SS p,t and SM p,t are respectively the minimum and maximum loss volumes of the ecological water volume from the p-th section to the i-th control section of the seasonal river, including evaporation, leakage and water consumption in the process of human activity water withdrawal and return, in 10,000 m 3 .

[0159] Step 7: Determine the ecological water requirements for the control section of the seasonal river.

[0160] Combined with the ecological water volume threshold requirements of the control section of the seasonal river and the ecological water volume threshold requirements of the downstream ecological water volume of the control section, a collaborative analysis is carried out to determine the ecological water volume requirements of the seasonal river, specifically: the minimum value of the ecological water volume requirements of the seasonal river is equal to the minimum value of the ecological water volume requirements of the aquatic organisms and terrestrial animals in the control section during their life cycles and the envelope curve of the minimum downstream ecological water volume required from the downstream section of the control section to this control section, plus the minimum value of the ecological water volume requirements of terrestrial plants between the control section and the upstream section; the maximum value of the ecological water volume requirements of the seasonal river is equal to the maximum value of the ecological water volume requirements of the aquatic organisms and terrestrial animals in the control section during their life cycles and the envelope curve of the maximum downstream ecological water volume required from the downstream section of the control section to this control section, plus the maximum value of the ecological water volume requirements of terrestrial plants between the control section and the upstream section. The specific calculation formula is as follows:

[0161] QH i,t =Max(QH1 i,t ,QH3 i,t )+QH2 i,t (37)

[0162] QM i,t =Min(QM1 i,t ,QM3 i,t )+QM2 i,t (38)

[0163] In the formula, QH i,t and QM i,t are the minimum and maximum values of the ecological water volume requirements of the i-th control section of the seasonal river in the t-th month, in 10,000 m 3 .

[0164] Example 1

[0165] This example is a specific application example of the above method.

[0166] Taking a typical seasonal river in North China as an example, this example has three river reaches (i.e., River Reach 1 and River Reach 2 converge into River Reach 3) and a connecting lake, which are divided into 4 control sections. The spatial distribution of the river-lake water system and its control sections is as Figure 2 shown. Among them, Control Section (i = 1) represents River Reach 1, Control Section (i = 2) represents River Reach 2, Control Section (i = 3) represents River Reach 3, and Control Section (i = 4) represents the downstream tail lake of River Reach 3.

[0167] Through on-site surveys of river channels, biological surveys, and analysis of satellite image data, the key species and parameters of seasonal rivers are identified. For the control section (i = 1), emergent plants are the key species; for the control section (i = 2), submerged plants and terrestrial plants are the key species; for the control section (i = 3), emergent plants, submerged plants, fish, birds, and terrestrial plants are the key species, and there is a fish spawning ground, which requires pulsed flood flow during the spawning period (May - June). The terrestrial plants on both sides of the river channel between the control section (i = 3) and the upstream section (i = 2) are mainly xerophytic grasslands, which mainly rely on underground groundwater to sustain life. In the downstream terminal lake represented by the control section (i = 4), there are no sensitive protected species, and it is necessary to maintain the basic shape, water area space, and ecological service function requirements of the lake.

[0168] Given that the key species of the control section (i = 3) are relatively complex, taking the reach 3 represented by it as an example, the quantitative calculation of ecological water volume is carried out. The elevation of the distribution of aquatic plants is measured using lidar, and combined with the suitable water depth data of the life cycle obtained by the biological survey method, the comprehensive ecological water level requirement curve for the life cycle of aquatic organisms and terrestrial animals is calculated as Figure 3 shown. Among them, the river bottom elevation of the control section 3 is 0.1m, and the elevation of the distribution of aquatic plants in the river channel is mainly at 0.4m and 0.6m.

[0169] According to Figure 3 the comprehensive ecological water level curve of the control section of the seasonal river, combined with the Manning formula, with the roughness coefficient taken as 0.045, and combined with the measurement results of the river channel cross-section and river channel slope given by the water conservancy survey and design department, the annual minimum ecological water volume requirement for the life cycle of aquatic organisms and terrestrial animals in the control section of this seasonal river is calculated to be 50.576 million m 3 ³, and the annual maximum ecological water volume requirement is 62.092 million m 3 .

[0170] Figure 4 The variation of the monthly average buried depth of the groundwater level at the control section (i = 3) of this seasonal river is given. The limiting buried depth of groundwater is taken as 5.0m, and groundwater simulation is carried out to obtain the plant area corresponding to different groundwater buried depths. Taking November and December as examples, the specific results are shown in Table 4. According to the statistical results of the monthly different groundwater buried depths and the corresponding plant distribution areas, summarized over the whole year, the annual minimum ecological water volume requirement for terrestrial plants at the control section of the seasonal river is calculated to be 33.032 million m 3 ³, and the annual maximum ecological water volume requirement is 35.353 million m 3 .

[0171] Table 4 Plant distribution areas corresponding to different groundwater buried depths in typical months (Reach 3)

[0172]

[0173] To meet the requirements of the basic form, water area space, and ecological service functions of the downstream connected lake of the seasonal river, according to the plans and implementation plans issued by the water administrative department, the ecological water level requirements for the downstream lake control section (i = 4) are determined to be 12.0 m and 15.0 m respectively. Considering the connection relationship between the seasonal river and the downstream lake, based on the evaporation and seepage losses of the river channel and the water consumption of human water intake activities, the minimum monthly ecological water discharge required from the downstream lake control section to this control section (i = 3) is calculated to be 3.5 million m 3 , and the maximum monthly ecological water discharge is 5 million m 3 , so as to promote the stability and diversity of the downstream lake ecosystem.

[0174] Carry out a collaborative analysis of the ecological water volume threshold of the seasonal river control section, and the minimum annual ecological water volume requirement for this seasonal river (section i = 3) is obtained as 83.608 million m 3 , and the monthly ecological water volume demand process is as Figure 5 shown; the maximum annual ecological water volume requirement is 97.810 million m 3 , and the monthly ecological water volume demand process is as Figure 6 shown.

[0175] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred layout scheme, those of ordinary skill in the art should understand that the technical solution of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for determining the ecological water volume of seasonal rivers oriented to the life cycle of key species, characterized in that The method includes the following steps: Step 1: Determine the control section and its associated sections for the ecological water requirement of seasonal rivers: Determine the control section for the ecological water requirement of seasonal rivers according to the control section selection principle. For the i-th control section of seasonal rivers, identify and determine its associated sections, including the (i - 1)-th section upstream and the (i + 1), (i + 2), …, (i + I)-th sections downstream, where I is the total number of downstream sections; Step 2: Identify the key species and species parameters of the control section and downstream sections of seasonal rivers: Identify the key species and species parameters of the control section and downstream sections of seasonal rivers. The key species are the dominant populations and indicator species that affect the structure and function of the seasonal river ecosystem. The key species include aquatic organisms and terrestrial organisms. The aquatic organisms include aquatic plants and aquatic animals, and the terrestrial organisms include terrestrial plants and terrestrial animals; The species parameters include species type, spatial location, distribution area, and elevation; Step 3: Determine the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals at the control section: Determine the ecological water level requirement curves for the life cycles of aquatic plants, aquatic animals, and terrestrial animals at the control section respectively, and then determine the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial organisms at the control section. Specifically, it includes the following steps: Step 31: Determine the ecological water level requirement curve for the life cycle of aquatic plants: Aquatic plants include floating plants, emergent plants, and submerged plants. The calculation formula for the ecological water level requirement curve of the life cycle of floating plants is: H1a i,t = H1a0 i,t + H1as i,t (1) M1a i,t = H1a0 i,t + H1am i,t (2) where, H1a i,t and M1a i,t are respectively the minimum water level and the maximum water level required for the life cycle of floating plants at the i-th control section of the seasonal river in the t-th month, m; H1a0 i,t is the elevation of the growth and distribution of floating plants at the i-th control section of the seasonal river in the t-th month, m; H1as i,t and H1am i,t are respectively the minimum water depth and the maximum water depth required for the growth and reproduction of floating plants at the i-th control section of the seasonal river in the t-th month; The calculation formula for the ecological water level requirement curve of the life cycle of emergent plants is: H1b i,t = H1b0 i,t + H1bs i,t (3) M1b i,t = H1a0 i,t + H1bm i,t (4) where H1b i,t and M1b i,t are respectively the minimum water level and the maximum water level required for the life cycle of emergent plants at the i-th control section of the seasonal river in the t-th month, in m; H1b0 i,t is the elevation of the growth distribution of emergent plants at the i-th control section of the seasonal river reach in the t-th month, in m; H1bs i,t and H1bm i,t are respectively the minimum water depth and the maximum water depth required for the growth and reproduction of emergent plants at the i-th control section of the seasonal river in the t-th month; The calculation formula for the ecological water level requirement curve of the life cycle of submerged plants is: H1c i,t = H1c0 i,t + H1cs i,t (5) M1c i,t = H1c0 i,t + M1cs i,t (6) Where, H1c i,t and M1c i,t are respectively the minimum water level and the maximum water level required for the life cycle of submerged plants at the i-th control section of the seasonal river in the t-th month, m; H1c0 i,t is the elevation of the growth distribution of submerged plants at the i-th control section of the seasonal river in the t-th month, m; H1cs i,t and M1cs i,t are respectively the minimum water depth and the maximum water depth required for the growth and reproduction of submerged plants at the i-th control section of the seasonal river in the t-th month; The formula for the ecological water level requirement curve of the life cycle of aquatic plants in seasonal rivers is: H1 i,t = Max(H1a i,t , H1b i,t , H1c i,t ) (7) M1 i,t = Min(M1a i,t , M1b i,t , M1c i,t ) (8) where H1 i,t and M1 i,t are respectively the minimum water level requirement and the maximum water level requirement for the aquatic plant life cycle in the t-th month at the i-th control section of the seasonal river, in m; Step 32: Determine the ecological water level requirement curves for the life cycles of aquatic animals and terrestrial animals: Aquatic animals and terrestrial animals include fish, zooplankton, benthic animals, and birds. The calculation formula for the ecological water level requirement curve of the life cycle of aquatic animals and terrestrial animals is: H2 i,t = Max(H2a i,t , H2b i,t , H2c i,t , H2d i,t ) (9) M2 i,t = Min(M2a i,t , M2b i,t , M2c i,t , M2d i,t ) (10) Where: H2a i,t = H0 i + H2as i,t (11) H2b i,t = H0 i + H2bs i,t (12) H2c i,t = H0 i + H2cs i,t (13) H2d i,t = H0 i + H2ds i,t (14) M2a i,t = H0 i + H2am i,t (15) M2b i,t = H0 i + H2bm i,t (16) M2c i,t = H0 i + H2cm i,t (17) M2d i,t = H0 i + H2dm i,t (18) In the formula, H2 i,t and M2 i,t are respectively the minimum water level and the maximum water level required for the life cycles of aquatic animals and terrestrial animals in the t-th month at the i-th control section of the seasonal river, in m; H0 i is the river bottom elevation of the i-th control section of the seasonal river, in m; H2as i,t , H2bs i,t , H2cs i,t , H2ds i,t are respectively the minimum water depths required for the life cycles of fish, zooplankton, benthic animals, and birds in the t-th month at the i-th control section of the seasonal river, in m; M2am i,t , M2bm i,t , M2cm i,t , M2dm i,t are respectively the maximum water depths required for the life cycles of fish, zooplankton, benthic animals, and birds in the t-th month at the i-th control section of the seasonal river, in m; Step 33: Determine the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals at the control section: According to the ecological water level requirement curves for the life cycles of aquatic organisms and terrestrial animals at the control section of seasonal rivers, take the maximum value of the lowest water levels as the comprehensive lowest water level of the river ecosystem, and take the minimum value of the highest water levels as the comprehensive highest water level of the river ecosystem, and establish the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals. The calculation formula is: H i,t = max(H1 i,t , H2 i,t ) (19) M i,t = min(M1 i,t , M2 i,t ) (20) Where, H i,t and M i,t are respectively the minimum and maximum values of the comprehensive ecological water level requirements for aquatic organisms and terrestrial animals at the i-th control section of the seasonal river in the t-th month, in m; Step 4: Determine the ecological water volume threshold requirements for the life cycles of aquatic organisms and terrestrial animals at the control section: Based on the comprehensive ecological water level requirement curve for the life cycles of aquatic organisms and terrestrial animals, calculate the ecological water volume threshold requirements for the life cycles of aquatic organisms and terrestrial animals. For seasonal rivers, assume it is a uniform flow in an open channel, and use the Manning formula to calculate the ecological water volume threshold requirements for the control section. The calculation formula is: QH1 i,t = max(8.64 × AH i,t × Vh i,t × T i , PH1 i,t ) (21) QM1 i,t = max(8.64 × AM i,t × Vm i,t × T i , PM1 i,t ) (22) Wherein, QH1 i,t and QM1 i,t are respectively the minimum and maximum values of the ecological water volume requirements for the life cycles of aquatic organisms and terrestrial animals in the t-th month at the i-th control section of the seasonal river, in 10,000 m 3 ; AH i,t and AM i,t are respectively the minimum and maximum values of the cross-sectional area of the flowing water at the i-th control section of the seasonal river in the t-th month, in m 2 ; Vh i,t and Vm i,t are respectively the average flow velocities corresponding to the minimum and maximum values of the ecological water volume at the i-th control section of the seasonal river in the t-th month, in m / s; T i is the number of days in the i-th month; PH1 i,t and PM1 i,t are respectively the minimum and maximum ecological water volumes approved monthly in the relevant plans or programs of the water administrative department or the ecological environment department at the i-th control section in the t-th month, in 10,000 m 3 ; S i is the riverbed slope of the i-th control section of the seasonal river, to reflect the influence brought by the topographic changes of the longitudinal riverbed section, dimensionless; n is the natural roughness of the river channel, dimensionless; Rh i,t and Rm i,t are respectively the minimum and maximum values of the hydraulic radius at the i-th control section of the seasonal river in the t-th month, in m. When the width-depth ratio of the river channel is greater than 100, the average water depth of the section is used to replace the hydraulic radius for calculation, and the error is within the allowable range; the average water depth of the section is the difference between the comprehensive ecological water level for the life cycles of aquatic organisms and terrestrial animals at the control section and the river bottom elevation, that is: Rh i,t = H i,t - H0 i (25) Rm i,t = M i,t - H0 i (26); Step 5: Determine the ecological water volume threshold requirements for terrestrial plants between the control section of the seasonal river and the upstream section: Terrestrial plants include herbs, shrubs, and forest land, which are distributed on both sides of the seasonal river channel. The growth of terrestrial plants depends on groundwater recharge. By calculating the phreatic evaporation of terrestrial plants at a certain groundwater depth, the ecological water volume threshold requirements are then deduced. The specific calculation formula is as follows: where QH2 i,t and QM2 i,t are respectively the minimum and maximum values of the ecological water requirements of terrestrial plants distributed on both sides of the river channel between the i-th control section and the (i - 1)-th control section of the seasonal river in the t-th month, in 10,000 m 3 ; j is the groundwater level grading at different buried depths, j = 1, 2, …, J; EH j,t and EM j,t are respectively the specific groundwater evaporation amounts corresponding to the minimum and maximum values of the j-th groundwater buried depth, in mm; F i,j is the plant area corresponding to the j-th groundwater buried depth at the i-th control section of the seasonal river, in km 2 , which is obtained through actual monitoring or groundwater simulation; K j is the influence coefficient of the j-th groundwater buried depth, dimensionless; E0 t is the water surface evaporation amount in the t-th month, in mm; a and b are empirical coefficients, which are determined according to the fitting curve of experimental results; ZH j and ZM j are respectively the minimum and maximum values of the j-th groundwater buried depth, in m; Z max is the limiting buried depth of groundwater evaporation, in m, with a value of 4.5 - 5.0 m; Step 6: Determine the ecological water volume threshold requirements for the downstream discharge of the control section of the seasonal river: The ecological water volume requirements for the downstream section of the control section of the seasonal river include the water volume requirements for the ecological protection targets of the terminal lake, estuary, wetland, and river valley section. The ecological water volume requirements for the downstream section are determined based on the ecological water volume approved by the water administrative department or the ecological environment department in the plan or plan approval. If there is no approved ecological water volume for the downstream section, the ecological water volume threshold for the downstream section is calculated using the life cycle of the key species in the downstream section. If there are multiple control sections for ecological protection targets downstream, the ecological water volume threshold requirements for the downstream discharge of this control section are determined by the method of layer-by-layer recursion, that is, the outer envelope of the minimum ecological water volume required by all downstream control sections plus the loss is the maximum value of the ecological water volume for the downstream discharge of this control section, and the inner envelope of the maximum ecological water volume required by all downstream control sections plus the loss is the minimum value of the ecological water volume for the downstream discharge of this control section. The specific formula is as follows: where, QH3 i,t and QM3 i,t are respectively the minimum and maximum values of the ecological water discharge requirements recursively calculated from all cross-sections downstream of the \(i\)-th control section in the \(t\)-th month of the seasonal river to this control section, in 10,000 \(m^3\) 3 ; PH1 p,t and PM1 p,t are respectively the minimum and maximum values of the ecological water volume of the \(p\)-th cross-section (\(p = i + 1, i + 2, \cdots, i + I\)) downstream of the \(i\)-th control section; SS p,t and SM p,t are respectively the minimum and maximum ecological water volume losses from the \(p\)-th cross-section to the \(i\)-th control section of the seasonal river, in 10,000 \(m^3\) 3 ; Step 7: Determine the ecological water volume requirements for the control section of the seasonal river: Combining the ecological water volume threshold requirements for the control section of the seasonal river and the ecological water volume threshold requirements for the downstream discharge of the control section, a collaborative analysis is carried out to determine the ecological water volume requirements for the seasonal river. Specifically: The minimum value of the ecological water volume requirements for the seasonal river is equal to the outer envelope of the minimum ecological water volume requirements for the life cycles of aquatic organisms and terrestrial animals at the control section and the minimum downstream discharge ecological water volume required from the downstream section of the control section to this control section, plus the minimum value of the ecological water volume requirements for terrestrial plants between the control section and the upstream section; The maximum value of the ecological water volume requirements for the seasonal river is equal to the inner envelope of the maximum ecological water volume requirements for the life cycles of aquatic organisms and terrestrial animals at the control section and the maximum downstream discharge ecological water volume required from the downstream section of the control section to this control section, plus the maximum value of the ecological water volume requirements for terrestrial plants between the control section and the upstream section. The specific calculation formula is as follows: QH i,t = Max(QH1 i,t , QH3 i,t ) + QH2 i,t (37) QM i,t = Min(QM1 i,t , QM3 i,t ) + QM2 i,t (38) Where, QH i,t and QM i,t are respectively the minimum and maximum ecological water volume requirements for the i-th control section in the lower reaches of the seasonal river in the t-th month, in 10,000 m 3 .

2. The method for determining the ecological water volume of seasonal rivers for the life cycle of key species according to claim 1, characterized in that The control section selection principle described in Step 1 is as follows: The control section of the seasonal river is determined based on the requirements of water administration management, following the principles of representativeness, operability, and systematicness, including: river administrative control or cross-administrative region sections, river mouth sections where the river enters the sea, enters the main stream, or enters the terminal, important ecological sensitive area control sections, and important controlled water project sections; Priority is given to selecting sections that can be monitored, evaluated, and regulated; The selection of control sections is coordinated with relevant water conservancy plans, ecological environment protection plans, and water volume allocation plans in the basin or region.

3. The method for determining the ecological water volume of seasonal rivers for the life cycle of key species according to claim 1, characterized in that The species parameters of aquatic organisms and terrestrial animals described in Step 2 are identified and determined through on-site inspection and biological surveys, and the species parameters of terrestrial plants are identified and determined through on-site inspection, biological surveys, and satellite image data.

4. The method for determining the ecological water volume of seasonal rivers for the life cycle of key species according to claim 1, characterized in that The calculation process of the cross-sectional area of the i-th control section of the seasonal river in the t-th month described in Step 4 is specifically as follows: The cross-sections of seasonal rivers include trapezoidal river channel cross-sections, rectangular river channel cross-sections, and irregular river channel cross-sections; Among them, for the trapezoidal river channel cross-section, the calculation formula for the cross-sectional area is: AH i,t =(a i +H i,t ×b i )×H i,t (27) AM i,t =(a i +M i,t ×b i )×M i,t (28) For the rectangular river channel cross-section, the calculation formula for the cross-sectional area is: AH i,t = a i × H i,t (29) AM i,t = a i × M i,t (30) In the formula, a i is the bottom width of the i-th control section of the seasonal river, in m; b i is the side slope coefficient of the i-th control section of the seasonal river, dimensionless; For the irregular river channel cross-section, the cross-sectional area is determined by the measuring point method, numerical integration method, or remote sensing and digitization method.

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