| Yangzhuang Basin,located in Zaozhuang City,Shandong Province,is a typical karst water-bearing system in northern China.In recent years,with the rapid development of industry and agriculture,a large number of groundwater resources are exploited,which makes the problems like groundwater resources reduction,water quality deterioration,karst collapse increasingly prominent.Therefore,the prediction and simulation of groundwater regime in Yangzhuang Basin can provide scientific basis for controlling groundwater environment in this area.And it can promote the rational planning of local groundwater exploitation.These have important significance to Yangzhuang Basin.In this paper,we investigated and analyzed the pollution sources in Yangzhuang Basin.The groundwater quality of important sites in Yangzhuang Basin was evaluated by BP neural network model.Then we use Visual MODFLOW software to establish and validate the groundwater numerical model and groundwater solute transport model in Yangzhuang Basin.Finally,the Yangzhuang Basin model is used to predict the present situation of groundwater and the condition of conservation and source increase.We get the result as follows:(1)The BP neural network model was used to synthetically evaluate the eight indexes of pH value,total hardness,total soluble solids,sulfate,chloride,nitrate nitrogen,nitrite nitrogen and fluoride in the important locations of Yangzhuang Basin.The results show that the groundwater quality in Yangzhuang Basin is good as a whole.Although there is no first-class water distribution in the whole region,the proportion of second-class water and third-class water distribution areas is 6.25%and 71.88%respectively.This shows that the water quality in most areas of the study area is not polluted.Fourth-class water and fifth-class water accounted for 15.63%and 3.31%respectively.Most of them were distributed near factories and farms.(2)Based on the generalization of various geological conditions in Yangzhuang Basin,the groundwater numerical model and groundwater solute transport model in Yangzhuang Basin are established by using Visual MODFLOW software.Recognition and verification using hydrogeological data from 2013 to 2015.The results show that the model fitting effect is better in the period of gentle fluctuation of water level in Yangzhuang Basin,which basically coincides with the validation data.During the period when the water level fluctuates greatly,the model fitting has a small prediction deviation,which belongs to the normal error.The prediction of the overall fluctuation trend of the model is correct,and the model can be used.(3)We used the model to predict the groundwater level in the next 20 years and nitrate concentration in the next 10 years in Yangzhuang Basin.The predictive conditions are divided into the current conditions and water source protection conditions.The prediction results show that the exploitable groundwater resources under the present condition are 2.615×105m3/d after 20 years.And the exploitable groundwater resources under the condition of protecting water source are 3.539×105 m3/d after 20 years.Groundwater in Yangzhuang Basin is in balance between exploitation and replenishment under the two conditions.But the exploitable groundwater can increase 41.45%with the protecting water source conditions.Under the two conditions,nitrate concentration did not exceed the standard in the next 10 years,and the trend of high concentration was the same,mainly extending to the southwest.But under the condition of conservation and increase of source,the increase of concentration is lower than the current condition.The main reason is that under the condition of conservation and increase of source,the amount of exploitable groundwater resources increases and nitrate concentration is diluted. |
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