| China has the most widely distributed and most developed karst areas in the world,because of the non-homogeneity of karst development,the evaluation and management of water resources in karst areas has a great challenge.Sixi Basin is located on the South Bank of the head of the Three Gorges Reservoir,and it is also a typical karst trough Valley basin.Because the spatial and temporal distribution of water resources in the river basin is uneven and the flood disaster is frequent,it seriously restricts the local economic and social development.Hydrological model is the main means to study watershed water cycle,and it is the basis of watershed flood forecasting and water resources planning.Because of its strong karst development and high heterogeneity,the southern Karst basin directly affects and controls the hydrological cycle,which makes it more complicated and difficult to establish the hydrological model to accurately depict the water cycle of karst basin,especially the development of underground fissures and pipelines makes the underground runoff occupy a large proportion in the process of water cycle.The description of the underground runoff part of the hydrological model can be divided into distributed parameter model and aggregate parameter model,and the hydrological model of distributed parameters is limited by the survey accuracy,which is often difficult to meet the requirements of its parameters,and the aggregate parameter model can not reflect the characteristics of the heterogeneity of the underlay surface.In order to solve this problem effectively,this paper compares the advantages and disadvantages and applicability of karst hydrological model at home and abroad,and on the basis of fully studying the conditions of different underlay surfaces in the SixiBasin,three analog evaluation units were divided into the Sixi basin.A typical watershed is selected in each unit,and the precipitation-runoff characteristics of each typical watershed are discussed,and based on the SAC model,the Yuquadong Underground Dark River system module,Huomaixi Surface Karst Spring module,Shunyangxi Karst Fountain-Underground Dark River module are constructed.Each module is equipped with a separate aggregate parameter model,and then the module is combined into a Sixi semi-distributed hydrological model by analogy,and finally,through the application of the model,the precipitation-runoff process,the spatial and temporal distribution of water resources in the basin and flood forecasting are characterized.In this paper,the meteorological,hydrogeological,geomorphological conditions,hydrological monitoring,drilling,geophysical exploration,tracer and other test data of the study area are fully analyzed,and the precipitation-runoff process of karst water system in Sixi Basin has the following characteristics: 1.The lower surface conditions of the Karst basin in Sixi are very complicated.It can be divided into three types of underground dark river type of Upper Cambrian,represented by Yuquandong,the surface Karst spring type of Ordovician,which is represented by the Huomaixi basin,and the karst spring-underground dark river type in the Sinian of Shunyangxi.The two landforms of depression and Canyon 2 exist in the basin at the same time,and the karst development is not uniform.Through the analysis of flow attenuation curve,the medium can be divided into three main types of pipeline-large fracture-fracture,and the spatial size of the medium is compared with the flow rate of each medium in the process of water release,and the Karst development degree of different karst water system is found to be inconsistent.Under different rain intensity conditions,the difference of each subtype reflects the phenomenon of the conversion of the two components of fast flow and slow flow and the influence of the water content of the early system on the precipitation-runoff process.3,the supply of a variety of ways.Precipitation is the main source of recharge,but the spatial and temporal distribution of precipitation is uneven,and the rate of decreasing rainfall is 37.7mm/100 m.,Precipitation can recharge groundwater through the point-like recharge of the underground aquifer or through the slow surface of the fracture,and there are two kinds of water recharge in the basin,both the inner source water of the Depression and the outer source water of the clastic rock area.4.Groundwater excretion mainly has two kinds of excretion methods,concentration and dispersion.The flow rate of the spring mouth is mainly affected by rainfall,the dynamic change can be 200 times times,and the dynamic response time of groundwater is affected by the water-bearing medium and rain intensity,ranging from 1 hours to several hours.This paper focuses on the characteristics of precipitation-runoff process in the underground dark river system of fish cave and the structure of the fish Cave module established according to this,and describes the process of rapid underground runoff and the mutual transformation of slow groundwater runoff and the irrigation of surface runoff in depressions.Combining with the precipitation-runoff characteristics of the other two watersheds,the fast underground runoff part is eliminated in the fire wheat stream module compared with the Cave underground Dark River module,and the process of recharge groundwater by exogenous water is described in the Shun Yang Creek module.The module analogy is applied to the sub-basin of the same kind of underlay surface condition,which is combined into a semi-distributed Sixi model.The model parameters are numerous,some of which are combined with other hydrogeological experimental methods to analyze the fixed value or rate setting interval of precipitation-runoff characteristics,and the other part is determined by genetic algorithm.The simulation rate of three module hour flow process is regular and the fitting effect of the test is good,and finally the fitting effect of the flow process of the stream test is verified by the total section of the nail station,and the NSE coefficient is 0.726,which conforms to the accuracy of grade C flood prediction.The application of Sixi model depicts the karst water of Fish cave system reveals the karst water precipitation-runoff cycle process,and the law of precipitation on the dynamic response of groundwater is discussed,and the effective rainfall value is 14 mm.This paper evaluates the spatiotemporal distribution law of water resources and the occurrence state of water resources from two directions of vertical and plane,and finds that fissures or large fissures are still the main water storage and release medium,while the surface Karst belt water resources account for 0.01-5.4 of the total storage amount of the system,and the local prone to drought and water shortage in the dry water season.Finally,the paper reveals the mechanism of the huge flood disaster caused by heavy precipitation in Sixi basin.In this paper,the establishment of the physical model of precipitation-runoff and the construction of the model can provide reference for the study of the Karst hydrological model of Karst Trough Valley,which has certain theoretical significance,and the model can be used to guide the basic construction of flood control and disaster relief and the rational development and utilization of services and water resources,which has certain practical value. |
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