CN113946964A - Flow convergence calculation method for grassland river and river channel - Google Patents
Flow convergence calculation method for grassland river and river channel Download PDFInfo
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Abstract
The invention provides a flow convergence calculation method for a river channel of an grassland river, which comprises the following steps: according to an extreme value selection principle, obtaining the flow direction of water flow in each grid through elevation data of each grid; extracting river characteristic quantity through high-definition remote sensing images and field measurement data; calculating and obtaining a runoff depth time sequence of each grid through air temperature, precipitation, actual evapotranspiration and grid area; calculating the production flow, the flow velocity and the river depth of the river channel according to the area of each grid and the runoff depth; according to the energy conservation law, calculating the on-way head loss of the river in the grid and the local head loss caused by the curve by utilizing the actual liquid element flow energy equation of the river in the grid respectively to obtain the flow speed of the water flow flowing out of the grid and the actual required time of the water flow flowing through the grid; acquiring the number of lattice point layers required to pass by each lattice point flow direction drainage port through the flow direction of each grid; and acquiring the flow of the current lattice point at the moment according to the runoff depth time sequence and the flow of the river channel.
Description
Technical Field
The invention relates to the technical field of river channel flow convergence, in particular to a flow convergence calculation method for a river channel of an grassland river.
Background
The rainfall or ice and snow melting water in the drainage basin flows into the river network from the ground and the ground under the action of gravity, and the water flow flowing out of the cross section of the drainage basin outlet becomes runoff. The formation process of the runoff can be generalized into a runoff producing process and a confluence process, the runoff producing process simulation is the loss simulation of rainfall, and can be divided into a evapotranspiration part and a infiltration part (the impounded water amount in the processes of plant interception, depression filling and the like finally enters the atmosphere through evaporation or infiltrates into soil, and is not listed separately); the confluence also includes confluence calculation and river confluence calculation (flood calculation) within the hydrologic response unit. At present, a great deal of research on evapotranspiration and infiltration is continuously carried out by combining a daily and monthly remote sensing technology and a field test which is easy to operate. Due to the factors that the confluence process is large in continuous observation difficulty in time and space, more in influencing factors, difficult in solving the partial differential equation of the flood wave and the like, the comprehension of the confluence process and related research are far from sufficient, and the method is more obvious in the semiarid grassland basin where the riverway meanders and changes and the water quantity rises steeply and falls steeply.
There are two major equations for calculating the open channel unsteady flow: continuity equations and momentum equations, which are the basis of the saint-wien system of equations. By simplifying the continuity equation into the river reach water balance equation and the dynamic equation into the water storage relation of the river reach water tank, the Maskyoto method widely applied to confluence calculation can be obtained. The key to applying the MaskGen method is how to reasonably determine parameters k and x, namely average propagation time of river reach and weight for measuring the effect of inflow and outflow on river channel storage. However, traditional hydrological variables, such as mean travel time, are not suitable for the grassland type rivers with serious ecological degradation today. The characteristics of sandy soil with rapid instantaneous change and low water storage capacity, irregular river shape, easy migration and the like make the existing model difficult to even have the confluence process of simulating a grass prototype river.
Therefore, the invention provides a novel grassland river channel flow convergence calculation method.
Disclosure of Invention
In order to achieve the above purpose, the present invention provides the following technical solutions.
A flow convergence calculation method for a grassland river channel comprises the following steps:
acquiring the flow direction of water flow in each grid in the grassland river basin;
acquiring river characteristic quantity of a grassland river;
calculating a runoff depth time sequence of each grid in unit time according to the air temperature, precipitation, actual evapotranspiration and grid area of the grassland river;
calculating the production flow, the flow velocity and the river depth of the river channel according to the area of each grid and the runoff depth;
based on an energy equation of actual liquid flow of river flow in the grid, according to the characteristic quantity of the river, the river width and the river depth, respectively calculating the on-way head loss of the river in the grid and the local head loss caused by the curve, and determining the flow speed of water flowing out of the grid and the time of the water flowing through the grid;
acquiring the number of lattice point layers passing by each lattice point flowing to a drainage port of a drainage basin according to the flow direction of water flow in each grid; and acquiring the actual earth surface runoff of the current grid point at each moment according to the runoff depth time sequence, the flow velocity of the water flow flowing out of the grid, the time of the water flow flowing through the grid and the production flow of the river channel.
Preferably, the flow direction of the water flow in each grid in the grassland river basin is obtained, and the flow direction obtaining method comprises the following steps: according to the extreme value selection principle, the flow direction of the water flow in each grid is obtained through the watershed boundary of the grassland river and the elevation data of each grid in the watershed.
Preferably, the obtaining of the river characteristic quantity of the grassland river comprises the following steps: and extracting river characteristic quantity of the grassland river through the high-definition remote sensing image and the field measurement data.
Preferably, the method further comprises the following steps: when the depression and the blocked lake terrain exist in the watershed, the flow direction calculation of the water flow in each grid comprises the following steps:
determining a drainage basin outlet, and searching a flow direction path of each grid to the outlet;
and when the path detects that dead circulation enters, judging the shape of the depression according to the circulation characteristics, searching a drain outlet of the depression, collecting the flow to the main flow, and finally determining the flow direction of the water flow in each grid.
Preferably, the river characteristic quantities include an actual river length, an average river width, a river curve angle and radius, a river roughness and a slope drop inside each grid.
Preferably, the production flow rate Qsim, the flow velocity v and the river width WRAnd river depth HRThe calculation formula of (a) is as follows:
RD＝QsimΔt/1000AG
Qsim＝AS×v＝WR×HR×v
in the formula, ASThe cross-sectional area of each grid; a. theGIs the area of the grid; Δ t is a unit time; RD is the radial flow deep time series.
Preferably, the calculation of the head loss along the way and the local head loss by the curve of the river in the grid comprises the following steps:
converting the length, angle and sum of the river curve to the same order of magnitude according to the concept of 1km bending radius equivalent, and using the length, angle and sum to unify the bending degree of the river channel in the river basin;
determining a collapse coefficient, namely judging whether the situation of overflowing occurs when the flood peak passes through the river according to the real-time river depth;
when the overflowing occurs, the grid river channel is reset to be in a state of no bending and having a basic river length; after the overflowing flow is finished, the river channel gradually starts to bend along with the influence of factors such as the turning deviation force and the like, namely the river length gradually recovers to the actual river length and a bent river reach appears;
constructing an energy equation of the actual liquid flow of the grid inland river flow:
in the formula, z1And z2Elevation at the grid inlet and outlet; p is a radical of1And p2The air pressure at the inlet and outlet of the grid; rho is the density of the liquid, and g is the acceleration of gravity; v. of1And v2Flow rates at the grid inlet and outlet; h iswTotal head loss;
calculating the on-way head loss of the river in the grid and the local head loss caused by the curve according to the river characteristic quantity, the river width and the river depth:
hw＝∑hf+∑hj
n＝(n0+n1+n2+n3+n4)×m5
in the formula, hwFor lost energy, including loss of head of water flowfAnd local head loss h at bendsj(ii) a λ is the coefficient of the loss of the on-way head; l isRThe actual river length; r is the hydraulic radius; re is Reynolds number; ζ is the local head loss coefficient; c is a metabolic factor; b is the width of the curved river; r is the bending radius of the river channel; n is the coefficient of friction resistance of the river, wherein n0To n4The basic roughness of the natural river channel, the influence of irregular water surface, the influence of the change of the cross section shape and the size of the river channel, the influence of water-blocking objects and the influence of plants are respectively adopted; m is5The influence of the tortuous condition of the river channel.
Preferably, the obtaining of the actual surface runoff of the current grid point at each time comprises the following steps:
acquiring the number j of grid points required to pass through by each grid point flowing to the drainage port of the drainage basin through the flowing direction of each grid, and setting the row number and the column number of the grid points of the drainage basin as m and n respectively, so that the grid point layers being processed can be expressed as m (j) and n (j); according to the runoff depth time sequence and the flow of the river channel, acquiring the flow of the current lattice point at the time t as Q (t)m(j),n(j)(ii) a The time (Δ t) for the radial flow to the next grid point at this time is:
in the formula, LRIs the river length;
average discharge velocity; when the flow is not an integer, dividing the flow according to the integer time, and enabling the flow flowing out of the grid at the time t to be q (t)m(j),n(j)And then:
where fix is a function rounded down.
Preferably, the method further comprises the following steps: when there is an influx of flows into the upstream grid, the initial flow obtained by the grid is calculated:
where qsim (t) is the flow rate per mesh calculated by the flow rate generation module, and dir is 1to7, which represents 1to7 upstream convergence directions.
The invention has the beneficial effects that:
the invention provides a flow convergence calculation method for a grassland river channel, which is a river network convergence method considering river overflowing during flood transit based on dynamic river length, river curve and 3hour scale unit flood peak duration. Specifically, the present invention achieves:
(1) dynamically simulating and depicting the change process of various parameters in the aspects of grassland river flow, river type and the like;
(2) exploring and verifying the applicability of the model to different input data sources, and determining and explaining the physical significance of each process parameter;
(3) the advance of the convergence module and the existing convergence calculation method is compared, and the space can be improved by digging;
(4) the fluctuation response relation of the river overflow to the earth climate and the regional ecological conditions is simulated and explored, and the unique phenomenon of the grass prototype river is further known.
Drawings
FIG. 1 is a flow chart of a method of an embodiment of the present invention;
FIG. 2 is a verification result of river flow data of a simulated cylinder river in a model with weather-driven data substitution according to an embodiment of the present invention;
fig. 3 is a flow situation at a cross section of a cylinder river national hydrological station according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
As shown in fig. 1, the method for calculating the flow convergence of the grassland river channel comprises the following steps:
according to an extreme value selection principle, obtaining the flow direction of water flow in each grid through the watershed boundary of the grassland river and elevation data of each grid in the watershed;
extracting river characteristic quantity of the grassland river through high-definition remote sensing images and field measurement data; the river characteristic quantities include actual river length, average river width, river curve angle and radius, river roughness and slope drop inside each grid.
Calculating and obtaining a runoff depth time sequence of each grid through air temperature, precipitation, actual evapotranspiration and grid area;
calculating the flow, the flow velocity and the river depth of the river channel according to the area of each grid and the runoff depth; production flow rate Qsim, flow velocity v, river width WRAnd river depth HRThe calculation formula of (a) is as follows:
RD＝QsimΔt/1000AG
Qsim＝AS×v＝WR×HR×v
in the formula, ASThe cross-sectional area of each grid; a. theGIs the area of the grid; Δ τ is unit time; RD is the radial flow deep time series.
According to the energy conservation law, the on-way head loss of the river in the grid and the local head loss caused by the curve are respectively calculated by utilizing the actual liquid element flow energy equation of the river in the grid, so that the flow speed of the water flow flowing out of the grid and the actual required time of the water flow flowing through the grid are obtained:
constructing an energy equation of the actual liquid flow of the grid inland river flow:
in the formula, z1And z2Elevation at the grid inlet and outlet; p is a radical of1And p2The air pressure at the inlet and outlet of the grid; rho is the density of the liquid, and g is the acceleration of gravity; v. of1And v2Flow rates at the grid inlet and outlet; h iswIs the total head loss.
Calculating the on-way head loss of the river in the grid and the local head loss caused by the curve according to the river characteristic quantity, the river width and the river depth:
hw＝∑hf+∑hj
n＝(n0+n1+n2+n3+n4)×m5
hwfor lost energy, including loss of head of water flowfAnd local head loss h at bendsj(ii) a λ is the coefficient of the loss of the on-way head; l isRThe actual river length; r is the hydraulic radius; re is Reynolds number; ζ is the local head loss coefficient; c is a metabolic factor; b is the width of the curved river; r is the bending radius of the river channel; n is the coefficient of friction resistance of the river, wherein n0To n4The basic roughness of the natural river channel, the influence of irregular water surface, the influence of the change of the cross section shape and the size of the river channel, the influence of water-blocking objects and the influence of plants are respectively adopted; m is5The influence of the tortuous condition of the river channel.
Meanwhile, in view of the international difficulty in unifying variables related to river curves, the invention provides a concept of 1km bending radius equivalent, and the length, angle and sum of the river curves are converted to the same order of magnitude for unifying the bending degree of the river channel in a flow domain; in order to reflect the characteristics of the grassland river more truly, the invention sets the collapse coefficient, and judges whether the situation of the overflowing flow occurs when the flood peak passes through the river according to the real-time river water depth. When a flood occurs, the grid river will be reset to a state of no curve and having a basal river length. After the flood, the river gradually starts to curve under the influence of factors such as yaw force, that is, the river length gradually recovers to the actual river length and a curved river reach appears.
Acquiring the number of lattice point layers required to pass by each lattice point flow direction drainage port through the flow direction of each grid; and acquiring the flow of the current lattice point at the moment according to the runoff depth time sequence and the flow of the river channel.
Further, the method also comprises the following steps: when the depression and the blocked lake terrain exist in the watershed, the flow direction calculation of the water flow in each grid comprises the following steps:
determining a drainage basin outlet, and searching a flow direction path of each grid to the outlet;
and when the path detects that dead circulation enters, judging the shape of the depression according to the circulation characteristics, searching a drain outlet of the depression, collecting the flow to the main flow, and finally determining the flow direction of the water flow in each grid.
According to the runoff depth time sequence and the flow of the river channel, the flow of the current lattice point at the moment is obtained, and the method specifically comprises the following steps:
acquiring the number j of grid points required to pass through by each grid point flowing to the drainage port of the drainage basin through the flowing direction of each grid, and setting the row number and the column number of the grid points of the drainage basin as m and n respectively, so that the grid point layers being processed can be expressed as m (j) and n (j); according to the runoff depth time sequence and the flow of the river channel, acquiring the flow of the current lattice point at the time t as Q (t)m(j),n(j)(ii) a The time (Δ t) for the radial flow to the next grid point at this time is:
in the formula, LRIs the river length;
average discharge velocity; when the flow is not an integer, dividing the flow according to the integer time, and enabling the flow flowing out of the grid at the time t to be q (t)m(j),n(j)And then:
where fix is a function rounded down.
Further comprising: when there is an influx of flows into the upstream grid, the initial flow obtained by the grid is calculated:
where qsim (t) is the flow rate per mesh calculated by the flow rate generation module, and dir is 1to7, which represents 1to7 upstream convergence directions.
The invention takes the Sinkian Lei union grassland type river of autonomous region Sinomene of inner Mongolia of China as a specific implementation case. In order to monitor the hydrological meteorological conditions of the river basin of the cylinder more accurately, three sets of automatic flow velocity and flow monitoring stations, one set of Bowen ratio meteorological station, six sets of self-metering rainfall stations and 7 manual flow measuring sections are arranged in a research area.
The meteorological driving data is brought into the model to simulate the river flow data of the cylinder river for verification, and the result is shown in fig. 2. The river daily flow inspection analysis result of the cross section of the national hydrological station shows that the model performs better in river runoff simulation by using two meteorological driving data sets, and from the aspect of evaluation indexes, R2The simulation result of the daily scale flow test result display model of three automatic hydrological stations of KGE and NSE is more than 0.9, R is more accurate2And NSE slightly lower than the test results at national hydrological station sections. The artificial flow measurement test result shows that NSE of the flow simulation value and the observed value is higher, R2And (3) the distribution condition of the scatter diagram is relatively convergent, and a linear fitting straight line is matched with the following parameters of 1: the 1 straight line is also consistent, which shows that the overall result is credible and the process simulation error is small. And the value is less than 0.3, which shows that the model has better performance in the control aspect of the trend of the whole ecological hydrological process.
The invention further carries out comparative analysis on the simulation of the confluence mode (the runoff volume in the mode is abbreviated as Qs) and two common confluence modes (the runoff volumes in the two confluence modes are called Qs1 and Qs2, respectively, and the confluence modes do not consider the actual river length, the river curve and the overflowing flow and the actual river length and the river curve but the overflowing flow) in the four-field flood. Firstly, two fields of flood meeting twenty years and two fields of flood meeting fifty years are respectively selected in a simulation period, a 3hour scale flood process is simulated by using two driving data sets and three convergence modes, yellow and red pentagons are respectively used for marking branch flows and the time when the branch flows and the main flows start to generate cross flow conditions, and the flow conditions at the cross section of the national hydrological station of the cylinder river are shown in figure 3.
The results show that the time for simulating flood peak convergence transit using the two data sources is substantially the same at the intra-day scale, with only slight differences in flood peak values, which is consistent with the foregoing universal results of the invention for different driving data sets at the cylinder river. In general, the arrival time of the flood is the fastest and the duration time of the flood is the shortest without considering the actual river length, the river curve and the overflowing Qs1, and the arrival time of the flood is the latest and the duration time of the flood is the longest without considering the actual river length and the river curve but without considering the overflowing Qs2, and Qs simulated by the confluence method used in the patent is located between the two.
Different confluence modes can cause different performances of arrival time of flood, flood peak value and even flood waveform and the like. By comparing the three confluence modes, the river network characteristics of the grassland river are reflected more truly by considering the actual river length and the river curve, but if the river channel overflowing situation is not considered, the arrival time of the flood is delayed, and the situation is more obvious when the flood peak is larger. The river channel overflow is a prominent characteristic of the grassy river, which can not only advance the arrival time of flood peak, but also increase the flood peak value to a certain extent. In order to refine and decompose the influence of the overflow flow, the overflow flow is divided into branch overflow flow and main overflow flow, and the main overflow flow channel is wider and deeper than the branch flow channel, so that the cylinder river basin is found to be generated firstly by the branch overflow flow in the whole simulation period, and the main overflow flow is generated again when the flood is large enough.
First, the present inventors studied the influence of the flow of the tributary overflow on the confluence of the grassland river in 1987 and 1998. Two small floods, 8/7/1987 and 6/2/1998, show that Qs differs from Qs1 mainly in that Qs1 slightly precedes Qs, and the values of the two are basically consistent. When the branch flow overflows, the peak value of Qs basically exceeds Qs1, which mainly reflects the influence of the river overflow on the runoff flood peak. In the extra-large flood in 2004 and 2012, when both the branch flow and the main flow are subjected to overflow, not only does the peak value of Qs exceed Qs1, but also the slope of the simulated runoff is gradually increased, the arrival time of the flood peak is continuously close to Qs1 of linear confluence, which is the influence of river overflow on the arrival time of the flood peak and the flood peak value. In the process of the overflow, the overflow shortens the path length of the water flow due to the interception and reduces the obstruction of the curve to the flow speed, so that the water flow can be collected to the downstream section more quickly. The shorter course of river water reduces losses including evaporation, infiltration, etc., and also provides a certain improvement in flood peak values over modes without flood flow.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (9)
1. A flow convergence calculation method for a grassland river and a river channel is characterized by comprising the following steps:
acquiring the flow direction of water flow in each grid in the grassland river basin;
acquiring river characteristic quantity of a grassland river;
calculating a runoff depth time sequence of each grid in unit time according to the air temperature, precipitation, actual evapotranspiration and grid area of the grassland river;
calculating the production flow, the flow velocity and the river depth of the river channel according to the area of each grid and the runoff depth;
based on an energy equation of actual liquid flow of river flow in the grid, according to the characteristic quantity of the river, the river width and the river depth, respectively calculating the on-way head loss of the river in the grid and the local head loss caused by the curve, and determining the flow speed of water flowing out of the grid and the time of the water flowing through the grid;
acquiring the number of lattice point layers passing by each lattice point flowing to a drainage port of a drainage basin according to the flow direction of water flow in each grid; and acquiring the actual earth surface runoff of the current grid point at each moment according to the runoff depth time sequence, the flow velocity of the water flow flowing out of the grid, the time of the water flow flowing through the grid and the production flow of the river channel.
2. The grassland river channel flow confluence computing method according to claim 1, wherein the obtaining of the flow direction of the water flow in each grid in the grassland river basin comprises: according to the extreme value selection principle, the flow direction of the water flow in each grid is obtained through the watershed boundary of the grassland river and the elevation data of each grid in the watershed.
3. The grassland river channel flow confluence calculation method according to claim 1, wherein the obtaining of the river characteristic quantity of the grassland river comprises: and extracting river characteristic quantity of the grassland river through the high-definition remote sensing image and the field measurement data.
4. The grassland river channel flow confluence calculating method according to claim 1, further comprising: when the depression and the blocked lake terrain exist in the watershed, the flow direction calculation of the water flow in each grid comprises the following steps:
determining a drainage basin outlet, and searching a flow direction path of each grid to the outlet;
and when the path detects that dead circulation enters, judging the shape of the depression according to the circulation characteristics, searching a drain outlet of the depression, collecting the flow to the main flow, and finally determining the flow direction of the water flow in each grid.
5. The grassland river channel flow confluence calculation method according to claim 3, wherein the river characteristic quantities comprise actual river length, average river width, river bend angle and radius, channel roughness and slope drop inside each grid.
6. The grassland river channel flow confluence computing method according to claim 5, wherein the production flow Qsim, the flow velocity v and the channel width W areRAnd river depth HRThe calculation formula of (a) is as follows:
RD＝QsimΔt/1000AG
Qsim＝AS×v＝WR×HR×v
in the formula, ASThe cross-sectional area of each grid; a. theGIs the area of the grid; Δ t is a unit time; RD is the radial flow deep time series.
7. The grassland river channel flow confluence computing method according to claim 1, wherein the computation of the on-the-way head loss of the river in the grid and the local head loss caused by the curve comprises the following steps:
converting the length, angle and sum of the river curve to the same order of magnitude according to the concept of 1km bending radius equivalent, and using the length, angle and sum to unify the bending degree of the river channel in the river basin;
determining a collapse coefficient, namely judging whether the situation of overflowing occurs when the flood peak passes through the river according to the real-time river depth;
when the overflowing occurs, the grid river channel is reset to be in a state of no bending and having a basic river length; after the overflowing flow is finished, the river channel gradually starts to bend along with the influence of factors such as the turning deviation force and the like, namely the river length gradually recovers to the actual river length and a bent river reach appears;
constructing an energy equation of the actual liquid flow of the grid inland river flow:
in the formula, z1And z2Elevation at the grid inlet and outlet; p is a radical of1And p2The air pressure at the inlet and outlet of the grid; rho is the density of the liquid, and g is the acceleration of gravity; v. of1And v2Flow rates at the grid inlet and outlet; h iswTotal head loss;
calculating the on-way head loss of the river in the grid and the local head loss caused by the curve according to the river characteristic quantity, the river width and the river depth:
hw＝∑hf+∑hj
n＝(n0+n1+n2+n3+n4)×m5
in the formula, hwFor lost energy, including loss of head of water flowfAnd local head loss h at bendsj(ii) a λ is the coefficient of the loss of the on-way head; l isRThe actual river length; r is the hydraulic radius; re is Reynolds number; ζ is the local head loss coefficient; c is a metabolic factor; b is the width of the curved river; r is the bending radius of the river channel; n is the coefficient of friction resistance of the river, wherein n0To n4The basic roughness of the natural river channel, the influence of irregular water surface, the influence of the change of the cross section shape and the size of the river channel, the influence of water-blocking objects and the influence of plants are respectively adopted; m is5The influence of the tortuous condition of the river channel.
8. The grassland river channel flow convergence calculation method according to claim 1, wherein the obtaining of the actual surface runoff of the current grid point at each moment comprises the following steps:
acquiring the number j of grid points required to pass through by each grid point flowing to the drainage port of the drainage basin through the flowing direction of each grid, and setting the row number and the column number of the grid points of the drainage basin as m and n respectively, so that the grid point layers being processed can be expressed as m (j) and n (j); according to the runoff depth time sequence and the flow of the river channel, acquiring the flow of the current lattice point at the time t as Q (t)m(j)，n(j)(ii) a The time (Δ t) for the radial flow to the next grid point at this time is:
in the formula, LRIs the river length;
average discharge velocity; when the flow is not an integer, dividing the flow according to the integer time, and enabling the flow flowing out of the grid at the time t to be q (t)m(j)，n(j)And then:
where fix is a function rounded down.
9. The grassland river channel flow confluence computing method according to claim 8, further comprising: when there is an influx of flows into the upstream grid, the initial flow obtained by the grid is calculated:
where qsim (t) is the flow rate per mesh calculated by the flow rate generation module, and dir is 1to7, which represents 1to7 upstream convergence directions.
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