A GENERAL PURPOSE MICROCOMPUTER AQUIFER TEST EVALUATION TECHNIQUE

Abstract. Although determination of aquifer characteristics from pumping test data is generally carried out using type curves or other graphical techniques, a number of computer methods have been developed recently for this purpose. Based on the principle of least squares, these methods of nonlinear regression analysis can be applied to any flow system for which analytical expressions of the drawdown distribution are known. In view of the growing general interest in the application of microcomputers in ground-water hydrology, a BASIC routine has been developed for estimating any number of aquifer parameters. The least squares solution is calculated by Marquardt's algorithm, using the singular-value decomposition of the Jacobian matrix. The robust computing method obtained can be applied to all kinds of pumping tests. Aquifer characteristics as well as their standard deviations are computed with optimal speed and accuracy. The technique is demonstrated by a simple application to steady flow in a leaky aquifer and an example is provided. Other applications are easily implemented and programs for unsteady-state aquifer tests, recovery tests and multiple aquifer tests are available.     

Recognition of cyclic steps in sandy and gravelly turbidite sequences,and consequences for the Bouma facies model

Preservation of cyclic steps contrasts markedly with that of subcritical‐flow bedforms, because cyclic steps migrate upslope eroding their lee face and preserving their stoss side. Such bedforms have not been described from turbidite outcrops and cores as yet. A conceptual block diagram for recognition of cyclic steps in outcrop has been constructed and is tested by outcrop studies of deep water submarine fan deposits of the Tabernas Basin in south‐eastern Spain. Experimental data indicate that depositional processes on the stoss side of a cyclic step are controlled by a hydraulic jump, which decelerates the flow and by subsequent waxing of the flow up to supercritical conditions once more. The hydraulic jump produces a large scour with soft‐sediment deformation (flames) preserved in coarse‐tail normal‐graded structureless deposits (Bouma Ta), while near‐horizontal, massive to stratified top‐cut‐out turbidite beds are found further down the stoss side of the bedform. The architecture of cyclic steps can best be described as large, up to hundreds of metres, lens‐shaped bodies that are truncated by erosive surfaces representing the set boundaries and that consist of nearly horizontal lying stacks of top‐cut‐out turbidite beds. The facies that characterize these bedforms have traditionally been described as turbidite units in idealized vertical sequences of high‐density turbidity currents, but have not yet been interpreted to represent bedforms produced by supercritical flow. Their large size, which is in the order of 20 m for gravelly and up to hundreds of metres for sandy steps, is likely to have hindered their recognition in outcrop so far.     

Unsteady flow to wells in layered and fissured aquifer systems

A solution has been developed for the calculation of drawdowns in leaky and confined multiaquifer systems, pumped by a well of constant discharge penetrating one or more of the aquifers. In contrast to earlier solutions the effects of elastic storage in separating and bounding aquitards have now completely been accounted for.

The computing technique is based on the numerical inversion of the Laplace transform. Two different methods are used and results are compared with an analytical solution. Both Stehfest's¹ algorithm and Schapery's² least squares method yield accurate results in a fraction of the computation time required for the analytical evaluation.

Selected sets of time-drawdown and distance-drawdown curves are plotted to illustrate multiple-aquifer well flow and to compare new solutions with results which were previously published. The analogy with flow is unconfined and fissured aquifers is demonstrated by multilayer models, representing multiple-porosity formations with linear and diffusive crossflow.     

探测和量化地表CO_2脱气的新遥感技术

地球脱气,尤其是CO2的释放,越来越引起人们的关注。它涉及到全球碳的估算、对气候的影响、地震和火山爆发的机制以及富气环境植被中植物生理反应等领域。这些领域的研究都需要检测地表CO2脱气的构成和量化各种构成。我们介绍一种基于红外成像的极小热变化检测的新遥感方法来探测地球表面热异常。该方法同样适于发现任何原产地的地球脱气的地点。该方法还可以在任何地域寻找非渗漏区（无裂缝区）以及监测脱气的构成。在意大利托斯卡纳区锡耶纳地堑东缘主断层的博索莱托喷气口进行的红外热成像测量是该方法有效性的一个证例。博索莱托喷气口有来自深部地热储的大量富含CO2的气体溢出。野外获取的数据证实了该方法是有效的。通过可靠处理红外图像时间序列,确定了CO2脱气位置的检测及其最佳检测条件（从黄昏到黎明之间天气干燥,无风,万里无云）。开发了一个研究、观测热交换过程的简单模型。第一次尝试是根据记录的图像序列,用这个模型测定了气体出口温度、热气体扩散面积和气体流量。这是仅用红外图像时间序列进行喷气区的遥感区域调查和量化CO2通量的首选方法。     

New remote sensing techniques for the detection and quantification of earth surface CO2 degassing

Earth degassing specifically of carbon dioxide CO₂ is of increasing interest with respect to the global carbon budget, related climate effects, earthquake and volcano eruption mechanisms, as well as plant physiological reactions in gas-rich environments. Investigations in all of these disciplines require the detection of surface CO₂ degassing structures and quantification of their emissions. We introduce minimal thermal change detection based on infrared imaging as a new remote sensing tool for the detection of earth surface thermal anomalies suiting among others to discover earth degassing locations of any origin. The method allows for seamless areal search and monitoring of degassing structures in any terrain. As proof of concept infrared imaging measurements were performed at the Bossoleto vent on the eastern master fault of the Siena Graben (Tuscany, Italy). It is known for the migration of a large amount of CO₂-rich gas from deep geothermal reservoirs. Field data acquired confirmed the qualification of the method. Detection of CO₂ degassing locations from infrared image time series worked reliably and optimal detection conditions were identified (dry, calm, cloudless weather between dusk and dawn). A simple model of heat exchange processes involved and observed was developed. In a first attempt this model was applied to determine the gas exit temperature, the area of gas thermal reach and the gas flux from recorded image series. It is the first method that allows remote areal survey of mofette fields and the associated CO₂ flux quantification sole from infrared image time series.     

Ground water whirls

Numerical experiments with steady-state ground water flow models show that spiraling flow lines occur in layered aquifers that have different anisotropic horizontal hydraulic conductivities in adjacent layers. Bundles of such flow lines turning in the same direction can be referred to as ground water whirls. An anisotropic layered block in a field of uniform horizontal flow results in one or more whirls with their axes in the uniform flow direction. The number of whirls depends on the number of interfaces between layers with different anisotropic properties. For flow to a well in an aquifer consisting of two anisotropic layers, with perpendicular major principal directions, whirls are found to occur in quadrants that are bounded by the principal directions of the hydraulic conductivity. The combined effect of flow to a well and a layered anisotropy implies that a single well in a system with a single anisotropic layer within an otherwise isotropic aquifer causes eight whirls. All adjacent whirls rotate in opposite directions.