Study Of The Allowable Groundwater Withdrawal In The North China Plain Based On Environmental Limited Groundwater Level

Over the past 50 years,with the rapid development of social economy,human activities had an unprecedented impact on groundwater in the North China Plain.Due to the longterm over-exploitation of groundwater,a series of environmental geological problems have been induced.In this paper,the GMS software and the modified Modflow2005 program have been used to establish the numerical model of groundwater flow in the North China Plain under the condition of long sequence mining from 2000 to 2010.Then,according to the previous research data and previous research results,the environmental limited groundwater levels of the North China Plain were made,and they were used to calculate the allowable groundwater withdrawal in the North China Plain.First of all,the groundwater rechargeable resources in the North China Plain are roughly estimated,mainly using two methods.The first method is based on the North China Plain groundwater withdrawal composition analysis to directly calculate allowable groundwater withdrawal in the North China Plain based on environmental limited groundwater level;the second is based on the conditions of current exploitation quantity,according to the principle of groundwater balance from the current water level evolution to the environmental limited groundwater level,and the amount of change of the groundwater in the process,so as to obtain the amount of allowable groundwater withdrawal under the environmental limited groundwater level.The theoretical basis of the two methods is the principle of groundwater equilibrium.According to the two methods,the amount of allowable groundwater withdrawal under the environmental limited groundwater level are between 150.00 ~ 176.00 × 10~8m~3 / a,148.50 ~ 166.00 × 10~8m~3 / a respectively,and the allowable groundwater withdrawal of the first mathod was used to do inverse calculation.According to the groundwater balance principle,combined with the above groundwater flow numerical model,the preliminary determination of the amount of allowable groundwater withdrawal can be calculated.After repeated calculations,the shallow groundwater level is basically restored to the shallow environmental limited groundwater level.The difference between the environmental limited groundwater level and the confined water level is no longer changed or the change is very small,and the difference between the two water levels is basically stable.After the six times of inverse calculation,there is a linear relationship between the difference value of groundwater level and the environmental limited groundwater level(Y_n)and the amount of recoverable resources(X_n)per unit area per unit time are calculated.When Y_n is 0,that is,the deep water level and the deep environmental limited groundwater level coincide,the amount of allowable groundwater withdrawal in each district and county.After the linear inversion,the total amount of groundwater exploitation resources in the North China Plain is 168.74 × 10~8m~3 / a,of which the amount of shallow allowable groundwater withdrawal is 150.56 × 10~8m~3 / a,which decreased 30.35 × 10~8m~3 / a compared with the present amount of groundwater mining.The amount of deep allowable groundwater withdrawal is 18.18 × 10~8m~3 / a,which decreased 15.01× 10~8m~3 / a compared with the present situation.And some suggestions are put forward for the reduction of groundwater exploitation in North China Plain according to the allowable groundwater withdrawal.