Leakage Of Plain Reservoir And Its Influence On Regional Groundwater Dynamics

The construction of plain reservoirs is an important means of deploying water resources in arid and semi-arid areas.Leakage,as one of the common problems faced in the construction and operation of plain reservoirs,will bring certain hidden dangers to the regional groundwater environment.For reveal the leakage characteristics of the plain reservoir and analyze its impact on the regional groundwater dynamics,this paper takes the test section of Doumen Reservoir in Xi'xian New Area as an example to analyze the influence of leakage on groundwater level and water quality,and studies the temporal and spatial distribution characteristics of leakage strength.And its impact factors,predicting the leakage characteristics of the Doumen Reservoir after completion and the variation of regional groundwater flow field,and achieved the following main results:(1)The sediment permeability coefficient of the Doumen Reservoir test section showed moderate spatial variability in the horizontal direction and strong spatial variability in the vertical direction.The results obtained by the empirical formula of the permeability coefficient(A&S formula)are less different from the results of the indoor penetration test and can be used for the estimation of the permeability coefficient.(2)Leakage in the reservoir area of the test section makes the overall groundwater flow field increase by 0.5-2.5m/a,and the annual leakage of the reservoir area is about 7026m~3/a,accounting for 4.53‰of the total storage capacity(1.55 million m~3).The resulting anti-seepage measures are feasible due to large water loss.(3)The leakage intensity in the reservoir area of the test section is characterized by a small period of high water period and a large dry season,which is spatially larger in the north(loam,silt,medium sand)and smaller in the south(loam)Characteristics.The main influencing factor of the spatial distribution difference of leakage strength is the permeability coefficient.The main influencing factors of time distribution difference are the eastern groundwater level(GWF1),reservoir water level,rainfall,western groundwater level(GWA1)and evaporation.(4)Leakage has obvious influence on the groundwater quality index of the eastern part of the test section(GWF1).The changes of temperature,pH and total phosphorus index are within a certain range,which will not bring water quality hazards,and the ammonia nitrogen concentration has exceeded the standard.(5)A numerical model of groundwater flow in the Doumen Reservoir area was established.The prediction analysis shows that the expansion of the reservoir water storage area will cause a large-scale water level uplift area in the groundwater flow field.The water level uplift area caused by the storage of Beihu Lake(the second stage construction)and Nanhu Lake(the third stage construction)is 18.8km~2 and31.44km~2 respectively,and the groundwater level elevation values of the uplifting area are 0.2m and 0.36m respectively.The overall water storage in Doumen Reservoir has been 5 years,and the regional groundwater level has risen by about 1.2-3m.The relationship between reservoir water and groundwater has always been expressed as replenishment of groundwater by reservoir water.(6)Under the overall water storage situation of Doumen Reservoir,the reservoir leakage shows obvious spatial and temporal distribution characteristics,and the spatial performance is South Lake>North Lake>Test Section.The leakage of the South Lake accounts for about 55%of the total leakage.In time,the leakage of the reservoir showed a downward trend,with an annual average decrease of 0.88 million m~3/a.The average annual leakage was about 224,000 m~3/a,accounting for 4.87‰of the storage capacity.The groundwater level and the reservoir water level are the main causes of the space caused by reservoir leakage.(7)Under the overall water storage situation of Doumen Reservoir,the leakage strength is negatively correlated with the groundwater level and linearly positively correlated with the reservoir water level.For every 1 m increase in groundwater level,the reservoir leakage strength is reduced by about 3.3-3.7 mm/a.The average water level rises by 1m,and the leakage strength increases by about 4.34mm/a.Reservoir leakage loss under different reservoir water levels accounts for less than 9‰,which has little effect on reservoir operation.