Research On Inland Shallow Salt-water Formation Mechanism And Evolution

The shortage of freshwater resources has become a bottleneck restricting the development of our country’s economy.The north China plain of shallow saline water-brackish water resources is rich and widely distributed. characteristics such as shallow buried depth, fast supply and easy mining make it a unconventional water source that draw more attention. In order to more scientific and reasonable development and utilization of shallow inland saline water, it is particularly important for the research of its formation mechanism. In This paper, the inland plain shallow salty- brackish water is taken as the research object. From two aspects of hydrodynamic field and chemical field, the dynamic change characteristics of shallow inland saline water is studied, and its formation mechanism is analyzed thus revealing the evolution regulation.The paper takes typical inland shallow saline water area of jiyang county in Yellow River Flood Plain as an example, on the basis of related literature at home and abroad, adopting the method of field investigation, drilling method, the geological and hydrogeological conditions in the study area is finded out.By taking field tests such as pumping test, water injection test and tracer test and indoor salinewater-freshwater displacement test, the hydrodynamic effect mechanism of inland shallow saline water formation was studied. According to distribution law of the shallow brackish water chemical composition and hydrochemistry type, using the mathematical statistics,Piper trilinear nomograph and methods of ion ratio coefficient etc.,spatial and temporal distribution of shallow groundwater water chemical field of jiyang were analyzed systematically. On this basis, the formation of shallow saline water and the internal connection of various water- rock action in the process of groundwater circulation flow were discussed. Finally, using hydrogeochemical simulation software PHREEQC was used to simulates three typical groundwater seepage path inversely. Simulation results revealed the shallow saline water formation mechanism and evolution laws.Through these method above, the following conclusions are drawed.(1) Shallow saline water in the inland Yellow River Flood Plain is located in the runoff lagging areas between old channels with poor runoff and circulation condition. With shallow buried depth,the groundwater presents typically “weather- evaporation ” type. Field testsrevealed that the hydraulic gradient is small being of 0.17‰ and runoff circulation condition is poor and clay content is high. It is conducive to the accumulation of salt. Significant groundwater mineralization play a decisive role to the formation of the inland saline water body.(2) Indoor salinewater-freshwater displacement test reveals the salinity(salt concentration)and pH value of the seepage water has obvious influence on the permeability of aquifer medium. With the salinity increasing and pH decreased, the permeability tend to decrease.When pH decrease to 7.4, the permeability reduce suddenly. Permeability reduction weakened groundwater runoff condition further,which is in favor of salt gathering. It is closely related to the complex hydrogeochemistry action in the process of salinewater-freshwater displacement.Indoor seepage tests reflect the scale effect and lag effect of solute migration.(3) 6050 groups monitor data reflect that precipitation and underground runoff have little impact on the horizontal diffusion of saline water. Inland saline water quality trends is relatively stable and generally conform to the characteristics of more and more high from recharge area-runoff area-drainage area of the groundwater solute content and more and more complex hydrochemistry type being, and distributes with zonation.(4) Inland shallow groundwater hydrochemistry type is complicated due to both lioxiviation and continental salinization. Jiyang saline water is mainly continental salinization factor. Ion ratio such as γNa/γCl equaling to 1.0~2.0 and value of γSO4/γHCO3 bigger than 4reveal ixiviation and concentration caused by evaporation have a close contact with saline water formation.(5) According to the 112 groups of water quality test results, the type of water chemistry of shallow groundwater in Jiyang area are divided into 16 categories. In different groundwater flow system, groundwater presents otherness of groundwater level dynamic and water quality,as well as different groundwater runoff circulation conditions. It cause the different type and degree of hydrogeochemistry action it experienced, which is the basic reason to the formation of the complex hydrochemistry type.As groundwater flow paths lengthens, TDS of shallow groundwater increases, high-salinity Cl·SO4-Mg·Na. Ca model and Cl·SO4-Na·Mg shallow saline water is Punctate sporadically distributed in inland areas.(6) The formation and evolution of inland saline water is effected by the hydrodynamicalternating intensity, evaporation,alternate adsorption and water-rock interaction.Hydrogeochemical backward simulation shows that in the evolution process along different groundwater seepage path,the dominated water chemical component is different which affects its formation, but it is not a complex chemical field under some single hydrogeochemistry action.In a word, the evolution of the shallow inland salt water has zonality in the runoff way. Affected by the radial flow conditions at the same time, the shallow inland salt water evolution is slow and long.In conclusion, the chemical characteristics change of inland shallow saline water depends on variety of reasons such as the terrain, atmosphere,sedimentary environment,hydrodynamic conditions and hydrogeochemistry action. In inland area, formation and evolution of the inland continental salinization saline groundwater hydro-chemical field controled by groundwater flow paths,atmosphere,lithology, circulation depth and hydrogeochemical effect jointly.