A nonlinear time series model is presented to describe the dynamics of ground water flow. The procedures for model‐establishing and parameter estimation are discussed. The proposed nonlinear model uses a threshold parameter that relates different precipitation processes, and a lag parameter that relates the time lag between precipitation events and observed increasing spring flow. This model is then applied to the prediction of time‐dependent flow of the Longzichi Spring, Shanxi Province, northwest China. The results in this analysis show that the proposed approach can accurately describe the complicated nonlinear time series and the discharge regime of the Longzichi Spring.

On the basis of the hydro-geological model of a confined aquifer, the propagation mechanism of geo-acoustic waves along the confined aquifer outlined as a plate wave-guide is proposed. The harmonic frequency equation for geo-acoustic propagation along confined aquifer as waveguide is derived from Biot theory. The basic frequency of the confined aquifer with a deep well for geo-acoustic observation, located at Juxian county, Shandong province, China, is 35.0 Hz. By Wigner distribution of geo-acoustic signals observed at Juxian geo-acoustic well, the frequencies of geo-acoustics are basically the integral multiple of the basic frequency. The results show that the responses of the confined aquifer to geo-acoustic waves are characterized by frequency selection and frequency dependence. Only the waves whose frequencyfis the integral multiple of basic frequency can propagate as guide waves in the aquifer, that is, the aquifer responds to the waves.

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The fluctuation of most of the hydrograph in the deep aqueous system records the fluid pulsation in lithosphere and variation of the earth's crust. Many observations have verified that groundwater is an ideal information carrier of the crust. In this paper, the series of input (precipitation, air pressure, Earth tide etc.) and output (water level, artesian flow) of the deep aqueous system are studied by using the spectrum analysis and system theory. The application concepts of transfer function and the spectral structure of the hydrograph enrich the knowledge of the deep aqueous system. Two typical spectral structures of the hydrograph of the deep aqueous system are obtained by comparing with many waterbearing systems of the Jizhong depression. One is from well Ma1 7 and the other is from the well Xinze-5. Finally, the physical models of forming the spectrum of the hydrograph are constructed on the basis of the spectrum research on the deep aqueous system. 1 Problems and Background Conditions of the Study AreaIt has been a rather long time that groundwater is studied as a utilizable resource and detrimental factor of environment. Recently, the third research domain of hydrogeology, that is to consider groundwater as an information source of the crust and to feed back the research result of information to the aqueous systems, has appeared. The research achievelemts of this domain have enriched the knowledge of the aqueous systems.Deep (which generally refers to a burial depth over 500 m) groundwater regime usually refers to the groundwater level fluctuation resulting from confined aquifer deformation. It is the exterior presentation of aquifer stress and strain state. This kind of regime is distinctfrom normal groundwater regime which is formed under the influence of water bal-