Review of the Integrated Groundwater and Surface-Water Model (IGSM)

Development of the finite-element-based Integrated Groundwater and Surface-Water Model (IGSM) began in the 1970s. Its popularity grew in the early 1990s with its application to California's Central Valley Groundwater Surface-Water Model in support of the Central Valley Project Improvement Act. Since that time, IGSM has been applied by federal, state, and local agencies to model a number of major basins in California. Our review of the recently released version 5.0 of IGSM reveals a solution methodology that deviates from established solution techniques, potentially compromising its reliability under many circumstances. One difficulty occurs because of the semi-explicit time discretization used. Combined with the fixed monthly time step of IGSM, this approach can prevent applications from accurately converging when using parameter values typically found in nature. Additionally, IGSM fails to properly couple and simultaneously solve ground water and surface water models with appropriate mass balance and head convergence under the reasonable conditions considered herein. As a result, IGSM-predicted streamflow is error prone, and errors could exceed 100%. IGSM does not inform the user that there may be a convergence problem with the solution, but instead generally reports good mass balance. Although our review touches on only a few aspects of the code, which exceeds 17,000 lines, our experience is that similar problems arise in other parts of IGSM. Review and examples demonstrate the potential consequences of using the solution methods in IGSM for the prediction, planning, and management of water resources, and provide perspective on the roles of standards and code validation in ground water modeling.     

Source process of the southeast Beni-Suef, northern Egypt earthquake Using Empirical Green's Function Technique

The rupture process of a moderateearthquake (ML4.9) occurred southeastBeni-Suef, northern Egypt was analyzed. Thecharacterization of the rupture process andsource properties were extracted fromstudying the relative moment rate function(RMRF). RMRFs were retrieved bydeconvolution of small aftershock recordsusing an inversion procedure for onlyP-wave part of the records.Although, this event is a moderateearthquake, its RMRFs exhibitedcomplexity and directivity of the rupturebehavior. The deconvolution pulses reflectthree subevents or more. The detailedanalysis of the distinct subevents revealedgross temporal and spatial characteristicsof the rupture propagation. The azimuthalvariation in the time delay of thesubevents with respect to the initiationrupture indicates that the subevents arelocated at 0.85 ± 0.17 and3.5 ± 0.07 km in directions of320^° ± 45^° and330^° ± 15^° with rupturevelocities 3.4 ± 0.45 and4.0 ± 0.7 km/sec, respectively. Thismeans that the rupture is predominatelypropagated toward the North. Estimation ofthe rupture direction was combined withP-wave focal mechanism to identify thefault plane for the initial rupture ofmainshock.Source parameters were calculated for eachdistinct subevent, including seismicmoments 8.53E14 to 6.80E15 Nm, fault radii713 to 1800 m and stress drops 0.725 to2.932 MPa. The large estimated stress dropfor the main subevent reflects failureasperity.     

Dependency of unit shaft resistance on in-situ stress: Observations derived from collected field data

In this study, a database comprised of 30 pullout pile load tests was collected from geotechnical literature and analyzed to investigate the dependency of unit shaft resistance on effective vertical stress. The collected database consists of steel pipe, timber, and concrete piles, with varying normalized penetration depth with respect to pile diameter, driven into loose to very dense sand. Different correlations for the uplift lateral earth pressure coefficient K, Bjerrum-Burland ratio , and the average unit shaft resistance f _ave were derived using different assumptions. A comparison between measured and predicted capacities of the collected piles using the developed correlations indicated that the assumption of values of K and that were constant with depth did not provide a reasonable fit for the measured capacities of the collected piles and thus this assumption is inappropriate. The best correlations for K and that yield a reasonable fit to the measured capacities of the collected piles were found to be functions of sand relative density, pile diameter, and level of effective vertical stress. This indicates that average unit shaft resistance does not reach a limiting value, but rather continues to increase with depth. Moreover, the correlations for K and in terms of effective stress revealed that average unit shaft resistance increases as pile diameter decreases and this increase depends on initial sand relative density. Comparisons of measured and predicted pullout capacities of the collected piles using the best-obtained correlations for K and were made and compared to predictionsobtained from other methods. On the basis of these comparisons, it is concluded that the correlations for K and in terms of effective stress give results comparable to those obtained from other methods, without stipulating limiting values for the average unit shaft resistance.     

Microcracks and Overpressure-Induced Fractures

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East-west stationkeeping requirements of nearly synchronous satellites due to Earth's triaxiality and luni-solar effects

A closed form solution, for longitude and semimajor axis deviations in the neighborhood of a prespecified station, is obtained for nearly synchronous satellites. The model use includes the important terms in Earth's zonal and tesseral harmonics as well as the luni-solar perturbations. The initial semimajor axis for two-maneuver east-west stationkeeping is then deduced. Due to the luni-solar effects, it is found that the initial semimajor axis deviation from synchronous orbit value is highly dependent on the initial position of the satellite relative to the Moon and the Sun. Verifications of the results by means of numerical integrations are also included.     

Description of the trajectory functions of TOPEX/POSEIDON navigation

TOPEX/POSEIDON is a joint American/French ocean topography experiment. It was launched by an Ariane launch vehicle on August 10, 1992 to study and map ocean circulation. The primary functions of the navigation subsystem of the TOPEX/POSEIDON project are to establish and maintain a pre-designed reference orbit, and to measure, monitor, and predict the satellite ground track continuously. To fulfill these functions, trajectory analysis is required to design and generate all trajectory related products. This paper is concerned with the trajectory functions of TOPEX/POSEIDON navigation. It describes various activities of this support function.     

A methodology for validating numerical ground water models

Ground water validation is one of the most challenging issues facing modelers and hydrogeologists. Increased complexity in ground water models has created a gap between model predictions and the ability to validate or build confidence in predictions. Specific procedures and tests that can be easily adapted and applied to determine the validity of site-specific ground water models do not exist. This is true for both deterministic and stochastic models, with stochastic models posing the more difficult validation problem. The objective of this paper is to propose a general validation approach that addresses important issues recognized in previous validation studies, conferences, and symposia. The proposed method links the processes for building, calibrating, evaluating, and validating models in an iterative loop. The approach focuses on using collected validation data to reduce uncertainty in the model and narrow the range of possible outcomes. This method is designed for stochastic numerical models utilizing Monte Carlo simulation approaches, but it can be easily adapted for deterministic models. The proposed methodology relies on the premise that absolute validity is not theoretically possible, nor is it a regulatory requirement. Rather, the proposed methodology highlights the importance of testing various aspects of the model and using diverse statistical tools for rigorous checking and confidence building in the model and its predictions. It is this confidence that will encourage regulators and the public to accept decisions based on the model predictions. This validation approach will be applied to a model, described in this paper, dealing with an underground nuclear test site in rural Nevada.     

Upper crustal podiform chromitite from the northern Oman ophiolite as the stratigraphically shallowest chromitite in ophiolite and its implication for Cr concentration

A new type of podiform chromitite was found at Wadi Hilti in the northern Oman ophiolite. It is within a late-intrusive dunite body, possibly derived from olivine-rich crystal mush, between the sheeted dike complex and upper gabbro. This chromitite forms small (<30 cm in thickness) pods with irregular to lenticular shapes. Neither layering nor graded bedding is observed within the pods. The chromitite is in the upper crust, by far shallower in ophiolite stratigraphy than the other podiform chromitites that have ever been found in the Moho transition zone to the upper mantle. It is distributed along a small felsic to gabbroic melt pool within the dunite body, which was formed by melting of gabbroic blocks captured by the mush. Chromian spinel was precipitated due to mixing of two kinds of melt, a basaltic interstitial melt from the mush and an evolved, possibly felsic, melt formed by the melting of gabbro blocks. The podiform chromitite reported here is strikingly similar in petrography and spinel chemistry to the stratiform chromitite from layered intrusions. The former contains plagioclase and clinopyroxene as matrix silicates instead of olivine as well as includes euhedral and fine spinel with solid mineral inclusions. Chromian spinel of the upper crustal podiform chromitite from Oman has relatively low content of (Cr₂O₃ + Al₂O₃), the Cr/(Cr + Al) atomic ratio of around 0.6, and the relatively high TiO₂ content ranging from 1 to 3 wt%. We conclude that assimilation of relatively Si-rich materials (crustal rocks or mantle orthopyroxene) by olivine-spinel saturated melts can explain the genesis of any type of chromitite.Editorial responsibility: V. Trommsdorff     

Response of the Dupi Tila aquifer to intensive pumping in Dhaka,Bangladesh

This paper focuses on the water-quantity issues facing Dhaka because of the rapid exploitation of the Dupi Tila aquifer. Dhaka is one of the world's largest groundwater-dependent cities, relying on water withdrawn from this underlying semiconfined sand aquifer. A meteoric rise in well construction in both the private and public sectors in recent years has produced an estimated 1,300 boreholes that tap the aquifer in urban and suburban parts of the city. Analysis of construction records for public-supply wells drilled between 1970 and 2000 shows that water levels are falling in several areas of the city despite apparently favorable recharge conditions. The productivity of boreholes as measured by specific capacity has also declined significantly. Even though the aquifer system is vital to the infrastructure of the city it remains a poorly quantified resource, and until this is resolved by investment in evaluation studies, attempts to efficiently manage the resource in a sustainable way will be frustrated.

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Resumen Este artículo trata de los aspectos cuantitativos relacionados con la sobreexplotación del acuífero de Dupi Tila, que suministra a la ciudad de Dhaka (Bangladesh). Ésta es una de las mayores ciudades del mundo con dependencia de las aguas subterráneas, y se abastece de un acuífero semiconfinado formado por arenas. El aumento meteórico en la construcción de pozos durante los últimos años, tanto en el sector público como en el privado, ha provocado que haya unas 1.300 captaciones del acuífero en las zonas urbana y suburbana de la ciudad. El análisis de los registros constructivos de pozos de abastecimiento público entre 1970 y 2000 muestra que los niveles piezométricos están descendiendo en diversas áreas de la ciudad, a pesar de la existencia de condiciones aparentemente favorables de recarga. La productividad de los pozos, determinada por su capacidad específica, también ha disminuido significativamente. Aunque el sistema acuífero es vital para la infraestructura de la ciudad, los recursos aún no han sido cuantificados adecuadamente. Hasta que este asunto no sea resuelto mediante la inversión en estudios de evaluación, los intentos por gestionar eficientemente los recursos de forma sustentable serán infructuosos.

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Résumé Cet article porte sur les pertes en quantité subies par Dacca du fait de l'exploitation rapide de l'aquifère de Dupi Tila. Dacca est l'une des villes dépendant de l'eau souterraine les plus importantes du monde, prélevant l'eau d'un aquifère sableux sous-jacent semi-captif. On estime à 1,300 forages l'accroissement des creusements de puits aussi bien dans le secteur privé que public dans ces dernières années; ils prélèvent dans l'aquifère dans la partie urbaine et à la périphérie de la ville. L'analyse des déclarations de creusement de puits pour l'AEP forés entre 1970 et 2000 montre que les niveaux d'eau ont chuté dans plusieurs zones de la ville malgré des conditions de recharge apparemment favorables. La productivité des puits mesurée par la capacité spécifique a également diminué significativement. Même si le système aquifère est vital pour l'infrastructure de la ville, il reste une ressource médiocrement quantifiée, et tant que ceci ne sera pas résolu par un investissement dans des études d'évaluation, les tentatives pour gérer efficacement la ressource de façon durable échoueront.

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P-wave spectra of the Füzesgyarmat, eastern Hungary earthquake sequence

On 29–30 September 1996, an earthquake sequence occurred in the Füzesgyarmat region in eastern Hungary. The main shock had a magnitude of M_L = 3.2 and was felt with a maximum intensity 4 MSK. It was preceded by a foreshock with a magnitude of M_L = 2.8 and was followed, within six hours, by five aftershocks with magnitudes 2.1M_L 3.1. The dynamic source parameters of the Füzesgyarmat earthquake sequence have been derived from P-wave spectra of the Hungarian seismograph stations. The average of the obtained values at different stations shows that the main shock occurred on a fault length of 610 m, with relative displacement of 1.13 cm, stress drop of 7 bar and seismic moment of 3.96*10₂₁ dyne.cm. The main shock was small to yield data for a full mechanism solution and no reliable single fault plane solution could be obtained due to the low signal to noise ratio at the recording stations. The parameters of the foreshock are fault length of 560m, seismic moment of 2.09*10₂₁ dyne.cm, stress drop of 5.53 bar and relative displacement of 0.73 cm. The five aftershocks show source parameters similar to the foreshock stress drops (5.26 5.76 bar), fault lengths (415 L 600 m), seismic moments (8.36*10²⁰ M_o 2.31*10₂₁ dyne.cm) and relative displacements (0.52 0.91 cm).