Study On Hydrological Process Simulation And Prediction And Eco-environmental Water Demand In Jinghe River Basin

The Jinghe River Basin is a typical watershed in the arid-semi-arid region of China,where water resources are relatively scarce and soil erosion is serious.Therefore,in the context of ecological restoration and vegetation reconstruction,analyzing the temporal and spatial variation characteristics in hydrological processes,exploring its response to changes in climate and land use,measuring the water demand of the ecological environment in the basin,is of great theoretical significance to understand and quantify the impact of climate change and human activities on the hydrological cycle,to recognize the surface energy balance and water exchange process of pavement.At the same time,has very important practical significance for the formulation of ecological protection,resource development and economic development planning.Based on the Jinghe River Basin as the research area,the DEM,land use,soil and meteorological data were input into the SWAT hydrological model,and the model was calibrated and verified according to the measured data,therefore,a hydrological model suitable for basin characteristics was constructed.The monthly runoff and sediment transport in the basin from 2006 to 2012 were simulated,and their temporal and spatial changes were analyzed.The CA-Markov model was used to predict the spatial distribution pattern of land use types of the basin in 2025,and to explore the impact of land use changes on the runoff and sediment transport in the basin.Based on the runoff and sediment transport data,the factors that affect the water demand of the ecological environment of the basin were analyzed,the water demand of the ecological environment was calculated,the time distribution characteristics are analysed,the relationship between water supply and demand was explored,and the countermeasures for the resonable utilization of water resources in the basin were provided.The main conclusions drawn in this article are as follows:(1)The calibrated SWAT model has good applicability in the Jinghe River Basin.The Arc SWAT module was used to complete river network generation,sub-basin division,and hydrological response unit generation,and to build a hydrological model of the Jinghe River Basin.The model was calibrated and verified based on the measured hydrological data.In calibration period,the correlation coefficient of runoff is 0.86,the Nash efficiency coefficient is 0.70.In verification period,the correlation coefficient of runoff is 0.76,the Nash efficiency coefficient is 0.71.In calibration period,the correlation coefficient of sediment transport is 0.89and the Nash efficiency coefficient is 0.86.In verification period,the correlation coefficient of sediment transport is 0.82 and the Nash efficiency coefficient is 0.67,indicating that the simulation results are relatively ideal,and the SWAT model with parameter adjustment fit with the Jinghe River Basin.(2)The distribution of runoff and sediment transport in the Jinghe River Basin differs greatly in time and space,and the runoff is more sensitive to external changes.On the time scale,the runoff and sediment transport are unevenly distributed throughout the year,showing the unimodal characteristic.After March,the river thawed and opened,resulting in the increase of runoff and sediment transport.From April to May,due to the affect of water diversion and irrigation in spring in the upper Yellow River,the runoff in the river was relatively stable.From July to August,there are heavy rains in the basin,coupled with large slope and low vegetation coverage,runoff and sediment transport have also increased rapidly.The amount of runoff during the flood season accounts for 61.96%of the annual runoff,and the amount of sediment transport accounts for 65.55%of the annual value.From November to December,the river channel is frozen,and the flow capacity and sediment transport capacity of the channel were obviously weakened,resulting in a significant decrease of the runoff and sediment transport in the river channel.The inter-annual variation coefficient of sediment transport is less than runoff,indicating that the inter-annual fluctuation of runoff is greater than that of sediment transport.The annual difference in sediment transport is relatively small,and the runoff has an overall increasing trend.The amount of runoff has a greater deviation from the multi-year average value than the sediment transport,which indicated that the runoff is more sensitive to the external changes.On the spatial scale,the runoff increased significantly from upstream to downstream,reaching the maximum at the outlet of the basin.The location of minimum value is near the Yuanchengchuan River,and the tributary value was less than the main stream value.Zhangjiashan Station,the outlet of the basin,is in the Shaanxi section of the Jinghe River,it is the gorge section with more than 120 kilometers from Zaofantou to Zhangjiashan Station,with steep mountains,tortuous rivers and rich hydropower resources.The tributaries in middle reches flow through the Longdong Loess Plateau,and the river channel has a strong sediment transport capacity.The channel is dominated by erosion and sedimentation.Therefore,the value of sediment transport of the tributary is greater than the value of the main stream in the middle and lower reaches.The smallest amount of sediment transport is at the junction of the upper reaches of Dongchuan and Malian Rivers,and the largest is mainly concentrated in the sub-basins of Daxi River and Sanshui River downstream of the Malian River,a tributary of Jinghe River.This is due to the the fact that the Dongzhiyuan tableland,the largest existing loess tableland in China,is located between Malian River and Puhe River.With repeated reclamation,soil erosion in the basin is very serious.(3)The changes of land use types from 2005 to 2025 are mainly manifested by the obvious mutual transformation among construction land,bare land,grassland and cultivated land.Based on the Markov model,the probability transition matrix of land use types from 2005 to 2015 was calculated.The results show that in 10 years,the transformation of water,construction land,and cultivated land was the most intense.Among them,the area of construction land remained unchanged was the largest,and the rest is mainly converted to water and woodland.The area of bare land remained unchanged was the least.Using the CA-Markov model,the spatial distribution of land use types in 2025 was predicted,it can be seen that the main land use types in 2025 will still be grassland and arable land,followed by woodland.Due to the promotion of the conversion of farmland to forests and the development of urbanization,compared with the data in 2015,the distribution of land use types in 2025 will show a gradual increase trend in woodland,waters,and construction land,and the change rate of construction land is the largest,Other types show a decreasing trend,and the decreasing rate of the bare land is the largest.Therefore,in the development plan of the river basin,it is recommended to appropriately develop the scale of the city,continue to promote the construction of ecological engineering,and strengthen the protection of forest and grass resources.(4)From 2005 to 2025,with the continuous changes in land use,especially the increase in construction land and the decrease in cultivated land resources,the runoff of the basin showed a trend of first increasing and then decreasing,while the amount of sediment transport showed a continuous increasing trend.In terms of time,the runoff in 2025 presents a bimodal distribution.Both the annual runoff and runoff in the flood season are lower than those in previous years.This may be related to the increase in woodland area and the decrease in grassland area.Forest land can block surface runoff by increasing water retention capacity and improving soil,and reducing runoff by affecting water circulation through evapotranspiration.The well-developed grassland vegetation can store precipitation in flood seasons and replenish flow during dry seasons.The amount of sediment transport is still unimodal distribution.The peak value occurs in September.Both the amount of sediment transport in flood season and in the whole year are greater than those in previous years.This is related to the reduction of grassland area and the substantial expansion of construction land.Grassland can block the initiation of sediment and reduce the role of sediment transport.The expansion of construction land destroys ground vegetation and stable topography,causing water and soil erosion.In terms of space,the spatial distribution of runoff in 2025 is basically like that of previous years,but the spatial distribution of sediment transport is different.It is no longer concentrated in the surrounding sub-basins of the lower reaches of the Malian River,but more evenly distributed in the lower reaches of the Yuluoping hydrologic station.It shows that afforestation projects,ecological restoration,and control of the balanced development of various types of land are the most effective ways to control soil erosion at the source.In the future,the ecological priority should be taken as the principle,the utilization rate of construction land should be increased,and the soil structure of cultivated land should be repaired reasonably.(5)The current situation of water resources supply in the Jinghe River Basin cannot meet the requirements of ecological environment water demand.Based on the relevant measured data,a model framework for calculating the ecological environmental water demand of the Jinghe River Basin was established according to the actual situation,and the ecological environmental water demand was calculated and analyzed.The results show that the ecological environment water demand of the river mainly comes from the sediment transport water demand,which is concentrated from July to October,and the ecological environmental water demand during the flood season accounts for 53.15%of the whole year.From the perspective of seasonal changes,autumn>summer>spring>winter.Because the precipitation in summer can meet the evaporation of the river,and the water demand for sediment transportation increases in autumn,the ecological environment water demand in autumn is slightly greater than that in summer.In spring,the evaporation of water surface is relatively large,and the replenishment of precipitation is small,which leads to the larger ecological environment water demand.The evaporation in winter decreased,and the ecological environment water demand reduced to the lowest value of the year.There is a significant temporal difference in the amount of ecological water shortage in the river channel.The multi-year average ecological water shortage mainly occurs in May of each year,with significant seasonal differences shows that spring>winter>summer>autumn.Agricultural irrigation water increases in spring,which is the season with the largest ecological environment water shortage.Summer and autumn are in the wet season,with heavy rainfall,and the runoff can meet the requirements of the ecological environment water.Winter is in the dry season,the river runoff is small,the rainfall has decreased rapidly,and the river is cut off or even exhausted in some areas,making the normal ecological functions of rivers unable to perform.The total ecological environment water demand in channel is 8.75 million m~3,accounting for 87.68%of the annual average runoff,and 73.65%of the annual runoff in 2025.The development and utilization rate of water resources far exceeds the internationally recognized warning line of 40%,and the water resources crisis is very significant.In order to ensure the sustainable and healthy development of the ecological function of the Jinghe River in the future,it is necessary to rationally utilize and recycle water resources,improve the water resources management system,and actively promote the construction of water conservancy projects and soil and water conservation projects,so as to achive the stable development of water resources.