A method for calculating the layout interval of a stepped ecological weir dam suitable for mountainous river channels
By calculating the spacing of tiered ecological weirs in mountainous river channels, the problem of dense weirs affecting hydrodynamics and ecology was solved, thus achieving the protection of river hydrodynamics and ecological environment and providing a technical basis for weir construction.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG INST OF HYDRAULICS & ESTUARY
- Filing Date
- 2023-09-05
- Publication Date
- 2026-05-29
AI Technical Summary
In the existing technology, the construction of cascade weirs and dams in mountainous rivers lacks regulations and standards, resulting in dense weirs and dams affecting the hydrodynamic conditions and ecological environment of the river, especially squeezing the living space of aquatic organisms, reducing biodiversity, and significantly altering the structure of the floodplain.
A method for calculating the spacing of cascade ecological weirs and dams in mountainous rivers is provided. By acquiring river data and topographic data, and combining hydraulic calculation standards and mathematical models, the spacing between backwater inundation and natural river sections is calculated to determine the spacing between weirs and dams in order to maintain hydrodynamic conditions and ecological environment. The method includes steps one to four.
It effectively maintains the hydrodynamic conditions and ecological environment of mountainous rivers, protects the habitats of aquatic organisms, ensures biodiversity, and provides technical basis for the construction or renovation of ecological weirs and dams, filling the gaps in existing technologies.
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Figure CN117132436B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of planning and design of ecological weir projects, and in particular to a method for calculating the spacing of cascade ecological weirs in mountainous river channels. Background Technology
[0002] Dams are small river-blocking structures commonly found in mountainous rivers. They achieve comprehensive water resource utilization and aquatic ecological environment improvement by intercepting water flow and raising water levels, such as water storage for irrigation, water diversion for power generation, and landscape enhancement. They are one of the important measures in mountainous river and small and medium-sized watershed management projects.
[0003] As an important habitat reinforcement structure, weirs and dams offer the following positive benefits: ① After the dam is built, the deep pools created by the impounded water are conducive to the precipitation of organic matter, providing nutrients for invertebrates; ② The deep pools formed downstream of the weir and dam help fish and other organisms to stay, providing refuge for fish during floods and dry seasons; ③ The stratosphere of the deep pools is a suitable spawning habitat; ④ After the construction and siltation of weirs and dams, the gradient of the riverbed along the course can be reduced, weakening the scouring effect of floods on the riverbed and the banks on both sides. However, most of the existing historical weirs and dams in the region were spontaneously constructed by local villages and towns, and the industry lacks relevant regulations and standards. This has led to problems such as insufficient planning and design and inadequate assessment of the impact on the river's aquatic ecological environment in current weir and dam construction. In particular, the negative impacts of densely packed, cascade-type weirs and dams are mainly manifested in the following ways: ① They alter the natural distribution pattern of the riverbed in mountainous areas. Especially when the backwater range of downstream weirs and dams extends upstream to the weir foot, the riverbank structure no longer exists, and the suitable feeding and breeding areas for aquatic organisms in mountainous rivers disappear; ② The hydrodynamic structure of the river section undergoes serious changes. Mountainous rivers were originally characterized by steep slopes and rapid flows. As the water level rises, the river section above the weir becomes like a lake or reservoir, with slower hydrodynamic conditions and reduced water purification capacity. The living space of native mountainous fish species that prefer clear water, rapid flow, and shallow beaches is constantly squeezed, resulting in a significant decline in biodiversity and population size, and problems such as species homogenization and simplified age structure; ③ The density of weirs and dams is too high. Some rivers even have seven or eight weirs and dams per kilometer, with a density as high as eight per kilometer, which seriously affects the natural ecological environment of the river. Summary of the Invention
[0004] The purpose of this invention is to overcome the shortcomings of the above-mentioned background technology and provide a calculation method for the spacing of cascade ecological weirs in mountainous rivers; so as to preserve the hydrodynamic conditions and ecological environment of mountainous rivers to the greatest extent. This calculation method is also simple and widely applicable.
[0005] To achieve the above objectives, the present invention adopts the following technical solution: a calculation method for the spacing of cascade ecological weirs and dams in mountainous river channels, comprising the following steps:
[0006] Step 1: Obtain and analyze relevant data. Using methods such as data statistics and topographic surveying, obtain the river's multi-year average flow and the topography of the planned river section. Statistically analyze the proportion of natural shoals (k), average river width (B), and gradient (i) along the planned river section. Investigate the local, economic, and protected fish species in the river where the weirs are located, and investigate the living habits of the target fish species.
[0007] Step 2: Calculate the backwater inundation spacing. Using the location of the lower-level weir as a reference, analyze its backwater range. The backwater range calculation can be performed using the reservoir backwater calculation method or mathematical model in the "Water Conservancy Engineering Hydraulic Calculation Specification" (SL 104-2015). The upstream water level is taken as the weir crest elevation, the starting point is the upstream vertical surface of the weir, the inflow condition is the river's multi-year average flow, and the end of the backwater surface line is calculated to a point where the backwater level is no higher than 0.3m above the natural water level of the same frequency at the same cross-section (point A). The backwater inundation spacing is L1 (using the horizontal projection length). For rivers with small catchment areas (catchment area of the river above the weir is less than 30km²),... 2 (The following) can be used directly as the intersection of the static water surface formed by the crest elevation of the downstream weir and the upstream riverbed under the condition of no upstream water inflow, and the area above 0.3m water depth is subtracted as the backwater inundation distance. The calculation formula is as follows:
[0008] L1=H / i-0.3 / i (1)
[0009] In the formula, L1 is the backwater inundation spacing, which is the horizontal projection length formed by the backwater inundation range of the weir, measured from the vertical surface upstream of the lower-level weir; H is the height of the weir; and i is the river slope.
[0010] Step 3: Calculate the distance between the natural river channel sections from the end of the backwater to the upstream weir. Mountainous rivers feature alternating shoals and channels. The shallow shoals, with their shallow depths, abundant pebbles, and rapid currents, provide ample food, rich dissolved oxygen, and good cover for small aquatic organisms, forming an important component of the river's ecological habitat. After the construction of the weir, a certain range of deep pools will form in the river channel above the weir, disrupting the deep pool-shallow shoal sequence. Therefore, during the planning and site selection phase, to ensure the ecological health of this section of the river, the ratio of shoals to channels should be reshaped. The formula for calculating the distance L2 between the natural river channel sections above the backwater range is:
[0011] L2=(S1 / (1-k)-S1) / B / k; (2)
[0012] In the formula, L2 is the horizontal projection length between the backwater end A of the lower-level weir and the downstream end of the upper-level weir; S1 is the area of the deep pool area formed by the backwater inundation range of the weir; k is the proportion of the area of natural shallows in the planned river section; and B is the average width of the planned river section.
[0013] The catchment area is relatively small (preferably less than 30 km² of the catchment area of the weir-adjacent river channel). 2For river channels with roughly equal width upstream and downstream, control can be implemented based on the lower limit of 30%–40% of the river habitat in the shallow section, as stated in "Ecological Hydraulic Engineering" (Dong Zheren, China Water Resources and Hydropower Press, March 2019), i.e., k = 0.3. The simplified calculation formula is as follows:
[0014] L2=(L1 / (1-0.3)-L1) / 0.3=1.43L1 (3)
[0015] Step four: Determine the weir-dam spacing. Weir-dam spacing includes the backwater inundation spacing and the spacing of natural river channel sections. The calculation formula is:
[0016] L = L1 + L2 = 2.43L1 (4)
[0017] In the formula, L is the weir-dam spacing, which is the horizontal projection length between the upstream vertical surface of the lower-level weir-dam and the downstream end of the upper-level weir-dam.
[0018] The beneficial effects of this invention are as follows: Aiming to maintain biodiversity, including fish, in mountainous rivers, this invention integrates natural channel patterns and hydrodynamic conditions to propose a calculation method for the spacing of cascade ecological weirs in mountainous rivers. This method preserves the hydrodynamic conditions and ecological environment of mountainous rivers to the greatest extent possible by maintaining a certain range of natural river sections and channel proportions between cascade weirs, creating habitats for aquatic organisms to forage and reproduce. Furthermore, this calculation method fills the gaps in domestic and international methods for controlling and calculating the spacing of weirs in mountainous rivers. The method is simple, widely applicable, and can provide technical support for the construction and reconstruction of ecological weirs in mountainous rivers, as well as a reference for the formulation of relevant regulations and standards. Attached Figure Description
[0019] Figure 1 This is a flowchart illustrating the method described in this invention.
[0020] Figure 2 This is a plan view of a mountainous river channel in an embodiment of the present invention.
[0021] Figure 3 This is one of the longitudinal cross-sectional views of a mountainous river channel in an embodiment of the present invention (a schematic diagram based on conventional calculations).
[0022] Figure 4 This is the second longitudinal cross-sectional view of a mountainous river in an embodiment of the present invention (simplified calculation diagram).
[0023] The diagram is labeled as follows: 1. Upper weir; 2. Natural river channel section; 3. Shoal; 4. Backwater end; 5. Backwater inundation area; 6. Lower weir; 7. Deep channel area; 8. Backwater surface line; 9. Original natural river channel water level; 11. Riverbed; L, weir spacing; L1, backwater inundation spacing; L2, natural river channel spacing; H, lower weir height. Arrows indicate the direction of upstream water flow. Detailed Implementation
[0024] The present invention will be further described in detail below with reference to the embodiments shown in the accompanying drawings.
[0025] Calculation Example 1:
[0026] The example selected a typical county-level river in the mountainous area of southwestern Zhejiang, with a catchment area of 200 km². 2 The average river width is 80m, and the average annual flow is 120m³. 3 The river has a gradient of 0.2% and a long-term average flow rate. The floodplain accounts for 42% of the river section, and the planned height of the downstream weir is 3m. The typical native and economically important fish species in this river are the mandarin fish and the pufferfish. The mandarin fish is a stream fish, widely distributed in mountain streams with low water temperature in hilly areas. It prefers to live in the upper layer of water bodies with abundant aquatic plants. After hatching, the juvenile fish forage and fatten in shallow water areas with pebbles. This type of fish has similar living habits to the mandarin fish. The two fish often gather together and like to play in shallow waters with fast-flowing water and sandy bottoms. They are more common in tributaries and less common in deep lakes.
[0027] (1) Calculation of backwater inundation spacing: A one-dimensional mathematical model of the river network was used for analysis, and the upstream inflow condition was based on the river's multi-year average flow rate of 120 m³ / h. 3 / s, the end of the backwater surface line 8 is calculated to a point where the backwater level is no higher than 0.3m above the natural water level of the same frequency at the same cross-section; the calculated backwater submersion spacing is:
[0028] L1 = 1650m
[0029] (2) Calculate the distance L2 of the natural river channel between the end of the backwater 4 and the upstream weir 1:
[0030] ①According to statistics, the river area within L1 is 132,000 km². 2 ;
[0031] ②L2=(S1 / (1-k)-S1) / B / k=(132000 / (1-42%)-132000) / 80 / 42%=2845m.
[0032] (3) Determine the spacing between weirs and dams:
[0033] L = L1 + L2 = 1650 + 2845 = 4495m
[0034] Therefore, the minimum distance between the lower-level weir and the upper-level weir is 4495m.
[0035] Calculation Example 2:
[0036] The example selected a typical township-level river in the mountainous area of southwestern Zhejiang, with a catchment area of 10 km². 2 The average river width is 40m, and the average annual flow is 20m³. 3 The river has a flow rate of / s and a gradient of 0.5%. The average annual flow rate is 46% of the riverbed, and the planned height of the downstream weir is 3m. Typical native and economically important fish species in this river are mainly the mandarin fish and the pufferfish.
[0037] Considering the small catchment area of the river channel and its regular width upstream and downstream, a simplified calculation is adopted:
[0038] (1)L1=H / i-0.3 / i=3 / 0.005 -0.3 / 0.005=540m
[0039] (2)L=2.43L1=2.43×540=1312m
[0040] Therefore, the minimum distance between the lower-level weir and the upper-level weir is 1312m.
[0041] The principle of this invention is as follows: Mountainous river channels feature alternating shoals and channels. The shallow shoals, with their shallow depth, abundant pebbles, and rapid currents, provide ample food, rich dissolved oxygen, and good cover for small aquatic organisms, forming a crucial component of the river's ecological habitat. After the construction of weirs, a certain range of backwater pools will form in the river channel above the weirs, disrupting the natural alternation of deep pools and shallow shoals. Therefore, during the planning and site selection phase, a certain ratio of shoals to channels should be maintained to ensure the ecological health of this section of the river. This invention aims to maintain biodiversity, including fish, in mountainous river channels. It integrates natural shoal and channel patterns with hydrodynamic conditions, and systematically studies a method for calculating the spacing of tiered ecological weirs suitable for mountainous river channels. First, based on the alternating deep pool and shallow shoal sequence pattern of mountainous river channels, the main objective of the invention was determined, namely, to maintain the ratio of shoals to channels and protect the habitat of target fish and other organisms. To this end, the current proportion of shallow shoals and the gradient of the riverbed along the course were analyzed. Second, several methods for calculating the backwater inundation distance on the upstream side of the weir were proposed according to the "Specifications for Hydraulic Calculation of Water Conservancy Projects" (SL 104-2015), and a simplified formula was proposed for rivers with small catchment areas (1). Then, based on the ratio of shoals to channels and the current proportion of river shoals, a method for calculating the natural river length upstream of the backwater area was proposed (2). For rivers with small catchment areas and basically equal width upstream and downstream, the calculation method was simplified according to the requirement in the literature "Ecological Hydraulic Engineering" (Dong Zheren, China Water Resources and Hydropower Press, March 2019) that the shallow shoal section generally accounts for 30% to 40% of the river habitat. Finally, the distance between the two weirs was obtained (4).
[0042] This invention proposes a calculation method for the spacing of cascade ecological weirs in mountainous rivers. This method can guide the spacing calculation during the design of cascade weirs in mountainous rivers, and to a certain extent maintain the hydrodynamic conditions and ecological characteristics of weirs after their construction in mountainous rivers. It provides a technical basis for protecting native fish species and maintaining the biodiversity of mountainous rivers.
Claims
1. A method for calculating the spacing of cascade ecological weirs and dams applicable to mountainous river channels, comprising the following steps: Step 1: Obtain relevant data and conduct investigation and analysis; Step 2: Determine the scope of the backwater zone; using the location of the lower-level weir as a reference, calculate its backwater range; Step 3: Calculate the distance between the natural river channel sections from the end of the backwater to the upstream weir; reshape the channel-shoal ratio of the river section; Step 4: Determine the spacing between the weirs and dams; The spacing between weirs and dams includes the backwater inundation spacing L1 and the spacing between natural river sections L2; the calculation formula is: L = L1 + L2 (4) In the formula, L is the weir-dam spacing, which is the horizontal projection length between the upstream vertical surface of the lower-level weir-dam and the downstream end of the upper-level weir-dam; The method used in step one involves obtaining the multi-year average flow of the river and the topography of the planned river section through data statistics and topographic surveys. It also involves statistically analyzing the proportion of natural shoals (k), average river width (B), and gradient (i) along the planned river section; investigating the local, economic, and protected fish species in the river where the weirs and dams are located; and investigating the living habits of the target fish species. The specific calculation method for step two is as follows: Calculation of backwater inundation spacing: The water level in front of the weir is based on the weir crest elevation, the starting point is the upstream face of the weir body, the inflow conditions are based on the multi-year average flow of the river, the end of the backwater surface line is calculated to a point where the backwater level is not higher than 0.3m above the natural water level of the same frequency in the same cross section, and the backwater inundation spacing L1 is based on the horizontal projection length. For rivers with small catchment areas, the area below the intersection of the static water surface formed by the crest elevation of the downstream weir (when there is no upstream inflow) and the upstream riverbed, minus 0.3m of water depth, is taken as the backwater inundation distance. The calculation formula is as follows: L1=H / i-0.3 / i (1) In the formula, L1 is the backwater inundation spacing; H is the weir height; and i is the river slope. The calculation method for the spacing between natural river sections in step three is as follows: L2=(S1 / (1-k)-S1) / B / k; (2) In the formula, L2 is the horizontal projection length between the backwater end A of the lower-level weir and the downstream end of the upper-level weir; S1 is the area of the deep pool area formed by the backwater section of the weir; k is the proportion of the area of natural shallows in the planned river section; B is the average width of the planned river section. For rivers with a small catchment area upstream of the weir and with roughly equal width upstream and downstream, the calculation formula simplifies to: L2=(L1 / (1-0.3)-L1) / 0.3= 1.43L1 (3).
2. The calculation method for the spacing of cascade ecological weirs and dams in mountainous rivers according to claim 1, characterized in that: The term "small catchment area" refers to a catchment area in the river channel upstream of the weir that is less than 30 km². 2 .