Assessment Of Shallow Groundwater Vulnerability In Huaihe Basin Plant Area Based On Improved DRASTIC Method

Groundwater vulnerability assessment and classification is an important basis for groundwater protection.Huaihe River Basin is one of the highest basins with higher degree of development.In recent years,groundwater resources are facing the serious pollution threat due to human activities.So,it's necessary and meaningful to carry out the groundwater vulnerability assessment research in Huaihe River Basin.This paper combined with the "special plan for the protection of groundwater resources in Huaihe Area",and focus on the research of the assessment of groundwater intrinsic vulnerability in Huaihe River Basin plant area,.The main studies are as follows:(1)Based on DRASTIC methods proposed by EPA,8 indexes were selected to carry out the groundwater intrinsic vulnerability assessment research in Huaihe River Basin,which were the depth of water table,net recharge,water abundance of aquifer,soil type,topographic slope,impact of vadose zone,hydraulic conductivity of the aquifer and drainage density.(2)According to the results of the groundwater intrinsic vulnerability assessment,the differences in spatial distribution of indexes,and the characteristics of human activity in Huaihe River Basin,two indexes,utilization of land index and coefficient of groundwater exploitation index,were added for the assessment of groundwater intrinsic vulnerability.The AHP(analytic hierarchy process)method was used for improve the DRASTIC intrinsic vulnerability assessment in Huaihe River Basin.(3)The nitrate concentrations of groundwater samples were selected in Shayinghe Basin,the largest tributary of the Huaihe River Basin,to verify the specific vulnerability assessment results,and identify the sensitive factors in the shallow groundwater vulnerability.(4)According to the comparison results of intrinsic vulnerability assessment and special vulnerability assessment,the distribution of shallow groundwater intrinsic vulnerability and specific vulnerability was discussed.The main conclusions are as follows:(1)The area of the intrinsic groundwater vulnerability accounts for 31%of the total area of the Huaihe River Basin(the high and higher vulnerability degree).The spatial distribution shows the intrinsic vulnerability on the top of Huaihe alluvial-diluvial plain was higher than that of on the bottom,on valley regions was higher than that of on flood area.In the Nansi Lake plain,the intrinsic vulnerability on the eastern part of the lake was higher than that of on the western part,and the lakeside belt was higher than the belt far from the lake.As to the Yishuhe alluvial-diluvial plain,the intrinsic vulnerability on piedmont was higher than that of on the coastal areas.The area of the specific groundwater vulnerability accounts for 43%of the total area of the Huaihe River Basin(the high and higher vulnerability degree).The spatial distribution between intrinsic vulnerability and specific vulnerability trends consistent.The north of Huaihe alluvial plain and the west of Nansi Lake had a higher degree of vulnerability,due to the high mining coefficient index.(2)The results of the distribution of intrinsic groundwater vulnerability showed that:In area with low degree of vulnerability,soil types were clay loam and silt loam with clay and silt soil in vadose zone;In area with middle degree of vulnerability,soil types were sandy loam with silt and silty sand in vadose zone;In area with high degree of vulnerability,soil types were sand and exposed limestone with thick medium in vadose zone.(3)With assessment of intrinsic groundwater vulnerability,8 indexes were selected and the weight distribution of these indexes were:depth of water table for 5,net recharge for 4,water abundance of aquifer for 2,soil type for 2,topographic slope for 1,impact of vadose zone for 4,hydraulic conductivity of the aquifer for 1,drainage density for 1.With AHP assessment,two indexes,landuse index and coefficient of groundwater exploitation index,were added to improve DRASTIC method,the weight distribution of these indexes were:depth of water table for 3.65,net recharge for 2.04,water abundance of aquifer for 1.19,soil type for 2.96,topographic slope for 0.68,impact of vadose zone for 2.96,hydraulic conductivity of the aquifer for 0.67,drainage density for 1.35,landuse for 3.00 and coefficient of groundwater exploitation for 1.50.