CN109736259B - Hydraulic determination method for mountain river compound beach utilization range and flood control safety position - Google Patents
Hydraulic determination method for mountain river compound beach utilization range and flood control safety position Download PDFInfo
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Abstract
The invention provides a hydraulic determination method for a mountainous area river compound beach utilization range and a flood control safety position, which comprises the following steps: (1) under the condition of different left beach effective water passing widths and right beach effective water passing widths, calculating corresponding flow rates when the relative water levels take different values, and drawing a water level-flow relation graph of a typical section; (2) calculating the maximum available width of the compound beach according to the design flow and the design flood control relative water level of the target river reach by combining a water level-flow relation graph; (3) after the actual utilization width of the left beach and the actual utilization width of the right beach are determined, corresponding flow rates when the relative water levels take different values are calculated, a water level-flow relation curve is drawn, the flood control safety relative water level is determined by combining the design flow rate of the target river reach and the design flood control relative water level, and the position above the flood control safety relative water level is the flood control safety position.
Description
Technical Field
The invention belongs to the field of utilization of mountainous river beaches and prevention and control of mountain flood disasters, and relates to a hydraulics determination method for a mountainous river compound beaches utilization range and a flood control safety position.
Background
China is a mountainous country, mountainous rivers are constrained by landform conditions and changes of flood steep rising and falling and incoming sand to form a compound river channel form, river beach land is often used as cultivated land by residents, and sometimes, the river beach land is also used for building residents. The area of the river basin in the mountain area of China is 100km2About 5 million rivers exist, and the compound river beach formed by the rivers is a main available area for people living and agricultural production in mountain areas. More than 1500 county administrative districts exist in mountainous areas in China, and the number of residents is about 5.5 hundred million, which accounts for 44.2% of the total population of the whole country. The influence of flood beaches and floods in flood season of the compound river channel, particularly sudden rainstorm mountain floods, frequently occurs that main river channels are silted up, the flood level is increased steeply, and the mountain floods quickly cause silting, washing and submerging on crops in a beach area, bank buildings, roads and the like close to the beach area, so that serious mountain flood disasters are caused, and serious loss is caused to life and property safety of people.
Due to the extremely shortage of available land in the mountainous area, the mountainous area river compound beach has become an important area for the social and economic development of the mountainous area. However, due to the influence of the water blocking effect of crops and buildings on the beach, the water passing area under the same water level condition is reduced, so that the flood carrying capacity of the compound river channel is reduced, and the reduction of the flood carrying capacity of the river channel often causes the occurrence of a flood disaster on the shore buildings close to the beach. At present, the scientific basis for the utilization of the compound beach by residents in the mountain river basin is deficient, no scientific method is provided for guiding the available range of the beach, and a proper method is also lacking for defining the range of the safe position of the area on the shore near the beach, so that the safe range of the utilization of the beach is difficult to determine, the problem that the compound beach of the mountain river is submerged after being utilized is often caused, and the situation that the buildings, roads, cultivated lands and the like on the shore near the beach are submerged due to the unreasonable utilization range of the beach is also frequent. Therefore, at present, a method capable of scientifically determining the available range of the mountain river compound beach is urgently needed, so that the compound beach is utilized in a reasonable range, the compound beach of the mountain river is fully utilized, the flood running safety of the mountain river is not affected, and the method has positive significance for the utilization of the mountain river compound river beach and the prevention and control of mountain flood disasters.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, and provides a hydraulic determination method for the utilization range and the flood control safety position of the compound beach of the mountain river, so that the utilization range of the compound beach of the mountain river and the flood control safety position of the river bank near the beach are determined more scientifically and reasonably, the full utilization of the compound beach of the mountain river is realized on the premise of reducing the flood control safety influence on the compound river, and scientific guidance is provided for the building position on the river bank near the beach.
The invention provides a hydraulic determination method for a mountainous area river compound beach utilization range and a flood control safety position, which comprises the following steps:
(1) drawing water level-flow relation diagram of typical section
Selecting a river reach needing to determine the beach utilization range from the mountain river as a target river reach, selecting a typical section from the target river reach, and drawing a water level-flow relation graph of the typical section;
the water level-flow relation graph of a typical section is drawn as follows:
the shapes of the water passing surfaces of a main groove, a left beach and a right beach on a typical section are approximate to rectangles, the width of the main groove is measured and recorded as B2Measuring the total width of the left beach and recording the total width as Bt1Measuring the total width of the right beach and recording the total width as Bt3；
Assuming that the effective water passing width of the left beach is B1The effective water passing width of the right beach land is B3When the relative water level of the typical section is Z, the relative water level refers to the elevation of the free water surface relative to the bottom bed of the main tank, and the depth h of the left beach land is determined by combining the relative heights of the left beach land, the right beach land and the bottom bed of the main tank or combining the relative heights of the left beach land, the right beach land and the bottom bed of the main tank and the sediment deposition thickness1Depth h of main trough2The depth h of the right beach land3The water passing area A of the left beach land1Water passing area A of the main tank2And the water passing area A of the right beach3；
Under the condition of different left beach effective water passing widths and right beach effective water passing widths, corresponding flow rates when the relative water levels take different values are calculated according to the formula (1), the corresponding flow rates and the relative water levels are expressed as points (Q, Z),
in the formula (1), Q is a flow rate, n1,n2,n3The respective coefficients of Manning roughness, i, of the left beach, the main trough and the right beach1,0,i2,0,i3,0The river bed slope of the left beach, the main trough and the right beach respectively;
constructing a plane rectangular coordinate system by taking the flow as an x axis, taking the relative water level as a y axis and taking the points (0,0) as the origin of coordinates, marking all the points (Q, Z) obtained by the calculation in the step I on the plane rectangular coordinate system, and then smoothly connecting all the points (Q, Z) obtained by the calculation under the conditions of the effective water passing width of the same left beach land and the effective water passing width of the right beach land by using the same curve to obtain a water level-flow relation graph comprising a plurality of water level-flow relation curves;
(2) calculating the maximum available width of the compound beach
Determining the design flow Q of the target river reach according to the hydrological datadAnd designing flood control relative water level ZdIn the water level-flow rate relation diagram, a straight line y is set as ZdAnd the straight line x ═ Qd，
From each water level-flow relation curve and straight line x ═ QdOf the intersections of (2), an AND point (Q) is selectedd,Zd) Closest and located on a line y ═ ZdThe lower point is taken as a critical point, a water level-flow relation curve comprising the critical point is taken as a critical curve, and the effective water passing width of the left beach land and the effective water passing width of the right beach land corresponding to the critical curve are respectively taken as Bg1,Bg3Calculating the maximum available width of the left beach and the maximum available width of the right beach of the target river reach according to the formulas (2) to (3),
Bmax1＝Bt1-Bg1 (2)
Bmax3＝Bt3-Bg3 (3)
in formulae (2) to (3), Bmax1Is the maximum available width of the left beach of the target river reach, Bmax3Is the maximum available width of the right beach of the target river reach, Bt1The total width of the left beach, Bt3The total width of the right beach, Bg1Is the effective water passing width of the left beach corresponding to the critical curve, Bg3The effective water passing width of the right beach corresponding to the critical curve;
when the compound beach of the target river reach is utilized, the water level is changed from [0, B ] in the left beachmax1]The interval is selected to be used from [0, B ] in the right beachmax3]Selecting any width for utilization;
(3) determining flood control safety locations
Suppose that the actual utilization width of the left beach land is b1，0≤b1≤Bmax1And the actual utilization width of the right beach land is b3，0≤b3≤Bmax3And drawing the actual utilization width of the left beach as b1The actual utilization width of the right beach is b3Temporal water level-Flow rate relation curve:
calculating the corresponding flow rate when the relative water level takes different values according to the formula (1), and B in the formula (1) during calculation1＝Bt1-b1，B3＝Bt3-b3The corresponding flow and relative water level are represented as points (Q, Z),
constructing a plane rectangular coordinate system by taking the flow as an x axis, the relative water level as a y axis and the points (0,0) as the origin of coordinates, marking all the points (Q, Z) obtained by the calculation in the step I on the plane rectangular coordinate system, and then smoothly connecting all the points (Q, Z) by using the same curve to obtain a water level-flow relation curve;
drawing a straight line x-Q in the water level-flow relation graphdLine x ═ QdThe longitudinal coordinate value of the intersection point of the relation curve of the water level and the flow is the flood control safety relative water level, the position above the flood control safety relative water level is the flood control safety position, and when the building is built on the bank of the compound beach land of the target river reach, the foundation of the building is in the flood control safety position.
In the method for determining the utilization range of the compound beach areas of the mountainous rivers and the hydraulics of the flood control safety positions, the shapes of the water flowing surfaces of the main trough, the left beach area and the right beach area on the typical cross section are all similar to rectangles in the step (1), because for the mountainous rivers, the shapes of the main trough of the river channel with the side beaches and the main trough of the river channel without the side beaches are different, the main trough of the river channel without the side beaches is V-shaped, the main trough of the river channel with the side beaches is U-shaped, and the side beaches are relatively flat.
In the method for determining the utilization range of the mountain river compound beach and the hydraulics of the flood control safety position, the formula (1) is adopted to calculate the corresponding flow when the relative water level takes different values, and the method is derived through the following processes on the basis that the shapes of the water passing surfaces of the main tank, the left beach and the right beach on the typical section are approximate to rectangles:
based on the hydraulics theory (the hydraulics of Sichuan university and the national key laboratory for developing and protecting mountain rivers, 2016), the complex section flow-through flow calculation formula can be expressed as formulas (4) to (5):
wherein Q is the flow rate, m is the total number of the divided sections, Kj、ij、nj、Aj、RjRespectively including flow modulus, energy slope ratio drop, Manning roughness coefficient, water passing area and hydraulic radius (the hydraulic radius is the ratio of water passing area to wet circumference) of j section, and the river bed ratio drop i can be used in actual calculationj,0Instead of energy slope ij。
If a compound cross-sectional shape is shown in fig. 1, the cross-sectional shape shown in fig. 1 is also a cross-sectional shape in which the shapes of the water passing surfaces of the main trough, the left beach and the right beach on a typical cross section are all approximated to rectangular shapes.
Then the flow corresponding to a certain relative water level at this time is calculated as:
using equation (5), equation (6) may become:
further, it may become:
in the method for determining the utilization range of the mountain river compound beach and the flood control safety position in hydraulics, when calculating the corresponding flow rate when the relative water level takes different values according to the formula (1), the value of the relative water level comprises designing the flood control relative water level ZdThat is, the value of the relative water level is taken from the water depth of the main tank to the designed flood control relative water level Z from 0dMore preferably, one is selected at intervals of 0.1 to 0.2mThe relative water level values were calculated.
In the method for determining the utilization range of the mountain river compound beaches and the hydraulics of the flood control safety position, the left beaches are beaches on the left side of the main trough when viewed along the direction of water flow, and the right beaches are beaches on the right side of the main trough when viewed along the direction of water flow.
In the method for determining the utilization range of the compound beach land of the mountain river and the hydraulics of the flood control safety position, in the step (3), the actual utilization width of the left beach land is calculated according to the direction from the shore of the left beach land to the river center, and the actual utilization width of the right beach land is calculated according to the direction from the shore of the right beach land to the river center.
Compared with the prior art, the technical scheme of the invention has the following beneficial technical effects:
the method is provided on the basis of the field investigation and the system analysis of the water level-flow relation change characteristics of the overflowing section of the mountain river with the beach, combines the siltation condition of the mountain river main trough, and can determine the usable range of the beach and the flood control safe water level of the target river reach after determining the usable range of the beach according to the water level-flow relation of the mountain river design overflowing capacity, thereby determining the flood control safe position of the target river reach. The method can solve the problems that the utilization range of the compound beach land is effectively guided by no proper method at present, the safety range of the utilization of the beach land cannot be accurately determined due to the fact that residents in mountain areas and river basin utilize the compound beach land blindly, and submerged disasters are often encountered on the utilized beach land and buildings, roads, cultivated lands and the like on the shore near the beach land. The method can provide scientific basis for safe utilization of mountainous area rivers and beaches and prevention and control of mountain torrent disasters.
Drawings
FIG. 1 is a schematic diagram of a multiple cross-section flow division calculation.
Fig. 2 is a photograph (from Google Earth) of 26 days 5 and 2014 of the target river reach in example 1, wherein the cross section indicated by the dotted line in fig. 2 is a typical cross section selected in example 1, and the arrow in fig. 2 is the water flow direction.
FIG. 3 is a schematic view of a typical cross section in example 1.
FIG. 4 is a water level-flow rate relationship diagram of a typical cross section in example 1.
Fig. 5 is a photograph (from Google Earth) of the target river course of example 2 in 2017, month 1 and day 20, the cross section indicated by the dotted line in fig. 5 is a typical cross section selected in example 2, and the arrow in fig. 5 indicates the water flow direction.
FIG. 6 is a schematic view of a typical cross section in example 2.
FIG. 7 is a water level-flow rate relationship diagram of a typical cross section in example 2.
Detailed Description
The method for determining the utilization range of the mountainous area river compound beach and the hydraulics of the flood control safety position provided by the invention is further explained by the embodiment. It should be noted that the following examples are only for illustrating the present invention and should not be construed as limiting the scope of the present invention, and those skilled in the art can make certain insubstantial modifications and adaptations of the present invention based on the above disclosure and still fall within the scope of the present invention.
Example 1
In this embodiment, the method for determining the hydraulic force of the mountain river compound beach use range and the flood control safety position provided by the present invention will be described in detail.
The Longxi river is a first-level branch flow growing upstream of Minjiang in Yujiang Wei city, the total length is 18.22km, and the area of a drainage basin is 79km2. A certain river section at the downstream of the Longxi river is influenced by upstream coming sand and river channel widening, a wider beach is formed on two sides of a main channel of the river channel, a residential house is built on a left beach due to the requirement of concentrated arrangement of residents in Wen river earthquake, as shown in figure 2, and figure 2 is a photograph of a target river section in 2014, 5 and 26 (from Google Earth). However, in 2010, 8-month and 13-month days, under the influence of continuous strong rainfall weather, rainstorm and mountain flood occur in earthquake-stricken areas of the Longxi river basin, a large amount of silt enters the main river channel of the Longxi river, so that the river bed is silt and about 2 meters, and the flood floods the beach, silts and submerges residential houses, thereby causing serious economic loss. In this embodiment, the river reach downstream of the dragon river is taken as an example to illustrate the recovery of the river reachThe hydraulics determination method of the utilization range of the formula beach and the flood control safety position comprises the following steps:
(1) drawing water level-flow relation diagram of typical section
Selecting the river reach at the downstream of the Longxi river as a target river reach, selecting a cross section with the position as indicated by a dotted line in figure 2 from the target river reach as a typical cross section, and drawing a water level-flow relation graph of the typical cross section;
the water level-flow relation graph of a typical section is drawn as follows:
firstly, on-site measurement of a river reach with a typical section is found, the width of a main groove of the river reach is 35-45 m, the average width of the main groove is about 40m, the depth of the main groove is about 3m, the main groove is U-shaped, the left side and the right side of the main groove are provided with beaches, and the beaches are flat. Based on the shapes of the main trough and the beach of the river reach where the typical section is located, the shapes of the water passing surfaces of the main trough, the left beach and the right beach on the typical section are all approximate to rectangles, and considering that the average silt height of the riverbed of the stream of the year 2010, 8 months and 13 days is about 2m, the silt siltation thickness is. Main slot width B of the typical cross section240m, the depth of the main groove is 3m, and the total width B of the left beacht190m, total width of right beach Bt3＝25m。
As an example, in the following four cases of the left beach effective water passing width and the right beach effective water passing width (more left beach effective water passing width and right beach effective water passing width can be considered in practical application) according to the formula (1), when the relative water levels respectively take the corresponding flow rates of 2.2m, 2.4m, 2.6m, 2.8m, 3.0m, 3.2m, 3.4m, 3.6m, 3.8m, 4.0m, 4.2m, 4.4m, 4.6m, 4.8m, 5.0m, 5.2m, 5.4m, 5.6m, 5.8m, and 6.0m, the corresponding flow rate and the relative water level are expressed as a point (Q, Z), and the relative water level refers to the elevation of the free water level relative to the main tank bottom bed.
The first condition is as follows: flood in single main trough, i.e. river width equal to main trough width B240m, left beach effective water width B1Effective water passing width B of right beach3＝0m；
Case two: compound beach flood and main trough width B240m, left beach effective water width B140m, effective right beach water passing width B3＝0m；
Case three: compound beach flood and main trough width B240m, left beach effective water width B10m, right beach effective water passing width B3＝25m；
Case four: compound beach flood and main trough width B240m, left beach effective water width B190m, the effective water passing width B of the right beach3＝0m；
In the formula (1), Q is a flow rate, n1,n2,n3Respectively the Manning roughness coefficients of the left beach, the main trough and the right beach, and calculating the time n according to the actual conditions of the left beach, the main trough and the right beach1,n2,n3All values are 0.025, i1,0,i2,0,i3,0The river bed gradients of the left beach, the main trough and the right beach respectively, i according to the actual field investigation condition1,0,i2,0,i3,0All values are 0.024.
Secondly, constructing a plane rectangular coordinate system by taking the flow as an x axis, taking the relative water level as a y axis and taking the point (0,0) as an origin of coordinates, marking all the points (Q, Z) obtained by the calculation in the first step on the plane rectangular coordinate system, then smoothly connecting all the points (Q, Z) obtained by the calculation in the first step with the same curve to obtain a water level-flow relation curve in the first step, smoothly connecting all the points (Q, Z) obtained by the calculation in the second step with the same curve to obtain a water level-flow relation curve in the second step, smoothly connecting all the points (Q, Z) obtained by the calculation in the third step with the same curve to obtain a water level-flow relation curve in the third step, smoothly connecting all the points (Q, Z) obtained by the calculation in the fourth step with the same curve to obtain a water level-flow relation curve in the fourth step, thus, a water level-flow rate relation graph including 4 water level-flow rate relation curves is obtained, as shown in fig. 4.
(2) Calculating the maximum available width of the compound beach
The peak flow of the torrential rain torrential flood which occurs in the target river reach 2010-8-13 th3In this embodiment, when determining the design flow rate of the target river reach, the peak flood flow rate may be used as the design flow rate, and when actually applying, the peak flood flow rate of the flood meeting at once in 5 years, 10 years, 15 years or 20 years may be selected as the design flow rate according to the actual situation, and may be specifically determined according to the hydrological data.
In this embodiment, the design flow Q of the target river reach is usedd＝321m3S, design flood control relative level ZdFor example, 5m, a method for calculating the maximum available width of the compound beach is described:
in the water level-flow rate relationship diagram, a straight line y is defined as 5 and a straight line x is defined as 321, a point closest to the point (321, 5) and located below the straight line y as 5 is selected as a critical point from the intersection points of the water level-flow rate relationship curves and the straight line x as 321, the water level-flow rate relationship curves including the critical point are defined as critical curves, and as can be seen from fig. 4, since the water level-flow rate relationship curve obtained under the condition of the case two is closest to the intersection point of the straight line y as 5, the water level-flow rate relationship curve obtained under the condition of the case two is defined as a critical point, and therefore, the water level-flow rate relationship curve obtained under the condition of the case two is defined as a critical curve corresponding to the left beach effective water flow width B corresponding to the critical curveg140m, the effective water passing width B of the right beachg3Calculating the maximum available width of the left beach and the maximum available width of the right beach of the target river reach according to the formulas (2) to (3) when the maximum available width of the left beach is 0m,
Bmax1＝Bt1-Bg1＝90-40＝50(m) (2)
Bmax3＝Bt3-Bg3＝25-0＝25(m) (3)
in formulae (2) to (3), Bmax1Is the maximum available width of the left beach of the target river reach, Bmax3Is the maximum available width of the right beach of the target river reach, Bt1The total width of the left beach, Bt3The total width of the right beach, Bg1Is the effective water passing width of the left beach corresponding to the critical curve, Bg3The effective water passing width of the right beach corresponding to the critical curve;
when the compound beach of the target river reach is used, any width is selected from the [0, 50] interval in the left beach and selected from the [0, 25] interval in the right beach.
(3) Determining flood control safety locations
Suppose that the actual utilization width of the left beach land is b1，0≤b1Less than or equal to 50, and the actual utilization width of the right beach land is b3，0≤b3Less than or equal to 25, and the actual utilization width b of the left beach is assumed to utilize the left beach and the right beach to the maximum extent150m, the actual utilization width of the right beach is b3The method for determining the flood control safety position is described as 25 m.
Drawing b1＝50m、b3Water level-flow curve at 25 m:
when the flow rates corresponding to relative water levels of 2.2m, 2.4m, 2.6m, 2.8m, 3.0m, 3.2m, 3.4m, 3.6m, 3.8m, 4.0m, 4.2m, 4.4m, 4.6m, 4.8m, 5.0m, 5.2m, 5.4m, 5.6m, 5.8m, and 6.0m are calculated from the formula (1), B in the formula (1) is calculated1＝40m，B3The corresponding flow rate and relative water level are represented as points (Q, Z) at 0 m.
Secondly, a plane rectangular coordinate system is constructed by taking the flow as an x axis, the relative water level as a y axis and the points (0,0) as the origin of coordinates, all the points (Q, Z) obtained by the calculation in the step I are marked on the plane rectangular coordinate system, and then the points are smoothly connected by the same curve to obtain a water level-flow relation curve, which is actually the water level-flow relation curve under the condition of the two conditions in the figure 4.
Thirdly, in the water level-flow relation graph, a straight line x is 321, a longitudinal coordinate value 4.83m of an intersection point (321, 4.83) of the straight line x is 321 and a water level-flow relation curve under the two conditions is a flood control safety relative water level, a position above the flood control safety relative water level is a flood control safety position, and when a building is built on a river bank of a compound beach of a target river reach, a foundation of the building is required to be in the flood control safety position.
Example 2
In this embodiment, the method for determining the hydraulic force of the mountain river compound beach use range and the flood control safety position provided by the present invention will be described in detail.
The Yangshan is a Hanjiang tributary, the total length is 163km, and the area of the watershed is 880km2. A certain river section in the midstream of the Yangshan forms a large beach which is a main local agricultural land on the right bank of the river channel under the constraint action of curve, widening and narrowing, and as shown in figure 5, figure 5 is a photograph (from Google Earth) of a target river section in 2017 in 1 month and 20 days. In 2012, 8 and 6 months, the flood is influenced by strong rainstorm flood, and the peak flow of Guanshan river reaches 2410m3And/s, the fertile farmland of the beach is completely destroyed, the water depth of the beach is about 3m, the right bank of the river is retreated by 10m in the post-disaster reconstruction started by 2013, and the river width is expanded to 82 m. In this embodiment, the river reach in the midstream of the river is taken as an example to illustrate a hydraulics determination method for the compound beach utilization range and the flood control safety position of the river reach, which includes the following steps:
(1) drawing water level-flow relation diagram of typical section
Selecting the river reach of the midstream of the official mountain river as a target river reach, selecting a cross section with the position as a typical cross section as shown by a dotted line in figure 5 from the target river reach, and drawing a water level-flow relation graph of the typical cross section;
the water level-flow relation graph of a typical section is drawn as follows:
firstly, based on field measurement of a river reach with a typical section, the width of a main groove of the river reach is about 82m, the depth of the main groove is about 6m, the main groove is U-shaped, the left beach is small in development, the right beach is wide, the terrain of the right beach is flat, the river reach can be considered to have no left beach or the width of the left beach is 0m, and meanwhile, the main groove and the river bed are relatively weak in sedimentation during flood. Based on the shapes of the main trough and the beach of the river reach where the typical section is located, the shapes of the water passing surfaces of the main trough, the left beach and the right beach on the typical section are all approximate to rectangles, and considering that the main trough and the river bed are less silted during the flood period of 8, 6 and 6 days in 2012, the embodiment analyzes the water level-flowThe typical cross-section is shown in fig. 6, which is summarized by considering that the river section is not silted up during the flood period. Main slot width B of the typical cross section282m, the depth of the main groove is 6m, and the total width B of the left beacht10m, total width B of right beacht3＝200m。
As an example, in the following five right beach effective water passing width cases (more right beach effective water passing width cases can be considered in practical application) calculated according to the formula (1), when the relative water levels are respectively 6.01m, 6.4m, 6.6m, 6.8m, 7m, 7.2m, 7.4m, 7.6m, 7.8m, 8m, 8.2m, 8.41m, 8.6m, 8.8m, and 9m, the corresponding flow and the relative water level are expressed as points (Q, Z), and the relative water level refers to the elevation of the free water surface relative to the main tank bottom bed.
The first condition is as follows: flood in single main trough, i.e. river width equal to main trough width B282m, left beach effective water width B1Effective water passing width B of right beach3＝0m；
Case two: compound beach flood and main trough width B282m, left beach effective water width B10m, right beach effective water passing width B3＝50m；
Case three: compound beach flood and main trough width B282m, left beach effective water width B10m, right beach effective water passing width B3＝100m；
Case four: compound beach flood and main trough width B282m, left beach effective water width B10m, right beach effective water passing width B3＝150m；
Case five: compound beach flood and main trough width B282m, left beach effective water width B10m, right beach effective water passing width B3＝200m；
In the formula (1), Q is a flow rate, n1,n2,n3Respectively the Manning roughness coefficients of the left beach, the main trough and the right beach, and calculating the time n according to the actual conditions of the left beach, the main trough and the right beach1,n2,n3All values are 0.025, i1,0,i2,0,i3,0The river bed gradients of the left beach, the main trough and the right beach respectively, i according to the actual field investigation condition1,0,i2,0,i3,0All take the value of 0.005.
Secondly, constructing a plane rectangular coordinate system by taking the flow as an x axis, taking the relative water level as a y axis and taking the point (0,0) as an origin of coordinates, marking all the points (Q, Z) obtained by the calculation in the first step on the plane rectangular coordinate system, then smoothly connecting all the points (Q, Z) obtained by the calculation in the first step with the same curve to obtain a water level-flow relation curve in the first step, smoothly connecting all the points (Q, Z) obtained by the calculation in the second step with the same curve to obtain a water level-flow relation curve in the second step, smoothly connecting all the points (Q, Z) obtained by the calculation in the third step with the same curve to obtain a water level-flow relation curve in the third step, smoothly connecting all the points (Q, Z) obtained by the calculation in the fourth step with the same curve to obtain a water level-flow relation curve in the fourth step, all the points (Q, Z) calculated under the condition of the case five are smoothly connected by the same curve to obtain a water level-flow rate relation curve under the condition of the case five, and thus a water level-flow rate relation graph including 5 water level-flow rate relation curves is obtained, as shown in fig. 7.
(2) Calculating the maximum available width of the compound beach
The peak flow of the torrential rain torrential flood which occurs in the target river reach 8 months and 6 days in 2012 reaches 2410m3In this embodiment, when determining the design flow rate of the target river reach, the peak flood flow rate may be used as the design flow rate, and when actually applying, the peak flood flow rate of the flood meeting at once in 5 years, 10 years, 15 years or 20 years may be selected as the design flow rate according to the actual situation, and may be specifically determined according to the hydrological data.
In this embodiment, the design flow Q of the target river reach is usedd＝2410m3S, design flood control relative level ZdThe calculation method of the maximum available width of the compound beach is described as 8.5m as an example:
in the water level-flow rate relationship diagram, a straight line y is 8.5 and a straight line x is 2410 are drawn, a point closest to the point (2410, 8.5) and located below the straight line y is 8.5 is selected as a critical point from the intersection points of the water level-flow rate relationship curves and the straight line x 2410, the water level-flow rate relationship curve including the critical point is designated as a critical curve, as can be seen from fig. 7, the intersection point (2410, 8.41) of the water level-flow rate relationship curve and x 2410 obtained under the condition of the case three is closest to the intersection point of the water level-flow rate relationship curve and x 2410 obtained under the condition of the case three, and the water level-flow rate relationship curve obtained under the condition of the case three is a critical curve corresponding to the left effective water width B of the water level corresponding to the critical curveg10m, right beach effective water passing width Bg3Calculating the maximum available width of the left beach and the maximum available width of the right beach of the target river reach according to the formulas (2) to (3) of 100m,
Bmax1＝Bt1-Bg1＝0-0＝0(m) (2)
Bmax3＝Bt3-Bg3＝200-100＝100(m) (3)
in formulae (2) to (3), Bmax1Is the maximum available width of the left beach of the target river reach, Bmax3Is the maximum available width of the right beach of the target river reach, Bt1The total width of the left beach, Bt3The total width of the right beach, Bg1Is the effective water passing width of the left beach corresponding to the critical curve, Bg3The effective water passing width of the right beach corresponding to the critical curve;
when the compound beach of the target river reach is used, only the right beach is used, and any width is selected from the [0, 100] interval in the right beach for use.
(3) Determining flood control safety locations
Suppose the actual utilization width of the right beach is b3，0≤b3The width of the actual utilization of the right beach is 100m and 50m, and the method for determining the flood control safety position is described.
Drawing a water level-flow relation curve when the actual utilization width of the right beach is 100 m:
calculating the corresponding flow rate when the relative water level takes 6.01m, 6.4m, 6.6m, 6.8m, 7m, 7.2m, 7.4m, 7.6m, 7.8m, 8m, 8.2m, 8.41m, 8.6m, 8.8m and 9m according to the formula (1), and calculating B in the formula (1)1＝0m，B3The corresponding flow rate and relative water level are represented as points (Q, Z) at 100 m;
drawing a water level-flow relation curve when the actual utilization width of the right beach is 50 m:
calculating the corresponding flow rate when the relative water level takes 6.01m, 6.4m, 6.6m, 6.8m, 7m, 7.2m, 7.4m, 7.6m, 7.8m, 8m, 8.2m, 8.41m, 8.6m, 8.8m and 9m according to the formula (1), and calculating B in the formula (1)1＝0m，B3The corresponding flow rate and relative water level are indicated as points (Q, Z) at 150 m.
Secondly, a plane rectangular coordinate system is constructed by taking the flow as an x axis, the relative water level as a y axis and the point (0,0) as the origin of coordinates, all the points (Q, Z) obtained by the calculation in the step I are marked on the plane rectangular coordinate system, then all the points (Q, Z) calculated when the actual utilization width of the right beach land is 100m are smoothly connected by the same curve, all the points (Q, Z) calculated when the actual utilization width of the right beach land is 50m are smoothly connected by the same curve, and two water level-flow relation curves are obtained, wherein the water level-flow relation curves are actually the water level-flow relation curves under the three conditions and the four conditions in the figure 7.
In the water level-flow relation diagram, a vertical coordinate value of an intersection point of a straight line x 2410 and the water level-flow relation curves under the third and fourth conditions is determined as a flood control safety relative water level, an intersection point of the straight line x 2410 and the water level-flow relation curves under the three conditions is (2410, 8.41), and an intersection point of the straight line x 2410 and the water level-flow relation curves under the four conditions is (2410, 8.07), that is, when the actual utilization width of the right beach is 100m, the flood control safety relative water level is 8.41m, and when the actual utilization width of the right beach is 50m, the flood control safety relative water level is 8.07 m. The position above the flood control safety relative water level is the flood control safety position, and when the building is built on the river bank of the compound beach land of the target river reach, the foundation of the building is in the flood control safety position.
Claims (1)
1. The method for determining the utilization range of the compound beach land of the mountain river and the hydraulics of the flood control safety position is characterized by comprising the following steps:
(1) drawing water level-flow relation diagram of typical section
Selecting a river reach needing to determine the beach utilization range from the mountain river as a target river reach, selecting a typical section from the target river reach, and drawing a water level-flow relation graph of the typical section;
the water level-flow relation graph of a typical section is drawn as follows:
the shapes of the water passing surfaces of a main groove, a left beach and a right beach on a typical section are approximate to rectangles, the width of the main groove is measured and recorded as B2Measuring the total width of the left beach and recording the total width as Bt1Measuring the total width of the right beach and recording the total width as Bt3；
Assuming that the effective water passing width of the left beach is B1The effective water passing width of the right beach land is B3When the relative water level of the typical section is Z, the relative water level refers to the elevation of the free water surface relative to the bottom bed of the main tank, and the depth h of the left beach land is determined by combining the relative heights of the left beach land, the right beach land and the bottom bed of the main tank or combining the relative heights of the left beach land, the right beach land and the bottom bed of the main tank and the sediment deposition thickness1Depth h of main trough2The depth h of the right beach land3The water passing area A of the left beach land1Water passing area A of the main tank2And the water passing area A of the right beach3；
Under the condition of different left beach effective water passing widths and right beach effective water passing widths, corresponding flow rates when the relative water levels take different values are calculated according to the formula (1), the corresponding flow rates and the relative water levels are expressed as points (Q, Z),
in the formula (1), Q is a flow rate, n1,n2,n3Respectively a left beachManning roughness coefficient of main trough and right beach i1,0,i2,0,i3,0The river bed slope of the left beach, the main trough and the right beach respectively;
constructing a plane rectangular coordinate system by taking the flow as an x axis, taking the relative water level as a y axis and taking the points (0,0) as the origin of coordinates, marking all the points (Q, Z) obtained by the calculation in the step I on the plane rectangular coordinate system, and then smoothly connecting all the points (Q, Z) obtained by the calculation under the conditions of the effective water passing width of the same left beach land and the effective water passing width of the right beach land by using the same curve to obtain a water level-flow relation graph comprising a plurality of water level-flow relation curves;
(2) calculating the maximum available width of the compound beach
Determining the design flow Q of the target river reach according to the hydrological datadAnd designing flood control relative water level ZdIn the water level-flow rate relation diagram, a straight line y is set as ZdAnd the straight line x ═ Qd，
From each water level-flow relation curve and straight line x ═ QdOf the intersections of (2), an AND point (Q) is selectedd,Zd) Closest and located on a line y ═ ZdThe lower point is taken as a critical point, a water level-flow relation curve comprising the critical point is taken as a critical curve, and the effective water passing width of the left beach land and the effective water passing width of the right beach land corresponding to the critical curve are respectively taken as Bg1,Bg3Calculating the maximum available width of the left beach and the maximum available width of the right beach of the target river reach according to the formulas (2) to (3),
Bmax1＝Bt1-Bg1 (2)
Bmax3＝Bt3-Bg3 (3)
in formulae (2) to (3), Bmax1Is the maximum available width of the left beach of the target river reach, Bmax3Is the maximum available width of the right beach of the target river reach, Bt1The total width of the left beach, Bt3The total width of the right beach, Bg1Is the effective water passing width of the left beach corresponding to the critical curve, Bg3The effective water passing width of the right beach corresponding to the critical curve;
at the compound beach to the target river reachIn use, from [0, B ] in the left beachmax1]The interval is selected to be used from [0, B ] in the right beachmax3]Selecting any width for utilization;
(3) determining flood control safety locations
Suppose that the actual utilization width of the left beach land is b1，0≤b1≤Bmax1And the actual utilization width of the right beach land is b3，0≤b3≤Bmax3And drawing the actual utilization width of the left beach as b1The actual utilization width of the right beach is b3Water level-flow relation curve:
calculating the corresponding flow rate when the relative water level takes different values according to the formula (1), and B in the formula (1) during calculation1＝Bt1-b1，B3＝Bt3-b3The corresponding flow and relative water level are represented as points (Q, Z),
constructing a plane rectangular coordinate system by taking the flow as an x axis, the relative water level as a y axis and the points (0,0) as the origin of coordinates, marking all the points (Q, Z) obtained by the calculation in the step (3) in the plane rectangular coordinate system, and then smoothly connecting all the points (Q, Z) by using the same curve to obtain a water level-flow relation curve;
drawing a straight line x-Q in the water level-flow relation graphdLine x ═ QdThe longitudinal coordinate value of the intersection point of the relation curve of the water level and the flow is the flood control safety relative water level, the position above the flood control safety relative water level is the flood control safety position, and when the building is built on the bank of the compound beach land of the target river reach, the foundation of the building is in the flood control safety position.
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