Study On Leakage Estimation Of Songhuaba Reservoir In Kunming Based On Stable Hydrogen And Oxygen Isotopes

Yunnan is located in the Southwest of China,where limestone is widely distributed.It is a typical karst area.Due to its tropical and subtropical monsoon climate,the annual distribution of precipitation is uneven and concentrated in the rainy season.Good hydrothermal combination conditions make regional dissolution strong,and karst caves and underground rivers are widely developed.After the fall of atmospheric precipitation,it seeps into the ground rapidly.The exploitation and utilization of groundwater is difficult.Lakes?reservoirs?have become the most important drinking water sources in the region,especially for plateau cities.However,the leakage of lakes?reservoirs?in karst areas is one of the important problems that have been perplexing and affecting the ecological environment and water security of the area,seriously endangering the social and economic development of Yunnan.Therefore,this study selects Songhuaba Reservoir in Kunming,a reservoir in the plateau karst region,as the research object.Through continuous sampling of precipitation and reservoir water in the study area,and analyzing the variation characteristics of hydrogen and oxygen stable isotopes in the water body,the temporal and spatial variation characteristics of water isotopes in Songhuaba Reservoir are discussed.Based on the hydrological and meteorological data in the reservoir area,the leakage of Songhuaba Reservoir,a water source in Kunming city,is estimated by using the water balance and stable isotope material balance model,and the regional water safety is discussed.The main conclusions are as follows:?1?The variation range of stable oxygen and hydrogen isotopes in reservoir water throughout the year is small.The?¹⁸O value ranges from-11.69‰to-9.86‰,with an average value of-10.73‰;and?D ranging from-83.91‰to-73.97‰,with an average value of-79.12‰,indicating that the reservoir's recharge source is stable and relatively single.The hydrogen and oxygen isotopes of the reservoir water have obvious spatial and temporal variation characteristics:the time distribution shows obvious seasonal variation characteristics,the rainy season is positive,while the dry season is negative.In terms of spatial variation,the distribution range of hydrogen and oxygen isotopes in the reservoir water is narrow,and the concentration of its components to the richest person in the reservoir is not obvious along with the flow direction,which may be related to the short renewal period and sufficient mixing caused by the daily water supply.According to the research on the hydrogen and oxygen isotope characteristics of the incoming river water,it is found that the stable hydrogen and oxygen isotope of the incoming river water has the same variation rule with the isotope of the incoming water in time,with positive variation in rainy season and negative variation in dry season.?2?The annual stable isotope relationship of reservoir water is?D=5.10?¹⁸O-24.887?r=0.99?.In the rainy season,the evaporation line of reservoir water is?D=5.58?¹⁸O-19.45?r=0.97?.In the dry season,it is?D=5.21?¹⁸O-23.07?r=0.98?.The slope and intercept of reservoir water evaporation line about rainy season and dry season are lower than global precipitation line,indicating that the reservoir water is subject to strong evaporation fractionation.The slope and intercept of evaporation line in the rainy season are higher than those in the dry season,indicating that the concentration of stable isotope in reservoir water in rainy season is mainly affected by equilibrium fractionation,and the dynamic fractionation coefficient in the dry season has a great influence on it.?3?During the rainy season,the variation range of excess deuterium in reservoir water was 3.47‰⁷.86‰,and the mean value was 5.36‰.For the dry season,the variation range of excess deuterium was 5.69‰to 9.53‰,which the mean value was8.28‰.During the rainy season,the variation range of excess deuterium in incoming river water was 5.01‰⁶.67‰,with an average value of 5.84‰.For the dry season,the variation range of excess deuterium was 6.17‰⁹.29‰,which the mean value was 8.01‰.The excess deuterium value of reservoir water and incoming river water has obvious seasonal variation,the rainy season is lower and the dry season is higher,which is contrary to the isotope variation rule of reservoir water.The higher the air humidity,the smaller the excess deuterium value.The excess deuterium value increases when air humidity decreases.?4?The stable isotope of hydrogen and oxygen in lake?reservoir?reflect the evaporation intensity and the hydrological status of the basin.The evaporation and leakage of lakes?reservoirs?can be estimated quickly and effectively by the method of water stable isotope material balance.The evaporation and leakage of Songhuaba Reservoir are estimated by water balance method and stable isotope leakage model.The annual evaporation capacity of Songhuaba Reservoir is 1072.8mm,the monthly average evaporation capacity is 89.4mm,and the evaporation capacity in the rainy season is 541.3mm,accounting for 50.5%of the total evaporation capacity.The evaporation capacity in the dry season is 531.5mm.And the annual net evaporation monitored by the Meteorological Bureau is close to 1060mm.The evaporation capacity in dry and rainy seasons is close,and both the maximum evaporation capacity and the minimum evaporation capacity occur in dry seasons,which is related to the special geographical location and climate of Kunming area.?5?The annual leakage of the reservoir is about 1.0675 million m³,accounting for 1.1%of the total storage capacity.The total leakage in dry and rainy seasons is close,accounting for 51%and 49%of the total leakage respectively.Among them,in rainy season,the storage capacity increases and the leakage quantity increases,whereas in dry season,the storage capacity decreases and the leakage quantity decreases.The change of the leakage is consistent with the change trend of the reservoir capacity,indicating that the reservoir leakage volume is related to the reservoir capacity change.The results of this study are basically consistent with the leakage volume designed for the construction of the reservoir?1%of the average annual storage capacity?.At the same time,it is close to the leakage quantity estimated by water balance method?1.2614 million m³?.The results of this study will provide scientific support for the quantitative study of lake?reservoir?leakage,especially the assessment of lake?reservoir?leakage in the plateau karst areas,the improvement of the utilization rate of freshwater resources,the rational allocation of water resources to cope with extreme weather events and the guarantee of regional water security.The research results lay a scientific foundation for the further development of water balance in karst areas,and enrich the research on water vapor circulation and water balance by using stable isotopes.