| The significant changes in the ecological environment of the river basin and the underlying surface due to human interference have amplified the complexity and uncertainty of the hydrological response of the basin.The combined effect of climate change and human activities has resulted in distinctly different hydrological evolution patterns and characteristics in the upstream mountainous regions and the middle and lower urban areas of urban rivers.The construction of water conservancy projects in the upper reaches of the river has resulted in a significant reduction in the downstream river channel’s runoff volume.In addition,human activities such as riverbank mining and urban water landscape engineering commonly occur in the river channel,floodplain,or first and second-level terraces of the river.These activities have resulted in significant changes in the transformation of the relationship between river water and groundwater in the riverbank zone.This change has caused a shift in the mechanism of water conversion in the riverbank zone,ultimately affecting the water resources and ecological environment of the basin.As urbanization continues to progress,the complexity and uncertainty of the hydrological response to human activities have become increasingly prominent.Moreover,the path and direction of urban river hydrological process changes,driven by multiple factors,have undergone significant changes.The profound impact of these changes cannot be underestimated,as they deeply affect the effectiveness of river water resources management and water ecology protection.Therefore,it is crucial to comprehensively consider the impact of human activities on the river basin and develop effective measures to mitigate adverse effects and promote sustainable resource management.This paper takes the Bahe River basin as the research object and establishes a distributed hydrological model Geomorphology-based hydrological model(GBHM)and a numerical groundwater model(Visual MODFLOW)based on topographic and meteorological data as well as land use and normalized vegetation index data of the basin to study the influence of climate change and We also conducted a study on the conversion mechanism of river water and groundwater in the riparian zone and the change pattern of river runoff.The main findings are as follows:(1)The trend analysis of the variation characteristics of hydro-meteorological elements in the Ba River basin was carried out,and the time periods were divided.The results showed that the multi-year precipitation in the basin showed a non-significant upward trend,the multi-year average temperature showed a significant upward trend,and the multi-year runoff showed a significant downward trend.A comprehensive analysis of the years of abrupt changes in meteorological elements identified the year of abrupt changes in the basin as 2000,so the period 1990-2000 was taken as the base period,the period 2000-2010 as the first change period,and the period 2010-2020 as the second change period.(2)The land use pattern and transformation pattern of the watershed were analyzed by calculating the land use transfer matrix,single land use dynamic attitude,etc.;the spatial MK trend test method and Sen slope estimation were used to analyze the spatial and temporal variation pattern of normalized vegetation index(NDVI).The results showed that the area pattern of land use types in the Ba River watershed was: forest land > cropland > construction land > grassland > water bodies > shrubs.The area of forest land,water bodies and building land showed an increasing trend,while the area of cropland,grassland and shrubs showed a decreasing trend.The overall vegetation cover of the watershed shows an increasing trend,and the vegetation cover of the watershed shows a continuous improvement trend in the future.The area with improved vegetation cover in the basin accounts for 80.21% of the total area,and the area with degraded vegetation accounts for 16.93% of the total area.(3)Based on the watershed topography,remote sensing,soil and river reservoir data,a distributed hydrological model of the GBHM watershed was established to simulate the changes in river water volume patterns caused by climate change and human activities in the Ba River basin.The results show that climate change is the main influencing factor for runoff changes in the basin,and the influence of human activities on runoff changes gradually increases.Due to the ecological construction in the Ba River basin,the conversion of arable land to forest land in the upper reaches of the basin and the increase of vegetation cover in the basin increase the actual evaporation and soil water depth in the basin;due to the construction of water conservancy projects such as reservoirs in the upper reaches of the basin and rubber dams in the lower reaches of the basin,the runoff in the basin tends to decrease.The operation of the Lijia River reservoir reduced the runoff in the Ba River basin by about 25% on average over the years,and the operation of the reservoirs in the upper reaches of the basin was the main reason for the decrease in runoff and the increase in water pollution in the lower reaches of the river.(4)A numerical simulation(Visual MODFLOW)model of groundwater in the lower Ba River basin was established based on basin meteorological data and hydrogeological data.Based on the construction of rubber dams and reservoirs in the Ba River basin,the study was divided into four simulation periods with the following simulation scenarios:Simulation period A1-scenario without human activity disturbance;Simulation period A2-scenario after completion of the rubber dam;Simulation period A3-scenario after completion of the reservoir;Simulation period A4-rubber dam collapse,scenario after siltation of the rubber dam reservoir area;According to the construction of rubber dams in the lower Ba River and the upstream Lijia River reservoir,and divided into three water balance zones according to the construction location of rubber dams in Chanba River,the water balance results under four different scenarios were simulated.The results show that after the completion of the downstream urban section of the river with the graded rubber dam,the groundwater level in the riverfront area of the Ba River rises by 1.1-9.6m compared with the condition without water conservancy project interference,and the groundwater recharge in the water equalization zone increases;after the upstream reservoir storage operation,the incoming water from the downstream river decreases,and the urban section lowers the rubber dam storage level operation,the groundwater level rises by0.4-6.5m on average compared with the condition without water conservancy project interference 0.4-6.5m,the water balance area groundwater recharge than the rubber dam storage period recharge has been reduced.After the rubber dam is removed,i.e.,the reservoir area is silt flat,the groundwater level rises 0.3-2.6m on average compared with the condition without water conservancy project interference,and the groundwater recharge in the water balance area is reduced compared with the recharge after the reservoir is built. |
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