Hydro-thermal Transport Laws Of Soils On The Typical Slope In The Vulnerable Ecological Regions In The Shaanxi Section Of The Yellow River Basin

The stratigraphy of the west bank of the Yellow River in Heyang County,Weinan City,Shaanxi Province,in the Yellow River Basin is a sediment-type dualistic structure of loess overlying and fine sand underlying,with unstable geological structure and easy water and nutrient loss.As a result of large-scale open-pit sand mining activities,many exposed sandy slopes have been formed,and their ecological restoration faces serious challenges.The region The research of eco-restoration under this special scenario has important theoretical value and practical significance to promote the sustainable development of the region.This paper,taking a typical slope of Shendong sand mining in Hechuan Town,Heyang County,Weinan City as the research object,by means of combinations field investigation and indoor analysis,monitoring in situ and numerical simulation,carries out eco-hydrogeological survey,analyzes the hydrothermal and nutrient transport pattern,establishes an in-situ test site for hydrothermal transport,constructs a two-dimensional hydrothermal transport numerical model based on Hydrus-2D,and simulates the hydrothermal transport process of the slope under different scenarios.A reference for soil moisture and nutrient management and ecological restoration on such slopes in the Yellow River Basin The following results were achieved:(1)The results of field survey and indoor analysis show that the soil on this slope is mainly fine sand and medium sand,containing fine gravels and medium gravels,and a clay layer at the bottom of the slope;water content and nutrient content of the soils at the bottom are higher than those at the middle and top of the slope,and the water content of the surface soils is lower than that of the deep soils,but the nutrient content is higher than that of the deep soils;the nutrient content on the whole slope is extremely short to relatively short.(2)Based on the field investigation,an in-situ test site of hydrothermal transport on the slope was constructed.The in-situ monitoring data showed that hydrothermal dynamics was more influenced in the shallower layers by diurnal fluctuation and precipitation,however,it was more stable in the deeper layers and less influenced by rainfall;the nutrient content was basically stable.(3)Based on field investigation and monitoring in situ,the hydrogeological conceptual model and mathematical model of hydrothermal transport on the slope were established.The in-situ monitoring data were used to identify and validate the mathematical model,and then relevant hydrothermal parameters were obtained.By means of the parameters obtained and the mathematical model,the moisture transport characteristics of the slope under 15 rainfall scenarios were simulated.The simulation results show that:(a)The greater the amount of rainfall,the greater the depth of infiltration,the greater the increment of water content;when the amount of rainfall is certain,the shorter the rainfall calendar time,the shorter the response time of each layer,the shorter the time for the soil water content to reach the peak,the greater the peak.(b)When the rainfall is small,the local clay layer at the bottom of the slope has less influence on the soil moisture transport;when the rainfall increases,the local clay layer plays an obstructive role on the deep soil moisture transport,and the lag time and peak time to rainfall are prolonged;but as the rainfall increases further,the influence of the clay layer on the deep soil decreases again.(c)When the rainfall and rainfall duration times are certain,the greater the width of the clay layer in the horizontal direction,the more significant the effect of impeding moisture,and the thickness of the clay layer has less influence on soil moisture transport.(4)The soil on the sandy slopes in the study area has poor ability to retain water and nutrients.After the end of rainfalls,the soil moisture content returned to the state before rainfall in a short time;nutrients on the surface were easily leached to the deeper layers.The stability coefficient of slopes decreases with the increase of slopes,and when the slope is less than 34.5°,the stability can be maintained under extreme rainfall conditions.Accordingly,the measures of ecological restoration for slopes are proposed:(a)Keep the slopes below 34.5°.(b)Spray a layer of clay on the surface of sandy slopes to increase the soil moisture of the surface soil and reduce loss of water and nutrient.(c)Selecting suitable plants to seed and restoring environment.(d)Set up drainage ditches and establish reservoirs to reduce soil erosion and collect water resources for slope maintenance.The research results above can provide reference for eco-restoration of slopes and sustainable development in the vulnerable ecological zone of the Yellow River basin.