CN105868579B - A kind of lake ecological water level computational methods - Google Patents

Abstract

The invention discloses a method for calculating the ecological water level of a lake. The steps are: 1. Calculation of the water level value in the germination period: A. Find or establish the water level-area of the lake; B. Calculate the germination area of hygrophytes and emergent plants at a given water level ; C, calculate the germination area of submerged plants; D, calculate the germination area of aquatic plants; E, calculate the coverage of hygrophytes, emergent plants, and submerged plants at a given water level; F, calculate the coverage under different water levels according to the step length The total area of aquatic plant germination area; G, the relationship between utilization water level and vegetation coverage; 2: Calculation of ecological water level value in seedling growth period; 3: Calculation of ecological water level value in growth and diffusion period; 4: Calculation of ecological water level value in mature period; 5: Seed Calculation of ecological water level during the propagation period; 6: Calculation of water level during the dormant period; 7: Lake ecological water level process line. The calculation process and parameters are simple, and can be widely used in the evaluation of the ecological water level of shallow lakes in subtropical regions.

Description

A Calculation Method of Lake Ecological Water Level

technical field

The invention relates to the fields of lake water resources management and lake ecological restoration, and more specifically relates to a lake ecological water level calculation method with aquatic vegetation as the management target, which is suitable for the management of shallow lake ecological water levels, ecological restoration and ecosystem protection in subtropical regions.

Background technique

Ecological water level assessment is an important problem facing lake water resources management and ecosystem protection and restoration. Currently, there are three main types of calculation methods used internationally: 1) Hydrological data method, based on the Q95 ^th method in hydrology to calculate the minimum ecological water level of lakes, Or take the lowest water level for many years as the lowest ecological water level; 2) Morphological analysis method, using the lake area as the functional index, in the water level-area relationship curve, the water level corresponding to the maximum change rate of the lake area is taken as the lowest ecological water level; 3) The biological minimum The space requirement method uses the living space requirements of various organisms in the lake to determine the minimum ecological water level. The above method has two main shortcomings. One is that the calculation is mostly based on hydrological data, and the weight of lake organisms and ecosystem needs is very small; the other is to calculate the minimum ecological water level of the lake, without considering the process of water level changes. In the present invention, lake aquatic vegetation is used as a representative group of the ecosystem, and the water level requirements of vegetation development in different life history periods are taken as a standard to calculate the lake ecological water level process line under different vegetation coverage targets. The invention takes the water level requirements of lake plants as the core, and the obtained ecological water level is a process line. The calculation process and parameters are simple, and can be widely used in the evaluation of the ecological water level of shallow lakes in subtropical regions.

Contents of the invention

The purpose of the present invention is to provide a lake ecological water level calculation method, which is easy to operate and easy to operate, and accurately calculates the water level process corresponding to different vegetation coverage, and provides reliable technical support for lake water resource management, ecological water level regulation and ecological restoration. Plants are the most sensitive to water level changes; aquatic plants provide the necessary basic conditions for other aquatic animals, such as food, habitat, breeding places, etc.; vegetation restoration is an important goal and assessment index of lake restoration; with vegetation coverage as an index, It is easy to track and monitor; aquatic plants can form a beautiful natural landscape, and its aesthetic value is easy to be understood and accepted by the public.

In order to achieve the above object, the present invention adopts the following technical measures:

The technical concept of the present invention is: 1) according to subtropical lake aquatic plant life history characteristics, it is divided into germination period (2-3 months), seedling growth period (4-5 months), growth diffusion period (6-7 months), Maturity period (August-September), seed diffusion period (October-November), dormancy period (December-January of the next year); 2) Establish the relationship between the water level in the germination period and the area that can germinate, and calculate the given vegetation 3) Then calculate the water level range of this period according to the water level requirements of plants in the seedling growth period, growth diffusion period, maturity period, seed diffusion period, and dormancy period; 4) Connect the ecological water level values in different periods into a line The process line is the ecological water level process line of the lake under a given vegetation coverage.

A method for calculating the ecological water level of a lake, the steps of which are as follows:

Step 1: Calculation of the ecological water level (W _germ ) during the germination period (2-3 months):

1-1: Find or establish the lake water level-area relationship F _A～W ;

1-2: Calculate the germination area (A _e ) of hygrophytes and emergent plants under a given water level (W _give ), which ranges from W _give -0.2m to W _C , where W _C is the annual average water level of the lake. According to the water level-area relationship, bring W _give -0.2m and W _C into F _{A ~ W} respectively, and calculate the difference between them, which is the value of A _e at a given water level;

1-3: Calculate the submerged plant germination area (A _s ), the water level range of this area is W _give -0.2m～W _give -2SD, SD is the lowest monthly transparency from March to June, and the transparency data of the previous year can be referred to. According to the water level-area relationship, bring W _give -0.2m and W _give -2SD into F _{A ~ W} respectively, and calculate the difference between them, which is the A _s value at a given water level;

1-4: Calculate the total area of the aquatic plant germination area (A _t ), A _t =A _e +A _s ;

1-5: Calculate the overall coverage of hygrophytes and emergent plants, submerged plants and aquatic plants at a given water level (C, %), hygrophytes and emergent vegetation coverage C _e =A _e /A _C ×100 %; A _C is the water surface area corresponding to the annual average water level of the lake; the submerged vegetation coverage C _s =A _s /A _C ×100%; the overall coverage of aquatic plants C=A _t /A _C ×100%;

1-6: Repeat steps 1-2 to 1-5 according to the step _length of _0.1m , _respectively calculate the total area of _aquatic plant germination area and The total coverage, W _L is the lowest water level over the years, and the water level-vegetation coverage relationship F _C～W is established;

1-7: Using the water level-vegetation coverage relationship, calculate the optimum ecological water level (W _germ ) in the germination period under a given vegetation coverage target (C _targ ). The given vegetation coverage target (C _targ ) is the lake management target;

Step 2: Calculation of the ecological water level (W _grow ) during the seedling growth period (April-May):

During the seedling growth period from April to May, the water level should be kept stable and rise slowly, and the increase should not exceed 0.4m per month. Therefore, the suitable range of the ecological water level in April is W _germ ~ W _germ +0.4m, and the suitable range of the ecological water level in May is W _germ ~ W _germ +0.8m;

Step 3: Calculation of the ecological water level (W _disp ) during the growth and diffusion period (June-July):

In June, keep the water level stable and rise slowly, and the increase should not exceed 0.4m per month. The suitable range for the ecological water level is W _germ ~ W _germ + 1.2m; in July, the water level needs to rise, but the increase should not exceed the top of the emergent plants, that is, 0.5m /month, so the suitable range of ecological water level in July is W _germ +(W _C -W _germ )/2～W _germ +2.5m; if (W _C -W _germ )/2≥2.5, then it is W _germ +1.3m ~W _germ +2.5m;

Step 4: Calculation of the ecological water level (W _matu ) in the mature period (August-September):

From August to September, the water level needs to rise to submerge the wet vegetation area, to prevent the invasion of terrestrial plants and the _swamping of the lake. The suitable range of ecological water level in mature stage is W _C ~ W _warn ;

Step 5: Calculation of the ecological water level (W _seed ) during the seed propagation period (October-November):

The water level during the seed propagation period needs to be gradually reduced according to the natural water level fluctuation pattern. The water level in October remains the same as in July, and the water level in November remains the same as in June. The suitable range of ecological water level in October is W _germ +(W _C -W _germ )/2～W _germ +2.5m; if (W _C -W _germ )/2≥2.5, it is W _germ +1.3m～W _germ + 2.5m; the suitable range of ecological water level in November is W _germ ~ W _germ +1.2m;

Step 6: Calculation of the ecological water level (W _wint ) during the dormant period (December-January of the next year):

The lowest water level in the dormant period needs to be consistent with the germination period, and the optimum range of the highest water level should be consistent with the water level in May. The suitable range of ecological water level from December to next January is W _germ ~ W _germ +0.8m;

Step 7: Lake ecological water level hydrograph (W _inte ):

Connect the ecological water level values in each period to form the ecological water level process line under a given aquatic vegetation coverage target W _inte = W _germ + W _grow + W _disp + W _matu + W _seed + W _wint ; when the vegetation coverage target changes , recalculate the ecological water level process line according to the above calculation procedure.

F _A～W is the relationship between lake water level and area; A _C is the water surface area corresponding to the average water level of the lake for many years, greater than 25 years, (unit: km ² ); W _C is the average water level of the lake for many years (unit: m); W _L is the lowest water level of the lake over the years since the water level record (unit: m); W _give is the given water level, which is the water level value specified in the calculation process (unit: m); W _warn is the lake warning water level (unit: m); SD is the minimum monthly transparency of lake water from March to June (unit: m); A _e is the distribution area of hygrophytes and emergent plants (unit: km ² ); A _s is the distribution area of submerged plants (unit: km ² ) ; A _t is the total area of aquatic plant distribution area (unit: km ² ); C _e is the coverage of wet and emergent vegetation (unit: %); C _s is the coverage of submerged vegetation (unit: %); C is The total coverage of aquatic plants (unit: %); C _targ is a given aquatic vegetation coverage target, that is, the protection target specified in lake management (unit: %); F _{C ~ W} is the relationship between aquatic vegetation coverage and water level; W _germ is the ecological water level value at the germination stage; W _grow is the ecological water level value at the seedling stage; W _disp is the ecological water level value at the growth diffusion stage; W _matu is the ecological water level value at the mature stage; W _seed is the ecological water level value at the seed propagation stage; W _wint is the Ecological water level value during dormant period; _Winte is the ecological water level process line under a given vegetation coverage target.

Compared with the prior art, the present invention has the following advantages and effects:

A: Through the water level-vegetation coverage relationship, the ecological water level under different vegetation coverage can be accurately calculated, and the calculation parameters are based on the water level requirements of aquatic plants, so the calculated ecological water level directly reflects the status of the ecosystem, which makes up for the inadequacy of existing calculation methods. Pay attention to the defects of biological and ecological systems;

B: The calculation of the ecological water level process line breaks through the limitation of the previous technology that only calculates the lowest ecological water level, and is expected to make the management of the lake's ecological water level more refined;

C: The ecological water level process line can be adjusted according to different management objectives, which is conducive to the adaptive management of lake water level, which cannot be achieved by existing calculation methods. The calculation process and parameters are simple, and can be widely used in the assessment of ecological water level of shallow lakes in subtropical regions .

Detailed ways

The implementation of the present invention will be further described in detail below.

Example 1:

A method for calculating the ecological water level of a lake, the calculation steps are as follows:

Step 1: Calculation of the ecological water level (W _germ ) during the germination period (2-3 months)

1-1: Find or establish the lake water level-area relationship F _A～W ;

1-2: Calculate the germination area (A _e ) of hygrophytes and emergent plants under a given water level (W _give ), which ranges from W _give -0.2m to W _C , where W _C is the annual average water level of the lake. For example, if the annual average water level of a lake is 20.0m, the corresponding water surface area of the lake is 100km ² , and when the calculated water level is 19.0m, the germination and distribution elevation range of hygrophytes and emergent plants is 18.8-20.0m. According to the water level-area relationship, bring W _give -0.2m and W _C into F _{A ~ W} respectively, and calculate the difference between them, which is the value of A _e at a given water level;

1-3: Calculate the submerged plant germination area (A _s ), the water level range of this area is W _give -0.2m～W _give -2SD, SD is the lowest monthly transparency from March to June, and the transparency data of the previous year can be referred to. According to the water level-area relationship, bring W _give -0.2m and W _give -2SD into F _{A ~ W} respectively, and calculate the difference between them, which is the A _s value at a given water level;

1-4: Calculate the total area of the aquatic plant germination area (A _t ), A _t =A _e +A _s ;

1-5: Calculate the overall coverage of hygrophytes and emergent plants, submerged plants and aquatic plants at a given water level (C, %), hygrophytes and emergent vegetation coverage C _e =A _e /A _C ×100 %; submerged vegetation coverage C _s =A _s /A _C ×100%; overall aquatic plant coverage C=A _t /A _C ×100%;

1-6: Repeat steps 1-2 to 1-5 according to the step _length of _0.1m , _respectively calculate the total area of _aquatic plant germination area and The total coverage, W _L is the lowest water level over the years, and the water level-vegetation coverage relationship F _C～W is established;

1-7: Using the water level-vegetation coverage relationship, calculate the optimum ecological water level (W _germ ) in the germination period under a given vegetation coverage target (C _targ ). Given the vegetation coverage target (C _targ ) as the lake management target, for example: in the management of a certain lake, the aquatic vegetation coverage is required to reach 40%, and at this time C _targ =40%.

Step 2: Calculation of the ecological water level (W _grow ) during the seedling growth period (April-May)

During the seedling growth period from April to May, the water level should be kept stable and rise slowly, and the increase should not exceed 0.4m per month. Therefore, the suitable range of the ecological water level in April is W _germ ~ W _germ +0.4m, and the suitable range of the ecological water level in May is W _germ ~ W _germ +0.8m;

Step 3: Calculation of the ecological water level (W _disp ) during the growth and diffusion period (June-July)

In June, keep the water level stable and rise slowly, and the increase should not exceed 0.4m per month. The suitable range for the ecological water level is W _germ ~ W _germ + 1.2m; in July, the water level needs to rise, but the increase should not exceed the top of the emergent plants, that is, 0.5m Every month, so the suitable range of ecological water level in July is W _germ +(W _C -W _germ )/2～W _germ +2.5m; if (W _C -W _germ )/2≥2.5, it is W _germ +1.3m ~W _germ +2.5m;

Step 4: Calculation of ecological water level (W _matu ) in mature period (August-September)

From August to September, the water level needs to rise to submerge the wet vegetation area, prevent terrestrial plant invasion and lake swamping, the low value of the ecological water level must be greater than or equal to the annual average water level (W _C ), and the highest value should not exceed the lake warning water level (W _warn ), so the suitable range of ecological water level at mature stage is W _C ～W _warn .

Step 5: Calculation of the ecological water level (W _seed ) during the seed propagation period (October-November)

The water level during the seed propagation period needs to be gradually reduced according to the natural water level fluctuation pattern. The water level in October remains the same as in July, and the water level in November remains the same as in June. The suitable range of ecological water level in October is W _germ +(W _C -W _germ )/2～W _germ +2.5m, if (W _C -W _germ )/2≥2.5, it is W _germ +1.3m～W _germ +2.5m; the suitable range of ecological water level in November is W _germ ~ W _germ +1.2m;

Step 6: Calculation of the ecological water level (W _wint ) during the dormant period (December-January of the next year)

The lowest water level in the dormant period needs to be consistent with the germination period, and the optimum range of the highest water level should be consistent with the water level in May. The suitable range of ecological water level from December to next January is W _germ ~ W _germ +0.8m;

Step 7: Lake ecological water level hydrograph (W _inte )

Connect the ecological water level values in each period to form the ecological water level process line under a given aquatic vegetation coverage target W _inte = W _germ + W _grow + W _disp + W _matu + W _seed + W _wint ; when the vegetation coverage management target changes , recalculate the ecological water level process line according to the above calculation procedure.

After the above steps, the current monthly ecological water level value and suitable range for a given aquatic vegetation coverage can be obtained.

The lakes described are suitable for the calculation of the ecological water level of any lake.

Example 2:

Calculation of the ecological water level of a lake in Hubei, the steps are as follows:

Step 1: Calculation of the ecological water level (W _germ ) during the germination period (2-3 months)

1-1: Find or establish the lake water level-area relationship F _A～W ;

After consulting the data, the lake water level-area relationship is obtained as the following equation (F _A～W ): A=-0.2811W ⁴ +20.862W ³ -582.37W ² +7267.9W-34015(14.0≤W≤20.0), where A is Area (unit: km ² ), W is water level (unit: m);

1-2: Calculate the germination area (A _e ) of hygrophytes and emergent plants under a given water level (W _give ), which ranges from W _give -0.2m to W _C , where W _C is the annual average water level of the lake. According to the water level-area relationship, bring W _give -0.2m and W _C into F _{A ~ W} respectively, and calculate the difference between them, which is the value of A _e at a given water level;

According to the data, the annual average water level of the lake is 19.0m, and the corresponding water surface area is 304.3km ² . For a given water level such as 17.0m, the water level range of hygrophytes and emergent plants is 17.0-0.2-19.0m, that is, 16.8-19.0m; respectively bring 16.8 and 19.0 into the water level-area equation (F _A～W ) , the corresponding area at 16.8m is 245.3km ² , the corresponding area at 19.0m is 304.3km ² , the difference between the two is 59.02km ² , which is the distribution area of hygrophytes and emergent water at 17.0m water level A _e .

1-3: Calculate the germination area of submerged plants (A _s ), the water level in this area ranges from W _give -0.2m to W _give -2SD, SD is the lowest monthly transparency (m) from March to June, refer to the previous year Transparency data. According to the water level-area relationship, put W _give -0.2m and W _give -2SD into the equations F _A~W respectively, and calculate the difference between them, which is the value of A _s at a given water level;

The lowest monthly transparency of the lake from March to June is 1.0m, and the water level range of submerged plants is 17.0-0.2～17.0-2×1.0m, that is, 16.8～15.0m; 16.8 and 15.0 are respectively brought into the equation F _A～W , calculate the difference between the two, which is the A _s value at a given water level, which is 96.46km ² .

1-4: Calculate the total area of the aquatic plant germination area (A _t ), A _t =A _e +A _s ;

In the case of a water level of 17.0m, the total area of the lake where aquatic plants can germinate is A _t =59.02+96.46, that is, 155.48km ² ;

1-5: Calculate the overall coverage of hygrophytes and emergent plants, submerged plants and aquatic plants at a given water level (C, %), hygrophytes and emergent vegetation coverage C _e =A _e /A _C ×100 %; submerged vegetation coverage C _s =A _s /A _C ×100%; overall aquatic plant coverage C=A _t /A _C ×100%;

When the water level is 17.0m, the coverage of wet and emergent vegetation in this lake is C _e = 59.02/304.3×100%, which is 19.4%; the coverage of submerged vegetation C _s = 96.46/304.3×100%, is 31.7% ; The overall coverage of aquatic plants C = 155.48/304.3 × 100%, which is 51.1%;

1-6: Repeat steps B to E in steps of 0.1m to calculate the total germination area and total coverage of aquatic plants at a given water level W _L , W _L +0.1m, W _L +0.2m...W _C , W _L is the lowest water level over the years, and the water level-vegetation coverage relationship F _C～W is established;

The lowest water level of the lake over the years is 16.0m, and the average water level for many years is 19.0m; according to the above calculation steps, according to the step size of 0.1m, the aquatic vegetation coverage value under 16.0-19.0m (16.0, 16.1, 16.2, 16.3...19.0) is calculated, Establish water level vegetation coverage relationship F _{C ~ W} as an equation: C = 5.1925W ² -204.57W + 2029.3.

1-7: Using the water level-vegetation coverage relationship, calculate the optimum ecological water level (W _germ ) in the germination period under a given vegetation coverage target (C _targ ). The given vegetation coverage target (C _targ ) is the lake management target;

Assuming that the current management target of the lake's aquatic vegetation is 30%, according to the water level vegetation coverage relationship F _C～W , it is concluded that the water level in the germination period should be kept at 18.0m, ie W _germ =18.0m.

Step 2: Calculation of the ecological water level (W _grow ) during the seedling growth period (April-May)

During the seedling growth period from April to May, the water level should be kept stable and rise slowly, and the increase should not exceed 0.4m per month. Therefore, the suitable range of the ecological water level in April is W _germ ~ W _germ +0.4m, and the suitable range of the ecological water level in May is W _germ ~ W _germ +0.8m;

In the case of aquatic vegetation coverage target of 30%, the suitable range of ecological water level in April is 18.0-18.4m, and the suitable range of ecological water level in May is 18.0-18.8m;

Step 3: Calculation of the ecological water level (W _disp ) during the growth and diffusion period (June-July)

In June, keep the water level stable and rise slowly, and the increase should not exceed 0.4m/month. The suitable range for the ecological water level is W _germ ~ W _germ + 1.2m; in July, the water level needs to rise, but the increase should not exceed the top of the emergent plants, that is, 0.5m Every month, so the suitable range of ecological water level in July is W _germ +(W _C -W _germ )/2～W _germ +2.5m; if (W _C -W _germ )/2≥2.5, it is W _germ +1.3m ~W _germ +2.5m;

In the case of aquatic vegetation coverage target of 30%, the suitable range of ecological water level in June is 18.0-19.2m; (W _C -W _germ )/2=(19.0-18.0)/2, which is 0.5, so the ecological water level in July The suitable range is 18.5~20.5m;

Step 4: Calculation of ecological water level (W _matu ) in mature period (August-September)

From August to September, the water level needs to rise to submerge the wet vegetation area, prevent terrestrial plant invasion and lake swamping, the low value of the ecological water level must be greater than or equal to the annual average water level (W _C ), and the highest value should not exceed the lake warning water level (W _warn ), so the suitable range of ecological water level in mature stage is W _C ~ W _warn ;

The warning water level of the lake is 20.5m, and the average water level for many years is 19.0m. In the case of aquatic vegetation coverage target of 30%, the suitable range of ecological water level in August is 19.0-20.5m, and the suitable range of ecological water level in September is 19.0-20.5m;

Step 5: Calculation of the ecological water level (W _seed ) during the seed propagation period (October-November)

The water level during the seed propagation period needs to be gradually reduced according to the natural water level fluctuation pattern. The water level in October remains the same as in July, and the water level in November remains the same as in June. The suitable range of ecological water level in October is W _germ +(W _C -W _germ )/2～W _germ +2.5m, if (W _C -W _germ )/2≥2.5, it is W _germ +1.3m～W _germ +2.5m; the suitable range of ecological water level in November is W _germ ~ W _germ +1.2m;

Under the condition that the aquatic vegetation coverage target is 30%, the suitable range of ecological water level in October is consistent with that in July, which is 18.5-20.5m; the suitable range of ecological water level in November is consistent with that in June, which is 18.0-19.2m;

Step 6: Calculation of the ecological water level (W _wint ) during the dormant period (December-January of the next year)

The lowest water level in the dormant period needs to be consistent with the germination period, and the optimum range of the highest water level should be consistent with the water level in May. The suitable range of ecological water level from December to next January is W _germ ~ W _germ +0.8m;

Under the condition that the target of aquatic vegetation coverage is 30%, the suitable range of ecological water level from December to next January is 18.0-18.8m.

Step 7: Lake ecological water level hydrograph (W _inte )

Connect the ecological water level values in each period to form the ecological water level process line under a given aquatic vegetation coverage target W _inte = W _germ + W _grow + W _disp + W _matu + W _seed + W _wint ; when the vegetation coverage target changes , recalculate the ecological water level process line according to the above calculation procedure.

Connecting the ranges of water levels in each period, the range of ecological water levels required for the lake's aquatic vegetation to reach 30% is shown in the table below.

month Ecological water level (m) January 18.0-18.8 February 18.0 March 18.0 April 18.0-18.4 May 18.0-18.8 June 18.0-19.2 July 18.5-20.5 August 19.0-20.5 September 19.0-20.5 October 18.5-20.5 November 18.0-19.2 December 18.0-18.8

Claims (1)

1. A lake ecological water level calculation method, the steps are as follows: Step 1: Calculation of the ecological water level in the germination period of 2-3 months: A. Find or establish the lake water level-area relationship F _A～W ; B. Calculate the germination area of hygrophytes and emergent plants at a given water level. The water level in this area ranges from W _give -0.2m to W _C . According to the relationship between water level and area, W _give -0.2m and W _C are respectively brought into F _A～W , calculate the difference between the two, the value of A _e at a given water level; C. Calculate the germination area of submerged plants. The water level in this area ranges from W _give -0.2m to W _give -2SD. According to the water level-area relationship, W _give -0.2m and W _give -2SD are respectively brought into F _{A to W} , to calculate the difference between the two, which is the A _s value at a given water level; D. Calculate the total area of the aquatic plant germination area, A _t =A _e +A _s ; E. Calculate the overall coverage of wet and emergent plants, submerged plants and aquatic plants at a given water level, the coverage of wet and emergent vegetation C _e = A _e /A _C × 100%; the coverage of submerged vegetation C _s =A _s /A _C ×100%; the overall coverage of aquatic plants C=A _t /A _C ×100%; F. According to the step length of 0.1m, repeat steps B~E, respectively calculate the total area and total coverage of the aquatic plant germination area under the given water level W _L , W _L +0.1m, W _L +0.2m...W _C , W _L For the lowest water level over the years, establish the water level-vegetation coverage relationship F _C～W ; G. Using the water level-vegetation coverage relationship, calculate the optimum ecological water level value in the germination period under the given vegetation coverage target, and the given vegetation coverage target is the lake management target; Step 2: Calculation of the ecological water level value from April to May during the seedling growth period: The water level during the seedling growth period from April to May is stable and rising, and the increase shall not exceed 0.4m per month. The ecological water level in April is W _germ ~ W _germ +0.4m, and the range of ecological water level in May is W _germ ~ W _germ +0.8m; Step 3: Calculation of the ecological water level in June-July during the growth and diffusion period: In June, the water level is stable and rising, and the increase shall not exceed 0.4m per month, and its ecological water level ranges from W _germ to W _germ +1.2m; in July, the water level rises, and the increase shall not exceed the top of emergent plants, that is, 0.5m per month. The range of ecological water level is W _germ +(W _C -W _germ )/2～W _germ +2.5m; Step 4: Calculation of the ecological water level in the mature period from August to September: The water level rises from August to September to submerge the wet vegetation area. The low value of the ecological water level is greater than or equal to the average water level for many years, and the highest value does not exceed the warning water level of the lake. The range of the ecological water level in the mature period is W _C ~ W _warn ; Step 5: Calculation of ecological water level during seed propagation period from October to November: During the seed propagation period, the water level gradually decreased according to the natural water level fluctuation pattern. The water level in October remained the same as in July, and the water level in November remained the same as in June. The ecological water level in October ranged from W _germ +(W _C -W _germ )/2～ W _germ +2.5m; the range of ecological water level in November is W _germ ~ W _germ +1.2m; Step 6: Calculation of ecological water level value from December to January of the next year during the dormant period: The lowest water level in the dormant period is consistent with the germination period, the highest water level range is consistent with the water level in May, and the ecological water level range from December to January of the next year is W _germ ~ W _germ +0.8m; Step 7: Lake ecological water level process line: Connect the ecological water level values in each period to form the ecological water level process line under a given aquatic vegetation coverage target W _inte = W _germ + W _grow + W _disp + W _matu + W _seed + W _wint ; when the vegetation coverage target changes, Recalculate the ecological water level process line according to the above calculation procedure; F _A～W is the lake water level-area relationship; A _C is the area corresponding to the average water level of the lake for many years, more than 25 years; W _C is the average water level of the lake for many years; W _L is the lowest water level of the lake since the water level record; W _give is the given water level; W _warn is the warning water level of the lake; SD is the minimum monthly transparency of lake water from March to June; A _e is the distribution area of wet plants and emergent plants; A _s is the distribution area of submerged plants; A _t is the total area of aquatic plant distribution; C _e is the coverage of wet and emergent vegetation; C _s is the coverage of submerged vegetation; C is the total coverage of aquatic plants; C _targ is the target of given aquatic vegetation coverage; F _{C ~W} is the relationship between aquatic vegetation coverage and water level; W _germ is the ecological water level value in the germination period; W _grow is the ecological water level value in the seedling period; W _disp is the ecological water level value in the growth and diffusion period; W _matu is the ecological water level value in the mature period; _seed is the ecological water level value during the seed propagation period; W _wint is the ecological water level value during the dormant period; W _inte is the ecological water level process line under a given vegetation coverage target.