CN112288183A

CN112288183A - Lake classification staged drought limit water level determination method and system

Info

Publication number: CN112288183A
Application number: CN202011257923.7A
Authority: CN
Inventors: 周建中; 武慧铃; 刘志明; 王权森; 贾本军; 娄思静; 田梦琦; 黄伟; 黄雯; 效文静
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2020-11-12
Filing date: 2020-11-12
Publication date: 2021-01-29
Anticipated expiration: 2040-11-12
Also published as: CN112288183B

Abstract

The invention provides a method and a system for determining a lake classification stage drought limit water level, which comprises the following steps: determining the lake ecological water level of each month under different incoming water frequencies based on a lake ecological water level analysis method; calculating the lake external water demand per month under different incoming water frequencies based on the predicted economic and social development indexes and the predicted water quota; determining lake-entering flow of each lake in each month under different incoming water frequencies based on the long-term flow data of the lake-entering port or the long-term flow data of the lake-exiting port; determining the lake surface evapotranspiration amount of each month under different incoming water frequencies based on the measurement data of the lake evaporation sites or the solar radiation intensity data and the meteorological data; determining the drought limit water level of each month under different incoming water frequencies based on the ecological water level of each month under different incoming water frequencies, the demand of water outside the lake, the inflow flow of the lake into the lake and the evapotranspiration amount of the lake surface; and (4) carrying out staging by adopting a Fisher optimal segmentation method, and further determining the drought limit water level of each stage under different incoming water frequencies. The invention can determine the lake drought limit water level by stages.

Description

Lake classification staged drought limit water level determination method and system

Technical Field

The invention belongs to the field of water resource management drought resistance, and particularly relates to a method and a system for determining a lake classified and staged drought limit water level.

Background

In the drought-resistant field, drought characteristic indexes such as water level (flow) and the like which can be used for drought-resistant emergency management work are not established in China so far, and the drought-resistant emergency management work such as hydrologic drought reporting, drought early warning, drought-resistant consultation, emergency response, water quantity scheduling and the like often lacks scientific basis, so that the phenomenon that the decision-making opportunity of drought-resistant disaster-reducing commanding is inaccurate or the emergency response is excessive exists, and the scientific and orderly development of the drought-resistant work is influenced to a certain extent. In a drought limit water level (flow) determination method formulated by the water conservancy department in 2011, a concept of drought limit water level is proposed for the first time, but a drought limit water level determination method is not formulated specifically for lakes, and only one drought limit water level is adopted as an drought early warning index all year round according to a river and reservoir drought limit water level determination method, so that grading and staging standards are lacked, and certain limitations and operability are existed.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide a method and a system for determining the classified and staged drought limit water level of a lake, and aims to solve the problems that the existing method for determining the drought limit water level of rivers and reservoirs adopts the only drought limit water level as a drought early warning index all year round, and has the defects of lack of classification and staging standards, certain limitation and operability.

In order to achieve the above object, in a first aspect, the present invention provides a method for determining a water level limit of a lake in a staged and staged manner, comprising the following steps:

determining the lake ecological water level of each month under different incoming water frequencies based on four lake ecological water level analysis methods; the four lake ecological water level analysis methods comprise the following steps: hydrological frequency analysis, lake morphology analysis, biospace method and worst month mean water level method;

calculating the lake external water demand in each month under different incoming water frequencies based on the predicted economic and social development indexes and the predicted water quota;

determining lake-in flow of each month under different incoming water frequencies based on long-term flow observation data of the lake-in port or long-term flow observation data of the lake-out port;

determining the lake surface evapotranspiration amount of each month under different incoming water frequencies based on the measurement data of the lake evaporation sites or the solar radiation intensity data and the meteorological data;

determining the lake drought limit water level of each month under different incoming water frequencies based on the lake ecological water level of each month under different incoming water frequencies, the lake external water demand of each month under different incoming water frequencies, the lake inflow flow of each month under different incoming water frequencies and the lake surface evapotranspiration amount of each month under different incoming water frequencies;

according to the method, months in a hydrological year are staged by adopting a Fisher optimal segmentation method in combination with the annual average monthly precipitation of a watershed, the annual average monthly inflow of a lake, the annual average monthly water level of the lake and the annual average monthly water demand of the lake, each stage comprises at least one month, and the lake drought limit water level of each stage under different incoming water frequencies is determined based on the lake drought limit water level of each month included in each stage under different incoming water frequencies.

It can be understood that the classified drought limit water level of the lake refers to the drought limit water level under different incoming water frequencies. The frequency of each incoming water is one level.

In an optional embodiment, the determining the lake ecological water level in each month under different incoming water frequencies based on four lake ecological water level analysis methods specifically includes:

H_emin＝max(H_min1，H_min2，H_min3，H_min4)

in the formula, H_eminIs the lake ecological water level under the incoming water frequency P; h_min1The lowest ecological water level calculated by a hydrological frequency analysis method under the incoming water frequency P; h_min2The lowest ecological water level calculated by a lake morphological analysis method under the incoming water frequency P; h_min3Minimum ecological water level, H, calculated for the biospace method at the incoming water frequency P_min4The lowest ecological water level is calculated by a worst month average water level method under the incoming water frequency P; p75% or P95%.

In an alternative embodiment, the calculating the lake external water demand per month under different incoming water frequencies based on the predicted economic and social development index and the predicted water usage quota specifically comprises:

W_ul,i＝0.365×P_ul,i×m_ul,i

W_rl,i＝0.365×P_rl,i×m_rl,i

W_al,i＝0.365×P_al,i×m_al,i

W_as,i＝0.365×P_as,i×m_as,i

W_F,i＝G_i×m_F,i×(1-c_i)

W_FP,i＝A_FP,i×m_FP,i

in the formula, W_ul,i、W_rl,i、W_al,i、W_as,i、W_F,i、W_LI,i、W_FI,i、W_GI,iAnd W_FP,iSequentially representing the water requirements of planned horizontal years of urban life, rural life, large livestock, small livestock, industrial added value, farmland irrigation, forest and fruit land irrigation, grassland irrigation and fishpond culture; p_ul,i、P_rl,i、P_al,i、P_as,i、G_i、A_LI,i、A_FI,i、A_GI,i、A_FP,iRespectively representing planned urban population, rural population, large livestock head number, small livestock head number, industrial added value, farmland irrigation area, forest and fruit land irrigation area, grassland irrigation area and fishpond area in the horizontal year; m is_ul,i、m_rl,i、m_al,i、m_as,i、m_F,i、m_LI,i、m_FI,i、m_GI,i、m_FP,iRespectively representing the water quota corresponding to planned horizontal years of urban life, rural life, large livestock, small livestock, industrial added value, farmland irrigation, forest and fruit land irrigation, grassland irrigation and fishpond culture; c. C_iRepresenting the reuse rate of industrial water; eta_iRepresenting an irrigation water effective utilization coefficient; i represents year.

In an optional embodiment, the lake-in flow per month at different incoming water frequencies is determined based on the long-term flow observation data of the lake-in port or the long-term flow observation data of the lake-out port; the method specifically comprises the following steps:

for the lake which is provided with the hydrological station at the lake inlet and has long-term flow observation data, taking the measured data of the controllable hydrological station close to the lake as the lake inlet flow of the lake; or

For lakes with hydrological stations at lake outlets and long-term flow observation data, the lake inlet flow is calculated according to the actual measurement data of the water level of the lake and the lake water level-volume curve through the water quantity balance principle: i is_Into-I_{Go out}＝ΔW_{Storage tank}＝V(Z₂)-V(Z₁) (ii) a In the formula I_IntoThe lake water amount of the lake in the period I_{Go out}Is the lake outlet water volume of the lake in the period of time, delta W_{Storage tank}For the change of the water storage capacity of the lake in the period, V () is a lake water level-volume conversion function for converting the water level into the volume, Z₂、Z₁Water levels at the end of a lake period and at the beginning of the lake period respectively; according to I_Into-I_{Go out}Calculating the lake water inflow amount of the lake in a time period, and converting to obtain the lake inflow flow of the lake; or

Under the condition that actually measured data of the lake inflow flow is incomplete, the hydrologic model simulates inflow of the lake to perform interpolation extension so as to obtain complete long-sequence inflow flow data, and the lake inflow flow is determined based on the complete long-sequence inflow flow data.

In an optional embodiment, the lake surface evapotranspiration amount of each month under different incoming water frequency is determined based on the measurement data of the lake evaporation site or the solar radiation intensity data and the meteorological data; the method specifically comprises the following steps:

for the lake with the evaporation observation site in the drainage basin, taking the measured data of the evaporation site close to the lake as the evaporation capacity of the lake surface of the lake; or

Solar irradiance is obtained based on satellite remote sensing data, daily average air temperature, dew point temperature and wind speed data are obtained through meteorological data, and the evapotranspiration quantity E of the lake surface is calculated by using a Liacle formula:

E＝(0.015+0.00042Ta+10^-6h)*(0.8Q_s-40+2.5×U₂F(Ta-Td))

wherein Ta represents the daily average temperature, Td represents the dew point temperature, Qs represents the solar irradiance, U₂Representing a wind speed of 2m, h an elevation, and F a coefficient related to the lake height.

In an optional embodiment, the determining the lake drought limit water level in each month under different incoming water frequencies specifically includes:

for an active lake with a water supply function, adding lake external water on the basis of the lowest ecological water level, and calculating by considering lake runoff and lake evaporation, wherein the drought limit water level is calculated as follows:

when (V)_{In need of water}-V_{Runoff flow}+V_{Evaporation of})>When 0, Z ═ Z (V (H)_emin)+V_{In need of water}-V_{Runoff flow}+V_{Evaporation of})；

When (V)_{In need of water}-V_{Runoff flow}+V_{Evaporation of}) When the ratio is less than or equal to 0, Z is equal to H_emin；

In the formula, Z is the drought limit water level under the incoming water frequency P; v (H)_emin) The volume of the converted lake ecological water level calculated under the incoming water frequency P is obtained; v_{In need of water}Planning the demand of external water of the lake in the horizontal year under the frequency P of the incoming water; v_{Runoff flow}The lake inflow flow rate under the incoming water frequency P; v_{Evaporation of}The evaporation capacity V of the lake surface under the incoming water frequency P_{Evaporation of}The evaporation capacity of the lake surface is multiplied by the area of the lake surface; z () is a lake volume-water level conversion function for converting the volume into a corresponding water level; when P is 75%, Z is the drought police water level; when P is 95%, Z is the drought protection water level;

for an active lake without a water supply function, the demand of water outside the lake is not considered, only the ecological water level is considered, and the drought limit water level is calculated as follows:

when (V)_{Evaporation of}-V_{Runoff flow})>When 0, Z ═ Z (V (H)_emin)-V_{Runoff flow}+V_{Evaporation of})；

When (V)_{Evaporation of}-V_{Runoff flow}) When the ratio is less than or equal to 0, Z is equal to H_emin。

In a second aspect, the invention provides a lake classification staging drought limit water level determination system, which comprises:

the ecological water level determining unit is used for determining the lake ecological water level of each month under different incoming water frequencies based on four lake ecological water level analysis methods; the four lake ecological water level analysis methods comprise the following steps: hydrological frequency analysis, lake morphology analysis, biospace method and worst month mean water level method;

the external water demand determining unit is used for calculating the external lake water demand of each month under different incoming water frequencies based on the predicted economic and social development indexes and the predicted water quota;

the lake-entering flow determining unit is used for determining lake-entering flow of each month under different incoming water frequencies based on long-term flow observation data of the lake-entering port or long-term flow observation data of the lake-exiting port;

the lake surface evaporation determining unit is used for determining the lake surface evaporation amount of each month under different incoming water frequencies based on the measurement data of the lake evaporation sites or the solar radiation intensity data and the meteorological data;

the drought limit water level grading calculation unit is used for calculating the lake drought limit water level in each month under different incoming water frequencies based on the lake ecological water level in each month under different incoming water frequencies, the lake external water demand in each month under different incoming water frequencies, the lake incoming flow in each month under different incoming water frequencies and the lake surface evaporation amount in each month under different incoming water frequencies;

the drought limit water level grading and staging determination unit is used for staging months in a hydrological year by adopting a Fisher optimal segmentation method in combination with the multi-year average monthly precipitation of a drainage basin, the multi-year average monthly inflow of a lake, the multi-year average monthly water level of the lake and the multi-year average monthly water demand of the lake, wherein each stage comprises at least one month, and the drought limit water level of the lake in each stage under different incoming water frequencies is determined based on the drought limit water level of the lake in each month in each stage under different incoming water frequencies.

In an alternative embodiment, the external water demand determination unit calculates the lake external water demand per month under different incoming water frequencies based on the predicted economic and social development index and the predicted water quota, specifically:

W_ul,i＝0.365×P_ul,i×m_ul,i

W_rl,i＝0.365×P_rl,i×m_rl,i

W_al,i＝0.365×P_al,i×m_al,i

W_as,i＝0.365×P_as,i×m_as,i

W_F,i＝G_i×m_F,i×(1-c_i)

W_FP,i＝A_FP,i×m_FP,i

In an optional embodiment, the lake inflow flow determination unit determines the lake inflow flow per month at different incoming water frequencies based on long-term flow observation data at the lake-entry port or long-term flow observation data at the lake-exit port; the method specifically comprises the following steps:

In an optional embodiment, the drought limit water level classification calculation unit calculates the lake drought limit water level of each month under different incoming water frequencies, specifically: for an active lake with a water supply function, adding lake external water on the basis of the lowest ecological water level, and calculating by considering lake runoff and lake evaporation, wherein the drought limit water level is calculated as follows:

Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

the invention provides a method and a system for determining a lake classified and staged drought limit water level, which comprehensively consider the differences of production, living and ecological water demand priority and guarantee levels in different periods and combine the lake water incoming characteristics to formulate the classification and staged standards of the lake drought limit water level; the invention provides a set of general drought limit water level making rules aiming at different lake types, comprising a drought limit water level calculation method, a grading and staging correction method and a rationality inspection method.

Drawings

FIG. 1 is a flow chart of a method for determining the graded and staged drought limit level of a lake according to the present invention;

FIG. 2 is a frame diagram of a method for determining the drought-limited water level of a natural lake according to the present invention;

FIG. 3 is a flow chart of the lake function and its drought-limited water level guarantee target analysis provided by the present invention;

fig. 4 is an ecological water bitmap of the hong lake provided by the present invention at a frequency of P75% and P95%;

FIG. 5 is a diagram of the early warning of drought stage of Honghu provided by the present invention;

FIG. 6 is a monthly drought limit level and phased drought limit level bitmap after flood lake correction provided by the present invention;

FIG. 7 is a schematic diagram of a system for determining the classified and staged drought limit level of a lake according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The invention aims to provide a method and a system for determining a lake classified and staged drought limit level, which comprehensively consider the differences of production, life and ecological water demand priority and guarantee levels in different periods, combine the characteristics of lake water coming, formulate the classification and staging standards of the lake drought limit level, provide a set of general drought limit level formulation rules aiming at different lake types, and provide scientific basis and technical support for drought defense command decision.

FIG. 1 is a flow chart of a method for determining the graded and staged drought limit level of a lake according to the present invention; as shown in fig. 1, the method comprises the following steps:

s101, determining the lake ecological water level of each month under different incoming water frequencies based on four lake ecological water level analysis methods; the four lake ecological water level analysis methods comprise the following steps: hydrological frequency analysis, lake morphology analysis, biospace method and worst month mean water level method;

s102, calculating the lake external water demand of each month under different incoming water frequencies based on the predicted economic and social development indexes and the predicted water quota;

s103, determining the lake-in flow of each month under different incoming water frequencies based on the long-term flow observation data of the lake-in port or the long-term flow observation data of the lake-out port;

s104, determining the lake surface evapotranspiration amount of each month under different incoming water frequencies based on the measurement data of the lake evaporation sites or the solar radiation intensity data and the meteorological data;

s105, determining the lake drought limit water level of each month under different incoming water frequencies based on the lake ecological water level of each month under different incoming water frequencies, the lake external water demand of each month under different incoming water frequencies, the lake-in flow of each month under different incoming water frequencies and the lake surface evaporation amount of each month under different incoming water frequencies;

s106, combining the annual average monthly precipitation of the watershed, the perennial average monthly inflow of the lake, the perennial average monthly water level of the lake and the perennial average monthly water demand of the lake, carrying out stage division on months in a hydrological year by adopting a Fisher optimal segmentation method, wherein each stage comprises at least one month, and determining the lake drought limit water level of each stage under different incoming water frequencies based on the lake drought limit water level of each month included in each stage under different incoming water frequencies.

In a more specific embodiment, as shown in fig. 2, the specific technical solution of the method for determining the graded and staged drought limit level of a lake provided by the present invention is as follows:

step one, classification of lake drought limit water level

According to the definition of the drought limit water level in the drought limit water level (flow rate) determination method, the drought limit water level is divided into two grades of a drought police water level and a drought water retention water level, and the two grades are respectively defined as the water levels capable of ensuring the water safety of lakes in general arid years (the water frequency is 75%) and in extreme withered years (the water frequency is 95%).

Secondly, lake function positioning and lake type division;

and developing lake function investigation, objectively and accurately positioning the functions of the lake on the basis of research and evaluation of the lake function investigation, and determining the guarantee requirement of the lake ecosystem on the water level of the lake and the water demand of guarantee targets corresponding to other functions of the lake.

According to the supply conditions of the water from the lakes, the lakes are divided into two types of active lakes and passive lakes, whether the active lakes have the water supply function or not is divided into the lakes with the water supply function and the lakes without the water supply function, and the drought limit water level guarantee targets of the lakes of different types are respectively analyzed on the basis.

Step three, calculating ecological water level of the lake and water demand outside the lake;

(1) lake ecological water level calculation method

According to the basic principle determined by the 'river and lake ecological water demand assessment guide rule', the ecological water level of the lake under the frequency of 75% and 95% is respectively calculated by combining the specific situation and the basic data situation of the lake by adopting a hydrological frequency analysis method, a lake form analysis method, a biospace method and a worst month average water level method.

A hydrological frequency analysis method: according to the actually measured data sequence (no less than 30 years) of the lake water level station, hydrologic frequency analysis and calculation are carried out on the average water level of each month, P-III type theoretical curve wiring is selected, the design result of the average water level of each month under different hydrologic frequencies of the lake is obtained, and the average water level of each month under the frequencies of P75% and P95% is obtained according to the result.

A lake form analysis method: adopting actually measured lake water level and lake area data to establish a relation function of the lake surface area change rate and the water level, wherein the lake surface area change rate is a first derivative of the relation function of the lake surface area and the water level, and the water level corresponding to the maximum value of the lake surface area change rate is the lowest ecological water level and can be expressed as follows:

wherein F is the lake area (m)²) (ii) a H is lake level (m); h_min2The lowest water level (m) of the lake in natural condition for many years; a and b are respectively positive numbers which are smaller than the amplitude of the lake water level.

③ the biospace method: according to the type of organisms most sensitive to the lake water level, determining the minimum space (water depth) required by the organisms for living and breeding, wherein the minimum water level is the required minimum ecological water level of the lake, and the calculation formula is as follows:

H_min3＝H₀+H_{most sensitive organisms} (2)

In the formula, H₀Is the average elevation of the lake bottom; h_{Most sensitive organisms}The fish is generally selected as the most sensitive organism for the minimum water depth required for the most sensitive organism to survive.

Fourthly, the witherest moon average water level method: the natural lowest water level is the lower limit of the water level threshold of the ecological system, and the average water level in the worst month can be taken as the lowest ecological water level.

(2) Determining ecological water level of lake

Because the theory and the side emphasis point of each ecological water level calculation method are different, the calculation results are different, and in consideration of the lake ecological water use safety, the outsourced maximum values of the calculation results of the several ecological water levels in the step (1) are selected as the ecological water levels, and the calculation method is as follows:

H_emin＝max(H_min1，H_min2，H_min3，H_min4) (3)

in the formula, H_eminIs the lake ecological water level under the frequency of 75 percent (or 95 percent); h_min1The lowest ecological water level is calculated by a hydrological frequency analysis method under the frequency of 75 percent (or 95 percent); h_min2The lowest ecological water level calculated by a lake morphological analysis method; h_min3Minimum ecological water level, H, calculated by the biospace method_min4The lowest ecological water level is calculated by the average water level method of the worst month.

(3) Predicting economic and social development indexes, wherein the economic and social development prediction indexes mainly comprise: population, livestock, total industrial output value, effective irrigation area of farmland, irrigation water utilization coefficient and irrigation scale of forestry, grazing and fishery.

Predicting population indexes:

general population:

P_i＝P₀(1+ε_i)ⁱ (4)

urban population:

P_1i＝P₁₀(1+ε_1i)ⁱ (5)

rural population:

P_2i＝P₂₀(1+ε_2i)ⁱ (6)

in the formula: p_i、P_1i、P_2iRespectively planning general population of each county and district, planning urban population and rural population in horizontal year; p₀、P₁₀、P₂₀Are respectively asThe general population of the benchmark year, the urban population and the rural population. Epsilon_i，ε_1i，ε_2iThe average annual growth rates of the general population, the urban population and the rural population in i years are respectively.

Secondly, livestock quantity prediction:

big livestock:

QM_i＝QM₀(1+a_m)ⁱ (7)

small livestock:

QN_i＝QN₀(1+a_n)ⁱ (8)

in the formula: QM_iAnd QN_iRespectively planning the number of heads of big livestock and small livestock in the horizontal year, QM₀And QN₀The total number of the stock columns at the end of the year of the big livestock and the small livestock in the reference year, a_m、a_nThe average annual growth rate of big livestock and small livestock in i years respectively.

Predicting the total industrial output value:

G_i＝G₀(1+b_i)ⁱ (9)

in the formula: g_iAnd G₀Respectively the planned horizontal year and the reference year total industrial output value, b_iThe average annual growth rate of the total industrial yield value in i years of the horizontal year is planned.

Fourthly, effective irrigation area of farmland:

A_{irrigation i}＝A_{Plough i}*ζ_i (10)

In the formula: a. the_{Irrigation i}To plan the effective irrigation area of the horizontal year farmland, A_{Plough i}Zeta to plan the horizontal annual cultivation area_iTo plan the effective irrigation rate of the farmland in the horizontal year.

Water scale for forest, grazing and fishery:

A_{forest land i}＝A_{Forest land 0}*(1+f_{Forest land})ⁱ (11)

A_{Grassland i}＝A_{Meadow 0}*(1+f_{Grass land})ⁱ (12)

A_{Fish pond i}＝A_{Fishpond 0}*(1+f_{Fish pond})ⁱ (13)

In the formula: a. the_{Forest land i}、A_{Grassland i}、A_{Fish pond i}Planning horizontal annual woodland, grassland and fish pond areas, respectively, A_{Forest land 0}、A_{Meadow 0}、A_{Fishpond 0}Respectively the area of the forest land, the grassland and the fish pond in the reference year f_{Forest land}、f_{Grass land}、f_{Fish pond}The average annual growth rates of the areas of the woodland, the grassland and the fish pond in i years respectively.

(4) Predicting water rate changes including domestic water rate prediction, industrial water rate prediction, agricultural irrigation water rate prediction, and forestry, fisheries water rate prediction.

Predicting the quota of the domestic water: the standard of the domestic water quota is determined according to the 'water quota for industry' and 'comprehensive planning of water resources' issued by xx provinces.

And secondly, forecasting the quota of the industrial water: the method adopts a repeated utilization rate and an industrial technology progress coefficient method, and the relational expression is as follows:

(1-k₁)/(1-k₂)＝(1-a)ⁿ(q₁/q₂) (14)

in the formula: q. q.s₁、q₂Respectively taking water amount for ten thousand yuan total value of a reference year and a planned horizontal year; k is a radical of₁、k₂The repeated utilization rates of the reference year and the planned horizontal year are respectively; a is a technical progress coefficient; n is the number of years from the reference year to the planned horizontal year.

Third, agricultural irrigation water quota prediction: reckoning by using 'xx agricultural water quota'.

Fourthly, forecasting the water quota for the forest, grazing and fishery: because the water quota data of the forestry, animal husbandry and fishery are few and the water consumption is not large, the existing water quota value is not used for prediction.

(5) Forecasting lake external water demand

And on the basis of the predicted economic and social development indexes and water quota of the planning level year, calculating the lake external water demand in a classified manner. According to the classification of the drought limit water level, the 75% water inflow frequency and the 95% water inflow frequency are calculated respectively.

W_ul,i＝0.365×P_ul,i×m_ul,i (15)

W_rl,i＝0.365×P_rl,i×m_rl,i (16)

W_al,i＝0.365×P_al,i×m_al,i (17)

W_as,i＝0.365×P_as,i×m_as,i (18)

W_F,i＝G_i×m_F,i×(1-c_i) (19)

W_FP,i＝A_FP,i×m_FP,i (23)

In the formula, W_ul,i、W_rl,i、W_al,i、W_as,i、W_F,i、W_LI,i、W_FI,i、W_GI,iAnd W_FP,iSequentially representing the planned horizontal urban life, rural life, large livestock, small livestock, industrial added value, farmland irrigation, forest and fruit land irrigation, grassland irrigation and fishpond culture water demand; p_ul,i、P_rl,i、P_al,i、P_as,i、G_i、A_LI,i、A_FI,i、A_GI,i、A_FP,iRespectively representing the planned horizontal annual urban population, rural population, large livestock head number, small livestock head number, industrial added value, farmland irrigation area, forest and fruit land irrigation area, grassland irrigation area and fishpond area; m is_ul,i、m_rl,i、m_al,i、m_as,i、m_F,i、m_LI,i、m_FI,i、m_GI,i、m_FP,iRespectively representing the water use quota corresponding to the planning of horizontal annual urban life, rural life, large livestock, small livestock, industrial added value, farmland irrigation, forest and fruit land irrigation, grassland irrigation and fishpond culture; c. C_iRepresenting the reuse rate of industrial water; eta_iRepresenting an irrigation water effective utilization coefficient; i represents year.

Step four, calculating the lake entering flow and evapotranspiration of the lake;

(1) calculating the flow of lake entering the lake

According to the existing basic data condition of the lake, different methods are adopted to calculate the lake-entering flow.

Firstly, actually measuring data: for the lake with the hydrological station at the lake-entrance port and long-term flow observation data, the measured data of the hydrological station close to the lake can be used as the lake-entrance flow of the lake.

Water balance method: for lakes with hydrological stations at the exit of the lake and long-term flow observation data (no hydrological station is arranged at the exit of the lake or long-sequence flow actual measurement data of the hydrological stations at the exit of the lake are not arranged), the flow of the lake entering can be deduced according to the actual measurement data of the water level of the lake and the water level-volume curve of the lake by the water balance principle.

In a certain period of time, the lake water balance equation is as follows:

I_into-I_{Go out}＝ΔW_{Storage tank}＝V(Z₂)-V(Z₁) (24)

In the formula I_IntoThe lake water amount of the lake in the period I_{Go out}Is the lake outlet water volume of the lake in the period of time, delta W_{Storage tank}For the change of the water storage capacity of the lake in the period, V () is a water level-volume conversion function of the lake, Z₂、Z₁Respectively the water levels at the end of the lake period and at the beginning of the lake period.

And (4) calculating the lake water inflow amount of the lake in the time period according to the formula (24), and converting to obtain the lake inflow flow of the lake.

③ hydrological model method: under the condition that the actually measured data sequence of the lake-in-lake flow is short or the data is discontinuous, the inflow of the lake can be simulated through the hydrological model to carry out interpolation and extension. The method comprises the steps of dividing the lake confluence basin, dividing actual runoff data into a rate period and a verification period based on actual measurement data conditions of the basin, simulating the production confluence process of the basin by adopting a proper hydrological model (lumped type, distributed type or artificial intelligence and the like), and inputting forecast factor data of a lack-of-measurement period into the model when the accuracy of the hydrological model meets requirements so as to obtain complete long-sequence lake-entering flow data.

(2) Calculation of evaporation from lake surface

Firstly, an actual data measurement method: for the lake with the evaporation observation station in the drainage basin, the actually measured data of the evaporation station close to the lake can be used as the lake surface evaporation and emission of the lake.

Secondly, calculating the evapotranspiration amount of the lake based on MODIS satellite remote sensing data.

Firstly, obtaining solar irradiance through an MCD18A1 product, then obtaining daily average air temperature, dew point temperature and wind speed data through a China meteorological office, and finally calculating lake evapotranspiration E by using a Liacre formula:

E＝(0.015+0.00042Ta+10^-6h)*(0.8Q_s-40+2.5×U₂F(Ta-Td)) (25)

Step five, calculating the drought limit water level of the lake;

(1) calculating the water level of the drought limit of the active lake

Firstly, a lake with a water supply function: the lake external water is superposed on the basis of the lowest ecological water level, and the lake runoff and the lake evaporation are considered for calculation, wherein the formula is as follows:

Z＝Z(V(H_emin)+V_{in need of water}-V_{Runoff flow}+V_{Evaporation of})((V_{In need of water}-V_{Runoff flow}+V_{Evaporation of})>0) (26)

Z＝H_emin((V_{In need of water}-V_{Runoff flow}+V_{Evaporation of})<0) (27)

Wherein Z is dry police water level (P is 75%) or dry keep water level (P is 95%); h_eminThe calculated lake ecological water level is calculated under the frequency that P is 75% or P is 95%; v () is the lake level-volume transfer function, V (H)_emin) Corresponding to the volume of the function converted for the ecological water level of the lake; v_{In need of water}Planning the demand of external water of the horizontal lake under the frequency of 75 percent or 95 percent of P; v_{Runoff flow}The runoff of the lake is controlled at the frequency of 75 percent or 95 percent; v_{Evaporation of}Is lake surface evaporation at a frequency of P75% or P95%, V_{Evaporation of}E × lake surface area; z () is a lake volume-water level conversion function.

② no water supply function lake: considering only the ecological water level without considering the demand of water outside the lake, the drought limit water level is calculated as follows:

Z＝Z(V(H_emin)-V_{runoff flow}+V_{Evaporation of})((V_{Evaporation of}-V_{Runoff flow})>0) (28)

Z＝H_emin((V_{Evaporation of}-V_{Runoff flow})<0) (29)

Wherein Z is dry police water level (P is 75%) or dry keep water level (P is 95%); h_eminThe calculated lake ecological water level is calculated under the frequency that P is 75% or P is 95%; v_{Runoff flow}The runoff of the lake is controlled at the frequency of 75 percent or 95 percent; v_{Evaporation of}The frequency of evaporation of lake surface is 75% or 95%.

(2) Because the passive lake is only supplied by rainfall and fissure water, the water storage capacity is not large, the regulation and storage function is weak, most passive lakes are positioned in unmanned areas, the drought limit water level is generally not required to be set, and the specific analysis on the drought limit water level calculation is not carried out.

Step six, carrying out lake drought water level limiting and staging;

different from the flood limit water level which is mainly subjected to stage division by short-term storm runoff characteristics, the drought limit water level stage division needs to consider not only the water inflow characteristics of lakes, but also the water demand characteristics of different guarantee targets.

The Fisher optimal segmentation method is a method for clustering ordered samples, and has the characteristics of considering multi-index factors, meeting the time sequence and determining the number of stages.

Comprehensively considering the annual average monthly rainfall of the drainage basin, the annual average monthly inflow rate of the lake, the annual average monthly water level and the annual average monthly water demand, and carrying out lake drought limit water level classification according to hydrological years by adopting a Fisher optimal segmentation method.

Seventhly, correcting and determining the drought limit water level of the lake;

the lake drought limit water level calculated according to the formula does not necessarily meet the requirements, and the lake drought limit water level needs to be corrected and finally determined according to the lake water quality protection requirements, the characteristic water level and the drought early warning staging in sequence.

(1) Correcting according to the requirements of water quality protection of lakes

According to the 'calculation regulation of the pollutant carrying capacity of a water area', the pollutant carrying capacity of lakes at a specified water level is calculated, and the calculation formula is as follows:

K＝10.3Q^-0.49 (31)

in the formula: m is the lake pollutant carrying capacity; c_sThe target concentration of water quality; c₀The concentration of pollutants at the lake inlet of the lake; k is the comprehensive attenuation coefficient of pollutants; phi is a diffusion angle; h is_LSubstituting the lake surface area S and the lake capacity V corresponding to the drought limiting water level into h for the average water depth of the lake in the expansion area_LCalculating as V/S; r is the distance from the outer boundary of the water area to a river sewage outlet; q_pThe discharge amount of waste water and the discharge amount Q of the waste water are the lake-entering flow.

And calculating whether the lake pollutant carrying capacity meets the requirement of water quality protection in the planned horizontal year. If the calculated lake drought limit water level meets the requirement, the calculated lake drought limit water level does not need to be corrected, if the calculated lake drought limit water level does not meet the requirement, the lake drought limit water level can be properly increased to be repeatedly calculated until the requirement is met, or more strict waste water discharge reduction measures are taken to protect the lake water quality; it should be noted that the higher the drought limit water level of the lake, the larger the dirt holding capacity of the lake, the fixed value of the discharge capacity of the lake, the raising of the drought limit water level can improve the dirt holding capacity of the lake to enable the water quality to meet the requirement, and the unchanged drought limit water level can reduce the discharge capacity to enable the water quality to meet the requirement.

(2) Correcting according to lake characteristic water level

The lake drought limit water level meets the requirements of lake characteristic water levels: firstly, the drought water limit level is not higher than the flood water limit level; secondly, the drought limit water level is not lower than the navigation water level; and thirdly, the drought protection water level is not higher than the drought police water level.

(3) Correcting according to early warning stages of lake drought

According to the lake drought early warning stage result, taking the maximum value of a plurality of monthly drought limit water levels in the same drought early warning stage as the staged drought limit water level.

Step eight, checking the reasonability of the lake drought limit water level;

(1) adopting the water storage amount distance percentage as a hydrological drought index for reasonable analysis of the drought limit water level of the lake, and judging the drought degree of the lake in the historical years according to the calculation result, wherein the calculation formula is as follows:

I_k＝[(S-S₀)/S₀]×100％ (32)

wherein S is the current lake water storage capacity, S₀The water storage capacity of years in the same period. When I is_kWhen the drought is in the range of-10% to-30%, the drought is mild drought; when I is_kModerate drought occurs when the drought is in the range of-31% to-50%; when I is_kSevere drought when the drought is in the range of-51% to-80%; when I is_kWhen the percentage is less than-80%, the drought is very big.

(2) Comparing the drought limit water level with the historical water level, and when the historical water level is lower than the contemporaneous drought limit water level, considering that drought occurs in the period; and when the historical water level is higher than the drought limit water level in the same period, the period is considered to have no drought.

(3) And (3) counting the consistent percentage of the drought degree in the time period judged by the hydrological drought index and the drought limit water level in the time period judged by the drought limit water level, checking the early warning capability of the drought limit water level on different drought degrees, and evaluating whether the early warning capability can meet the early warning requirement of the drought.

In a more specific embodiment, the present invention is embodied in a lake hong to verify the effect of the present invention. The specific technical scheme is as follows:

step one, classification of lake drought limit water level

Secondly, lake function positioning and lake type division;

as shown in fig. 3, on the basis of research, evaluation and analysis of functions of the lagoon, the main functions and the secondary functions of the lagoon are further located, and the guarantee requirements of the lagoon ecosystem on the water level of the lagoon and the guarantee targets corresponding to the functions of the lagoon are determined. The lake function survey contents comprise lake ecological environment and economic characteristics thereof, lake functions and resource utilization status situations thereof. According to the water supply conditions of lakes, the lakes are divided into active lakes and passive lakes, the active lakes are divided into lakes with water supply functions and lakes without water supply functions according to the existence of water supply, and the drought limit water level guarantee targets of the lakes of different types are analyzed respectively. The selected test point lake is a lake with an active water supply function. The test point Honghu selected in the research is investigated and researched, only the ecological environment target needs to be ensured, and the water level target of shipping, fishery and entertainment projects is not considered.

Step three, calculating the lowest ecological water level of the lake and the demand of water outside the lake;

(1) according to the actual measurement data sequence of the water level station of the water level of the dredging nozzle of the flood lake (1962-.

(2) Through the latest measured flood lake and lake level Z and lake area F data (the 'one lake one survey' data in 2012) by the Jingzhou city hydrology office in 2012, a relation curve of the lake level Z and the lake surface area change rate dF/dZ is constructed, the water level corresponding to the maximum value of the relation curve of the lake surface area change rate is 23.20m, the relation curve belongs to a lower water level, and therefore the ecological water level of the flood lake is 23.20 m.

(3) The fish have special effect on the lake ecosystem and are most sensitive to low water levels. The ecological water level of the fish can be considered to be satisfied, and the ecological water level of other types of organisms can be satisfied. The average elevation of the bottom of the lake of the Honghu is 22.50m, and the minimum water depth required by the survival of fishes in the Honghu is about 1.0m by combining various data analysis with reference to the research results of relevant documents of ecological water level. Therefore, the ecological water level of the flood lake is 23.50 m.

(4) The interference of low water level to the ecosystem in the natural situation is in the elastic range of the ecosystem and does not affect the stability of the ecosystem. Therefore, the natural minimum water level is the lower limit of the water level threshold of the ecosystem, and the average water level of the worst month can be taken as the natural minimum water level. The average water level of the most withered month of the Honghu is 23.03 m.

(5) From the perspective of the ecological safety of lake waters, the greater of the 4 methods, i.e., the hydrological frequency analysis method, the lake morphology analysis method, the biospace method, and the worst average water level method, is taken as the ecological water level of the lake, so that the ecological water level of the lake with the frequency of P being 75% and P being 95% is shown in fig. 4.

(6) The demand of water outside the lake of the Honghu is mainly to carry out agricultural irrigation on the coastal farmland of the lower Nerviliae irrigation area. According to the scheme of implementation of continued construction and modernization transformation of the inland river irrigation area under the Honghu city, the actual annual water consumption in the inland river irrigation area under the year of 2015-2017 is analyzed.

(7) And carrying out planned horizontal annual water demand prediction. The calculation takes 2020 as a planned horizontal year, so that the irrigation area prediction of 2020 is 67.1 ten thousand mu, and the average comprehensive irrigation quota of multiple years is 254m³And/s, irrigation water effective utilization coefficient is 0.516. Therefore, the predicted integrated irrigation quota for 75% and 95% frequency is 269m³S and 339m³The water requirement for irrigation is 34980 km per second³And 44083 km³. The total water consumption control index of the irrigation area of the lower Nerviliae is 38400 ten thousand meters³Therefore, the water requirement for irrigation of the lower vitex river irrigation area under the condition of adjusting the frequency of 95 percent is 38400 ten thousand meters³. And calculating the monthly water demand according to the agricultural irrigation coefficient of each month.

Step four, calculating lake inflow flow of the lake and researching evapotranspiration characteristics;

the actual measurement data of the closer controllable hydrological station of the lake can be directly used as the lake-entering flow of the lake, so that the evapotranspiration amount and the lake-entering flow are not required to be calculated.

Step five, calculating the drought limit water level of the lake;

the flood lake is a lake with an active water supply function, and the driving formula (26-27) calculates the drought limit water level of each month, and the result is shown in the attached table 1.

Table 1 shows the water level limiting table for the drought in each month of the Honghu

Step six, carrying out lake drought water level limiting and staging;

comprehensively considering characteristic factors such as the perennial average monthly rainfall of the flood lake basin, the perennial average monthly inflow rate of the lake, the perennial average monthly water level, the perennial average monthly water demand and the like, and performing lake drought water level limiting stage division according to hydrological years by adopting a Fisher optimal segmentation method. The stage of the water limiting level of the flood lake drought is shown in the attached figure 5.

(1) the flood lake gate pumps are too many, so that the water quality monitoring data cannot be acquired, and the correction cannot be carried out according to the water quality protection requirement.

(2) The flood limit water levels corresponding to 5/month 1 to 8/month 31/year and 9/month 1 to 10/month 15/year are respectively 24.5m and 25.5m, so the calculated drought limit water level needs to be corrected according to the characteristic water level limit, the lake drought protection water level is not higher than the drought alarm water level, and the drought limit water level is corrected month by month under different frequencies of the flood lake as shown in table 2.

TABLE 2 modified drought limit water level table (unit: m) month by month under different frequency of Honghu

(3) Considering that the span of the flood season is long, the flood season is further staged, and the stage correction drought limit water levels of the flood lake under different frequencies are shown in table 3. The monthly drought limit positions of the lagoons after correction are shown in table 3 and the staged drought limit positions are shown in fig. 6.

Table 3 shows the corrected drought limit water level table (unit: m) for different frequency periods of the Honghu

Step eight, checking the reasonability of the lake drought limit water level;

adopting the water storage amount flat percentage as a hydrological drought index, calculating the water storage amount of the lake flood in 1962 to 2017 by using the monthly water level data of the lake flood in 1962 to 2017 and the water level-volume relation thereof, and further calculating the water storage amount flat percentage I by substituting formula (29)_kAnd judging the occurrence of each stage of drought in the month. And (5) screening historical drought months according to the month-by-month and staged drought limit water levels of the Honghu obtained by calculation in the step seven, judging with hydrological indexes to obtain the drought month comparison, and calculating the percentage of the drought results which are consistent, wherein the results are shown in an attached table 4 and a table 5.

Table 4 is a table of the percentage of the drought limit level of the Honghu monthly to the result of the hydrological drought

Table 5 is a table of the percentage of the drought limit level of the flood lake in different periods consistent with the results of the hydrological drought

Fig. 7 is a structural diagram of a system for determining the classified and staged drought limit level of a lake according to the present invention, as shown in fig. 7, including:

an ecological water level determining unit 710, configured to determine a lake ecological water level of each month under different incoming water frequencies based on four lake ecological water level analysis methods; the four lake ecological water level analysis methods comprise the following steps: hydrological frequency analysis, lake morphology analysis, biospace method and worst month mean water level method;

the external water demand determination unit 720 is used for calculating the lake external water demand of each month under different incoming water frequencies based on the predicted economic and social development indexes and the predicted water quota;

the lake-entering flow determination unit 730 is used for determining the lake-entering flow of each month under different incoming water frequencies based on the long-term flow observation data of the lake-entering port or the long-term flow observation data of the lake-exiting port;

the lake surface evaporation determining unit 740 is used for determining the lake surface evaporation amount of each month under different incoming water frequencies based on the measurement data of the lake evaporation sites or the solar radiation intensity data and the meteorological data;

the drought limit water level grading calculation unit 750 is used for calculating the lake drought limit water level in each month under different incoming water frequencies based on the lake ecological water level in each month under different incoming water frequencies, the lake external water consumption in each month under different incoming water frequencies, the lake incoming flow in each month under different incoming water frequencies and the lake surface evaporation amount in each month under different incoming water frequencies;

the drought limit water level grading and staging determination unit 760 is used for staging months in a hydrological year by adopting a Fisher segmentation method in combination with the multi-year average monthly precipitation of a drainage basin, the multi-year average monthly inflow of a lake, the multi-year average monthly water level of the lake and the multi-year average monthly water demand of the lake, wherein each stage comprises at least one month, and the drought limit water level of the lake in each stage under different incoming water frequencies is determined based on the drought limit water level of the lake in each month included in each stage under different incoming water frequencies.

It should be noted that, the detailed functions of each unit in fig. 7 refer to the descriptions in the foregoing method embodiments, and are not described herein again.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A lake classification staged drought limit water level determination method is characterized by comprising the following steps:

2. The lake classification staged drought limit water level determination method according to claim 1, wherein the determination of the lake ecological water level per month under different incoming water frequencies based on four lake ecological water level analysis methods specifically comprises:

H_emin＝max(H_min1，H_min2，H_min3，H_min4)

3. The lake classification staged drought limit water level determination method according to claim 1, wherein the lake external water demand per month under different incoming water frequencies is calculated based on the predicted economic and social development index and the predicted water usage quota, and specifically comprises:

W_ul,i＝0.365×P_ul,i×m_ul,i

W_rl,i＝0.365×P_rl,i×m_rl,i

W_al,i＝0.365×P_al,i×m_al,i

W_as,i＝0.365×P_as,i×m_as,i

W_F,i＝G_i×m_F,i×(1-c_i)

W_FP,i＝A_FP,i×m_FP,i

4. The lake classification staged drought limit level determination method as claimed in claim 1, wherein the lake-in flow rate per month under different incoming water frequencies is determined based on the long-term flow observed data at the lake-in port or the long-term flow observed data at the lake-out port; the method specifically comprises the following steps:

For lakes with hydrological stations at lake outlets and long-term flow observation data, the lake inlet flow is calculated according to the actual measurement data of the water level of the lake and the lake water level-volume curve through the water quantity balance principle: i is_Into-I_{Go out}＝ΔW_{Storage tank}＝V(Z₂)-V(Z₁) (ii) a In the formula I_IntoThe lake water amount of the lake in the period I_{Go out}Is thatVolume of lake water, Δ W, of lake interval_{Storage tank}For the change of the water storage capacity of the lake in the period, V () is a lake water level-volume conversion function for converting the water level into the volume, Z₂、Z₁Water levels at the end of a lake period and at the beginning of the lake period respectively; according to I_Into-I_{Go out}Calculating the lake water inflow amount of the lake in a time period, and converting to obtain the lake inflow flow of the lake; or

5. The lake classification staged drought limit water level determination method according to claim 1, wherein the lake surface evapotranspiration amount per month under different incoming water frequencies is determined based on measurement data of lake evaporation sites or solar radiation intensity data and meteorological data; the method specifically comprises the following steps:

E＝(0.015+0.00042Ta+10^-6h)*(0.8Q_s-40+2.5×U₂F(Ta-Td))

6. The method for determining the lake classification staged drought limit water level according to any one of claims 1 to 5, wherein the determining the lake drought limit water level per month under different incoming water frequencies specifically comprises: for an active lake with a water supply function, adding lake external water on the basis of the lowest ecological water level, and calculating by considering lake runoff and lake evaporation, wherein the drought limit water level is calculated as follows:

7. A lake classification staged drought limit water level determination system is characterized by comprising:

8. The lake classification staged drought limit level determination system according to claim 7, wherein the external water demand determination unit calculates the lake external water demand per month at different incoming water frequencies based on the predicted economic and social development index and the predicted water rate, and specifically comprises:

W_ul,i＝0.365×P_ul,i×m_ul,i

W_rl,i＝0.365×P_rl,i×m_rl,i

W_al,i＝0.365×P_al,i×m_al,i

W_as,i＝0.365×P_as,i×m_as,i

W_F,i＝G_i×m_F,i×(1-c_i)

W_FP,i＝A_FP,i×m_FP,i

9. The lake-classified staged drought limit level determination system according to claim 7, wherein the lake-entering flow determination unit determines the lake-entering flow per month at different incoming water frequencies based on the long-term flow observation data at the lake-entry port or the long-term flow observation data at the lake-exit port; the method specifically comprises the following steps:

10. The lake classification and staging drought limit water level determination system according to any one of claims 7 to 9, wherein the drought limit water level classification calculation unit calculates the lake drought limit water level per month at different incoming water frequencies, specifically: for an active lake with a water supply function, adding lake external water on the basis of the lowest ecological water level, and calculating by considering lake runoff and lake evaporation, wherein the drought limit water level is calculated as follows:

when (V)_{In need of water}-V_{Runoff flow}+V_{Evaporation of})>At the time of 0, the number of the first,Z＝Z(V(H_emin)+V_{in need of water}-V_{Runoff flow}+V_{Evaporation of})；