| Representative gully heads were selected to study the topographic change processes and estimate amounts and rates of soil erosion in gully heads of bare land(hereafter referred to as gully ?)and cultivated land(hereafter referred to as gully ?)in catchment area in dry-hot valley region using scouring experiment.An in-situ scouring experiment was used to measure runoff velocity,depth and width,and the hydrodynamic factors were calculated,such as Reynolds number,Froude number,resistance coefficient,runoff shear stress and runoff energy consumption.Soil erodibility and critical cohesion were measured by using a mini-flume and a fluidized bed,respectively.In addition,physical and chemical properties of soil,such as soil bulk density,organic matter content were measured.A numerical model was run to simulate the erosion process of gully head.This research would be helpful to ascertain the evolution law of gully erosion process and provide reference for the construction projects in the dry-hot valley region.Land use changes in catchment area have significant influences on runoff resistance coefficient of gully catchment area and gully bed.After the land use type in upstream of bank gully changed from bare land to cultivated land,the resistance coefficient of runoff increased.Meanwhile,the resistance coefficients of catchment area and gully bed of gully ? was smaller than that of gully ?,respectively.Besides,the resistance coefficients of catchment areas in gully ? and gully ? were smaller than that in gully ? and gully ?.For the gully ?,a gradually increasing trend in resistance coefficient was observed in the upstream catchment areas and downstream gully beds as the experiment progressed.However,a decreasing trend in resistance coefficient was observed in the gully ? over time.Land use changes in catchment area have significant influences on runoff shear stress of gully catchment area and gully bed.The runoff shear stress of ?-J(catchment area of gully ?)increased by 31.41%compared with that of ?-J(catchment area of gully?).The runoff shear stress of ?-G(gully bed of gully ?)increased by 78.10%compared with that of ?-G(gully bed of gully ?).Besides,the runoff shear stress of gully ? and gully ? of catchment area were smaller than that of gully bed.For the gully ? and gully?,a gradually increasing trend in runoff shear stress was observed in the catchment areas and gully beds as the experiment progressed.Land use changes in catchment area have certain influences on runoff energy consumption of gully head.After the land use changed,the energy consumption increased,and the energy consumption of ?-J were larger than that of ?-J.Meanwhile,the energy consumption of ?-B(gully wall of gully ?)were larger than that of ?-B(gully wall of gully ?).However the runoff energy consumption of ?-G was similar to that of?-G.Besides,the energy consumption of gully ? and gully ? of gully bed were larger than those of catchment area and gully wall,respectively.For the gully ? and gully ?,a gradually increasing trend in energy consumption was observed in the catchment areas and gully beds as the experiment progressed.Influences of land use type on runoff energy consumption per unit soil were obvious among catchment area,gully wall and gully bed.The energy consumption per unit soil of ?-J was larger than that of ?-J,Meanwhile,the energy consumption per unit soil of II-B was larger than that of ?-B,and the energy consumption per unit soil of ?-G was similar to that of ?-G.Besides,the energy consumption per unit soil of gully ? and gully ? of gully bed were larger than those of catchment area and gully wall.For the gully ? and gully ?,a gradually increasing trend in energy consumption per unit soil was observed in the catchment areas and gully beds as the experiment progressed.Land use changes in catchment area have obvious influences on soil erosion rates of gully head.The soil erosion rate of ?-J was two or three times higher than that of ?J.However,no significant difference in soil erosion rates could be found between ?-B and ?-B,and ?-G and ?-G,respectively.As the experiment progressed,soil erosion rates of gully ? was similar to that of gully ?,and the steady state of the soil erosion rate was arrived at following an initial period of decrease.Soil erosion rates in the gully bed of gully ? and gully ? were the highest,and soil erosion rates in the catchment area of gully I and gully ? were the lowest.Meanwhile,soil erosion volume of ?-J was 2.02?2.47 times higher than that of ?-J,while no significant difference could be found between ?-B and ?-B,and ?-G and ?-G,respectively.Soil erosion volumes in the gully bed of gully ? and gully ? were the highest,and soil erosion volumes in the catchment area of gully ? and gully ? were the lowest.This result indicates that changes of land use types in the catchment area has the most significant impact on soil erosion rate in the catchment area,while the impact on other parts is not significant.Furthermore,a significant difference in soil erodibility and critical shear stress could be found in the different parts of gully head under different hydrological conditions.The values of soil erodibility were highest in the gully bed,and the values of soil erodibility were lowest in the catchment area.Soil erodibility in the gully bed was 1.57-3.44 times higher than that in the catchment area,and soil erodibility in the gully bed was 1.46-1.84 times higher than that in the gully wall.In addition,the soil erodibility in the gully wall was 2.01-1.08 times higher than that in the catchment area.Under different hydrological conditions,soil erodibility of gully head was highest under seepage condition,while soil erodibility of gully head was lowest under drainage condition.This result indicated that soil erodibility in different parts of the gully head increased as the vertical hydraulic pressure increased,and soil was most vulnerable to erode under seepage condition.The critical cohesion of soil in the catchment area was highest in the gully bed,and critical cohesion of soil in the gully bed was lowest.The critical cohesion of soil was 8.05 kPa in the catchment area,6.82 kPa in the gully wall,and 3.86 kPa in the gully bed.Obvious differences in physical and chemical properties of soils were found in different parts of gully head in dry-hot valley region.Soil bulk density in the catchment area was lowest and soil bulk density in the gully wall was highest among different parts of gully head.The content of soil organic carbon in the gully wall was the lowest and the content of soil organic carbon in the catchment area was the highest among different parts of gully head.In addition,the content of sand was highest,and the content of clay was lowest among different particle size fraction.The clay content of soil in the catchment area was highest,and the clay content of soil in the gully bed was lowest.This result indicated that sand was the main soil particle size fraction in dry-hot valley regions.A numerical simulation model of gully head was established using particle flow code.Some differences in the amounts of soil erosion in different parts of the gully head appeared during the process of erosion using the scouring experiment.Similarly,there were also some differences in the amounts of soil displacement in different parts of the gully head during the process of numerical simulation.The result of numerical simulation was similar to that of the scouring experiment. |
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