Study On Landscape Connectivity, Hydrological And Sediment Delivery Effects In The Yanhe River Catchment Based On 3S Technology

The configuration of the landscape unit regulates the surface processes on a series of spatial and temporal scales in the catchment.The landscape connectivity is a key indicator for measuring the landscape unit pattern and the surface process.In recent years,the transformation of the surface landscape by human activities on the Loess Plateau has caused changes in landscape connectivity.The reshaping of landscapes by human activities has led to changes in the surface processes of the catchment.As a typical loess hilly and gully region,the water and sediment process in the Yanhe River Catchment is very sensitive to landscape changes.In order to reveal the effect of landscape on the hydrological and sediment transport process in the catchment,this study uses the Yanhe River Catchment on the Loess Plateau as the research area,uses landscape connectivity as the core concept,employs 3S integration technology as the main technical means,uses remote sensing technology(RS)and global navigation satellite system(GNSS)technology to extract and verify the surface landscape information of the Yanhe River catchment in 2015,and adopts the GIS method to establish quantitative indicators of landscape connectivity for hydrological and sediment transport on the catchment scale.Combined with the expression of the watershed landscape structure connectivity,the hydrological and sediment transport effects under the background of human and natural factors in the catchment are explained.The following main results have been achieved:1.Quantification of hydrological connectivity and its hydrological effects.This study constructs a new humidity index(humidity parameter)based on the SAGA humidity index,which considers rainfall and evapotranspiration,uses the network index method to quantify the hydrological connectivity of the Yanhe River Catchment,and explains the structural connectivity and functional connectivity from the perspective of precipitation and evapotranspiration,quantifies respectively the hydrological connectivity of the effective source area of rivers and reservoirs.Main conclusions are as follows:(1)Improvement of wetness index: SAGA wetness index improves flat area prediction ability compared with topographic wetness index.The wetness parameter is better than the traditional topographic wetness index and the SAGA wetness index to predict the soil moisture,which can more accurately reflect the soil moisture distribution in the catchment.(2)Quantifying hydrological connectivity: The network index method describes accurately the spatial distribution of hydrological connectivity in the Yanhe River Catchment.The hydrological connectivity of the Yanhe River Catchment is dominated by structural connectivity.The effective source area method quantifies accurately the hydrological connectivity of rivers and reservoirs.The effective source areas of rivers and reservoirs in the Yanhe River Catchment account for 35% and 65% of the total area of the catchment,respectively.(3)Hydrological effects of the Yanhe River Catchment: The reservoir construction event is one of the main reasons for the decrease of runoff and sediment transport in the Yanhe River in recent years.Changing from hydrological connectivity has caused change of the hydrological response in the temporal and intensity in the catchment.2.Seasonal water yield model and its landscape structure response in the catchment.In this study,the InVEST seasonal water yield model was used to simulate the water yield in the Yanhe River Catchment,and analyzed the correlation between water yield and hydrological connectivity.Main conclusions are as follows:(1)Water yield simulation: The monthly quick flow yield was simulated by the InVEST seasonal water yield model to reflect the seasonal water yield pattern caused by climate differences,which is conducive to the management of water resources and the trade-off of water resources.The seasonal variation of the spatial distribution of water yield in the Yanhe River Catchment was obvious.The lack of quantification of the runoff transmission process and the uncertainty of the parameters of the water yield model leads to deviations between the simulated water yield and the actual runoff.(2)Response of water yield to landscape connectivity: There is a significant positive correlation between quick flow and hydrological connectivity calculated by the InVEST seasonal water yield model where hydrological connectivity can be used to characterize surface water yield.There is no obvious correlation between the base flow and hydrological connectivity where the hydrological connectivity cannot describe the water yield of the underground base flow.3.Quantifying sediment connectivity and its sediment transport effect.Sediment index of connectivity(IC)was used to construct sediment connectivity in Yanhe river basin,which was fitted by Boltzmann s-shaped curve to obtain sediment transport ratio(SDR).Sediment transport volume in the basin was simulated by SDR ratio which was calculated by RUSLE model and soil erosion volume which was calculated by RUSLE model.The sediment transport of check dam,reservoir and river is quantified with the method of effective source area.Main conclusions are as follows:(1)Quantifying sediment connectivity: The IC index indicates accurately the probability of sediment connectivity.SDR describes accurately the sediment transport rate from the slope point to the sink area,which provides a means to accurately estimate the sediment yield in the catchment.The effective source area of sediment transport in the reservoir and pond and check dams in the Yanhe River Catchment is as high as 57.7% of the total area of the catchment.(2)Sediment transport effect in the Yanhe River Catchment: Decoupling of obstacles such as reservoir and pond and check dams will greatly reduce the amount of sediment actually reaching the river,and the longitudinal decoupling of the dam on the channel will further lead to the reduction of sediment at the exit of the catchment.Human transformation of the landscape has changed the traditional sediment connectivity pattern and sediment transport model.The research method uses RS data as the main data source,which is convenient to obtain;GIS is used as the main technical means to facilitate the rapid and accurate quantification of hydrology and sediment connectivity.This method can well explain and quantify the reduction of runoff and sediment volume in the Yellow River in recent years.This study also provides means for monitoring water yield and sediment transport in the catchment,providing decision-making reference for water resources management and flood control and disaster reduction,and providing technical support for hydrology and soil conservation services.