Study On The Influence Of Water Saving Reform On Groundwater Environment In Shenwu Irrigation Area

Water-saving renovation is an important measure to alleviate the serious shortage of water resources in the Inner Mongolia Hetao Irrigation District.Based on the water-saving reconstruction project carried out in Shenwu Irrigation Area of Hetao Irrigation District,this study takes the groundwater environment as the entry point,analyzes the changes of groundwater environment on the two sides of the water-saving reconstruction channel,the farmland characteristic area and the ecological characteristic area,and reveals the regional water-saving.Transforming the impact on the groundwater environment and changing trends,providing a theoretical basis for optimizing water resources allocation and scientific and rational water use.Main conclusions are as follows:(1)The lining changes the leakage law to a certain extent.After the water is brought into the channel,the shallowest depth of groundwater at 0～500m on both sides of the lining channel decreased by 0.13～0.52m compared to unlined channels,and the time required for the shallowest depth to was significantly prolonged in summer irrigation.The effect of autumn irrigation was not obvious.The change law of groundwater buried depth on both sides after the water supply in summer irrigation period changes from the rapid rise before lining to the short-term rapidly increase-long-term fluctuations-rapid rise in a short time.During the autumn irrigation period,the groundwater buried depth on both sides changes from the rise rapidly in a short time before the lining-the long-term slow rise-the short-term rapid rise to the long-term slow rise-the short-term large rapid rise.Lining also has a certain impact on the quality of groundwater on both sides of the river.The annual variation of groundwater conductivity of the two banks decreased after lining(0.72～2.75ms/cm)compared with that before lining(0.66～3.53ms/cm),and the change of total dissolved solids(TDS),salinity,total salt and total hardness are similar to the conductivity,the annual variation is reduced after lining,the total alkalinity(137～350mg/L)changed little,the total nitrogen(0.07～2.54mg/L)and total phosphorus(0.07～0.76mg/L)content were small,however,the variation after lining has also decreased.The type of groundwater quality after lining has not changed,and it is still Cl-+SO42-+HCO3-·Ca+Na+type.(2)The water saving reform has certain influence on the groundwater environment in the characteristic area of farmland.The groundwater depth in the farmland characteristic area decreased,and the downstream farmland characteristic area(average drop of 0.56 m)decreased more than the upstream farmland characteristic area(average drop of 0.20 m).The farmland characteristic area with high groundwater conductance(5ms/cm)decrease range is 0.26～3.18ms/cm,and the characteristic area with small groundwater conductance(5ms/cm)decrease range is 0.01-2.61ms/cm.The variation law of TDS,salinity,total salt content,total hardness,total alkalinity and total nitrogen are similar to the conductivity.The anions in groundwater are mainly Cl-+SO42-+HCO3-,and the cations are converted between Na++Ca+and Ca++Na+during the irrigation period.(3)Groundwater environment in ecological characteristic area responds to water saving reform.The groundwater buried depth in the characteristic areas of wasteland and forestland showed a downward trend.After the transformation,the average buried depth decreased by 0.49m and 0.20m respectively compared to the groundwater depth before the transformation.The groundwater conductivity of the saline-alkali land and the characteristic area next to the channel decreased significantly.The average annual conductivity of the area with higher degree of salinization decreased from 16.18ms/cm before the transformation to 12.71ms/cm after the transformation.The TDS,salinity,total salt content,total hardness and total alkalinity of groundwater in the ecological characteristic area have such a rule:the area with higher content has a larger decline.The anion in groundwater is mainly Cl-+SO42-+HCO3-,and the cation is converted between Na++Ca+and Ca++Na+during the irrigation period.(4)The area occupied by groundwater depth of 3～5m in irrigation field showed an increasing trend,increased by about 25%,and the area occupied by 1.5-3m showed a decreasing trend,decreasing by about 25%;the area occupied by groundwater conductivity 0.46～1.5ms/cm showed an increasing trend,increased by about 31%,and the area occupied by more than 1.5ms/cm is decreasing,decreasing by about 32%.The area of TDS content less than 3g/L shows an increasing trend,increased by about 3%,and the area of more than 3g/L shows a decreasing trend,decreasing by about 3%.The area of salinity of 1～3PPT showed an increasing trend,increased by about 6%,and the area of 5～10PPT showed a decreasing trend,decreasing by about 2%.The contents of HCO3-、Cl-、SO42-、Mg2+and Na++K+,total salt,total hardness and total alkalinity in groundwater also showed a downward trend,and the change of Ca+ was small.The content of CO32-,total nitrogen and total phosphorus is small and the change is not obvious.The impact of the comprehensive water-saving channel on both sides of the river,the farmland characteristic area and the ecological characteristic area of groundwater environment,the overall analysis found that after the water-saving transformation,the groundwater depth of the irrigation area increased,and the groundwater quality did not change significantly.