A heat perturbation flow meter for application in soft sediments     

Richard B. Greswell  Michael S. Riley  Patricia Fernandes Alves  John H. Tellam 《Journal of Hydrology》2009,370(1-4):73-82

A prototype flow meter has been developed, based upon the heat perturbation principle, to monitor groundwater specific discharge in soft sediments. The device is designed for use in spatially intensive, long-term monitoring campaigns in remote or inconvenient locations, and is cheap, robust and capable of being logged automatically. The results of the laboratory tests indicate that the heat perturbation principle is suitable for determining the magnitude of specific discharge to a degree of accuracy that would be useful in practical applications in dynamic groundwater systems with rapidly changing flows of approximately 1 md⁻¹ or more and that the groundwater flow direction can generally be determined to a high level of precision. The accuracy and reliability of the estimates of specific discharge have been shown to depend strongly upon the geometrical precision of manufacture and the quality of the temperature monitoring system. These factors become most significant in the estimation of lower flows and further investigation is required to determine the detection limit of the device. Specific discharge estimates have been shown to be insensitive to dispersivity values appropriate to the scale of the device. Unlike the majority of heat perturbation devices, calibration is unnecessary.  相似文献   

Fine grain sediment transport and deposition in the Patos Lagoon–Cassino beach sedimentary system     

L.J. Calliari  J.C. Winterwerp  E. Fernandes  D. Cuchiara  S.B. Vinzon  M. Sperle  K.T. Holland 《Continental Shelf Research》2009

Extensive mud deposits superimposed on the predominantly sandy inner continental shelf adjacent to the Patos Lagoon estuary, indicates that the Lagoon is a potential source of fine sediments to the coastal sedimentary system. The lagoon is large and shallow, and the water movement is mainly controlled by wind-driven set-up and set-down. The mean river inflow is around 2000 m³ s⁻¹, although peak flow rates exceeding 20,000 m³ s⁻¹ have been observed during El Niño periods. Though the tidal elevations are small, tidal velocities in the lagoon's inlet can be significant due to the large extension of the backwaters. Moreover, significant exchange flows can be generated between the estuary and coastal area due to barotropic pressure gradients established as a function of wind and freshwater discharge. The predominant net flow is seawards, but opposite near-bed flows due to pronounced vertical salinity stratification can also be observed. The coastal area is characterized by small tidal effects, large scale ocean circulation, wind-induced residual flows and wave-driven currents, where the waves originate from swell or are locally generated.  相似文献   

Determination of the wave climate for the southern Brazilian shelf     

D.C. Cuchiara  E.H. Fernandes  J.C. Strauch  J.C. Winterwerp  L.J. Calliari 《Continental Shelf Research》2009

The main objective of this study is the characterization of the wave climate in the Southern Brazilian Shelf (SBS) based on a thorough review of existing field data and on numerical modeling experiments. A quantitative knowledge about the wave climate of this area is important to understand the mechanisms driving episodic mud bank attachments to the sandy shore, and the interaction of these banks with the flow and waves. The statistical analysis of existent data on the wave climate throughout the SBS indicates that the predominant wave directions are 100° and 160° (E–SE), with wave heights varying between 1 and 1.50 m. The wave period varies between 6 and 14 s, with predominance of mean wave period of 8 s (sea conditions) and 12 s (swell conditions). The spectral wave model SWAN version 40.41 [Booij, N., Haagsma, I.J.G., Holthuijsen, L.H., Kieftenburg, A.T.M.M., Ris, R.C., van der Westhuysen, A.J., Zijlema, M., 2004. SWAN Cycle III Version 40.41 Users Manual, Delft University of Technology, Delft, The Netherlands, p. 118, http://fluidmechanics.tudelft.nl/swan/index.htm] is used to simulate the wave climate for the region. Special attention is given to Cassino Beach, describing the wave climate observed during the Cassino Experiment, carried out in 2005. The verification of the standard SWAN model was carried out based on the comparison between numerical modeling results and available data of significant wave height, peak period, mean wave direction and energy density for the period relative to February of 1998. Results showed satisfactory model predictions of significant wave height and reasonably accurate predictions of peak spectral wave period and direction. The model performance is also considered satisfactory in the representation of the wave climate of the region when the wave spectrum has only one spectral peak, but presents limitations for bimodal wave spectrum. When two spectral peaks are observed, the SWAN model agrees with the spectral level observed in the low frequency, but underestimates the spectral level in the high-frequency band. When considering the presence of mud deposits in the area, model results predict that although the presence of mud attenuates most of the wave energy on the low frequency peak, it has a smaller effect in attenuating the wave energy on the high frequency peak.  相似文献   

Modelling Watersheds as Spatial Object Hierarchies: Structure and Dynamics   总被引：1，自引：0，他引：1  

Lawrence E. Band  Christina L. Tague  Soren E. Brun  David E. Tenenbaum  & Richard A. Fernandes 《Transactions in GIS》2000,4(3):181-196

The generation, transport and fate of non-point source pollutants in surface water systems is recognized as a major threat to water supplies, aquatic and coastal ecosystems. The transformation and movement of water, carbon and nutrients through watersheds integrates a set of ecosystem processes along hydrologic flowpaths. Human individual and institutional interactions with these processes involve direct addition or abstraction of these substances, or the alteration of land cover and drainage systems. In natural and developed catchments, these processes often vary at granularities ranging from below the level of a hillslope, up through regional watersheds. This suggests the need for the development of hierarchical analysis tools that can address the integration of a set of biophysical, biogeochemical and socioeconomic processes over a spectrum of scales. We describe and illustrate the use of a watershed model implemented as a spatial object hierarchy, representing successively contained landform classes associated with class specific processes as member functions. The model has been linked in a range of looser and tighter couplings with GRASS and ArcView, supplemented by specific terrain analytical functions. We illustrate the data and model system for an instrumented catchment monitored as part of the Baltimore Ecosystem Study (BES), a Long Term Ecological Research (LTER) site centering on integrated carbon, water and nutrient cycling.  相似文献   

The excitation and kinematical properties of H₂ and [Fe ii] in the HH 46/47 bipolar outflow     

A. J. L. Fernandes 《Monthly notices of the Royal Astronomical Society》2000,315(4):657-668

Long-slit spectra of the molecular outflow Herbig–Haro (HH) 46/47 have been taken in the J and K near-infrared bands. The observed H₂ line emission confirms the existence of a bright and extended redshifted counter-jet outflow south-west of HH 46. In contrast with the optical appearance of this object, we show that this outflow seems to be composed of two different emission regions characterized by distinct heliocentric velocities. This implies an acceleration of the counter-jet.
The observed [Fe  ii ] emission suggests an average extinction of 7–9 visual magnitudes for the region associated with the counter-jet.
Through position–velocity diagrams, we show the existence of different morphologies for the H₂ and [Fe  ii ] emission regions in the northern part of the HH 46/47 outflow. We have detected for the first time high-velocity (−250 km s⁻¹) [Fe  ii ] emission in the region bridging HH 46 to HH 47A. The two strong peaks detected can be identified with the optical positions B8 and HH 47B.
The H₂ excitation diagrams for the counter-jet shock suggest an excitation temperature for the gas of T _ex≈2600 K . The lack of emission from the higher energy H₂ lines, such as the 4–3 S(3) transition, suggests a thermal excitation scenario for the origin of the observed emission. Comparison of the H₂ line ratios with various shock models yielded useful constraints about the geometry and type of these shocks. Planar shocks can be ruled out whereas curved or bow shocks (both J- and C-type) can be parametrized to fit our data.  相似文献   

An atlas of calcium triplet spectra of active galaxies     

A. Garcia-Rissmann  L. R. Vega  N. V. Asari  R. Cid Fernandes  H. Schmitt  R. M. González Delgado  T. Storchi-Bergmann 《Monthly notices of the Royal Astronomical Society》2005,359(2):765-780

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Influences of the unsaturated,saturated, and riparian zones on the transport of nitrate near the Merced River,California, USA   总被引：1，自引：0，他引：1  

Joseph L. Domagalski  Steven P. Phillips  E. Randall Bayless  Celia Zamora  Carol Kendall  Richard A. WildmanJr  Janet G. Hering 《Hydrogeology Journal》2008,16(4):675-690

Transport and transformation of nitrate was evaluated along a 1-km groundwater transect from an almond orchard to the Merced River, California, USA, within an irrigated agricultural setting. As indicated by measurements of pore-water nitrate and modeling using the root zone water quality model, about 63% of the applied nitrogen was transported through a 6.5-m unsaturated zone. Transport times from recharge locations to the edge of a riparian zone ranged from approximately 6 months to greater than 100 years. This allowed for partial denitrification in horizons having mildly reducing conditions, and essentially no denitrification in horizons with oxidizing conditions. Transport times across a 50–100-m-wide riparian zone of less than a year to over 6 years and more strongly reducing conditions resulted in greater rates of denitrification. Isotopic measurements and concentrations of excess N₂ in water were indicative of denitrification with the highest rates below the Merced River. Discharge of water and nitrate into the river was dependent on gradients driven by irrigation or river stage. The results suggest that the assimilative capacity for nitrate of the groundwater system, and particularly the riverbed, is limiting the nitrate load to the Merced River in the study area.  相似文献   

Incorporation of trivalent actinides into calcite: A time resolved laser fluorescence spectroscopy (TRLFS) study     

M. Marques Fernandes  T. Stumpf  T. Rabung  Th. Fanghänel 《Geochimica et cosmochimica acta》2008,72(2):464-474

In order to characterize and quantify the substitution of Ca(II) by Cm(III) (coordination, charge compensation), homogeneous Cm(III) coprecipitated calcite was synthesized in a mixed-flow-through experiment. Two sets of experiments were conducted at pH 8.1 and at pH 12.5.At pH 8.1 two calcites, a calcite with a low Cm³⁺ concentration (LCMpH8.1) and a calcite with a high M³⁺ (Gd³⁺ and Cm³⁺) concentration (HCMpH8.1) were grown and investigated by time resolved laser fluorescence spectroscopy. The Cm(III) emission spectra of LCMpH8.1 and HCMpH8.1 show the same Cm(III) fluorescence signals for two Cm(III) species; Cm(III) species (1) with a peak maximum at 606.2 nm and Cm(III) species (2) with a peak maximum at 620.3 nm. Cm(III) species (1) has a mean lifetime of τ = 386 ± 40 μs and Cm(III) species (2) has a mean lifetime of τ = 1874 ± 200 μs. A lifetime of 386 μs correlates with 1.3 water molecule in the first coordination sphere of the Cm ion whereas a lifetime of 1874 μs indicates the total loss of the Cm(III) hydration sphere. According to the fluorescence emission peak position and the fluorescence emission lifetime, Cm(III) species (1) is identified as a surface sorbed species whereas Cm(III) species (2) is identified as a Cm(III) incorporated into the calcite lattice.Cm(III) fluorescence emission spectra of Cm(III) doped calcite grown at pH 12.5 (LCMpH12.5) show the same peak maxima which are found for LCMpH8.1 and HCMpH8.1 grown at pH 8.1 but an additional emission band at 608.2 nm (3) is found, which can be assigned to a further Cm(III) species. Fluorescence emission lifetime measurements show that this Cm(III) species (3) has a lifetime of τ = 477 ± 25 μs, which correlates with 0.9 water molecules in the first coordination sphere. Cm(III) species (3) is suggested to be a CmOH²⁺ incorporated species.  相似文献   

Fast error analysis of continuous GPS observations   总被引：4，自引：1，他引：3  

M. S. Bos  R. M. S. Fernandes  S. D. P. Williams  L. Bastos 《Journal of Geodesy》2008,82(3):157-166

It has been generally accepted that the noise in continuous GPS observations can be well described by a power-law plus white noise model. Using maximum likelihood estimation (MLE) the numerical values of the noise model can be estimated. Current methods require calculating the data covariance matrix and inverting it, which is a significant computational burden. Analysing 10 years of daily GPS solutions of a single station can take around 2 h on a regular computer such as a PC with an AMD Athlon^TM 64 X2 dual core processor. When one analyses large networks with hundreds of stations or when one analyses hourly instead of daily solutions, the long computation times becomes a problem. In case the signal only contains power-law noise, the MLE computations can be simplified to a process where N is the number of observations. For the general case of power-law plus white noise, we present a modification of the MLE equations that allows us to reduce the number of computations within the algorithm from a cubic to a quadratic function of the number of observations when there are no data gaps. For time-series of three and eight years, this means in practise a reduction factor of around 35 and 84 in computation time without loss of accuracy. In addition, this modification removes the implicit assumption that there is no environment noise before the first observation. Finally, we present an analytical expression for the uncertainty of the estimated trend if the data only contains power-law noise. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.  相似文献   

The influence of Cenozoic tectonics on the groundwater-production capacity of fractured zones: a case study in Sao Paulo, Brazil   总被引：1，自引：0，他引：1  

Amelia Fernandes  David L. Rudolph 《Hydrogeology Journal》2001,9(2):151-167

A new procedure is developed to correlate structural lineaments recognised through air-photo interpretation with subsurface fracture features that are associated with zones of high groundwater production in fractured-rock environments. The analysis approach is referred to as the homogeneous tectonic domain (HTD) method and involves correlating the lineament features of a given area with the orientation of the primary stress fields and fracture structures associated with the recent tectonic history that affected the region of study. The main premise of the method is that the most recent tectonic events in a given area have had the most significant influence on the nature of the existing fracture network and subsequently on the regional groundwater flow characteristics. A study site was selected within the state of S?o Paulo, Brazil, where a complex tectonic history dating back to Precambrian time has generated significant fracture porosity in the bedrock environment. The bedrock is heavily used in this area as a domestic and industrial aquifer. The most recent tectonic activity is associated with five distinct Cenozoic events that generated fracture features through both shear and extension stress fields. Due to the mode of formation, fracture zones generated by extension tend to have the largest effective apertures and are the most conductive to groundwater. By applying the HTD method in a series of test areas where specific Cenozoic events were dominant, fracture trends generated by shear and extension mechanisms could be identified. Water-well production capacity was correlated with proximity to extension-type structures in most cases. Other factors, such as the type of rock the well was completed in, had a much weaker influence on well capacity. Through this application, the HTD approach is shown to provide a methodology for delineating fractured areas within rock environments that have high potential for groundwater-resource development by combining classical lineament analysis with a clear understanding of the tectonic history of a given area. Electronic Publication  相似文献