Showing papers on "Water flow published in 1999"

Water Permeability and Autogenous Healing of Cracks in Concrete

Abstract: The well-known practical phenomenon of autogenous healing in cracks plays a significant role in relation to the functional reliability of structures subjected to water-pressure loads. Because of the autogenous healing, the water flow through the cracks gradually reduces with time, and in extreme cases, the cracks seal completely. In the past, there has been no deliberate technical exploitation of self-healing, because too little is known about the phenomenon itself and about the chemical/physical processes involved. Based on theoretical and experimental research, the effect of crack healing was investigated on a larger scale for the first time. The experimental studies showed the formation of calcite in the crack to be almost the sole cause for the autogenous healing. A comprehensive theoretical discussion of the laws, which govern the calcite nucleation and the subsequent crystal growth of water-bearing cracks in concrete, revealed that the crystal growth responds to two different crystal growth processes that are determined by the changes in the chemical and physical conditions in the crack. Further, the crystal growth rate is dependent on the crack width and water pressure, whereas concrete composition and water hardness have no influence on autogenous healing. On the basis of the experimental studies, an algorithm that can be used to estimate the reduction in water over time as a result of autogenous healing was developed.

Time scale for local scour at bridge piers

Abstract: The temporal development of clear-water local scour depth at cylindrical bridge piers in uniform sand beds is considered. New data are presented and used to quantify the influence of flow duration on the depth of local scour. An equilibrium time scale (t*) is defined. The data show that both t* and the equilibrium scour depth (dse) are subject to similar influences of flow and sediment parameters, as might be expected because they are inherently interdependent. A method is given for determination of the time for development of dse for a given pier, sediment, and approach flow velocity and the concomitant estimation of the scour depth at any stage during development of the equilibrium scour hole. The results show that the scour depth after 10% of the time to equilibrium is between about 50% and 80% of the equilibrium scour depth, depending on the approach flow velocity. of local scour d se is rapidly attained in live-bed conditions, but rather more slowly in clear-water conditions (Fig. 1). Clear- water scour occurs for mean flow velocities up to the threshold velocity for bed sediment entrainment, i.e., V # Vc, while live- bed scour occurs for V > Vc. The maximum equilibrium scour depth dse)max occurs at V = Vc. In armored cobble or cohesive sediment bed streams, multiple flood events may be required before the maximum clear-water scour is reached. This may take many years. The equilibrium scour depth in live-bed con- ditions fluctuates due to the effects of bed form migration. The dashed lines in Fig. 1 represent the temporal average scour depth under live-bed conditions. The diagram also shows the time taken, te, for the equilibrium scour depth to develop. The equilibrium time, te, is the focus of this paper. It increases rapidly with flow velocity under clear-water conditions, but then decreases rapidly for live-bed scour. Existing equations for depth of local scour at bridge piers give the equilibrium depth and are therefore conservative re- garding temporal effects. For the live-bed conditions that typ- ically pertain in floods, equilibrium scour depths are appro- priate. However, where clear-water scour conditions exist, the equilibrium depth of scour may be overly conservative. Peak flood flows may last only a number of hours or a few days in the field, and short floods have insufficient time to generate equilibrium depths. For example, bridge piers situated on the floodplain may be wet for periods of less than one day during a flood; typically, clear-water conditions pertain at such sites. The actual scour may be only a small fraction of the equilib- rium scour depth, which could take weeks to fully develop. Johnson and McCuen (1991) developed an analytical model to simulate the temporal process of local scour at piers. The model was applied to a hypothetical bridge pier using a gen- erated sequence of flood flows over a 75 year period, the in- dividual storms being of 24 h duration. At the end of the 75 year period, the scour depth was still increasing.

Mechanics of Sediment Transport

Abstract: Nearly 40 years of theoretical development and practical experience has been incorporated in this book, which has won numerous awards as a scientific and technical publication in China. Now updated and fully translated into English, this volume is the first attempt in the field to unify the movement of sediment and boundary conditions. Going far beyond any book of its kind, it presents a synthetic analysis and thorough coverage of many schools of thought and provides practical survey of this discipline of the science. The authors introduce a synthesis of information gleaned from more than 800 papers spanning the fields of hydraulic engineering, mathematics, physics, geology, rheology, and chemistry, giving the reader a profound understanding of the present status and direction of the industry's research efforts. The volume includes chapters dedicated to rate phenomena and topics such as hyperconcentrated flows, effect of sediment existence on water flow, large-scale hydraulic construction on sediment-laden streams, and specialized research not available outside of China.

Fish, Flows and Flood Plains: Links between Freshwater Fishes and their Environment in the Murray-Darling River System, Australia

Abstract: Knowledge of the biology of native fishes of the Murray-Darling Basin is based largely on studies conducted under hatchery conditions and on a limited number of recreationally important species. From observations that increases in water level in aquaculture ponds initiate spawning in some species, and from limited studies of wild fishes and studies in overseas floodplain river systems, a perception has emerged of the importance of flooding and the flood plain in the life cycles of Murray-Darling fishes in general. However, there is little confirmatory evidence of the use of temporary floodplain habitats by larvae, juveniles or adults. The significance of in-channel habitats, especially for rearing, has received little attention. Murray-Darling fish species can be placed into three life history modes, based mainly on spawning style and time and developmental intervals of larvae at first feeding. Fish in each group may be able to take advantage of floods if the timing is right and prey are plentiful, however, the larvae of some species are able to recruit under non-flood conditions within the main river channel. This forms the basis of the ‘low flow recruitment hypothesis’, which attempts to explain why some species spawn during the warmest months and lowest flows and how they are able to recruit under these conditions. This hypothesis is then placed in the context of the current state of knowledge of the relationships between flow and the biology of Murray-Darling fishes, specifically cues for spawning, movement and recruitment. The lack of widespread evidence for floodplain use by any life history interval of fish may be due to a paucity of study, however, there are some fundamental factors, such as the predictability of timing and duration of high flow events as well as the lack of coincidence of high flows and high temperatures in some regions of the Basin, which may be important in determining the use of floodplain habitats by fish.

Locomotor forces on a swimming fish: three-dimensional vortex wake dynamics quantified using digital particle image velocimetry.

Abstract: Quantifying the locomotor forces experienced by swimming fishes represents a significant challenge because direct measurements of force applied to the aquatic medium are not feasible. However, using the technique of digital particle image velocimetry (DPIV), it is possible to quantify the effect of fish fins on water movement and hence to estimate momentum transfer from the animal to the fluid. We used DPIV to visualize water flow in the wake of the pectoral fins of bluegill sunfish (Lepomis macrochirus) swimming at speeds of 0.5-1.5 L s(-)(1), where L is total body length. Velocity fields quantified in three perpendicular planes in the wake of the fins allowed three-dimensional reconstruction of downstream vortex structures. At low swimming speed (0.5 L s(-)(1)), vorticity is shed by each fin during the downstroke and stroke reversal to generate discrete, roughly symmetrical, vortex rings of near-uniform circulation with a central jet of high-velocity flow. At and above the maximum sustainable labriform swimming speed of 1.0 L s(-)(1), additional vorticity appears on the upstroke, indicating the production of linked pairs of rings by each fin. Fluid velocity measured in the vicinity of the fin indicates that substantial spanwise flow during the downstroke may occur as vortex rings are formed. The forces exerted by the fins on the water in three dimensions were calculated from vortex ring orientation and momentum. Mean wake-derived thrust (11.1 mN) and lift (3.2 mN) forces produced by both fins per stride at 0.5 L s(-)(1) were found to match closely empirically determined counter-forces of body drag and weight. Medially directed reaction forces were unexpectedly large, averaging 125 % of the thrust force for each fin. Such large inward forces and a deep body that isolates left- and right-side vortex rings are predicted to aid maneuverability. The observed force balance indicates that DPIV can be used to measure accurately large-scale vorticity in the wake of swimming fishes and is therefore a valuable means of studying unsteady flows produced by animals moving through fluids.

Mechanics of sediment transport

Abstract: Comprehensive coverage of the phenomena of sediment movement - from the origin and formation of sediment to its properties in pipelines. Nearly 40 years of theoretical development and practical experience has been incorporated in this book, which has won numerous awards as a scientific and technical publication in China. Now updated and fully translated into English, this volume is the first attempt in the field to unify the movement of sediment and boundary conditions. Going far beyond any book of its kind, it presents a synthetic analysis and thorough coverage of many schools of thought and provides practical survey of this discipline of the science. The authors introduce a synthesis of information gleaned from more than 800 papers spanning the fields of hydraulic engineering, mathematics, physics, geology, rheology and chemistry, giving the reader a profound understanding of the present status and direction of the industry's research efforts. The volume includes chapters dedicated to rate phenomena and topics such as hyperconcentrated flows, effect of sediment existence on water flow, large-scale hydraulic construction on sediment-laden streams, and specialized research not available outside of China.

Variation of Roughness Coefficients for Unsubmerged and Submerged Vegetation

Abstract: This paper investigates the variation of the vegetative roughness coefficient with the depth of flow. A horsehair mattress is used in the experimental study to simulate the vegetation on the watercourses. Test results reveal that the roughness coefficient reduces with increasing depth under the unsubmerged condition. However, when fully submerged, the vegetative roughness coefficient tends to increase at low depths but then decrease to an asymptotic constant as the water level continues to rise. A simplified model based on force equilibrium is developed to evaluate the drag coefficient of the vegetal element; Manning's equation is then employed to convert the drag coefficient into the roughness coefficient. The data of this study are compared with those of selected previous laboratory and field tests. The results show a consistent trend of variation for the drag coefficient versus the Reynolds number. This trend can be represented by a vegetative characteristic number k. Given information such as the bed ...

Streams and Ground Waters

Abstract: Streams around the world flow toward the sea in floodplains. All along this transit, there is exchange of water between the stream itself and the surrounding sediments which form the floodplain. Many chemical, biological, and geological processes occur when water moves back and forth between streams and these flood plain sediments. Streams and Groundwaters focuses on the consequences of water flow between streams, their underlying sediments, and surrounding landscapes. Certain to appeal to anyone interested in stream ecology, the management of stream ecosystems, or landscape ecology, this volume should become a oft-opened reference.

Crab predation, waterborne cues, and inducible defenses in the blue mussel, mytilus edulis

Abstract: Inducible defenses are found in both terrestrial and aquatic organisms and appear to be a common defensive strategy of both sessile and mobile species. Here we report the presence of previously undescribed inducible defenses in marine mussels, a dominant member of temperate rocky intertidal communities. In the Gulf of Maine, estuarine shorelines with low water flow are characterized by high crab predation on the common blue mussel, Mytilus edulis, compared to nearby shore- lines with high water flow. Mussels at these high predation sites had thicker shells, relatively more shell mass, and were more tightly attached to the substrate than mussels at low predation sites. Field and laboratory experiments were used to test whether the between- site differences in these traits were the result of phenotypic plasticity. Mussels outplanted to high predation sites produced more byssal threads and attached more firmly to the substrate than did mussels outplanted to low predation sites. In the laboratory, thicker shells were induced by waterborne cues from both the common predator, Carcinus maenus, and damaged conspecifics, and these thicker shells were mechanically stronger than thinner, noninduced ones. Our results contribute to growing evidence that inducible defenses are a pervasive feature of intertidal assemblages. In addition to the bivalve example presented here, gastropods, barnacles, bryozoans, and seaweeds are also known to have inducible defenses. Phenotypic plasticity for defensive traits has likely evolved repeatedly in intertidal organisms and appears to play a major role in the dynamics of rocky intertidal communities.

Changes to water repellence of soil aggregates caused by substrate-induced microbial activity

Abstract: Summary Soil microbes produce exudates which upon drying become water-repellent, thus altering hydraulic properties. The influence of microbial activity caused by adding plant nutrients on the hydraulic characteristics of soil aggregates is reported. Soil aggregates were collected from a field that had been fertilized with different amounts of nitrogen. Aggregates were also incubated with different nutrient treatments in the laboratory. Their sorptivity, hydraulic conductivity and water repellency were measured with a new device. Adding nitrogen was found to decrease sorptivity and hydraulic conductivity because of increased water repellency in the field. In the laboratory studies, the addition of nutrients caused severe water repellency in the soil aggregates. Respiration studies identified a large increase in biological activity following nutrient amendment which produces water-repellent materials.

Diurnal variations in hydraulic conductivity and root pressure can be correlated with the expression of putative aquaporins in the roots of lotus japonicus

Abstract: The hydraulic conductivity of excised roots (Lpr) of the legume Lotus japonicus (Regel) K. Larsen grown in mist (aeroponic) and sand cultures, was found to vary over a 5-fold range during a day/night cycle. This behaviour was seen when Lpr was measured in roots exuding, either under root pressure (osmotic driving force), or under an applied hydrostatic pressure of 0.4 MPa which produced a rate of water flow similar to that in a transpiring plant. A similar daily pattern of variation was seen in plants grown in natural daylight or in controlled-environment rooms, in plants transpiring at ambient rates or at greatly reduced rates, and in plants grown in either aeroponic or sand culture. When detached root systems were connected to a root pressure probe, a marked diurnal variation was seen in the root pressure generated. After excision, this circadian rhythm continued for some days. The hydraulic conductivity of the plasma membrane of individual root cells was measured during the diurnal cycle using a cell pressure probe. Measurements were made on the first four cell layers of the cortex, but no evidence of any diurnal fluctuation could be found. It was concluded that the conductance of membranes of endodermal and stelar cells may be responsible for the observed diurnal rhythm in root Lpr. When mRNAs from roots were probed with cDNA from the Arabidopsis aquaporin AthPIP1a gene, an abundant transcript was found to vary in abundance diurnally under high-stringency conditions. The pattern of fluctuations resembled closely the diurnal pattern of variation in root Lpr. The plasma membranes of root cells were found to contain an abundant hydrophobic protein with a molecular weight of about 31 kDa which cross-reacted strongly to an antibody raised against the evolutionarily conserved N-terminal amino acid sequence of AthPIP1a.

Characteristics of microencapsulated PCM slurry as a heat‐transfer fluid

Abstract: The hydrodynamic and heat-transfer characteristics of slurry containing microencapsulated phase-change materials (MCPCMs) were investigated experimentally for use as a heat-transfer fluid. Pressure drop and local convective heat-transfer coefficients of the slurry flows in a circular tube with uniform heat flux were measured. Slurries consisting of octadecane (C{sub 18}H{sub 38}) contained in 2--10-{micro}m-dia. microcapsules and pure water were used. The particle volume fractions in the slurry were varied up to 0.3. Results showed that increases in particle volume fractions caused the slurry flow structure to change from turbulent to laminar, and the pressure-drop reduction of the slurry flow relative to a single-phase water flow was under the same flow-rate conditions. The heat-transfer performance of the slurry also depended on the change in flow structure. When the MCPCMs melted, the local heat-transfer coefficients for turbulent slurry flows increased relative to those for nonmelting slurry. This phenomenon was influenced by the MCPCM fraction, the degree of turbulence, and the heating rate at the tube wall. The experimental data will be useful in the design of thermal-energy transportation systems using MCPCM slurry.

Inhibition of water channels by HgCl2 in intact wheat root cells

Abstract: To assess the extent of water flow through channels in the membranes of intact higher plant cells, the effects of HgCl 2 on hydraulic conductivity ( L P ) of wheat ( Triticum aestivum L.) root cells were investigated using a pressure probe. The L P of root cells was reduced by 75% in the presence of 100 μm HgCl 2 . The K + -channel blocker tetraethylammonium had no effect on the L P at concentrations that normally block K + channels. HgCl 2 rapidly depolarized the membrane potential ( V m ) of the root cells. The dose-response relationship of inhibition of L P and depolarization of V m were not significantly different, with half-maximal inhibition occurring at 4.6 and 7.8 μm, respectively. The inhibition of L P and the depolarization of V m caused by HgCl 2 were partially reversed by β-mercaptoethanol. The inhibition of L P by HgCl 2 was similar in magnitude to that caused by hypoxia, and the addition of HgCl 2 to hypoxia-treated cells did not result in further inhibition. We compared the L P of intact cells with that predicted from a model of cortical cells incorporating water flow across both the plasma membrane and the tonoplast using measured values of water permeability from isolated membranes, and found that HgCl 2 has other effects in addition to the direct inhibition of water channels.

On the breakup of an air bubble injected into a fully developed turbulent flow. Part 2. Size PDF of the resulting daughter bubbles

Abstract: Based on energy principles, we propose a statistical model to describe the bubble size probability density function of the daughter bubbles resulting from the shattering of a mother bubble of size D0 immersed in a fully developed turbulent water flow. The model shows that the bubble size p.d.f. depends not only on D0, but also on the value of the dissipation rate of turbulent kinetic energy of the underlying turbulence of the water, e. The phenomenological model is simple, yet it predicts detailed experimental measurements of the transient bubble size p.d.f.s performed over a range of bubble sizes and dissipation rates e in a very consistent manner. The agreement between the model and the experiments is particularly good for low and moderate bubble turbulent Weber numbers, Wet = ρΔu2(D0)D0/σ where the assumption of the binary breakup is shown to be consistent with the experimental observations. At larger values of Wet, it was found that the most probable number of daughter bubbles increases and the assumption of tertiary breakup is shown to lead to a better fit of the experimental measurements.

Soil water repellency: effects of water content, temperature, and particle size

Abstract: Water repellency (WR) of soils is a common problem in many countries. It can cause a reduction in the rate of water infiltration into soils as well as an unstable water flow within the soil matrix. Water repellency has typically been related to dry soils. We investigated the effect of soil water content and soil pretreatment temperature on the degree of WR in soils and soil size fractions. Water repellency was measured with an ethanol test as the minimum liquid surface tension of an aqueous ethanol droplet that can stay on the soil surface for at least 5 sec. The WR varied greatly with water content. The lowest water contents were achieved by drying soil at different temperatures between 40 and 105°C. Hence, the apparent effect of water content on WR for low water contents may be a combination of a direct water content effect and the effect of pretreatment temperature. High WR was observed at soil water contents up to 0.08 g g 1 . Out of 14 soil samples, three did not show WR regardless of temperature treatment or soil water content, four had single peaks in WR as a function of water content, and seven had double peaks in WR, one peak at very low and one peak at higher soil water content. Results from comparison experiments with freeze-dried soil samples implied that the WR peak at lower soil water contents was caused mainly by temperature effects, while the peak at higher soil water contents was related to water content only. In water repellent soil the smaller soil size fractions exhibited the highest degree of water repellency. This can partly be explained by higher organic matter content in the fractions with smaller particle size. As water repellency is dependent on soil water content, performing the WR test solely on dry soils can lead to the wrong classification regarding whether a soil is water repellent or not.

The Nicotiana tabacum plasma membrane aquaporin NtAQP1 is mercury-insensitive and permeable for glycerol.

Abstract: A new aquaporin from Nicotiana tabacum (cv. Samsun) was characterized. It shares sequence homology to the Arabidopsis thaliana PIP1 protein family. By two-phase partitioning and immunoblot analysis, plasma membrane localization could be demonstrated. The corresponding mRNA is highly abundant in roots and flowers, while it is rarely expressed in leaves and stems. Functional expression in Xenopus oocytes revealed that NtAQP1 can mediate glycerol transport in addition to water flow. However, NtAQP1 is impermeable for Na+, K+ and Cl- ions. The water permeability and selectivity could not be modulated by addition of mercurials or the activity of cAMP-dependent protein kinases.

Discharge coefficient for sharp-crested side weir in subcritical flow

Abstract: To estimate the outflow over a rectangular sharp-crested side weir, the discharge coefficient in the weir equation needs to be known. Although this type of structure has been designed and used extensively by hydraulic engineers, a universally acceptable discharge coefficient does not exist. In this study over 250 laboratory tests were conducted, and the results were analyzed to find the influence of the flow hydraulics and the geometric, channel, and weir shapes on the coefficient. The results show that for subcritical flow the De-Marchi assumption of constant energy is acceptable, and the weir discharge can therefore be used. Furthermore, it was discovered that the De-Marchi coefficient of discharge is a function of the upstream Froude number and the ratios of weir height to upstream depth and weir length to channel width, whereas the channel slope in subcritical flow can be ignored. Hence, an accurate equation for the coefficient of discharge is introduced.

Regional regression models of annual streamflow for the united states

Abstract: Estimates of annual streamflow volumes are needed in many different types of hydrologic studies. Usually a streamgauge is unavailable at the location of interest, hence regional methods that relate streamflow to readily measured geomorphic and climate characteristics provide a practical solution. Hydrologic, geomorphic, and climatic characteristics of 1,553 undeveloped watersheds across the United States are used to develop regional regression equations that relate the first two moments of annual streamflow to readily measured basin and climate characteristics. These relations are summarized for each of 18 major U.S. water resource regions. The relationships are remarkably precise, with adjusted R2 values ranging from 90.2–99.8% and an average value of 96.2% across the continent. The usefulness of these relationships is evaluated by deriving their information content in terms of equivalent record length. These results indicate that regional models of annual streamflow, including runoff maps, are less accu...

Morphological Characteristics of Macropores and the Distribution of Preferential Flow Pathways in a Forested Slope Segment

Abstract: Water flow through soil macropores is important in determining hydrologic responses in forested watersheds. Morphological characteristics of macropores and distribution of preferential flow pathways were evaluated in a forest hillslope segment using a combination of staining agents. Almost 80% of described macropores were roughly elliptical with eccentricities ranging from 0.256 to 0.998 (mean of 0.652) and lengths ranging from 2.0 to 61.8 cm (mean of 11.6 cm). Tortuosity of macropores tended to increase with increasing length up to about 30 cm, with a mean value of 1.14. Macropores were aggregated in large clumps within the soil profile. Living and decayed roots and associated vertical zones of loose soil and humus contributed to preferential flow pathways in this soil. Subsurface flow patterns, detected by upslope injection of dilute white paint solution, showed a strong interaction between the soil matrix and macropores. Subsurface flow was lateral along the bedrock and between A and B horizons, with a perched water table occurring on sections of both. Dye tests also showed that flow occurred within surface bedrock fractures. This fracture flow was sometimes connected to macropores through zones of local wetness. Thus, we conclude bedrock topography and fracture characteristics may contribute significantly to preferential flow pathways at the hillslope scale. Even though individual macropores were rather short, the coupling of these flow paths with the soil matrix, bedrock fractures, living and decayed roots, and perched water tables produced complex networks of interconnected preferential flow pathways, all of which help explain the stormflow response observed in the catchment. Water flow through soil macropores is important in determining hydrologic responses in forested watersheds. Morphological characteristics of macropores and distribution of preferential flow pathways were evaluated in a forest hillslope segment using a combination of staining agents. Almost 80% of described macropores were roughly elliptical with eccentricities ranging from 0.256 to 0.998 (mean of 0.652) and lengths ranging from 2.0 to 61.8 cm (mean of 11.6 cm). Tortuosity of macropores tended to increase with increasing length up to about 30 cm, with a mean value of 1.14. Macropores were aggregated in large clumps within the soil profile. Living and decayed roots and associated vertical zones of loose soil and humus contributed to preferential flow pathways in this soil. Subsurface flow patterns, detected by upslope injection of dilute white paint solution, showed a strong interaction between the soil matrix and macropores. Subsurface flow was lateral along the bedrock and between A and B horizons, with a perched water table occurring on sections of both. Dye tests also showed that flow occurred within surface bedrock fractures. This fracture flow was sometimes connected to macropores through zones of local wetness. Thus, we conclude bedrock topography and fracture characteristics may contribute significantly to preferential flow pathways at the hillslope scale. Even though individual macropores were rather short, the coupling of these flow paths with the soil matrix, bedrock fractures, living and decayed roots, and perched water tables produced complex networks of interconnected preferential flow pathways, all of which help explain the stormflow response observed in the catchment.

The functional relationship between peak spring floods and survival and growth of juvenile Atlantic Salmon (Salmo salar) and Brown Trout (Salmo trutta)

Abstract: 1. The effects of high spring floods on survival and growth of juvenile Atlantic Salmon, Salmo salar, and Brown Trout, Salmo trutta, are explored, using data from a long-term study in the River Saltdalselv, northern Norway. The flow regime in this river is typical for northern rivers. 2. There was considerable variation in year class strength of both species. 3. Mortality of Atlantic Salmon increased significantly in years with high discharge during the alevin stage as well as the first week after emergence. High discharge during the egg stage and more than 1 week after emergence seemed to be of minor importance. Water temperature at emergence was rather high (average 10·5 °C) and did not significantly affect year class strength. 4. Brown Trout emerged earlier than Atlantic Salmon at an average water temperature of 8·2 °C. Highest mortality was observed in years with low water temperatures at emergence as well as high discharge during the alevin stage. 5. For 1-year-old fish or older, the size of the spring peak flood did not influence mortality significantly. 6. Growth of Atlantic Salmon parr was diminished in years with a high peak spring flood. A similar effect on Brown Trout was not detected.

Multiquadric Solution for Shallow Water Equations

Abstract: A computational algorithm based on the multiquadric, which is a continuously differentiable radial basis function, is devised to solve the shallow water equations. The numerical solutions are evaluated at scattered collocation points and the spatial partial derivatives are formed directly from partial derivatives of the radial basis function, not by any difference scheme. The method does not require the generation of a grid as in the finite-element method and allows easy editing and refinement of the numerical model. To increase confidence in the multiquadric solution, a sensitivity and convergence analysis is performed using numerical models of a rectangular channel. Applications of the algorithm are made to compute the sea surface elevations and currents in Tolo Harbour, Hong Kong, during a typhoon attack. The numerical solution is shown to be robust and stable. The computed results are compared with measured data and good agreement is indicated.

Climatic changes in the Aegean Sea influence the eastern Mediterranean thermohaline circulation (1986–1997)

Abstract: Recent changes of water mass characteristics in the south Aegean Sea have considerably influenced the Eastern Mediterranean thermohaline circulation. A combination of salinity increase (1987–92) and temperature drop (1992–94) caused massive dense water formation and strong outflow towards the deep and bottom parts of the Eastern Mediterranean. This climatic shift, the most important since the existence of observations in the basin, is a combined effect of extreme meteorological events superimposed on large-scale trends. It has initiated a series of modifications in the hydrology and dynamics of the entire Eastern Mediterranean, with possible influence on the Mediterranean outflow in the North Atlantic Ocean.

Water flow in tide- and wave-dominated beds of the seagrass Thalassia testudinum

Abstract: Biological processes in seagrass meadows are regulated by the exchange of momentum, heat and mass between the surrounding water and the plants and thus may strongly depend on the characteristics of water flow and turbulence. Comparisons of mean flow profiles, turbulence distribution and mixing in meadows of the seagrass Thalassia testudinum colonizing 2 hydrodynamically different sites (wave-dominated and tide-dominated) suggest that the hydrodynamic microclimate and consequently mixing within seagrass beds strongly depend on the hydrodynamic forces (waves and currents) acting on the plants. Unidirectional flows deflect the water over the meadow (skimming flows), which potentially leads to lower mixing between the water above and within the meadow. In contrast, waves cause the blades to move back and forth, increasing the exchange between the water column and that within the meadow. Therefore, the hydrodynamic conditions prevailing in the seagrass habitat (waves, tides) change the pattern of flow attenuation and mixing within the vegetation.

Water Quality in Walnut Creek Watershed: Nitrate-Nitrogen in Soils, Subsurface Drainage Water, and Shallow Groundwater

Abstract: Nonpoint source contamination of surface and groundwater resources with nitrate-N (NO 3 -N) has been linked to agriculture across the midwestern USA. A 4-yr study was conducted to assess the extent of NO 3 -N leaching in a central Iowa field. Water flow rate was monitored continuously and data were stored on an internal datalogger. Water samples for chemical analysis were collected weekly provided there was sufficient flow. Twelve soil cores were collected in spring, early summer, mid-summer, and after harvest for each of the 4 yr. Nitrate-N concentrations in shallow groundwater exhibited temporal trends and were higher under Clarion soil than under Okoboji or Canisteo soil. Denitrification rates were two times higher in Okoboji surface soil than in Clarion surface soil and the highest denitrification potential among subsurface sediments was observed for deep unoxidized loess. Soil profile NO 3 -N concentrations decreased with depth and were the same below 30 cm for fertilized corn (Zea mays L.) and soybean (Glycine max L. Merr.). Nitrate-N concentrations in subsurface drainage water exceeded 10 mg L -1 for 12 mo and were between 6 and 9 mg L -1 for 32 mo during the 4-yr study. The temporal pattern of NO 3 -N concentrations in subsurface drainage water was not related to the timing of fertilizer N application or the amount of fertilizer N applied. Total NO 3 -N losses to subsurface drains were greatest in 1993 (51.3 kg ha 1 ) and least in 1994 (4.9 kg ha -1 ). Most of the subsurface drainage water NO 3 -N was lost when crop plants were not present (November-May), except in 1993. Our results indicate that NO 3 -N losses to subsurface drainage water occur primarily as a result of asynchronous production and uptake of NO 3 -N in the soil and the presence of large quantities of potentially mineralizable N in the soil organic matter.

Signatures of the Mediterranean outflow from a North Atlantic climatology 1. Salinity and density fields

Abstract: Using historical data from the National Oceanic Data Center, the climatology of the eastern North Atlantic basin has been investigated for the purpose of detailing the Mediterranean outflow water in terms of its salinity, density, and flow patterns. Part 1 of this work is a descriptive analysis of the fate of the Mediterranean Water once it flows out of the Strait of Gibraltar. Tracing the salinity and density signatures, high-resolution maps of the climatological outflow are presented, with an emphasis on the continuity of the water from its source. From the climatological fields a continuous signal of Mediterranean Water is tracked northward to ∼50°20′N, yet its westward advection is limited to the Tagus Basin. Recirculations of Mediterranean Water in the Gulf of Cadiz and in the Bay of Biscay, deduced from property signals, are also detailed. Iorga and Lozier [this issue] present absolute velocity fields from a diagnostic model constrained by geostrophic dynamics, conservation of mass, and no-flux boundary conditions.

Phosphorus and nitrogen inputs to Florida Bay: The importance of the everglades watershed

Abstract: A large environmental restoration project designed to improve the hydrological conditions of the Florida Everglades and increase freshwater flow to Florida Bay is underway. Here we explore how changing freshwater inflow to the southern Everglades is likely to change the input of nutrients to Florida Bay. We calculated annual inputs of water, total phosphorus (TP), total nitrogen (TN), and dissolved inorganic nitrogen (DIN) to Everglades National Park (ENP) since the early 1980s. We also examined changes in these nutrient concentrations along transects through the wetland to Florida Bay and the Gulf of Mexico. We found that the interannual variability of the water discharge into ENP greatly exceeded the interannual variability of flow-weighted mean nutrient concentrations in this water. Nutrient inputs to ENP were largely determined by discharge volume. These inputs were high in TN and low in TP; for two ENP watersheds TN averaged 1.5 mg l−1 (0.11 mM) and 0.9 mg l−1 (0.06 mM) and TP averaged 15 μg l−1 (0.47 μM) and 9 μg l−1 (0.28 μM). Both TP and DIN that flowed into ENP wetlands were rapidly removed from the water. Over a 3-km section of Taylor Slough, TP decreased from a flow-weighted mean of 11.6 μg l−1 (0.37 μM) (0.20 μM) and DIN decreased from 240 μg l−1 (17μM) to 36 μ l−1 (2.6 μM). In contrast, TN, which was generally 95% organic N, changed little as it passed through the wetland. This resulted in molar TN:TP ratios exceeding 400 in the wetland. Decreases in TN concentrations only occurred in areas with relatively high P availability, such as the wetlands to the north of ENP and in the mangrove streams of western ENP. Increasing freshwater flow to Florida Bay in an effort to restore the Everglades and Florida Bay ecosystems is thus not likely to increase P inputs from the freshwater Everglades but is likely to increase TN inputs. Based on a nutrient budget of Florida Bay, both N and P inputs from the Gulf of Mexico greatly exceed inputs from the Everglades, as well as inputs from the atmosphere and the Florida Keys. We estimate that the freshwater Everglades contribute <3% of all P inputs and <12% of all N inputs to the bay. Evaluating the effect of ecosystem restoration efforts on Florida Bay requires greater understanding of the interactions of the bay with the Gulf of Mexico and adjacent mangrove ecosystems.

Numerical Model for Channel Flow and Morphological Change Studies

Abstract: In this paper a depth-integrated 2D hydrodynamic and sediment transport model, CCHE2D, is presented. It can be used to study steady and unsteady free surface flow, sediment transport, and morphological processes in natural rivers. The efficient element method is applied to discretize the governing equations, and the time marching technique is used for temporal variations. The moving boundaries were treated by locating the wet and dry nodes automatically in the cases of simulating unsteady flows with changing free surface elevation in channels with irregular bed and bank topography. Two eddy viscosity models, a depth-averaged parabolic model and a depth-averaged mixing length model, are used as turbulent closures. Channel morphological changes are computed with considerations of the effects of bed slope and the secondary flow in curved channels. Physical model data have been used to verify this model with satisfactory results. The feasibility studies of simulating morphological formation in meandering chan...