| The geological environment in mountainous areas of China is complex and diverse,with strong tectonic activities,fragile ecological environment,and frequent extreme rainfall events,resulting in frequent geological disasters in mountainous areas,among which debris flow disaster is widely distributed,occurring with high frequency and causing great losses.Therefore,it is urgent to prevent debris flow disaster scientifically and effectively.As an important means for debris flow prevention,eco-engineering can prevent debris flow in a more economical,effective and environment-friendly way.However,currently there is a paucity of rearch in the globe on the quantitative research of eco-engineering on the prevention and control effect ondebris flow disaster.In particular,the research on ecological engineering of debris flow designed for the special natural endowment of the region is very scarce,resulting in the eco-engineering of debris flow has not played its due role in debris flow disaster management.Therefore,this paper intends to take Goulinping,a representative small debris flow gully in the middle reaches of the Bailong River Basin,as an example,and uses the SWAT model and the BASEMENT model to simulate the whole process from the surface hydrological process to the initiation and movement of debris flow based on the debris flow event on August 17,2020.On this basis,37 ecological engineering management modes are designed for debris flow disaster prevention.By using the dynamic parameters of debris flow depth,flow velocity and debris flow intensity index,the disaster prevention effects of different ecological engineering management modes on debris flow disaster prevention are quantitatively evaluated at multiple scales of watershed,slope,channel and section.It provides scientific basis and technical support for the ecological engineering design and implementation of debris flow disaster prevention and control in the middle reaches of bailong River basin and the construction of a complete ecological debris flow prevention and control system.The main conclusions are as follows:(1)Through the sensitivity analysis of SWAT model parameters,it is pointed out that the parameters highly sensitive to the simulation results of Goulinping basin are runoff curve parameters,basal flow decline coefficient,groundwater lag time,shallow groundwater runoff coefficient,groundwater retranspiration coefficient and so on.SWAT model was used to simulate daily flow process in Goulinping basin.The correlation coefficient R~2 of the daily simulation calibration process is 0.76 and the Nash coefficient is 0.71,while the correlation coefficient R~2 of the daily simulation verification process is 0.70 and the Nash coefficient is 0.69.(2)Based on the parameter sensitivity analysis of BASEMNET model,the parameter setting conditions with high sensitivity to the dynamic process simulation of debris flow in Goulinping Basin were determined.The maximum mesh area of the computational domain was selected as 10m~2,the failure angle of the deposition was selected as 7°,and the bedload coefficient was selected as 1.0.(3)By coupling the SWAT model and the BASEMNET model,the"2020·8.17"mountain torrent and debris flow event in the Goulinping watershed in 2020 was simulated,and key parameters such as debris flow velocity and debris flow depth were obtained,and the Debris flow intensity index was selected for quantitative evaluation.The degree of hazard of mudslides.The results show that the maximum debris flow depth is 4.712m,which is located at the first bend after the intersection of No.2 small ditch and the main ditch;the maximum debris flow velocity is 4.762m/s,which is located at the bridge in the circulation accumulation area of Goulinping;the entire debris flow The maximum value of the maximum debris flow intensity index in the ditch is 20.19m~3/s~2,which is located at the bridge crossing in the circulation accumulation area of Goulinping.(4)The ecological engineering governance mode is designed from three aspects:slope governance mode,gully governance mode and the combination of slope governance mode and gully governance mode.Among them,31 types of slope management modes were designed according to three management criteria:"Returning farmland to forest and grassland","natural vegetation restoration"and"protecting farmland".Taking the width of vegetation buffer zone as variable,three gully governance modes were designed.Based on the simulation results of gully governance mode and slope governance mode,a comprehensive governance mode is designed.(5)The average annual surface runoff depth of Goulinping from 2018 to 2020 was simulated under 18 ecological engineering management modes based on the principle of"Reforestation".The results show that compared with the current situation,the annual average surface runoff depth of the basin is effectively reduced by all the scenarios.Among them,the scenario with the best governance effect is S12 scenario:the farmland between 6°and 25°in Goulinping Basin is converted to thick,and the farmland above 25°is converted to forest.In this scenario,the annual average surface runoff depth is 45.60mm,17.24%less than the current situation.Two groups of models with the same slope condition and different vegetation types were compared and analyzed.It was found that under P1 slope combination scenario,the average annual surface runoff depth was less than that under shrub scenario(S2,47.99mm).Under the combined slope of P2,the average annual surface runoff depth was less than that under the shrub scenario(S5,47.34mm)than that under the grassland scenario(S6,48.15mm).It shows that the ecological engineering management effect is the best in forestland scenario,followed by shrub scenario and grassland scenario.(6)Taking"8·17"debris flow event as the present situation,the change of maximum debris flow intensity index under 31 eco-engineering treatment scenarios was simulated,and the containment effect of various ecological engineering modes on debris flow was compared and analyzed.The main conclusions are as follows::(a)Comparing the simulation results of 18 eco-engineering model scenarios based on the criterion of"returning farmland to forests and grasslands":all scenarios have lower maximum debris flow intensity compared with the current situation.Among them,the maximum debris flow intensity index of the middle S12 scenario is the smallest,and its value is 8.00m~3/s~2,which is 60.38%lower than the current scenario.Comparing the models with different slope conditions and different vegetation coverage are as follows:woodland scenario(S2,10.36 m~3/s~2)Z5>Z4>Z1>Z3>Z2,indicating that the Z2 scenario(6°-15°slope grassland is restored to shrubs,15°The governance effect of the grassland on the above slope is restored to forest land)is the best,and the Z6 scenario(6°-25°slope is restored to forest,and the slope above 25°is restored to shrub)is the worst,but it also achieves better governance effect.In addition,the Z2 scenario has the best effect in reducing debris flow intensity,with a debris flow intensity index of 9.09 m~3/s~2,a decrease of 54.98%compared with the current scenario,and the Z6 scenario has the worst control effect,with a debris flow intensity index of 18.36 m~3/s~2,This is a decrease of 9.06%compared to the status quo scenario.(c)Comparing the simulation results of seven eco-engineering model scenarios with the criterion of"protection of cultivated land":After analyzing the selected sections 3 and 4,it was found that compared with the current situation,the two sections had the largest debris flow in all ecological engineering governance model scenarios.The depth,flow velocity,and maximum debris flow intensity index have been effectively reduced.The maximum flow depth and maximum flow velocity are in the order of M3>M5>M1>M4>M6>M2>M7,indicating that the M7 scenario(6-25°bare land in the Goulinping watershed is changed to grassland,the original grassland is changed to forest land,the farmland above 25°is converted to forest land,and the grassland is changed to forest land)The treatment effect is the best,followed by M2,and M3 is the worst,but it also achieves a good treatment effect.From the maximum debris flow intensity index,the M7 scenario has the best governance effect.The maximum debris flow intensity index under this scenario is 11.70 m~3/s~2,a decrease of24.02%compared with the current scenario.(7)Under the conditions of a 100-year rainfall in Goulinping,the control effects of three ecological engineering scenarios were simulated for the revegetation areas of 1m(B1),3m(B2)and 5m(B3)in the channel of the mudflow ditch flow and accumulation areas,respectively.The results show that the three eco-engineering scenarios are effective in controlling debris flow compared to the no-vegetation scenario,with B3>B2>B1 in this order.Compared with the unvegetated scenario,The reduction rates of B1,B2 and B3 scenarios are 31.79%,40.1%and 52.60%respectively.This indicates that the benefits of ecological engineering treatment tend to decrease as the vegetation area increases.(8)Based on the above conclusions,three models of slope management,full channel management and the combination of the two are selected,and the debris flow control effects under each model are simulated and analyzed.The results show that,compared with the current situation,the three control scenarios can effectively reduce the maximum flow depth,maximum flow velocity and maximum debris flow intensity of debris flow,and the comprehensive control scenario has the best effect.The maximum debris flow intensity index under the comprehensive management scenario is 8.54 m~3/s~2,a reduction rate of 57.68%compared with the current scenario.In conclusion,the combined simulation method of SWAT model and BASEMNET model constructed in this paper can quantitatively simulate the whole process of debris flow events,which provides a new method for quantitative evaluation of ecological engineering control benefits of debris flow gullies at multiple scales.All eco-engineering design in this paper the governance model can effectively reduce the scale and dangerous degree of debris flow,have the effect of curb landslide disaster,the effect of governance and ultimately selected the best mode of comprehensive ecological engineering,the results of this study can provide scientific and effective governance bailong river basin and similar landslides parts of debris flow disasters to provide theoretical basis and technical support. |
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