Prediction And Research On The Change Of Groundwater Environment On The Conditions Of Different Diversion Level In Hetao Irrigation District Of Inner Mongolia

Water resources is an important natural resources for human survival and development, and it is also an main constraint resources for natural environment. With the quickly development of economic and social, the contradiction of water supply and demand has become increasingly prominent.So it has become one of the strategic issues to solve the world water crisis.Water shortage which restric the economic development of Inner Mongolia has become a bottleneck.How to solve the problem of water efficient use and rational allocation and proposing the threshold value which will keep groundwater environmental cycle at benige conditions was one of key technologies of economic rapidly development in Inner Mongolia autonomous region.This paper based on the Hetao irrigation district.The field experiments,numerical simulation and theory analysis were combinated in this paper. We analysised the influence factors of groundwater level and groundwater quality.The paper investigated the change law of groundwater level and groundwater quality after water-saving irrigation transformed in the typical area and project area.Then we forecosted the groundwater environmental influence factors becouse of irrigation water levels.The experimental study showed that the groundwater level was mainly affected by irrigation, rainfall and evaporation. When the evaporation changed little, the groundwater table was mainly affected by irrigation and rainfall, while the evaporation changed obvious, the groundwater level was mainly affected three factors. Main factors affecting the groundwater quality were the irrigation water quality, groundwater depth and outside pollutants .The correlation coefficient was 0.73 (about moderate correlation degree) between groundwater quality and irrigation water quality and the the correlation coefficient was 0.46(about lower correlation degree) between groundwater depth and irrigation water quality.The groundwater level varied by obvious trend in the typical and project area scales before and after reconstruction. Because of different regional and geographical location, a typical area the differences between .The groundwater level of different observation groundwater wells in typical area changed from 1.5 to 3m.But the groundwater level of different observation groundwater wells in project area changed obvious between 2 to 7m.During one year, groundwater level decreased and increased two times. Groundwater level was downward during the growth period of crop .So crops consumed some groundwater storage. After transformation the groundwater level were significantly lower than before water saving reform. Longsheng demonstration area decreased after transformation in the range of 0.29 to 0.58m ,and the reduction of the six project areas between 0.02 to 0.55 m .After water-saving irrigation transformed, the distribution of groundwater salinity was very complex, and the overall trend was changed large from the upstream to the downstream. Underground water quality maxmun average volume increased 3.78g/l gradually from 2007 to 2009 in the six project area. Excepting a part of wells water quality changed little of Wuyuan and Qianqi, other project areas groundwater is salt. Underground water quality changes over time can be divided into thawing period, crop growth stage, crop harvest, autumn irrigation period. The groundwater salinity increased in cold season and decreased in warmer season. The groundwater salinity fluctuated during the crop growth. Because of evaporation increased in crop harvest time the groundwater salinity ineased, while the groundwater salinity decreased because of the effects that autumn irrigation watered will leach the salinity in the soil.The numerical simulation results showed that, the groundwater level of first plan in regional scale(4 billion m~3/a) have reached the appropriate depth while the mean groundwater level was about of 2.50m in the second plan(3.6 billion m~3/a) and during the crop growth the valun would be under the mean value,the two plans has been reduced in groundwater freshwater area, but the second plan has decreased significantly, less than the total area of 1/6.The groundwater level changing of first plan was not obvious. The groundwater level decreased about 1m of second plan. The salinity of groundwater of the two plans have increased in upstream, the second plan increased significantly .The water enviroument would be worsen Obviously in the second plan.So,the threshold water volume would be 4 billion m~3/a in order to keep the water environment benign cycle.Becouse the lack of field experiments data ,the simulation and forecost results would be tested and verified after much observation data and perfect border data.