Evolution Characteristics and Influence Factors of Deep Groundwater Depression Cone in North China Plain,China——A Case Studyin Cangzhou Region

The North China Plain（NCP） is one of the global hotspots of groundwater depletion, groundwater is almost the only source of water for agricultural, industrial and drinking water in this region. After long-term＇s over-exploitation of deep groundwater, there appeared several deep groundwater depression cones, such as Cangzhou cone, Dezhou cone, Hengshui cone, Tianjin cone, etc., in which the Cangzhou cone is one of the typical cones for its special geography and hydrogeology conditions. In this study, the authors intended to analyze the evolution characteristics and influence factors of deep groundwater depression cone in Cangzhou region, especially the No. III aquifer depression cone, which is the main exploitation zone in this region. Analysis of the evolution of the groundwater depression cone of the No. III aquifer group in Cangzhou region showed that this process can be divided into four stages, namely, development, stable development, rapid expansion, and gradual recovery. The shape and evolution characteristics of the depression cone at different stages are described by analyzing the evolution of the-30,-40, and-50 contours of the groundwater table, for example the closed area of water table contour of-50 m has been enlarged from 95 km2 in 1985 to 6 528.5 km2 in 2005. The dominant factors that affect the evolution characteristics at different stages are proposed. The results showed that relatively long dry periods with less precipitation, special geological and hydrogeological conditions, and sharply increased water consumption for industrial and agricultural development are the main factors that cause the formation of deep groundwater depression cones. Meanwhile, an environmental response against groundwater exploitation is presented, and rational solutions are suggested to avert water crisis.

Changes of groundwater flow field of Luanhe River Delta under the human activities and its impact on the ecological environment in the past 30 years

The Luanhe River Delta is located in the center of the Circum-Bohai Sea Economic Zone.It enjoys rapid economic and social development while suffering relatively water scarcity.The overexploitation of groundwater in the Luanhe River Delta in recent years has caused the continuous drop of groundwater level and serious environmental and geological problems.This study systematically analyzes the evolution characteristics of the population,economy,and groundwater exploitation in the Luanhe River Delta and summarizes the change patterns of the groundwater flow regime in different aquifers in the Luanhe River Delta according to previous water resource assessment data as well as the latest groundwater survey results.Through comparison of major source/sink terms and groundwater resources,the study reveals the impacts of human activities on the groundwater resources and ecological environment in the study area over the past 30 years from 1990 to 2020.The results are as follows.The average annual drop rate of shallow groundwater and the deep groundwater in the centers of depression cones is 0.4 m and 1.64 m,respectively in the Luanhe River Delta in the past 30 years.The depression cones of shallow and deep groundwater in the study area cover an area of 545.32 km^(2)and 548.79 km^(2),respectively,accounting for more than 10%of the total area of the Luanhe River Delta.Overexploitation of groundwater has further aggravated land subsidence.As a result,two large-scale subsidence centers have formed,with a maximum subsidence rate of up to 120 mm/a.The drop of groundwater level has induced some ecological problems in the Luanhe River Delta area,such as the zero flow and water quality deterioration of rivers and continuous shrinkage of natural wetlands and water.Meanwhile,the proportion of natural wetland area to the total wetland area has been decreased from 99%to 8%and the water area from 1776 km^(2)to 263 km^(2).These results will provide data for groundwater overexploitation control,land subsidence prevention,and ecological restoration in plains and provide services for water resources management and national land space planning.

Steady-State Radial Flow Modeling through the Production Well in the Confined Aquifer of Monzoungoudo,Benin

This study aims to develop a mathematical analysis for one-dimensional modeling of a radial flow through a production well drilled in a confined aquifer, in the case of steady-state flow conditions. An analytical solution has derived from that expression for estimation of drawdowns according to different flowrates. Through that process, the evaluation of static pressure, the calculation of hydraulic charge due to the waterflow through the well is evaluated, the drawdowns curves are drawn and at last, the obtained curves are analyzed. The curves obtained for the different flow rates have an asymptotic direction, the axis of the hydraulic charges. The variation of the hydraulic charge depends on the radial distance for different flow rates. The P point, is a common point of all curves obtained for different production flowrates in the well. This point is where the well production flowrate is optimum for the optimal hydraulic charge.