Stage Fluctuations Research Articles

Large-scale spheroidal redoximorphic features around plinthite nuclei in Orinoco River sediments reflect mean seasonal fluctuation in river stage and ENSO-related anomalies

In sediments emerging on the scarp of Lower Orinoco River, Venezuela, we have discovered and studied large (0.5 m) features formed by a plinthite nucleus surrounded by evenly spaced concentric spheroidal structures of iron oxides separated by depletion zones. These features are located in sediments subjected to the mean annual river fluctuation (approx. 14 m) and hence are submerged for several months each year. To the best of our knowledge, structures like these have never been reported or studied. The nuclei and concentric ring formations found in the Orinoco sediments represent an extreme case of regular currently alternating redox conditions. Here we show that the concentric ferric rings surrounding the nuclei could be the result of repeated cycles of diffusion of ferrous ions during flood and subsequent precipitation as ferric oxide during the dry period, thus reflecting the seasonal fluctuation in river level. Our results are consistent with a simple proposed model of ferrous iron diffusion/oxidation according to the flood/dry intervals imposed by river dynamics. This paper is a contribution toward understanding these redoximorphic features (RFs) by: (1) describing their composition and mineralogy; (2) suggesting a possible mode of their formation using the switch to reducing conditions and diffusion of soluble Fe during flood, and its subsequent oxidation and hence immobilization and partial crystallization once exposed to the air; (3) by confirming how this theoretical approach fits the actual pattern of river hydrology in Orinoco, both under average conditions, and as modified by climatic extreme conditions influenced by the El Nino/La Nina Southern Oscillation (ENSO) affecting the ratio of flood/emergence.

Spatially variable stage‐driven groundwater‐surface water interaction inferred from time‐frequency analysis of distributed temperature sensing data

Characterization of groundwater‐surface water exchange is essential for improving understanding of contaminant transport between aquifers and rivers. Fiber‐optic distributed temperature sensing (FODTS) provides rich spatiotemporal datasets for quantitative and qualitative analysis of groundwater‐surface water exchange. We demonstrate how time‐frequency analysis of FODTS and synchronous river stage time series from the Columbia River adjacent to the Hanford 300‐Area, Richland, Washington, provides spatial information on the strength of stage‐driven exchange of uranium contaminated groundwater in response to subsurface heterogeneity. Although used in previous studies, the stage‐temperature correlation coefficient proved an unreliable indicator of the stage‐driven forcing on groundwater discharge in the presence of other factors influencing river water temperature. In contrast, S‐transform analysis of the stage and FODTS data definitively identifies the spatial distribution of discharge zones and provided information on the dominant forcing periods (≥2 d) of the complex dam operations driving stage fluctuations and hence groundwater‐surface water exchange at the 300‐Area.

Principal component analysis of time series for identifying indicator variables for riverine groundwater extraction management

Summary Although alluvial aquifers connected to rivers can be a rich source of drinking water, they are susceptible to contamination by infiltrating river water. The processes governing river–groundwater interaction are variable in time and space. Natural filtration mechanisms are often not sufficient during high discharge events in the river. To capture the dynamics of river–groundwater interaction, indicator parameters that can serve as proxies for river water infiltration need to be derived. Principal component analysis of continuously measured time series was used to identify indicator wells and derive indicator parameters for a study area in NW Switzerland. The results showed different sources of variation in the parameters, including river stage fluctuations. The multivariate approach highlighted differences between observation wells based on the response of the measured parameters to effects of damping and delay of the input signals. Three observation wells were shown to be representative of river–groundwater interaction dynamics in the study area. Of the three parameters analysed, groundwater head and electrical conductivity are recommended as a combined proxy for river water infiltration in the study area. In contrast, temperature proved not to be a reliable indicator.

Wetland inundation modeling of Dongting Lake using two-dimensional hydrodynamic model on unstructured grids

Abstract To understand the inundation process (wetting and drying) in the bottomlands of Dongting Lake, a two-dimensional hydrodynamic model based on shallow water equations has been developed to model complex flow regime controlled by both the Yangtze River and its own basins. The governing equations are discretized using the finite volume method with the combination of quadrilateral and triangular grids and the mass and momentum fluxes are solved using the approximate Riemann solver, HLLC scheme with high spatial resolution. The processes of wetting and drying are specially treated to simulate the flow routing over dry bed. Verification shows that the proposed method can accurately capture flow propagation over dry bed resulting from suddenly breach of the dam. This performance is preferred for inundation modeling. After theoretical test, we applied the model to simulate the inundation process in Dongting Lake. Setting the calibrated roughness parameters, we successfully simulated flow processes in the lake from 2006 to 2010. The water extent changes rapidly along with the stage fluctuation in the lake. In dry season, water is mainly limited in channels, large parts of bottomlands are exposed and water extent reaches the yearly minimum. The whole lake is inundated in the flood season and the maximum of water extent reaches. After the flood season, the bottomlands expose again along with the gradual decrease of water. Particular hydrological regimes cause the regular zonal distribution of vegetation in Dongting Lake Wetland. Hydrology in the middle Yangtze River Basin is undergoing great changes. This model can be applied to assess possible responses of lake wetland for the changing environment.

A conceptual framework for incorporating surface–groundwater interactions into a river operation–planning model

Groundwater discharge constitutes a significant proportion of the total flow volume in most rivers. The exchange flux between surface and groundwater greatly impacts the surface as well as the groundwater balance with serious implications on ecosystem health especially during low flow conditions. There is a move towards conjunctive river–aquifer management with the integration of surface–groundwater exchange fluxes into surface and groundwater models to manage water as a single resource. Groundwater–Surface water (GW–SW) exchange fluxes are seldom integrated into river operation and planning models. The time lags associated with the impacts of groundwater processes on nearby rivers can greatly compromise the forecasting capacity of river models especially during low flow conditions. This paper presents a conceptual framework for integrating GW–SW exchange fluxes into the new generation river operation–planning model ‘Source Integrated Modelling System’. The proposed GW–SW Link Module adopts a simple pragmatic approach for estimating the exchange fluxes between a river reach and the underlying aquifer using explicit analytical solutions. This flux becomes an inflow/outflow to that river reach and forms part of the routing and calibration processes. The exchange flux comprises four components: (1) natural exchange flux resulting from river stage fluctuations during low flow conditions, within bank and overbank fluctuations; (2) flux due to groundwater extraction; (3) flux due to changes in aquifer recharge; and (4) flux due to changes in evapotranspiration. The sum of those components during every time step dictates whether the river loses water to or gains water from the aquifer. The proposed analytical solutions were found to provide flux predictions that agree favourably with those derived from a numerical groundwater model. Recognising that the simplifying assumptions that underpin the explicit analytical solution are likely to be violated in the natural world, a suite of criteria was recommended for their use under many violating conditions related to boundary conditions, head gradients, and aquifer heterogeneity. Low flow indices were adopted to demonstrate the critical role of GW–SW exchange flux when predicting river low flows. Explicit accounting of GW–SW interactions into river operation and planning models greatly enhances their forecasting capacity during low flow conditions.

Horizontal hydraulic conductivity of shallow streambed sediments and comparison with the grain‐size analysis results

AbstractStreambed horizontal hydraulic conductivity (Kh) has a substantial role in controlling exchanges between stream water and groundwater. We propose a new approach for determining Kh of the shallow streambed sediments. Undisturbed sediment samples were collected using tubes that were horizontally driven into streambeds. The sediment columns were analysed using a permeameter test (PT) on site. This new test approach minimizes uncertainties due to vertical flow in the vicinity of test tube and stream stage fluctuations in the computation of the Kh values. Ninety‐eight PTs using the new approach were conducted at eight sites in four tributaries of the Platte River, east‐central Nebraska, USA. The Kh values were compared with the nondirectional hydraulic conductivity values (Kg) determined from 12 empirical grain‐size analysis methods. The grain‐size analysis methods used the same sediment samples as Kh tests. Only two methods, the Terzaghi and Shepherd methods, yielded Kg values close to the Kh values. Although the Sauerbrei method produced a value relatively closer to Kh than other nine grain‐size analysis methods, the values from this method were not as reliable as the methods of Terzaghi and Shepherd due to the inconsistent fluctuation of the average estimates at each of the test sites. The Zunker, Zamarin, Hazen, Beyer, and Kozeny methods overestimated Kh, while the Slichter, US Bureau of Reclamation (USBR), Harleman, and Alyamani and Sen methods underestimated Kh. Any of these specific grain‐size methods might yield good estimates of streambed Kh at some sites, but give poor estimates at other sites, indicating that the relationship between Kg and Kh is significantly site dependent in our study. Copyright © 2011 John Wiley & Sons, Ltd.

Interference of river level changes on riparian zone evapotranspiration estimates from diurnal groundwater level fluctuations

Groundwater evapotranspiration (ET) by phreatophytes is an important component of the water budget in riparian zones of many arid and semiarid environments. Diurnal fluctuations in groundwater levels have been used to estimate groundwater ET, but interference between nearby surface water (e.g., rivers, streams) and groundwater levels complicates the ET estimate. The objective of this study is to utilize spectral analysis to investigate the influence of surface water stage changes on the ET estimates in a riparian environment, thereby elucidating the potential caveats of using groundwater level diurnal fluctuations to estimate groundwater ET. The study is conducted in a stand of Tamarisk Ramossisima on the Colorado River near Blythe, California, USA. Results show that the most significant diurnal signal from the measurement of water levels of monitoring wells can be attributed to ET; however, distance of the groundwater level monitoring wells to the river directly impacts our ability to separate the two different signals from ET and river stage changes. Water level signals at groundwater monitoring stations close to the river (∼200 m in this study) are related to both ET and changes in river stages, which vary at frequencies other than diurnal. The spectral analyses of water level in time and frequency domains provide strong indications of the sensitivity of groundwater levels to fluctuation in the river stage. As a result, ET estimated from diurnal fluctuations of groundwater levels from the well near the river possesses large errors, even resulting in negative ET. No significant influence of river stage changes are observed on water levels at locations farther from the river (>800 m).

Field‐scale model for the natural attenuation of uranium at the Hanford 300 Area using high‐performance computing

High‐resolution, three‐dimensional, reactive flow and transport simulations are carried out to describe the migration of hexavalent uranium [U(VI)] at the Hanford 300 Area bordering the Columbia River and to better understand the persistence of the uranium plume at the site. The computer code PFLOTRAN developed under a DOE SciDAC‐2 project is employed in the simulations that are executed on ORNL's Cray XT4/XT5 supercomputer Jaguar. The conceptual model used in the simulations is based on the recognition of three distinct phases or time periods in the evolution of the U(VI) plume. These correspond to (1) initial waste emplacement; (2) initial presence of both labile and nonlabile U(VI) with an evolved U(VI) plume extending from the source region to the river boundary, representing present‐day conditions; and (3) the complete removal of all nonlabile U(VI) and labile U(VI) in the vadose zone. This work focuses primarily on modeling Phase II using equilibrium and multirate sorption models for labile U(VI) and a continuous source release of nonlabile U(VI) in the South Process Pond through dissolution of metatorbernite as a surrogate mineral. For this case, rapid fluctuations in the Columbia River stage combined with the slow release of nonlabile U(VI) from contaminated sediment are found to play a predominant role in determining the migration behavior of U(VI) with sorption only a second‐order effect. Nevertheless, a multirate model was essential in explaining breakthrough curves obtained from laboratory column experiments using the same sediment and is demonstrated to be important in Phase III. The calculations demonstrate that U(VI) is discharged to the river at a highly fluctuating rate in a ratchet‐like behavior as the river stage rises and falls. The high‐frequency fluctuations must be resolved in the model to calculate the flux of U(VI) at the river boundary. By time averaging the instantaneous flux to average out noise superimposed on the river stage fluctuations, the cumulative U(VI) flux to the river is found to increase approximately linearly with time. The flow rate and U(VI) flux are highly sensitive to the conductance boundary condition that describes the river‐sediment interface. By adjusting the conductance coefficient to give a better match to the measured piezometric head, good agreement was obtained with field studies for both the mean flux of water of 109 kg/yr and U(VI) of 25 kg/yr at the river‐aquifer boundary for a computational domain encompassing the South Process Pond. Finally, it is demonstrated that, through global mass conservation, the U(VI) leach rate from the source region is related to the U(VI) flux at the river boundary.

Water table dynamics and groundwater–surface water interaction during filling and draining of a large fluvial island due to dam‐induced river stage fluctuations

Dam‐controlled river stage fluctuations alter groundwater–surface water interaction between persistent bars and islands and the rivers bounding them by rapidly changing hydraulic gradients and expanding hyporheic zones. A 300‐m long and 80‐m wide sand‐gravel island with established vegetation located on the Colorado River (Austin, Texas, USA) is subjected to >1 m daily river stage variations due to upstream dam operations. Piezometer nests with probes monitored the evolution of the water table and groundwater flow paths through several cycles of dam‐induced stage fluctuations. Results show that hydraulic head and the water table within the island closely track the river stage associated with dam release. Water table mounds and depressions which overlap in time were mapped through the course of one storage‐release cycle over which >4,000 m3 of water moved in and out of the island. Dam operations have drastically altered groundwater–surface water connectivity between the Colorado River and the fluvial island aquifer by pumping substantial amounts of water in and out of the aquifer during dam release and storage cycles.

Poroelastic Loading of an Aquifer Due to Upstream Dam Releases

Short-term changes in the hydraulic head of surface water bodies are known to influence the shallow response of hydraulically connected groundwaters. Associated with these fluctuations is the physical increase in stream water creating a mechanical load on the ground surface. This load is supported by the geologic materials (sediment or rock) and the pore fluid contained within the pores. Changes in this surface load have a direct effect on the total stress of the aquifer causing either a change in effective stress or fluid pressure. This response, predicted by the framework of linear poroelasticity, is a well-understood phenomenon in geologic materials. Currently, field measurements of the hydraulic response (i.e., fluid pressure) of aquifer materials are undergoing poroelastic loading due to dam releases in the Deerfield River Watershed in Massachusetts. An increase in stream stage from upstream dam releases causes an instantaneous pore fluid pressure increase at multiple depths and locations in the aquifer. This increase lasts anywhere from 15 to 40 minutes depending on the magnitude of the rise in the stream stage. Pore-pressure changes are well correlated to stream stage fluctuations for all of the recorded events. Poroelastic models created using basin stratigraphy and hydraulic properties of the aquifer response match the field observations well. Model results suggest that the overall stratigraphy is important in controlling the magnitude and duration of the poroelastic response. An improved understanding of responses such as these can be used to constrain uncertainties in model calibration and simulations of the contaminant migration in low permeability fine-grained (compressive) materials.

El Niño–Southern Oscillation Link to South Florida Hydrology and Water Management Applications

This study evaluates the relationships between El Nino-Southern Oscillation (ENSO) indices and South Florida hydrology and proposes applications to water management decision making. ENSO relations to the Upper Kissimmee Basin rainfall, watershed for Lake Okeechobee, and cumulative sea surface temperature (SST) anomalies at Nino 3.4 were evaluated. Additionally, relationship between ENSO and Lake Okeechobee inflows, Arbuckle Creek and Josephine Creek flows were analyzed. Hydrology of the northern watersheds of the South Florida water management system is linked to ENSO events. Dry season (November-May) rainfall and flows are higher than average during El Nino years and lower during La Nina years, at the 90% confidence level or higher. The relationship is strongest when the ENSO event is strong as shown with analysis of correlation. ENSO prediction has more certainty than hydrologic prediction for a region. Identifying ENSO and hydrologic relationships can aid water management decision making by providing a lead-time of months to mitigate drought or flood impacts. The ENSO tracking method, which was published in a previous study, is presented to track ENSO strength and event type to provide supplemental outlook on dry season rainfall for Lake Okeechobee operations. Lake Okeechobee, which is the main storage in the South Florida water management system, is regulated by a schedule with a limited band of stage fluctuation because of susceptibility of the Herbert Hoover Dike to wave erosion and seepage at high stages. An early decision making approach to storage management with respect to ENSO related hydrology, is presented based on tracking the strength of ENSO events.

Lessons from and assessment of Boussinesq aquifer modeling of a large fluvial island in a dam-regulated river

The suitability of a numerical Boussinesq aquifer model for representing groundwater dynamics in a fluvial island surrounded by a regulated river is assessed and the model is used to compare exchange fluxes for varying configurations of island hydraulic conductivity ( K) and diffusivity. The model results are qualitatively similar to field observations of the water table although there is obvious dissimilarity between modeled and observed heads suggesting that a Boussinesq aquifer model may not be the best option for representing the island. Nonetheless, the simulations show that pronounced ridges and valleys form in the water table and that their spatial configuration may change drastically with small variations in diffusivity. Stage fluctuations significantly increase exchange flux across the island relative to the case where stage is constant. The flux increases non-linearly when island K is low but then becomes quasi-linearly dependent on K with further increases in K. Regulated river stage fluctuations due to dams significantly affect surface water–groundwater interactions between a fluvial island and a river. This deserves further inquiry for both scientific and management reasons.

Impact of dam operations on hyporheic exchange in the riparian zone of a regulated river

AbstractDam operations commonly cause large, frequent fluctuations in river stage, which persist for long distances downstream. The stage fluctuations force river water into and out of the banks, defining lateral hyporheic exchange paths. To evaluate the penetration distance and rates of dam‐induced hyporheic exchange, we monitored water‐table elevation, temperature, and specific conductivity along a transect perpendicular to the Colorado River (Austin, Texas, USA), 15 km downstream of the Longhorn dam. Stage fluctuates daily by almost a metre. The daily hyporheic exchange volume per metre of bank is 1·0 m3. Dam‐induced hyporheic exchange penetrates several metres into the riparian aquifer, while water‐table fluctuations propagate 30 m into the riparian aquifer. Water chemistry and temperature fluctuate near the channel in response to the flow oscillations. In the absence of dam operations, groundwater would flow steadily through the riparian aquifer towards the river, laterally limiting hyporheic exchange and stabilizing temperatures and water chemistry near the channel. Therefore, dam operations fundamentally change the hydrological, thermal, and geochemical dynamics of riparian aquifers and their hyporheic zones. Copyright © 2009 John Wiley & Sons, Ltd.

Snowmelt‐induced diel fluxes through the hyporheic zone

Snowmelt processes result in diel fluctuations in streamflow and stream stage that propagate into riparian aquifers and cause a daily pumping of the hyporheic zone. This diel pumping was observed in stream stage and water table records collected in Tuolumne Meadows, Yosemite National Park, California. A model was developed using Fourier analysis to represent the stream stage fluctuations and a solution to the 1‐D, linearized Boussinesq equation for groundwater flow. The modeling demonstrates that a substantial volume of water is pumped in and out of the aquifer via this process on a daily basis. In addition, since the snowmelt‐induced groundwater fluctuations exhibit both reduced amplitudes and increased time lags at distances away from the stream, the model can be used to estimate the hydraulic parameters of the riparian aquifer. Snowmelt‐induced hyporheic pumping may have implications for biogeochemical processes in the hyporheic zone and may provide important ecosystem services related to water filtration, thermal buffering, nutrient cycling, and water quality. Consideration should be given to recognizing, quantifying, and monitoring snowmelt‐induced pumping of the hyporheic zone and the ecosystem services it provides since climate and land use changes may alter the magnitude of this process in the future.

Microstructure evolution of Ge+ implanted silicon oxide thin films upon annealing treatments

The structural evolution of silicon oxide films with Ge+ implantation was traced with a positron beam equipped with positron annihilation Doppler broadening and lifetime spectrometers. Results indicate that the film structure change as a function of the annealing temperature could be divided into four stages: (I) T<300°C; (II) 300°C⩽T⩽500°C; (III) 600°C⩽T⩽800°C; (IV) T⩾900°C. In comparison with stage I, the increased positron annihilation Doppler broadening S values during stage II is ascribed to the annealing out of point defects and coalescence of intrinsic open volumes in silicon oxides. The obtained long positron lifetime and high S values without much fluctuation in stage III suggest a rather stable film structure. Further annealing above 900°C brings about dramatic change of the film structure with Ge precipitation. Positron annihilation spectroscopy is thereby a sensitive probe for the diagnosis of microstructure variation of silicon oxide thin films with nano-precipitation.

A general framework of stream–aquifer interaction caused by variable stream stages

Stream–aquifer interface is a critical zone where surface water and groundwater exchange mass, energy, and chemicals. Previous analytical studies of stream–aquifer interaction consider stream stage fluctuations that are only functions of time. This study improves those solutions by simultaneously considering temporally and spatially variable stream stages, low-permeability streambeds, and pumping wells nearby the streams. Semi-analytical solutions of drawdown and stream–aquifer flow rate in the Laplace–Fourier domain are provided and used to obtain solutions in the real time–space domain after the inverse Laplace–Fourier transform, where the stream–aquifer flow rate refers to the rate of discharge between a stream and an adjacent aquifer. The stream–aquifer flow rate caused by the temporally variable stream stage is found to decline with time and becomes negligible when time is sufficiently long. A closed-form analytical solution for the stream–aquifer flow rate caused by a diffusive-type flood wave is obtained, and it can be used to predict the response of an aquifer upon a passing flood wave. For a diffusive-type flood wave that dies out in about 24 h, we find that the stream–aquifer flow rate drops nearly exponentially with time and dies out at about 13.4 h for a sandy aquifer and an alluvial streambed. Sensitivity analysis shows that the stream–aquifer flow rate increases with the diffusion coefficient of the flood wave ( D ) which controls the width and amplitude of the wave, and decreases with the average flood wave velocity ( v ). Low-permeability streambeds reduce stream–aquifer flow rate and also delay the response to the stream stage fluctuations. For a time-dependent cosine stream stage function with a period of 30 days, the maximal stream–aquifer flow rate with a 0.5 m thick low-permeability streambed is 24% less than that obtained without the streambed.

Implications of anthropogenic river stage fluctuations on mass transport in a valley fill aquifer

In humid regions a strong coupling between surface water features and groundwater systems may exist. In these environments the exchange of water and solute depends primarily on the hydraulic gradient between the reservoirs. We hypothesize that daily changes in river stage associated with anthropogenic water releases (such as those from a hydroelectric dam) cause anomalous mixing in the near‐stream environment by creating large hydraulic head gradients between the stream and adjacent aquifer. We present field observations of hydraulic gradient reversals in a shallow aquifer. Important physical processes observed in the field are explicitly reproduced in a physically based two‐dimensional numerical model of groundwater flow coupled to a simplistic surface water boundary condition. Mass transport simulations of a conservative solute introduced into the surface water are performed and examined relative to a stream condition without stage fluctuations. Simulations of 20 d for both fluctuating river stage and fixed high river stage show that more mass is introduced into the aquifer from the stream in the oscillating case even though the net water flux is zero. Enhanced transport by mechanical dispersion leads to mass being driven away from the hydraulic zone of influence of the river. The modification of local hydraulic gradients is likely to be important for understanding dissolved mass transport in near‐stream aquifer environments and can influence exchange zone processes under conditions of high‐frequency stream stage changes.

Facies and Stratigraphic Anatomy of a Temperate Carbonate Sequence (Capo Colonna Terrace, Late Pleistocene, Southern Italy)

Abstract Accurate interpretation of ancient non-tropical carbonate systems requires the development of appropriate facies and sequence stratigraphic models. These models should account for the marked differences in sedimentation style among non-tropical carbonates formed under different energy settings. This paper presents data and a conceptual model of the sequence architecture of non-tropical carbonates of moderate energy environments based on the late Pleistocene deposits of Capo Colonna marine terrace (Calabria, southern Italy). These deposits have the advantage of being continuously exposed along a proximal–distal transect across the paleo-shelf and their geometry has not been disturbed by later tectonic activity. They consist of a transgressive–regressive (T–R) cycle whose genesis can confidently be related to one of the interstadial glacio-eustatic fluctuations of marine isotope stage (MIS) 5. Eight different mixed carbonate–siliciclastic and carbonate facies are present in the studied sequence. Of these, biogenic-dominated facies are invariably made up of skeletal remains of light-independent organisms plus or minus red calcareous algae (the heterozoan association). The relatively young age of the deposits allows calibration of the paleoecological significance of observed facies by direct comparison with modern analogues from the Mediterranean Sea. Four laterally persistent discontinuity surfaces were identified along the transect, and interpreted, from bottom to top, as (1) a basal ravinement surface, (2) a submarine hardground locally acting as a substrate for algal boundstones, (3) a regressive surface of marine erosion, and (4) a surface of subaerial exposure. Sequence stratigraphic analysis indicates that the preserved T–R cycle is asymmetric, with a thicker regressive portion. Highstand deposits can be subdivided into a shore-connected sandy prism and more distal autochthonous and parautochthonous skeletal accumulations and algal boundstones. During forced regression, a thin, sharp-based, strongly progradational unit of calcarenites was deposited above the regressive surface of marine erosion. The deposits of Capo Colonna terrace document the response of non-tropical, moderate-energy carbonate ramps to sea-level fluctuations during icehouse conditions. Their architecture can facilitate the interpretation of other successions from similar settings and provide an end member to be compared and contrasted with high-wave-energy cool-water carbonates.

Patterned Floating Dummy Fill for On-Chip Spiral Inductor Considering the Effect of Dummy Fill

This paper discusses the effect of dummy fills on the performance of spiral inductors. In Si-CMOS processes that use copper wire, metal dummy fills are required to prevent thickness fluctuation in the chemical mechanical polishing stage. Dummy fills have been thought to affect the wire capacitance; however, in high frequency, dummy fills also affect the wire resistance and the wire inductance due to the eddy current in dummy fills. This work evaluates the effect of the dummy fills by three-dimensional field solver and proposes a structure to suppress the effect of dummy fills. Experimental results show that the proposed method can decrease the effect of dummy fills on the Q-factor by 83% compared with the conventional dummy fill insertion.

On the onset of the instability of a three-dimensional jet in a stratified fluid

The onset of a three-dimensional jet flow in a stratified fluid is studied with the aid of a direct numerical simulation. An initially cylindrical jet with a Gaussian velocity profile is considered in a fluid with stable linear density stratification. The results indicate that, if an initial small perturbation of the velocity field has a wide spectrum, an exponential growth of the isolated quasi-two-dimensional mode occurs and its spectral maximum is shifted toward smaller wave numbers in comparison with the maximum of the helical mode of the instability of a nonstratified jet. The growth rate is proportional to Ri0.5, where Ri is the global Richardson number. The onset of the instability leads to the formation of the flow’s vortex structure, which consists of a collection of different-polarity quasi-two-dimensional vortices located in a horizontal plane near the longitudinal axis of the jet. At sufficiently long times (Nt > 100, where N is the buoyancy frequency and t is time), the growth of instability reaches the saturation stage and further fluctuations in velocity and density decay under the effect of viscous diffusion. At this stage, the flow becomes self-similar and the time dependences of the transverse and vertical widths of the jet are consistent with the asymptotic behaviors of integral parameters of the flow that are observed experimentally in the far stratified wake. The results suggest that the onset of the instability of a quasitwo-dimensional mode can play the determining role in the dynamics of flow in the far stratified wake.