Selection and construction method of reference point in interfered submergence type river water ecology

Abstract

To have a high nature imitation effect of reference point micro inhabitation environment, hold water ecological space heterogeneity of a target water body at the maximum without changing a microorganism / organic feature in a natural water ecological system in the whole construction process, and realize a natural water ecological environmental status.SOLUTION: A selection and construction method of a reference point in interfered submergence type river water ecology includes steps of: dividing a basin basic space unit S1; analyzing an influence on an ecological environment stress of human activity in the basin basic space unit and extracting a water ecological feature S2; selecting a reference candidate point S3; evaluating an aquatic organism status of the reference candidate point S4; constructing a nature imitation reference point S5; and evaluating the aquatic organism status of the nature imitation reference point S6.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention belongs to the field of watershed ecology technology, in particular the present invention relates to a method for selecting and constructing reference points in disturbed flooded river water ecology. [Background technology]

[0002] During the 14th Five-Year Plan period, China's aquatic ecological environmental protection will gradually move from simple water environment quality management to a three-pronged water management mode of "water environment, water resources, and aquatic ecology". Rational evaluation of aquatic ecological measures will be the basic need for aquatic ecological environmental protection work in the long term. Aquatic ecological monitoring and evaluation are the foundation and premise of aquatic ecological protection and measures. Whether it is the US aquatic ecological monitoring and evaluation system, which is the earliest to implement aquatic ecological monitoring and evaluation, or the European Union aquatic ecological monitoring and evaluation system, which has the widest scope of application, both are concerned with the establishment and determination of the reference state in aquatic ecology. There are currently four main types of methods for establishing the reference state: the point reference method, the historical data method, the optimal available state method, and the expert experience judgment method. The latter three methods have the following shortcomings:

[0003] (1) Regarding the historical data method, the data is insufficient and the quality of the data cannot be guaranteed. Historical data obtained from different routes have different origin routes and observation purposes, so the synchronization and consistency of the obtained data on water quality, hydrology, aquatic organisms, etc. is low, and the acquisition of set data is insufficient. In addition, due to the interference of regional external environments, hydrological rhythms change significantly and aquatic organism communities change. The reference state based on historical data does not reflect the response expression of species changes, and it is difficult to guarantee the quality of the historical reference state data.

[0004] (2) Expert judgment methods are highly subjective and localized. Expert consultations are also based on historical data and the experience of experts, which is somewhat subjective. Although there is a certain degree of similarity in the aquatic ecological integrity of similar water environmental conditions, there are differences in the aquatic ecological functions and aquatic ecological environments in different regions due to changes in factors such as hydrology, topography, climate, and microbial environment. This makes it of little value as a model for different forms of reference conditions in different regions, and the limitations of expert consultations are great.

[0005] (3) Regarding the optimal availability state method, based on the desired state or the damage state, the reference state is predicted by the model method, which has uncertainty and needs to be verified in practice. The main process is to investigate the damage degree or the desired state by investigating the biological indicators, physicochemical indicators and other parameter indicators of the damage point, and then use some mature mathematical model methods to select the reference point or simulate the ideal reference state. In principle, this method can predict the water ecological information of the river, but the prediction result has a certain uncertainty and may need to be verified in practice.

[0006] The reference point method determines the reference state by searching for a comparable biological status point that can represent monitoring and evaluation of no interference (or little interference) in the water body, and the biological parameter indicator obtained from that point. As can be seen from this, the reference point method is the most direct and most reliable method for determining the reference state.

[0007] China is a country with few water resources, and due to the influence of industrialization, urbanization and agricultural intensification, most rivers are subject to interference from anthropogenic activities such as water conservancy development, pollution discharge, and agricultural non-point sources. Reference points are defined as those that are not subject to anthropogenic interference (or are subject to only minor anthropogenic interference) and have optimal biological conditions. At present, it is not clearly defined how to select and construct reasonable and acceptable hydroecological reference points for disturbed rivers. Summary of the Invention [Problem to be solved by the invention]

[0008] The technical problem that the present invention aims to solve is, in the context of most rivers being disturbed, to provide a method for selecting and constructing reference points in the water ecology of disturbed rivers for floodable river water by analyzing the spatial heterogeneity of hydrological forms, the differences in the physicochemical characteristics of the water environment under different disturbances, and the conditions of aquatic organisms, and to solve the problem of obtaining reference points in the water ecology of rivers after they are disturbed by human activity. [Means for solving the problem]

[0009] To achieve the above objectives, the technical solutions adopted in the present invention are as follows:

[0010] A method for selecting and constructing reference points in a disturbed flooded river ecology, comprising: In the division of the watershed basic spatial unit, a step S1 is to determine a reasonable catchment area threshold value based on the natural waterlogging characteristics and DEM data of the target watershed by using a constant threshold method or a moderate index method, and input the DEM data and the determined catchment area threshold value into the SWAT model to divide the watershed basic spatial unit; In the analysis of the impact of human activities on ecological environmental stress in each basic spatial unit of a watershed and the extraction of hydro-ecological characteristics, the external environmental stresses received are determined based on the analysis of the impact of human activities on the eco-environment stress in each basic spatial unit of a watershed. Then, in step S2, the basic spatial units of a watershed in step S1 are classified, and for the basic spatial units of a watershed affected by the same type of stress, the bank sediment type, maximum water depth, average water depth, long-term average water depth, bank mean flow velocity, bank maximum flow velocity and average sea level are extracted, and the bank mean water flow value, average water depth, average sea level and bank sediment type of the basic spatial units of a watershed in the same cluster affected by the same type of stress are extracted as the hydro-ecological characteristics of the basic spatial units of a watershed in the same cluster; In the selection of the reference candidate points, a step S3 is performed in which at least one reference candidate point is selected from within the watershed basic spatial unit of the same water ecological features in the step S2; In the step S4, four biological indicators are selected for evaluating the aquatic life status of the reference candidate points, namely, the Shannon-Wiener diversity index, the percentage of biomass of pollution-resistant species, the percentage of abundance (abundance) of pollution-resistant species, and the percentage of abundance (abundance) of sensitive species. The aquatic life status of the reference candidate points in the step S3 is evaluated and scored. It is determined whether each reference candidate point meets the designated standard. If the designated standard is met, the point with the highest score is selected as the reference point, and the selection of the reference point is completed. If the designated standard is not met, the step S5 is carried out to construct a nature-mimicking reference point. In constructing the nature-mimicking reference point, the point with the highest biological score among the reference candidate points is selected, and three staircase units, an upper shallow water unit, a middle depression unit, and a lower shallow water unit, are constructed by sequentially connecting them using stones of different sizes. The three staircase units are fitted together using blocks, crushed stones, boulders, and small crushed stones on one side away from the riverbank to form a water cut-off zone. The water cut-off zones of the three staircase units are sequentially connected to form a wavy water cut-off wall, and the riverbed of the middle depression unit forms a concave depression (pit), and the middle depression unit and the upper shallow water unit / lower shallow water unit are connected to form a water cut-off zone. Step S5, in which the difference in elevation between the knit and the riverbed is equal to the difference between the maximum water depth value and the average water depth value extracted in step S2, an upper water cutoff wall is provided between the middle depression unit and the upper shallow water unit, and a lower water cutoff wall is provided between the middle depression unit and the lower shallow water unit, both ends of the upper water cutoff wall and the lower water cutoff wall are connected to the water cut zone of the middle depression unit and the river bank, respectively, and both the upper water cutoff wall and the lower water cutoff wall are provided with overflow ports, and a small habitat made of lumps and boulders is laid on the riverbed of the three staircase units; In the evaluation of the aquatic biological situation of the natural imitation reference point, within the specified time after construction in step S5, sampling and identification of benthic animals are carried out for the natural imitation reference point, and the evaluation and scoring of the aquatic biological situation are carried out with reference to the method of step S4 to determine whether the natural imitation reference point reaches the specified standard. If it does not reach the specified standard, after adjusting the two physical element conditions of the water depth and flow velocity of the microhabitat environment, the benthic animal survey and the evaluation of the aquatic biological situation are repeated within the specified time until the evaluation of the aquatic biological situation is above the specified standard, and step S6 of completing the construction of the natural imitation reference point is included.

[0011] In addition to the above solutions, in another improved solution, the microhabitat environment in the upper riffle unit / the lower riffle unit includes one central boulder and a plurality of jade stones stacked around the central boulder. The plurality of microhabitat environments in the upper riffle unit / the lower riffle unit are arranged in a shape similar to the Chinese character 'zhi'. The microhabitat environment in the middle depression unit is arranged at the deepest position of the middle depression unit and includes two adjacent central boulders and a plurality of jade stones stacked around the two central boulders.

[0012] In addition to the above solutions, in another improved solution, the stacked height of the water stop belt in the upper riffle unit / lower riffle unit is higher than the average water depth value extracted in step S2, or 3 - 5 cm higher than the long-term average water level of the target basin. The stacked height of the water stop belt in the depression unit is higher than the maximum water depth value extracted in step S2, or 7 - 15 cm higher than the long-term average water level of the target basin. The heights of the upper water stop wall and the lower water stop wall are equal to the height of the water stop belt in the middle depression unit. At least one overflow port with a diameter of 5 cm is provided on the upper water stop wall, and at least one overflow port with a diameter of 10 cm is provided on the lower water stop wall.

[0013] In addition to the above solution, in another improved solution, the width of the recession toward the river bank of the middle section of the wavy waterstop wall is 15°±2°, the straight-line length of the wavy waterstop wall is 200 cm, both ends of the wavy waterstop wall are 75 cm away from the river bank, the shortest distance between the middle section of the wavy waterstop wall and the river bank is 50 cm, the straight-line lengths of the waterstop zones of the upper shallow water unit and the lower shallow water unit are both 75 cm, and the length of the waterstop zone of the middle recess unit is 50 cm.

[0014] In addition to the above solution, in another improved solution, the sediment type of the nature-mimicking reference point is the same as the shore sediment type extracted in step S2, and in principle the sediment types in the three staircase units are kept consistent, and if the three staircase units are of mixed sediment type, they are laid according to the sediment type with the smallest grain size.

[0015] In addition to the above-mentioned solution, in another improved solution, the step of constructing a nature-mimicking reference point in step S5 is to first use stones of different sizes to construct a wavy water cutoff wall 50-70 cm away from the bank, then use stones of different sizes to construct an upper end water cutoff wall and a lower end water cutoff wall between the wavy water cutoff wall and the river bank to form three staircase units, further excavate a depression in the riverbed between the upper end water cutoff wall and the lower end water cutoff wall to form a middle depression unit, and finally construct a small habitat in the riverbed of each staircase unit.

[0016] In addition to the above solution, in another improved solution, in the case of constructing the natural mimicking reference points in step S5, the grain size of the block stone used is 10-20cm, the grain size of the gravel is 5-10cm, the grain size of the boulder is 1-5cm and the grain size of the small crushed stone is <1cm.

[0017] In addition to the above solution, in another improved solution, in the step S1, the constant threshold method is a catchment area threshold determined according to experience or by repeated comparison with an accurate watershed diagram, and the suitability index formula is:

number

number

number

number

number

[0018] Biometrics Scoring Criteria [Table 1]

[0019] The aquatic life condition scores are ranked as follows: 12-20 points are excellent, 9-12 points are good, 5-10 points are fair, and 0-5 points are difference. In determining whether each reference candidate point meets the specified criterion in step S3, the specified criterion is to select as reference points those reference candidate points that are rated as good in the above scoring criteria, i.e., whose aquatic life condition is rated as good or better.

[0020] In addition to the above solution, in another improved solution, the specific steps of extracting the hydrological characteristics of the homogeneous watershed basic spatial units in step S2 are as follows:

[0021] S21. In determining the bank sediment type of the drainage basin basic spatial unit, the sediment type is determined by the grain size of the bank bed within 1 meter from the river bank. If the river channel width is less than 1 meter, the range from the river centerline to the river bank is taken. S22, perform pre-clustering based on the shore sediment type of the watershed spatial basic unit, i.e., distinguish the shore sediment type of the basic spatial unit affected by the same main stress, and perform clustering using the shore sediment type as a cluster factor; S23. In the classification and measurement of the basic requirements for the water ecology of the basic spatial unit of the basin, the water flow is the flow velocity measured in the mid-water period of the coastal water body, the water depth is the water depth measured in the mid-water period of the coastal water body, and the sea level is the average sea level within the basic spatial unit of the basin; S24, in the stepwise clustering method, all the watershed basic spatial units affected by the same kind of stress are taken as samples, and the watershed spatial basic units affected by the same kind of stress are clustered using bottom sediment type as the pre-cluster variable factor, and then the water flow velocity, water depth, and sea level are taken as the post-cluster variables, and after normalization processing, the clustering is performed again using the clustering shortest distance method to obtain the final result; S25, in the extraction of the hydrological ecological characteristics of the same type of watershed basic spatial unit, the average water flow, average water depth, average sea level, and bottom sediment type of the watershed basic spatial unit of the same cluster affected by the same type of stress are taken as the hydrological ecological characteristics of that type of watershed.

[0022] In addition to the above solution, in another improved solution, in step S3, the reference candidate point should simultaneously satisfy six requirements: (1) water quality should be maintained at or above Level III within 1 km upstream and downstream on both sides of the coast, or the measured concentrations of non-anthropogenic pollutants should be maintained within the background level range; (2) there should be no sewage outlet within 1 km upstream and downstream on both sides of the coast; (3) there should be no agricultural cultivation with a wide area of ​​100 mu (about 666.7 square meters) or more within 1 km upstream and downstream on both sides of the coast; (4) there should be no known aquaculture within 1 km upstream and downstream on both sides of the coast; (5) there should be no main roads, urban trunk roads, or expressways within 1 km upstream and downstream on both sides of the coast; and (6) the resident population should be less than 100 people within 1 km upstream and downstream on both sides of the coast. Effect of the Invention

[0023] The technical solution of the present invention has at least the following beneficial technical effects:

[0024] (1) The present invention provides a method for selecting and constructing reference points in the water ecology of rivers that are reliably operable and tolerable to be interfered with. Humans cannot live without water resources, and human activities will cause more or less interference to the water ecological environment. Therefore, the reference points with optimal biological conditions that are not subject to human interference, defined in the quality monitoring and evaluation of the water ecological environment, cannot be found in natural river basins. In accordance with the concept of sustainable harmonious development of humans and nature, the present invention provides a method for selecting and constructing a reference point in the water ecological environment of rivers that are subject to tolerable interference through a series of steps including stress analysis on the interference of human activities, extraction of the characteristics of the water ecological environment affected by stress, selection of reference candidate points, evaluation of the aquatic organism status of the candidate points, and construction of natural mimicking reference points, and in particular provides a method for constructing reference points in the water ecology of rivers that are seriously interfered with by the construction of natural mimicking reference microhabitats, which can be widely applied to the acquisition of reference points in the water ecological environment of flooded rivers that are subject to interference, and has practical operativity.

[0025] (2) The reference points selected by the method of the present invention have remarkable representativeness. The present invention fully considers the spatial heterogeneity of water ecological environment characteristics and the difference in the impact of different human interference on the water ecological environment, analyzes the spatiotemporal variability of hydrological regime and the spatial heterogeneity of water ecological environment by dividing the basic spatial unit of the water basin, analyzes different types of physical and chemical interference on the water ecological environment due to the stress of human activities on the water ecological environment, extracts the water ecological characteristics of the basic spatial unit of the water basin affected by the same stress, and extracts the water body physical characteristics affected by different stress, and judges the biological integrity of the selected reference points by evaluating the aquatic biological situation. It can be seen that the reference points selected according to the present invention can represent the spatial heterogeneity, physical and chemical characteristics and aquatic biological integrity of the water ecological environment to a certain extent, and are well consistent with the meaning and characteristics represented by the reference points.

[0026] (3) The effect of the natural mimicry reference point constructed by the method of the present invention is high. In a river where the river has been seriously disturbed and the integrity of aquatic organisms has been greatly damaged, the present invention, in view of the three physical factors of bottom sediment, water depth, and flow velocity that most directly affect the existence of aquatic organisms, uses different types of bottom sediment to be embedded in each other to build up three tiered units, namely, upper shallow, middle depression, and lower shallow, to create micro-scale water depth diversity and flow velocity diversity, create habitat diversity for macrobenthos, and construct an acceptable water habitat environment situation at the site, thereby realizing the construction of a natural mimicry reference point. The entire construction process does not change the microbial and organic characteristics in the natural water ecosystem, and can maximally retain the bottom sediment heterogeneity of the target water body, embodying the natural water ecological environment situation. [Brief description of the drawings]

[0027] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention, and the illustrative embodiments of the present invention and their explanations are used to interpret the present invention and are not intended to unduly limit the present invention. [Figure 1] FIG. 2 is a schematic diagram of the main steps of the method for selecting and constructing reference points in disturbed river water ecology of the present invention; [Diagram 2] FIG. 1 is a schematic diagram of the steps of extracting water ecological characteristics of homogeneous watershed basic spatial units of the present invention. [Diagram 3] FIG. 2 is a plan view of a nature mimicking reference point in the present invention. [Figure 4] FIG. 2 is a longitudinal cross-sectional view of a nature mimicking reference point in the present invention. [Diagram 5] FIG. 2 is a vertical cross-sectional view of the water stop zone of the upper shallow water unit / lower shallow water unit in the present invention. [Figure 6] FIG. 13 is a longitudinal cross-sectional view of the water stop band of the middle recess unit of the present invention. [Figure 7] A vertical cross-sectional view of a water blocking wall at the upper end of a middle recess unit of the present invention. [Figure 8] A vertical cross-sectional view of a water blocking wall at the lower end of a middle recess unit of the present invention. [Figure 9]FIG. 2 is a schematic plan view of the middle recess unit of the present invention; [Figure 10] FIG. 1 is a schematic diagram showing the layout of small habitats in the upper shallow water unit / lower shallow water unit of the present invention. [Figure 11] FIG. 2 is a schematic diagram showing the plan layout of the small habitats of the middle recess unit of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present invention will be described in detail below with reference to the drawings, and the description in this section is only schematic and interpretive, and does not have any limiting effect on the protection scope of the present invention. In addition, those skilled in the art can make corresponding combinations of the features of the embodiments and different embodiments in this specification based on the description in this specification.

[0029] Referring to the schematic diagram of FIG. 1, the method for selecting and constructing reference points in the disturbed flooded river water ecology of the present invention is as follows: In the division of the watershed basic spatial unit, a step S1 is to determine a reasonable catchment area threshold value based on the natural waterlogging characteristics and DEM (Digital Elevation Model) data of the target watershed using a constant threshold method or a moderate index method, and input the DEM data and the determined catchment area threshold value into the SWAT model (Soiland Water Assessment Tool) to divide the watershed basic spatial unit; The constant threshold method is a catchment area threshold determined empirically or by repeated comparison with accurate watershed maps, and is based on the moderateness index formula (reference: Wen-Tzul et al., Hydro Process, 2006(20):289-306),

number

[0030] The stress of human activities on the water ecological environment is limited to disturbances extending within 1 kilometer of the land side based on the coastline, and the degree of impact is judged based on the proportion of the interference area to the basic spatial unit area of ​​the basin, with the largest proportion being the main stress impact. The interference area of ​​non-point sources such as riverbank farmland cultivation, mining, bank sedimentation, bank mountain debris flow or landslides is the direct influence area within 1 kilometer of the coast, the interference area of ​​hydropower development is the drainage area of ​​the reduced river segment in the basic unit of the basin, and the interference area of ​​point source disturbances such as domestic sewage discharge and industrial sewage discharge is the drainage area of ​​the mixing process segment after direct discharge. If the same disturbance activity exists on the left and right banks, the degree of impact on stress is the overlap of the disturbance areas on the left and right banks.

[0031] Referring to the outline of FIG. 2, the specific steps of extracting the hydrological characteristics of the homogeneous watershed basic spatial units in step S2 are as follows:

[0032] S21, in determining the bank sediment type of the basic spatial unit of the basin, the sediment type is determined by the grain size of the bank bed within 1 meter from the riverbank, if the river channel width is less than 1 meter, the range from the river centerline to the riverbank is taken, and the specific determination of the bank sediment type is shown in Table 1 below. If it does not meet the requirements of Table 2 below and the ratio difference of different sediment types is 10% or more, the sediment type with the largest ratio is selected as the sediment type of the basic spatial unit of the basin, and if the ratio difference of different substrate types is less than 10%, the two main sediment types are selected as the mixed sediment.

[0033] Shore bottom type [Table 2]

[0034] S22, perform pre-clustering based on the shore sediment type of the watershed spatial basic unit, i.e., distinguish the shore sediment type of the basic spatial unit affected by the same main stress, and perform clustering using the shore sediment type as a cluster factor; S23: In classifying and measuring the basic water ecological requirements of a watershed basic spatial unit, obtain the basic requirements through on-site measurements during the mid-water period (March-May or September-November). Within 1 meter from the shore of the upper, middle and lower river segments in the watershed basic spatial unit, use a portable ultrasonic flowmeter to measure the flow velocity, and the average flow velocity of the upper, middle and lower river segments is taken as the water flow velocity of the water body unit. Within 1 meter from the shore of the upper, middle and lower river segments in the watershed basic spatial unit, use a handheld depth meter to measure the water body depth on the shore, and the average flow velocity of the upper, middle and lower river segments is taken as the average water depth of the water body unit. According to the division boundary of the watershed basic spatial unit, obtain the average value above sea level of the watershed basic spatial unit based on the DEM data as the mean sea level. S24: In the stepwise clustering analysis, all the watershed basic spatial units affected by the same stress are taken as samples, and the main stress impact type and bottom sediment type are used as the pre-cluster variable factors to cluster the watershed spatial basic units affected by the same stress. Then, the water flow rate, water depth, and altitude are used as the post-cluster variables. After normalization, the clustering is performed again using the clustering shortest distance method (Reference: Chen Jiangli et al., 2014, v.31; No.142(12):29-33) to obtain the final result. S25, in the extraction of the hydrological ecological characteristics of the same type of watershed basic spatial unit, the average water flow, average water depth, average sea level, and bottom sediment type of the watershed basic spatial unit of the same cluster affected by the same type of stress are taken as the hydrological ecological characteristics of that type of watershed.

[0035] S3. In selecting reference candidate points, at least one reference candidate point is selected from within the basic spatial unit of the basin with the same water ecological characteristics in step S2. The reference candidate point should simultaneously satisfy the following six requirements: (1) the water quality should be maintained at or above Level III within 1 km upstream and downstream on both sides of the coast, or the measured concentrations of non-anthropogenic pollutants should be within the background level range; (2) there should be no sewage outlet within 1 km upstream and downstream on both sides of the coast; (3) there should be no agricultural cultivation with a broad area of ​​100 mu (approximately 666.7 square meters) or more within 1 km upstream and downstream on both sides of the coast; (4) there should be no known aquaculture within 1 km upstream and downstream on both sides of the coast; (5) there should be no main roads, urban trunk roads, or expressways within 1 km upstream and downstream on both sides of the coast; and (6) the resident population should be less than 100 people within 1 km upstream and downstream on both sides of the coast.

[0036] S4, in the evaluation of the aquatic biological status of the reference candidate points, four biological indicators, namely, the Shannon-Wiener diversity index, the percentage of pollutant-resistant species biomass, the percentage of pollutant-resistant species abundance, and the percentage of sensitive species abundance, are selected, and the aquatic biological status of the reference candidate points of step S3 is evaluated and scored. It is judged whether each reference candidate point meets the designated criterion. If it meets the designated criterion, the point with the highest score is selected as the reference point, and the selection of the reference point is completed. If it does not meet the designated criterion, the step S5 is carried out to construct the natural mimicking reference point; In assessing the aquatic biota status of the reference candidate points, the formula for calculating the Shannon-Wiener diversity index is:

number

number

number

number

[0037] After calculating the biological index of the reference candidate point based on the above formula, the biological evaluation index is scored by referring to the scoring criteria of Table 1 listed in the above-mentioned content of the invention.

[0038] The minimum score for the aquatic life condition score is 0 points, and the maximum score is 20 points. The scores for the aquatic life condition are ranked, with 12-20 points being excellent, 9-12 points being good, 5-10 points being fair, and 0-5 points being difference. In step S3, in determining whether each reference candidate point meets the designated criterion, the designated criterion is to select as the reference point a reference candidate point that is rated as good in the above scoring criteria, i.e., that the aquatic life condition is rated as good or better.

[0039] S5. In constructing a nature-mimicking reference point, the point with the highest biological score among the reference candidate points is selected, and a nature-mimicking reference point is constructed using stones of different sizes. The nature-mimicking reference point includes three staircase units, namely, an upper shallow water unit, a middle depression unit, and a lower shallow water unit, which are connected in sequence. The three staircase units are fitted together on one side away from the riverbank using blocks, crushed stones, boulders, and small crushed stones to form a water-stopping zone (a mixture of two, three, or four of the four types of blocks, crushed stones, boulders, and small crushed stones). The water-stopping zones of the three staircase units are connected in sequence to form a wavy water-stopping wall, and the riverbed of the middle depression unit is connected in sequence to form a wavy water-stopping wall. forms a concave depression, the elevation difference between the middle depression unit and the upper shallow water unit / lower shallow water unit is equal to the difference between the maximum water depth value and the average water depth value extracted in step S2, an upper cutoff wall is provided between the middle depression unit and the upper shallow water unit, a lower cutoff wall is provided between the middle depression unit and the lower shallow water unit, both ends of the upper cutoff wall and the lower cutoff wall are connected to the water stop zone and the river bank of the middle depression unit, and both the upper cutoff wall and the lower cutoff wall are provided with overflow ports, and a small habitat made of lumps and boulders is laid on the riverbed of the three step units. Based on the living habit of benthic animals that prefer to attach to the surface of boulders or hide in the gaps between boulders, a small habitat is arranged in each unit to provide a living space for benthic animals. Small habitats suitable for the survival of benthic fauna are constructed at the reference candidate points using bottom sediments of different sizes, and information on the corresponding aquatic life conditions is obtained by collecting benthic fauna on the surface and in gaps of the small habitats within the three staircase units.

[0040] S6. In the evaluation of the aquatic biological situation of the natural imitation reference point, within the specified time after construction in step S5, sampling and identification of benthic animals are carried out for the natural imitation reference point, and the evaluation and scoring of the aquatic biological situation are carried out with reference to the method in step S4 to determine whether the natural imitation reference point reaches the specified standard. If it does not reach the specified standard, two ecological element characteristics, namely the water depth and flow velocity of the microhabitat environment, are adjusted to reach the relevant index conditions. The specific method is to adjust the height of the overflow opening from the riverbed to achieve the purpose of adjusting the water depth of the microhabitat environment, and directly achieve the purpose of adjusting the flow velocity of the microhabitat environment by adjusting the arranged overflow opening, increase the number of overflow openings, and achieve the purpose of improving the flow velocity of the microhabitat environment. The benthic animal investigation and the evaluation of the aquatic biological situation are repeated within the specified time until the evaluation of the aquatic biological situation reaches or exceeds the specified standard, and the construction of the natural imitation reference point is completed.

[0041] Referring to the schematics from FIG. 3 to FIG. 11, in the present invention, the microhabitat environment in the upper riffle unit / lower riffle unit includes one central boulder and a plurality of jade stones stacked around the central boulder. The plurality of microhabitat environments in the upper riffle unit / lower riffle unit are arranged in a shape similar to the Chinese character "zhi", and the interval between each microhabitat environment is 20 cm. The microhabitat environment in the middle depression unit is arranged at the deepest position of the middle depression unit and includes two adjacent central boulders and a plurality of jade stones stacked around the two central boulders. The particle size of the boulders used is 10 - 20 cm, the particle size of the crushed stones is 5 - 10 cm, the particle size of the jade stones is 1 - 5 cm, and the particle size of the small crushed stones is <1 cm.

[0042] Referring to the schematics of FIG. 5 and FIG. 6, the stacked height of the water stop belts in the upper riffle unit / lower riffle unit is higher than the average water depth value extracted in step S2, or 3 - 5 cm higher than the long-term average water level of the target watershed. The stacked height of the water stop belts in the depression unit is higher than the maximum water depth value extracted in step S2, or 7 - 15 cm higher than the long-term average water level of the target watershed. The heights of the upper water stop wall and the lower water stop wall are equal to the height of the water stop belt in the middle depression unit.

[0043] Referring to the schematic in Figure 3, the width of the concave angle of the middle section of the wavy cutoff wall toward the riverbank is 15°±2°, the straight-line length of the wavy cutoff wall is 200cm, both ends of the wavy cutoff wall are 75cm away from the riverbank, the shortest distance between the middle section of the wavy cutoff wall and the riverbank is 50cm, the straight-line lengths of the waterstop bands of the upper shallow water unit and the lower shallow water unit are both 75cm, and the length of the waterstop band of the middle recess unit is 50cm. The concave shape of the wavy cutoff wall toward the riverbank can reduce the lateral impact of the outer water body to a certain extent and improve the stability of the nature-mimicking reference point.

[0044] Referring to the schematic diagrams of Figures 3 and 10, the sediment types of the three staircase units at the natural imitation reference point are the same as the bank sediment type extracted in step S2. In principle, the sediment types in the three staircase units are kept consistent, and the three staircase units are laid according to the sediment type with the smallest grain size if they are mixed sediment types. For example, sand is filled in the voids of the boulders and laid with sand. When different sediment types are distributed in different areas, differences will occur in the sediment types of each unit, for example, boulders are mainly distributed in the shallow water area of ​​the riverbed, and sludge is distributed in the deep pool area of ​​the bottom of the riverbed, so that the boulder sediment is laid in the corresponding shallow water unit, and the sludge sediment is laid in the corresponding hollow unit.

[0045] Referring to the schematic diagrams of Figures 4, 7 and 8, the hydraulic connection between the upper shallow water unit / lower shallow water unit and the middle basin unit is realized by providing overflow ports, and the water flow and water depth of the natural imitation reference point are determined by the position and number of overflow ports on the cutoff wall of the basin unit. Generally, two overflow ports with a diameter of 5 cm are provided on the cutoff wall at the upper end, and the two overflow ports are horizontally spaced 10 cm apart to ensure that the river water of the upper shallow water unit flows into the middle basin unit. An overflow port with a diameter of 10 cm is provided on the cutoff wall at the lower end, and the river water of the middle basin unit flows into the lower shallow water unit through the overflow port. The height and number of overflow ports can be adjusted as required, and the cutoff wall at the lower end is provided with an overflow port with a diameter of 10 cm on the river bottom.

[0046] The step of constructing a nature-mimicking reference point in step S5 is to first construct a wavy water cutoff wall 50-70 cm away from the shore using stones of different sizes, then construct an upper water cutoff wall and a lower water cutoff wall using stones of different sizes to form three staircase units, and finally construct a small habitat in each staircase unit.

[0047] Example 1 The method of the present invention is used to select and construct reference points in the water ecology for the Baoxing River Basin in Ya'an City. The Baoxing River is the main source of the Qingyi River, flows through nine towns in Baoxing County, Ya'an City, and merges with the Minjiang Channel along the Qingyi River. The river has crisscrossing valleys and is rich in water resources and marble deposits. There are currently 47 small hydroelectric plants in operation and 12 mines. Therefore, the water ecological environment of the Baoxing River Basin is greatly affected by human activities such as hydroelectric power development and mine development. The method steps are shown in Figure 1, and the water process is as follows:

[0048] S1, in the basic spatial unit division of the watershed, based on the moderateness index analysis, 7500m 2 The catchment area threshold of is determined and input into the SWAT model to divide the Baoxing River Basin into 13 watershed basic spatial units.

[0049] S2. In analyzing the impact of human activities on the stress of the water ecological environment and extracting the water ecological characteristics of the basic spatial units of the basin, the disturbances extending within 1 kilometer from the land side based on the coastline were mainly considered. The degree of impact was judged based on the proportion of the interference area to the area of ​​the basic spatial units of the basin. Four basic spatial units were mainly affected by geological disaster stress, three basic spatial units were mainly affected by domestic pollution stress, four basic spatial units were mainly affected by hydropower development stress, one basic spatial unit was mainly affected by industrial pollution stress, and one basic spatial unit was mainly affected by mining stress.

[0050] During the mid-water period (March-May or September-November), the bank sediment type, maximum water depth, average water depth, long-term average water depth, bank average flow velocity, bank maximum flow velocity, and mean sea level of the basic spatial units of the geological disaster, domestic pollution, hydroelectric power generation, and industrial pollution basins were measured respectively. The hydroecological characteristics of each basic spatial unit based on the measurements are shown in Table 3.

[0051] Hydroecological characteristics of each basic spatial unit in the Baoxing River Basin during the mid-water period [Table 3]

[0052] Pre-clustering was performed with bank sediment type as the cluster factor, and then post-clustering was performed using the clustering shortest distance method with water flow speed, water depth and altitude as cluster factors, and the 13 basic watershed units were clustered into 6 water ecological types, namely, high altitude good ecological unit, medium altitude good ecological unit, hydropower development interference ecological unit, mining interference ecological unit, domestic pollution interference ecological unit and industrial interference ecological unit.

[0053] The average current velocity, average water depth, average elevation, and bottom sediment type of the same basic spatial unit were extracted as the hydroecological characteristics of the corresponding type. Details are shown in Table 4.

[0054] Aquatic ecological characteristic values ​​for each aquatic ecological type [Table 4]

[0055] S3. Selection of reference candidate points: The selection criteria for reference candidate points are: (1) within 1 km upstream and downstream of the coast, water quality should be maintained at or above Level III, or the measured concentration of non-anthropogenic pollutants should be maintained within the background level range; (2) there should be no wastewater outlets within 1 km upstream and downstream of the coast; (3) there should be no agricultural cultivation with a broad area of ​​100 mu (approximately 666.7 square meters) or more within 1 km upstream and downstream of the coast; (4) there should be no known aquaculture within 1 km upstream and downstream of the coast; and (5) there should be no major roads or urban trunk lines within 1 km upstream and downstream of the coast. (5) there is no road or expressway route, and (6) the resident population within 1 km upstream and downstream on both sides of the coast is less than 100 people. Ten reference candidate points are selected, among which, the high altitude ecologically good unit selects two reference candidate points, the medium altitude ecologically good unit selects two reference candidate points, the living disturbance ecological unit selects two reference candidate points, the mining disturbance ecological unit selects one reference candidate point, the industrial disturbance ecological unit selects one reference candidate point, and the hydropower development disturbance ecological unit selects two reference candidate points, thereby completely covering each ecological characteristic unit.

[0056] S4. In the evaluation of the aquatic ecological status of the reference candidate points, survey and sampling are carried out on the benthic fauna of the 10 reference candidate points during the mid-water period (March-May or September-November), and four biological indicators, namely, the Shannon-Wiener diversity index, the percentage of biomass of pollution-resistant species, the percentage of abundance of pollution-resistant species, and the percentage of abundance of sensitive species, are selected to evaluate the aquatic ecological status of the reference candidate points described in the invention (the evaluation results are shown in Table 5). The evaluation of the aquatic organism status of 6 of the 10 reference candidate points is good or better, which corresponds to the high altitude good ecological unit, the medium altitude good ecological unit, the water disturbance ecological unit, and the mine disturbance ecological unit, respectively. Among them, in the high altitude good ecological unit, the aquatic ecological status score of 2# is higher than the 1# point, and in the hydropower development interference ecological unit, the 5# point is higher than the 3# point. Therefore, the four reference candidate points 2#, 5#, 7#, and 4# are selected as the reference points.

[0057] Reference candidate point information and aquatic ecological status scoring results [Table 5]

[0058] S5, in constructing the natural mimicking reference point, among the reference candidate points of the living interference ecological unit and the industrial interference ecological unit, select 9# and 10# with high water ecological situation score to construct the natural mimicking reference point, the specific construction method refers to the above-mentioned S5 step of the present invention, where the stacked height of the water stop belt of 9# natural mimicking reference point is 5cm higher than the long-term average water level, that is, the stacked height is 20cm, the water depth difference between the depression unit and the shallow unit is 10cm, the upper end water stop wall is provided with one overflow port with a diameter of 5cm, and the lower end water stop wall is provided with one overflow port with a diameter of 10cm, the stacked height of the water stop belt of 10# natural mimicking reference point is the maximum water depth height of the bank, that is, 45cm, the water depth difference between the depression unit and the shallow unit is 7cm, the upper end water stop wall is provided with two overflow ports with a diameter of 5cm, and the lower end water stop wall is provided with one overflow port with a diameter of 10cm.

[0059] S6, evaluation of the aquatic ecological status of the natural mimicry reference point: 20 days after the microhabitat was constructed, the benthic fauna were measured and four biological indicators, namely, the Shannon-Wiener diversity index, the percentage of biomass of pollution-resistant species, the percentage of abundance of pollution-resistant species, and the percentage of abundance of sensitive species, were calculated, and the ecological status of the natural mimicry reference point was evaluated according to the method of S4 described above in the present invention. The results are shown in Table 6.

[0060] Assessment of the aquatic ecological status of natural mimic reference points [Table 6]

[0061] It can be seen that if the aquatic biological conditions of the constructed 9# and 10# natural mimicry reference points are evaluated as "good" or above, the construction of the disturbed river reference point can be realized, and the biological parameters such as biotope configuration, aquatic biodiversity, aquatic biological sensitivity, and functional state including ecological type units can be obtained from the constructed reference point, thereby determining the reference state of the aquatic ecological environment, effectively solving the problem that the river ecological unit cannot find the reference standard after interference, and providing support for the aquatic ecological restoration or management of subsequent disturbed river segments.

[0062] The above examples are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above examples. Any changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention are equivalent replacement forms, and all fall within the protection scope of the present invention. [Explanation of symbols]

[0063] 1-Upper shallow water unit 2-Middle recess unit 3-Lower shallow water unit 4-Wavy water cutoff wall 5-Top water cutoff wall 6-Bottom water cutoff wall 7-Small Habitat 8-Riverbank 9-Lump stone 10- Crushed Stone 11-Cobblestone 12-Overflow 13-Natural Sediment 14 - Water Stop

Claims

1. A step S1 of dividing a watershed basic spatial unit, which is to determine a reasonable catchment area threshold value by using a constant threshold method or a moderate index method based on the natural waterlogging characteristics and DEM data of the target watershed, and input the DEM data and the determined catchment area threshold value into the SWAT model to divide the watershed basic spatial unit; A step of analyzing the impact of human activities on ecological environmental stress in each basic spatial unit of a watershed and extracting hydroecological characteristics, in which the type of external environmental stress received is determined based on the analysis of the impact of human activities on the ecological environmental stress in each basic spatial unit of a watershed, and then classifying the basic spatial units of the watershed in step S1, extracting the bank sediment type, maximum water depth, average water depth, long-term average water depth, bank mean flow velocity, bank maximum flow velocity and average sea level for the basic spatial units of the watershed affected by the same type of stress, and extracting the bank mean water flow, average water depth, average sea level and bank sediment type of the basic spatial units of the same cluster affected by the same type of stress as the hydroecological characteristics of the basic spatial units of the watershed in the same cluster; A step S3 of selecting a reference candidate point, in which at least one reference candidate point is selected from within the watershed basic spatial unit of the same kind of water ecological features in the step S2; Step S4 of evaluating the aquatic life status of the reference candidate points, in which four biological indicators, namely, Shannon-Wiener diversity index, percentage of pollutant-resistant species biomass, percentage of pollutant-resistant species abundance, and percentage of sensitive species abundance, are selected, and the aquatic life status of the reference candidate points of step S3 is evaluated and scored, and whether each reference candidate point meets the designated standard is determined. If the designated standard is met, the point with the highest score is selected as the reference point, and the selection of the reference point is completed. If the designated standard is not met, step S5 is executed to construct a nature-mimicking reference point. A step of constructing a nature-mimicking reference point includes selecting a point with the highest biological score among the reference candidate points, constructing three staircase units, an upper shallow water unit, a middle depression unit, and a lower shallow water unit, which are sequentially connected using stones of different sizes, and the three staircase units are fitted together using blocks, crushed stones, boulders, and small crushed stones on one side away from the riverbank to form a waterstop, the waterstop of the three staircase units is sequentially connected to form a wavy waterstop wall, the riverbed of the middle depression unit forms a concave depression, and the middle depression unit and the upper shallow water unit / the lower shallow water unit are connected to form a waterstop wall. Step S5, in which the difference in elevation between the knit and the riverbed is equal to the difference between the maximum water depth value and the average water depth value extracted in step S2, an upper water cutoff wall is provided between the middle depression unit and the upper shallow water unit, and a lower water cutoff wall is provided between the middle depression unit and the lower shallow water unit, both ends of the upper water cutoff wall and the lower water cutoff wall are connected to the water stop zone and the river bank of the middle depression unit, respectively, and both the upper water cutoff wall and the lower water cutoff wall are provided with overflow ports, and a small habitat made of lumps and boulders is laid on the riverbed of the three staircase units; A step of evaluating the aquatic life status of the nature-mimetic reference point includes a step S6 of performing sampling and identification of benthic animals for the nature-mimetic reference point within a specified time after the construction in the step S5, and evaluating and scoring the aquatic life status by referring to the method in the step S4, and judging whether the nature-mimetic reference point meets the specified standard. If the specified standard is not met, the two physical element conditions of the water depth and flow speed of the microhabitat are adjusted, and then the sampling and identification of benthic animals and the evaluation and scoring of the aquatic life status are repeated within the specified time until the aquatic life status evaluation is equal to or higher than the specified standard, thereby completing the construction of the nature-mimetic reference point. A method for selecting and constructing reference points in a flooded river water ecology affected by interference, characterized in that

2. The small habitat environment in the upper riffle unit / the lower riffle unit includes one central boulder and a plurality of jade stones stacked around the central boulder. The plurality of small habitat environments in the upper riffle unit / the lower riffle unit are arranged in a shape similar to the Chinese character 'zhi'. The small habitat environment in the middle depression unit is arranged at the deepest position of the middle depression unit and includes two adjacent central boulders and a plurality of jade stones stacked around the two central boulders. The method for selecting and constructing a reference point in the flooded river aquatic ecosystem affected by interference according to claim 1, characterized in that.

3. The stacked height of the water stop belts in the upper riffle unit / lower riffle unit is higher than the average water depth value extracted in step S2, or 3 - 5 cm higher than the long-term average water level of the target river basin. The stacked height of the water stop belts in the depression unit is higher than the maximum water depth value extracted in step S2, or 7 - 15 cm higher than the long-term average water level of the target river basin. The heights of the upper water stop wall and the lower water stop wall are equal to the height of the water stop belt in the middle depression unit. At least one overflow opening with a diameter of 5 cm is provided on the upper water stop wall, and at least one overflow opening with a diameter of 10 cm is provided on the lower water stop wall. The method for selecting and constructing a reference point in the flooded river aquatic ecosystem affected by interference according to claim 2, characterized in that.

4. The concave width of the middle section of the wavy water stop wall towards the river bank side is 15° ± 2°. The straight-line length of the wavy water stop wall is 200 cm. Both ends of the wavy water stop wall are 75 cm away from the river bank. The shortest distance between the middle section of the wavy water stop wall and the river bank is 50 cm. The straight-line lengths of the water stop belts in the upper riffle unit and the lower riffle unit are both 75 cm. The length of the water stop belt in the middle depression unit is 50 cm. The method for selecting and constructing a reference point in the flooded river aquatic ecosystem affected by interference according to claim 3, characterized in that.

5. The substrate type of the natural imitation reference point is the same as the shore substrate type extracted in step S2. In principle, the substrate types in the three stepped units are kept consistent. If the three stepped units have a mixed substrate type, they are laid according to the substrate type with the smallest particle size. The method for selecting and constructing a reference point in the flooded river aquatic ecosystem affected by interference according to claim 4, characterized in that.

6. The method for selecting and constructing reference points in the water ecology of a flooded river subjected to interference, as described in claim 5, characterized in that the step of constructing nature-mimicking reference points in step S5 comprises first constructing a wavy cutoff wall at a position 50-70 cm away from the bank using stones of different sizes, then constructing an upper cutoff wall and a lower cutoff wall using stones of different sizes between the wavy cutoff wall and the river bank to form three staircase units, further digging a depression in the riverbed between the upper cutoff wall and the lower cutoff wall to form a middle depression unit, and finally constructing a small habitat in the riverbed in each staircase unit.

7. A method for selecting and constructing reference points in an interfered flooded river water ecology, as described in any one of claims 1 to 6, characterized in that in the case of constructing natural mimicking reference points in step S5, the grain size of the lumps used is 10-20 cm, the grain size of the gravel is 5-10 cm, the grain size of the boulders is 1-5 cm, and the grain size of the small crushed stones is <1 cm.

8. In step S1, the constant threshold method is a catchment area threshold determined empirically or by repeated comparison with an accurate watershed diagram, and the suitability index formula is: [0010] In formula 1, L ｉ : Shortage of water flow, L ｒ : Extra water flow length, L Ｔ : Total length of river system, Z: River section with excess or deficit water length; n: the total number of river sections with excess or deficit flow length; In the evaluation of the aquatic biological status of the reference candidate point in step S4, the calculation formula of the Shannon-Wiener diversity index is: [0025] In formula 2, H: Shannon-Wiener diversity index; n: total number of candidate point benthos; s: number of species of benthic fauna at the candidate point; n ｉ : the number of benthic animals of the i-th candidate point, The pollutant-resistant and sensitive species are distinguished based on the pollution tolerance value (TV) of the benthic animals. If the TV is less than or equal to 3, the species is sensitive, and if the TV is more than or equal to 7, the species is pollutant-resistant. The pollution tolerance value of the benthic animals is obtained by referring to Appendix K. List of Pollution Tolerance Values ​​of Benthic Animals in the "Technical Guide for Monitoring and Evaluation of River Water Ecological Environment Quality". The formula for calculating the percentage of pollutant-tolerant species richness is: [0030] In formula 3, B ｗ : Percentage of species richness tolerant to contamination, n ｗ : Number of species of benthic resistant species, s: the number of species of candidate point benthos, The formula for calculating the percentage of sensitive species abundance is: [0045] In formula 4, B ｍ : Sensitive species abundance percentage value, n ｍ : Number of species of benthic resistant species, s: the number of species of candidate point benthos, The formula for calculating the percentage of tolerant biomass is: [0050] In formula 5, M ｗ : Percentage value of the fouling-resistant biomass, m ｗ : Biomass of pollutant-resistant benthic species, m: total biomass of the candidate point benthos, The method for selecting and constructing reference points in the water ecology of a flooded river affected by interference, as described in claim 7, characterized in that after calculating the biological index of the reference candidate point based on the above calculation formula, the biological evaluation index is scored by referring to a preset scoring criterion for the biological evaluation index, and the scores are ranked, with 12-20 points being excellent, 9-12 points being good, 5-10 points being average, and 0-5 points being difference, and in determining whether each reference candidate point meets the designated criterion in step S3, the designated criterion is to select as a reference point a reference candidate point that is evaluated as good in the scoring criterion, i.e., the aquatic organism condition is good or above.

9. The specific steps of extracting the hydrological characteristics of the homogeneous watershed basic spatial units in step S2 are as follows: S21: In determining the bottom sediment type of the drainage basin basic spatial unit, the bottom sediment type is determined by the grain size of the riverbed on the bank within 1 meter of the river bank. If the river channel width is less than 1 meter, the range from the river centerline to the river bank is taken. S22: Pre-clustering is performed based on the watershed spatial basic unit of the shore sediment type, i.e., distinguishing the shore sediment type of the basic spatial unit affected by the same main stress, and using the stress-affected type and the shore sediment type as clustering factors to perform clustering; S23: In the classification and measurement of the basic requirements characteristics of the water ecology of the basic spatial unit of the basin, the water flow is the flow velocity measured in the mid-water period of the coastal water body, the water depth is the water depth measured in the mid-water period of the coastal water body, and the sea level is the average sea level within the basic spatial unit of the basin; S24: In the stepwise clustering analysis, all the watershed basic spatial units affected by the same stress are taken as samples, and the watershed spatial basic units affected by the same stress are clustered using the bottom sediment type as the pre-cluster variable factor, and then the water flow speed, water depth, and elevation as the post-cluster variable. After normalization, the clustering is performed again using the clustering shortest distance method to obtain the final result. S25: The method for selecting and constructing reference points in the hydrological ecology of flooded rivers affected by interference, as described in claim 7, characterized in that in extracting the hydrological environmental characteristics of the same type of watershed basic spatial unit, the method includes using the average water flow, average water depth, average sea level, and bottom sediment type of the watershed basic spatial unit of the same cluster affected by the same stress as the hydrological characteristics of that type of watershed.

10. 8. The method for selecting and constructing reference points in the hydrological ecology of a flooded river subjected to interference according to claim 7, characterized in that in step S3, the reference candidate points should simultaneously satisfy the following six requirements: (1) the water quality should be maintained at or above Level III within 1 km upstream and downstream on both sides of the coast, or the measured concentrations of non-anthropogenic pollutants should be maintained within the background level range; (2) there should be no sewage outlet within 1 km upstream and downstream on both sides of the coast; (3) there should be no agricultural cultivation with a wide area of ​​100 mu (about 666.7 square meters) or more within 1 km upstream and downstream on both sides of the coast; (4) there should be no known aquaculture within 1 km upstream and downstream on both sides of the coast; (5) there should be no main roads, urban trunk roads, or expressways within 1 km upstream and downstream on both sides of the coast; and (6) the resident population should be less than 100 people within 1 km upstream and downstream on both sides of the coast.

Images