Aquifer System Response And Its Adaptability Countermeasures To Exploitation In The Hohhot Basin

For a long time, groundwater has been the only source of water supply in Huhhot city. Significant changes of the groundwater system in Huhhot basin such as large-scale concentrated exploitation of groundwater and water conservancy construction and so onas well as some geological environment problems like regional groundwater level continuous decline and consistent extensionof depression cone of the confined water have emerged under the influence of human activities.Study of the response process and characteristics of groundwater systems under the stress of human activities will provide a scientific basis forgroundwater sustainabilityin Huhhot basin and important instructionpurpose oflnner Mongolia groundwater protection planbeing implemented.Groundwater system has been evolving under the influence of human activities, which has also been constrained by geological factors. This dissertation first studiedthe hydrogeological conditions aiming to explore the aquifer structure and groundwater circulation patterns.Spatial distribution of the silt clay layer in the study area was first defined by use of borehole datas combined with drilling and geophysical methods in the study. It is found that the area with the thickness of the silt clay layer less than70metersshould be where the leakage occurs.The Quaternary aquifer system was divided into the single-layeraquifer system and the shallow aquifersystem and the deep confined aquifer system based on the silt clay layer. There is close hydraulic connection between the three systems.The groundwater circulation patterns were identified using isotope and hydrogeochemical methods.It is revealedthat the main groundwater supply source is the precipitation in the surrounding mountains and the lateral runoff recharge as undercurrent in the valleysandthe infiltrationin the piedmont of the riversor fioodsfrom the mountainsare the main groundwater supply mechanism. The modern cycle depth of the shallow groundwater water is identified as60m and160m for the single-layer phreatic modern water cycle depth.The CFCs and3H dating results show that the age of the shallow groundwater is generally less than60a and it is gradually increasing from the piedmont to thesouthwest of the plain area. The age is greater than60a in the area west toTaohua-Baimiaozi. The14C adjustment age of the deep confined water is24.0Ka ago and it gradually increases from downtown to Baimiaozi in the southwest area.The response characteristics of the groundwater system under the stress of human activity and controlling factors were suggested by analyzing thegroundwater observation and flow field data. On thevariation characteristics, groundwater level continuous declinemainly represents the evolutionary characteristics of the groundwater system and the groundwater level states stable at a certain time. The phased stability of groundwater level ismainly restrainedby the aquiferstructural factors. On the flow field characteristics,regional groundwater level decline mainly represents the evolutionary characteristics of the groundwater system and the decline rate is closely related to the intensity of human activity. The main anthropogenic factors controlling groundwater evolution are groundwater exploitation in the plain area and groundwater closure projects and reservoir engineering in the mountain.A numerical simulation model wasestablished by use of GMS numerical simulation software andthe groundwater miningschemes were made based on Inner Mongolia groundwater protection plan and the response of groundwater systems was predicted using the model.Compared different periods of groundwater resources evaluation results, the resource effect of the groundwater system evolution shows up as the decrease of the shallow groundwater exploitable resource modulus and the increase of the deep confined water available resource modulus.Meanwhile, the potential geological environmental effectsare land subsidence and deep groundwater pollution.Finally, the countermeasures and suggestions of groundwater sustainable use were proposed from the pointof the main controlling factor of the groundwater system evolution and the geological environmental effects.