Dynamic evolutionary tendency of groundwater in irrigation district in changing environment and its driving factors
Du Wei1, Wei Xiaomei1, Li Ping1, Li Peng1, Han Yezhen2
1.College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling, Shaanxi 712100, China; 2.Water Conservancy Construction Survey and Design Institute of Yantai City, Yantai, Shandong 264001, China
The tendency of variation in environmental factors, namely precipitation, evaporation, amount of surface water irrigation and groundwater mining amount during 30 years(1981—2010)in Baojixia Irrigation District was analyzed by using three statistic methods and starting with the relationship between groundwater system and external environment. The results showed that precipitation declines but not significantly, its average decline slope is 2.900 mm/a; evaporation rises in increasingly fluctuation manner, its average increase slope is 3.270 mm/a, suggesting precipitation and evaporation have an opposite variation tendency. Amount of surface water irrigation shows a significant decrease, and groundwater mining amount decreases but not obviously. The temporal evolutionary tendency and spatial distribution features of groundwater were explored by means of the GIS technology and geostatistical methods too. It was presented that the groundwater level declines obviously from 1995 to 2005 in the north-west area in the irrigation district, eventually it has decreased about 7-8 m within 10 years; even though the groundwater level also decreases in the central and south-east area in the district, the declination is less than 1m. Fortunately, after 2005, the groundwater levels exhibit a less decline tendency only in Wugong which is located in the north bank of Weihe river, in the south of Xingping, and in the central south of Xianyang, respectively. Finally, the main factors for deriving change in groundwater level in the irrigation district were identified by using grey relational analysis, showing that the grey relational degree for each environmental factor is all above 0.5. Clearly, surface water irrigation and groundwater mining are the main factors of human activity related that derive change in the groundwater level in both highland and lowland areas in the irrigation district.
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