Calculation method for dry season ecological base flow in arid and semi-arid region

Abstract

The invention relates to the technical field of ecological hydrology and river ecological restoration, and particularly discloses an arid and semi-arid region dry season ecological base flow calculation method which comprises the following steps: S1, based on actually measured hydrological large section data, establishing a relation curve of a water level and a wetted week; s2, identifying a sudden change point in the water level-wetted week relation curve, and taking the water level corresponding to the sudden change point as a beach protection threshold value; s3, ecological constraint conditions are determined according to habitat water depth requirements of main aquatic organisms, the suitable water depth of sturgeon is 2-4 m, the suitable average water depth of salmon is 0.5 m, and the suitable average water depth of general fish is 0.3 m; and S4, establishing a water level-flow relation curve by using actually measured day-by-day water level-flow data, and reversely deducing a corresponding flow value by using a beach abrupt change point water level or a biological constraint water depth to obtain a dry season ecological base flow. According to the calculation method for the dry season ecological base flow in the arid and semi-arid region, the beach protection threshold value can be recognized based on the wetted week sudden change of the cross section of the river channel.

Description

Technical Field

[0001] This invention relates to the field of ecohydrology and river ecological restoration technology, specifically a method for calculating the dry season ecological baseflow in arid and semi-arid regions. Background Technology

[0002] In arid and semi-arid regions, seasonal river flow interruptions or droughts are common. Insufficient water flow during the dry season leads to the degradation of river wetland ecosystems, decreased biodiversity, and loss of aquatic ecological functions. Existing methods for calculating ecological baseflow, such as the minimum monthly average flow method, the Tennant method, and the IFIM model, struggle to take into account river morphology, biological water requirement depth, and shoreline habitat characteristics, failing to accurately reflect the water requirement characteristics of ecosystems under dry season conditions. Therefore, a comprehensive calculation method that considers water level-wetline perimeter relationships, shoreline abrupt changes, and biological water requirement depth is urgently needed. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for calculating the ecological base current during the dry season in arid and semi-arid regions, comprising the following steps:

[0004] S1. Based on measured hydrological cross-sectional data, establish the relationship curve between water level and wetted perimeter;

[0005] S2. Identify abrupt change points in the water level-wet perimeter relationship curve, and use the water level corresponding to the abrupt change point as the protection threshold for the beach.

[0006] S3. Determine ecological constraints based on the habitat depth requirements of major aquatic organisms. The suitable water depth for sturgeon is 2-4m, the suitable average water depth for salmon is 0.5m, and the suitable average water depth for most fish is 0.3m.

[0007] S4. Using measured daily water level-flow data, establish a water level-flow relationship curve, and use the water level at the abrupt change point on the beach or the biologically constrained water depth to back-calculate the corresponding flow value to obtain the dry season ecological base flow.

[0008] S5. During the freezing period, the flow rate of 90% of the dry years in historical data is selected as the ecological base flow supplement.

[0009] Preferably, the wetted perimeter can be approximately obtained by measuring the width of the water surface in the cross-section of the river channel.

[0010] Preferably, the abrupt change point on the beach is identified by the location of the abrupt change in the first derivative of the wetted perimeter-water level relationship curve.

[0011] Preferably, the ecological constraints can be modified based on a survey of typical species habitats in the target river or a regional biological water demand database.

[0012] Preferably, the method is applicable to rivers in arid and semi-arid regions. When calculating the ecological baseflow, sediment transport and bird habitat requirements can be temporarily disregarded, and can be further modified according to the needs of ecological expansion.

[0013] This invention provides a method for calculating the ecological base current during the dry season in arid and semi-arid regions. It has the following beneficial effects:

[0014] 1. Identify the protection threshold of the riverbank based on the wet perimeter change of the river section.

[0015] 2. Introduce biological water depth constraints to improve the ecological suitability of the ecological baseflow.

[0016] 3. Use long-term monitoring data to infer traffic flow and improve spatiotemporal representativeness.

[0017] 4. Consider the ecological water demand during the freezing period to enhance seasonal applicability. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall process of the method of the present invention;

[0019] Figure 2 This is a schematic diagram of a typical river channel water level-wetted perimeter relationship curve;

[0020] Figure 3 The wetted perimeter variation characteristic curve is based on the identification of abrupt change points;

[0021] Figure 4 A diagram showing the river cross-section and wetted perimeter below the protection threshold water level (H1=149.172m);

[0022] Figure 5 A schematic diagram of the river cross-section and wetted perimeter morphology at the ecological water level (H2=150.352m);

[0023] Figure 6 The curve is derived by inversely from the water level-flow rate relationship. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The first embodiment provides a method for calculating the ecological base current during the dry season in arid and semi-arid regions. The dry season is defined as April-May and October-December of the current year, with December, January, February, and March being the freezing period. The method includes the following steps:

[0026] S1. Establish the water level-wet perimeter relationship curve and identify the beach protection threshold water level H1:

[0027] Based on measured hydrological cross-sectional data (starting point distance and riverbed elevation data), the wetted perimeter P of the cross-section under different simulated water levels H was calculated using geometric methods. A scatter plot sequence of water level-wetted perimeter relationship was constructed. The water level-wetted perimeter curve was analyzed using the first derivative abrupt change identification method. Since the sensitivity of wetted perimeter to water level (dP / dH) changes significantly when water flows from the main channel to the side bank, the abrupt change point (inflection point) of the curve was identified. The water level corresponding to the abrupt change point was determined as the side bank protection threshold water level H1.

[0028] S2. Determine the biological constraint water level H2:

[0029] Based on the key aquatic organisms and their suitable habitats in the target river, determine the suitable average water depth for different species. In this embodiment, sturgeon (suitable water depth) was selected. ≈4.0m), salmon (suitable water depth) (≈0.5m) and common fish (suitable water depth) (≈0.3m) was used as an indicator species, combined with the cross-sectional riverbed reference elevation. Convert the appropriate water depth into the corresponding absolute water level elevation. Following the principle of "strictest protection," the maximum water level required by each species is taken as the comprehensive ecological constraint water level.

[0030]

[0031] S3. Establish water level-flow relationship and reverse-calculate control flow:

[0032] Daily water level and flow rate data measured over many years in the study area were selected, and sample data from the dry season (non-freezing period, such as April-May and October-November) were screened to establish a water level-flow rate (HQ) relationship model. Logarithmic multinomial or power function models were preferred for fitting.

[0033]

[0034] The fitting accuracy was tested by calculating the coefficient of determination (R²) and the root mean square error (RMSE). Using the established functional relationship, the threshold water level for shoal protection was determined. and ecological constraint water level Substituting into the equation, the corresponding morphological protection flow rate is obtained by reverse calculation. and biological suitable flow ;

[0035] S4. Determine the ecological base current during the dry season and freezing period:

[0036] To simultaneously meet the needs of river channel stability and biological habitat, and The larger value is used as the ecological base current during the dry season (non-freezing period). ;

[0037]

[0038] For the freezing period (December to March of the following year), the conventional water level-discharge relationship fails due to the influence of the ice sheet. Therefore, a historical hydrological statistical method is used. Based on multi-year daily discharge sequences, the average discharge of the driest month during the freezing period each year is extracted to form a sample set, and the discharge value corresponding to a 90% guarantee rate (P=90%) is calculated. This is used as a supplementary value for the ecological baseflow during the freezing period.

[0039] Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art and related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention. Structures, devices, and operating methods not specifically described and explained in the present invention, unless otherwise specified or limited, shall be implemented according to conventional means in the art.

Claims

1. A method for calculating the ecological base current during the dry season in arid and semi-arid regions, characterized in that, Includes the following steps: S1. Based on measured hydrological cross-sectional data, establish the relationship curve between water level and wetted perimeter; S2. Identify abrupt change points in the water level-wet perimeter relationship curve, and use the water level corresponding to the abrupt change point as the protection threshold for the beach. S3. Determine ecological constraints based on the habitat depth requirements of major aquatic organisms. The suitable water depth for sturgeon is 2-4m, the suitable average water depth for salmon is 0.5m, and the suitable average water depth for most fish is 0.3m. S4. Using measured daily water level-flow data, establish a water level-flow relationship curve, and use the water level at the abrupt change point on the beach or the biologically constrained water depth to back-calculate the corresponding flow value to obtain the dry season ecological base flow. S5. During the freezing period, the flow rate of 90% of the dry years in historical data is selected as the ecological base flow supplement.

2. The method according to claim 1, characterized in that, The wetted perimeter can be approximately obtained from the width of the water surface in the cross-section of the river channel.

3. The method according to claim 1, characterized in that, The abrupt change points on the beach are identified by the abrupt change locations of the first derivative of the wetted perimeter-water level relationship curve.

4. The method according to claim 1, characterized in that, The ecological constraints can be modified based on a survey of typical species habitats in the target river or a regional biological water requirement database.

5. The method according to claim 1, characterized in that, The method is applicable to rivers in arid and semi-arid regions. When calculating the ecological baseflow, sediment transport and bird habitat requirements can be temporarily disregarded, and can be further modified according to the needs of ecological expansion.

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