| Groundwater is an important part of the basin's water resources.Especially in the Loess Plateau where the ecological environment is relatively fragile and water resources are scarce,groundwater resources are more precious and it is an important source of protection for local ecological restoration and the production and living of the people.Precipitation is the main source of recharge for groundwater in the loess hilly region.Quantitatively estimating the characteristics of precipitation recharge to groundwater is the key to the evaluation of groundwater resources.Due to the high cost of hydrogen and oxygen isotope tracer methods and difficulties in long-term monitoring,it is particularly important to estimate groundwater recharge volume through easily monitored runoff data.The study of the relationship between precipitation factors and groundwater recharge is of great significance to the rational use of groundwater resources.This study was conducted in the Zhifanggou basin in Ansai County,northern Shaanxi Province,and in the Chabagou River basin in Zizhou County.This study was conducted through the collection of the Zhifanggou watershed from June 2016 to October 2017 and April-August 2017.The precipitation,surface water and groundwater samples in the Gully Basin were measured for hydrogen and oxygen isotopes in each water body.Combined with the daily precipitation and daily runoff data from the Chiba Gully Basin in the 1959-1969 and the 2002-2014 Zhifanggou Watershed,groundwater recharge was estimated by the water withdrawal analysis method.the amount.The oxygen and oxygen isotope tracer method and water withdrawal analysis method were used to explore the space-time distribution characteristics of groundwater recharge in the hilly area of the Loess Plateau,and the mechanism of the impact of rainfall characteristics on groundwater recharge was preliminarily elucidated,with a view to providing research on the characteristics of groundwater reserving and transforming in the loess hilly region.Scientific basis.The main conclusions are as follows:(1)Among the three types of precipitation,surface water,and groundwater,the hydrogen and oxygen isotopes of precipitation are the most abundant,the hydrogen and oxygen isotopes of groundwater are the most depleted,and the hydrogen and oxygen isotopes of water have obvious temporal and spatial changes.Hydrogen and oxygen isotopes in the three types of water are gradually enriched from the upstream to the downstream.The d-excess of precipitation in June-September of the Zhifanggou watershed from June to September in the Weigou Valley is less than 10‰.It mainly comes from the sea,and isotopes are relatively abundant.It is the main source of recharge for groundwater in the drainage basin,and precipitation in other months.The d-excess>10‰,the water vapor from the mainland,isotopes are depleted.There is a hysteresis effect on the response of hydrogen and oxygen isotopes of surface water and groundwater to precipitation hydrogen and oxygen isotopes.There is a negative linear relationship between hydrogen and oxygen isotopes in precipitation and precipitation,and a positive linear correlation with temperature.There is a positive linear correlation between hydrogen and oxygen isotopes in surface and groundwater and temperature.(2)The characteristics of groundwater recharge season are obvious based on the hydrogen and oxygen isotope tracer method.The summer and autumn seasons are the main recharge periods of groundwater in the basin,but the spatial difference of groundwater recharge is not obvious.From June to October 2016,there was no significant difference in the recharge rate of groundwater between precipitation and surface water in different parts of the Zhifanggou watershed.The recharge ratio was 43.64% and 55.95%,respectively.From June 2016 to October of the following year,the average recharge ratio of precipitation and surface water to groundwater in the Zhifanggou watershed was 26.89% and 73.11%,respectively.Among them,summer precipitation has the highest proportion of recharge to groundwater(43.87%),and spring precipitation basically does not supply groundwater.According to the Yingyingyu mass balance method,about 88% of precipitation is supplied from the precipitation in the summer(4-9)and 12% from the winter half-year(10-3).Based on the isotope model of hydrogen and oxygen isotopes,it is estimated that the period of precipitation-groundwater transmission and conversion is 409-457 d,and that of surface water-groundwater is 53-77 d.There is little difference in the transmission time of surface water in different parts of the basin..The period of transmission and conversion of precipitation recharge groundwater is about 6.72 times that of surface water into groundwater.Groundwater recharge has obvious characteristics of monthly changes.Based on the hydrogen and oxygen isotope tracer method,the recharge in the half-groove area in April-October 2017 mainly occurred in August and October,and the ratio of recharge to annual precipitation was 2.11%.The supply in the Zhifanggou watershed mainly occurred in October,and the ratio of replenishment was approximately 3.33%,which was 3.80% lower than that of 2016.The evaporative losses during the precipitation-recharge of groundwater during the April-October 2017 period of the two basins are approximately 81%,and the losses from evaporation from June to October 2017 in the Zhifanggou watershed are approximately 21% higher than those from June to October 2016.Based on the Freon dating method,the groundwater age in the Zhifanggou watershed was 28-51 years,and the groundwater age in the Fangou watershed was 31-40 years.(4)The estimated groundwater recharge in the Loess Hilly Area is less than that of the hydrogen and oxygen isotope tracer method.The interannual change of groundwater recharge from 2002-2014 estimated from the water reclamation analysis method in the Zhifanggou watershed has three distinct stages of change.Since the aquifer was damaged after 2008,it was only for the first stage(2002-2007).The results are analyzed.The proportion of precipitation recharge to groundwater at the first stage was 1.11%,which was about 4.27 times smaller than that of the 2017 hydrogen and oxygen isotope traces,which was 9.14 times smaller than that of the 2016 tracer.From 1959 to 1969,the amount of groundwater recharge in the Chabagou watershed showed an increasing trend,and the replenishment from the upstream to the downstream gradually increased(p>0.05).The average amount of replenishment is 11.66 mm,and the recharge ratio of precipitation to groundwater is 3%,which is about 2.31 times that of the Zhifanggou watershed.(5)The more rainfall in the middle and heavy rain and the long calendar time in the basin,the greater the precipitation recharge to groundwater.The different types of precipitation in the Zhifanggou and Qiabagou watersheds followed moderate rain(40,34%)> light rain(31,28%)> heavy rain(22,20%)> heavy rain(7,18%),The rain is the most stable and the heavy rain variability is greatest.There was a significant positive linear correlation between groundwater recharge and precipitation in both river basins(p<0.05),and a negative correlation linear relationship with recharge ratios.The amount of groundwater recharge in the Zhifanggou and Chabagou watersheds was positively correlated with the rainfall of light rain,moderate rain and heavy rain,and negatively correlated with the short rainstorm.The Pearson correlation coefficients of recharge and different types of rainfall were moderate(0.53,0.92)> heavy rain(0.37,0.80)> light rain(0.31,0.73)> heavy rain(0,0.61).The long-term rainfall in the Zhifanggou and Qiabagou watersheds was about 3.02 and 3.74 times shorter than the short-term rainfall,and the coefficient of rainfall variation was small in the long calendar.There was a negative linear relationship between short-term rainfall and groundwater recharge in the two basins,and there was a significant positive linear correlation between rainfall and groundwater recharge(p<0.01). |
PDF Full Text Request