Analysis On Impacts Of Plain Reservoirs Leakage On Groundwater In Manas River Basin

The plain reservoirs in Xinjiang can effectively relieve the temporal and spatial distribution of water resource,which is very significant for the agriculture in irrigation district.Previous studies show that the reservoirs leakage is the main reason for groundwater level rising,soil salinization,dam failure,etc.Therefore,exploring the mutual recharge between plain reservoirs and groundwater,then analyzing the influence of plain reservoirs leakage on groundwater level and water quantity,which is of great significance to the management and safe operation of reservoirs,prevention and treatment on soil salinization around reservoirs.In this thesis,the Moguhu Reservoir,Daquangou Reservoir and the area around reservoirs were selected as the typical example of plain reservoirs groups in Xinjiang.Guided by the underground water dynamics and isotope hydrology,the relationship between reservoir water and groundwater was explored by means of isotope hydrology method and numerical simulation method.Under various working conditions,the influence of reservoir leakage on groundwater level and water quantity around reservoir area was also discussed.The main research conclusions are as follows:(1)The isotopic composition of reservoirs and groundwater is near to the local meteoric water line of Urumqi,which show that their common recharge source is precipitation.Their isotopic slopes in different periods are both lower than the local meteoric water line,which suggest that they were both influenced by evaporation.The isotopic content of reservoirs water is higher than that of groundwater and the variation trend of there is similar.The content of ?18O in both reservoir water and groundwater ordered from high to low was October,July and May.Therefore,the reservoirs water and groundwater have a close hydraulic connection.(2)The annual recharge of groundwater is 0.13 billion m3.The lateral recharge and vertical recharge is 70.89 million m3,41.08 million m3,and the proportion is 57.72%,42.28%,respectively.Among the vertical discharge,the reservoirs leakage is 22.47 million m3 and its proportion among groundwater recharge is 16.72%.The artificial exploitation is the main discharge form of groundwater and the proportion is 54.65%.(3)When the water level of the reservoirs keep at the normal water level,the reservoirs leakage is the largest,which has the greatest influence on groundwater level around the reservoir area,and the maximum monthly increase is 1.04 m.The dynamic changes of groundwater level around the reservoirs are affected by both the reservoirs leakage and the groundwater exploitation.Therefore,increasing the amount of groundwater around the reservoirs area is helpful to reduce the occurrence probability of soil salinization.(4)The recharge of groundwater to reservoirs is 0.10 million m3,7.30 million m3,0.25 million m3 when the reservoirs water levels keep at the normal level,the lowest level over the years,and the operation water level,respectively.The recharge of groundwater to reservoirs is affected by reservoirs water level and groundwater level.In spring irrigation period,the reservoirs leakage decrease while the recharge of groundwater increase when the reservoirs water level are closer to groundwater level.In summer irrigation period,the recharge of reservoirs to groundwater increase when the difference between them is too large,which suggest that the difference between the reservoir water level and groundwater level is the main influencing factors of their relationship and the amount of transformation.There is a positive correlation between the recharge of groundwater and the difference of water level,and the recharge of the groundwater to the reservoirs is negatively correlated with the water level difference.