Changes In Hydraulic Conditions Research Articles

Intraspecific differences in drought tolerance and acclimation in hydraulics of Ligustrum vulgare and Viburnum lantana

An adequate general drought tolerance and the ability to acclimate to changing hydraulic conditions are important features for long-lived woody plants. In this study, we compared hydraulic safety (water potential at 50% loss of conductivity, Psi(50)), hydraulic efficiency (specific conductivity, k(s)), xylem anatomy (mean tracheid diameter, d(mean), mean hydraulic diameter, d(h), conduit wall thickness, t, conduit wall reinforcement, (t/b)(h)(2)) and stomatal conductance, g(s), of forest plants as well as irrigated and drought-treated garden plants of Ligustrum vulgare L. and Viburnum lantana L. Forest plants of L. vulgare and V. lantana were significantly less resistant to drought-induced cavitation (Psi(50) at -2.82 +/- 0.13 MPa and -2.79 +/- 0.17 MPa) than drought-treated garden plants (- 4.58 +/- 0.26 MPa and -3.57 +/- 0.15 MPa). When previously irrigated garden plants were subjected to drought, a significant decrease in d(mean) and d(h) and an increase in t and (t/b)(h)(2) were observed in L. vulgare. In contrast, in V. lantana conduit diameters increased significantly but no change in t and (t/b)(h)(2) was found. Stomatal closure occurred at similar water potentials (Psi(sc)) in forest plants and drought-treated garden plants, leading to higher safety margins (Psi(sc) - Psi(50)) of the latter (L. vulgare 1.63 MPa and V. lantana 0.43 MPa). These plants also showed higher g(s) at moderate Psi, more abrupt stomatal closure and lower cuticular conductivity. Data indicate that the development of drought-tolerant xylem as well as stomatal regulation play an important role in drought acclimation, whereby structural and physiological responses to drought are species-specific and depend on the plant's hydraulic strategy.

Modelling ripple development under non-uniform flow and sediment supply-limited conditions in a laboratory flume

Results are reported herein of an open channel flow laboratory based study of the development of ripples on a fine silica sand bed, and under non-uniform turbulent subcritical flow conditions. The hydraulic model used included a diverging channel, which resulted in a variation of hydraulic and sediment transport parameters along the channel. Sediment supply limitation occurred during experimentation, impacting bed form development. The overall aim of this study was to improve the understanding and modelling capability of the development of bed forms under limited sediment supply and non-uniform flow conditions. In particular, the applicability of an existing empirical model capable of predicting ripple development was tested for the conditions of this study, using measured ripple dimensions. The ripple height and length results were extracted from detailed bed profile records, obtained using an acoustic Doppler probe traversed longitudinally over the sediment bed, at various experimentation time intervals. It was found that the non-uniform flow conditions affected the development rate of the bed forms, while sediment supply limitation impacted their steady state dimensions. The measured steady state ripple dimensions were lower, on average, than the corresponding equilibrium dimensions predicted using existing empirical equations. Non-uniform flow also caused the simultaneous occurrence of bed forms at different stages of development along the hydraulic model, where 3D and 2D ripples and incipient bed forms were recorded. Such a scenario can occur in estuarine and coastal flows, due to changing hydraulic conditions and/or a limitation of sediment supply. The ripple development model tested was verified for the conditions of this study, with its accuracy being shown to depend on an accurate determination of steady state parameters.

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A study of the effects of the longitudinal arrangement sediment behavior near intake structures

Constructing intake structures to divert some part of the flow from rivers causes some changes in hydraulic conditions of the flow in front of the intake port. These changes, like flows in river bends, induce secondary flows, thereby causing sedimentation in the intake port and erosion in the bank facing the intake. Submerged vanes have been used for different purposes such as reducing erosion in river bends, bank stabilization, increasing flow into the intake and so on. The vanes are typically installed with an angle of 15°–25° to the flow direction and with an initial height of about 20%–50% of the flow depth (Marelius and Sinha, 1998; Nakato et al., 1990). In this study, the possibility of the submerged vanes to control and direct the flow and river thalweg toward the intake port with different longitudinal arrangements has been investigated. Three longitudinal distances 3H, 4H, and 6H (H being the initial height of the vanes) have been considered and the experiments have been done for the regular and zigzag arrangements for different intake discharges. The results showed that using submerged vanes in the longitudinal spacing of 3H to 6H in regular and zigzag arrangements makes it possible to direct the thalweg toward the intake port. In addition, with the use of the vanes, a trench is made toward the intake, which in turn increases the impoundment efficiency by 50%–80% in the regular arrangement and by 25%–50% in the zigzag arrangement. Submerged vanes can also reduce the sedimentation by 40% over that without vanes.

Sensor for Injection Rate Measurements

A vast majority of the medium and high speed Diesel engines are equipped withmulti-hole injection nozzles nowadays. Inaccuracies in workmanship and changinghydraulic conditions in the nozzles result in differences in injection rates between individualinjection nozzle holes. The new deformational measuring method described in the paperallows injection rate measurement in each injection nozzle hole. The differences in injectionrates lead to uneven thermal loads of Diesel engine combustion chambers. All today knownmeasuring method, such as Bosch and Zeuch give accurate results of the injection rate indiesel single-hole nozzles. With multihole nozzles they tell us nothing about possibledifferences in injection rates between individual holes of the nozzle. At deformationalmeasuring method, the criterion of the injected fuel is expressed by the deformation ofmembrane occurring due to the collision of the pressure wave against the membrane. Thepressure wave is generated by the injection of the fuel into the measuring space. For eachhole of the nozzle the measuring device must have a measuring space of its own into whichfuel is injected as well as its measuring membrane and its own fuel outlet. Duringmeasurements procedure the measuring space must be filled with fuel to maintain anoverpressure of 5 kPa. Fuel escaping from the measuring device is conducted into thegraduated cylinders for measuring the volumetric flow through each hole of the nozzle.Themembrane deformation is assessed by strain gauges. They are glued to the membrane andforming the full Wheatstone’s bridge. We devoted special attention to the membrane shapeand temperature compensation of the strain gauges.

Modelling discolouration in a Melbourne (Australia) potable water distribution system

Reducing customer complaints of discoloured water is a major challenge for the water industry. The ability to predict the spatial probability and severity of discolouration events in distribution systems could lead to the implementation and optimisation of proactive operational and maintenance strategies to minimise discolouration. This paper explores the transfer of a predictive, semi-empirical model developed to describe iron dominated discolouration problems in the UK to an Australian system, where discolouration is primarily associated with clay type material. The paper presents the application of the model to a large diameter water main that forms part of the Melbourne system within a single source water quality zone. The model is based on cohesive transport theory and for this application includes the concept of a ‘self-cleaning threshold’, defined as a shear stress that the pipe experiences regularly, due to normal daily demand, that prohibits the accumulation of sufficient material within the pipe and hence poses no discolouration risk. Results presented here show that the model can be calibrated to simulate the turbidity response measured in real systems due to changes in hydraulic conditions, for clay driven discolouration problems. These changes in hydraulic condition resulted from various ‘natural’ events which occurred during the available data period. Through such simulation the semi-empirical model parameters were evaluated. These simulations demonstrate the capabilities of the model, which could be applied to operational and maintenance practice. For example, to identify and prioritise network cleaning operations to minimise discolouration risk, at pipe level, through simulation of discolouration responses to various possible events (burst, fire fighting etc) and ranking the resulting predicted discolouration, or through prior simulation to identify the cleaning necessary to mitigate discolouration risk of planned operations such as valve movements.

Measuring method for diesel multihole injection nozzles

Abstract A vast majority of the medium and high speed diesel engines are equipped with multihole injection nozzles nowadays. Inaccuracies in workmanship and changing hydraulic conditions in the nozzles result in differences in injection rates between individual injection nozzle holes. The new deformational measuring method described in the paper allows injection rate measurement in each injection nozzle hole. The differences in injection rates lead to uneven thermal loads of diesel engine combustion chambers. The criterion of the injected fuel is expressed by the deformation of membrane occurring due to the rapid rise of the fuel in the measuring space and the collision of the pressure wave against the membrane. The pressure wave is generated by the injection of the fuel into the measuring space. The pressure wave is analysed by the theory of hydraulic impact in the high-pressure pipes. The membrane deformation is measured using strain gauges, glued to the membrane and forming the Wheatstone bridge. We devoted special attention to the temperature compensation of the Wheatstone bridge and the membrane, heated up during the measurements. All four strain gauges were arranged in a full Wheatstone bridge configuration and glued to the membrane. The strain gauges are all exposed to identical temperature resulting in a temperature compensated Wheatstone bridge. Described in the paper are the measurements of a three-hole nozzle and the reasons analysed of injection rate differences in the injection nozzle holes. We divided the causes of the inequality in the injection rate into structural and hydraulic groups.

Integrating geophysical and hydrochemical borehole-log measurements to characterize the Chalk aquifer, Berkshire, United Kingdom

Geophysical and hydrochemical borehole-logging techniques were integrated to characterize hydraulic and hydrogeochemical properties of the Chalk aquifer at boreholes in Berkshire, UK. The down-hole measurements were made to locate fissures in the chalk, their spatial extent between boreholes, and to determine the groundwater chemical quality of the water-bearing layers. The geophysical borehole logging methods used were caliper, focused resistivity, induction resistivity, gamma ray, fluid temperature, fluid electrical conductivity, impeller and heat-pulse flowmeter, together with borehole wall optical-imaging. A multiparameter data transmitter was used to measure groundwater temperature, electrical conductivity, dissolved oxygen, pH, and redox potential of the borehole fluid down-hole. High permeability developed at the Chalk Rock by groundwater circulation provides the major flow horizon at the Banterwick Barn study site and represents a conduit system that serves as an effective local hydraulic connection between the boreholes. The Chalk Rock includes several lithified solution-ridden layers, hardgrounds, which imply a gap in sedimentation possibly representing an unconformity. Lower groundwater temperature, high dissolved-oxygen content, and flowmeter evidence of preferential groundwater flow in the Chalk Rock indicated rapid groundwater circulation along this horizon. By repeating the logging at different times of the year under changing hydraulic conditions, other water-inflow horizons within the Chalk aquifer were recognized.

Behaviour of gold in the weathered mantle at Shewushan, Hubei, China

A supergene gold dispersion halo has been developed at Shewushan, Hubei, central China, from the weathering of an auriferous limestone under warm, humid climate conditions. The distributions of gold and associated elements were determined in soils and in both fresh and weathered rocks. Fresh mineralized rocks contain 0.1 to 1 g/t Au. 55% of the gold occurs as small Ag-bearing particles (<0.02 μm) associated with illite and kaolinite, and 45% is incorporated within the lattice of pyrite. The Au content of the supergene deposits ranges from 1.05 to 19.49 g/t, again mostly as very small particles (<0.02 μm) in kaolinite and illite and partly as particles of <0.6 μm within limonite. In the pH range of 5 to 8, which is similar to surficial conditions at Shewushan, bisulphide and thiosulphate ligands are possibly present in significant concentrations to complex Au. Particulate Au and Au within pyrite would both dissolve as ionic complexes and be transported downward in groundwater percolating through the clay-rich rock. Most of the Au complexes are adsorbed by clays and Mn and Fe oxyhydroxides, resulting in secondary concentration. Some of the small native gold particles associated with clay minerals could also migrate downwards and accumulate close to the water-table in response to changes in hydraulic conditions. Weathering has promoted gold accumulation in the centre of the halo and dispersion at its margins. Gold concentrations progressively increase from the surface to the base of the weathering mantle and decrease from the centre to the margin of the halo. The dispersion halo results from the lateral migration of both complexed and particulate gold in groundwater during weathering.

A perspective on the abiotic processes sustaining the ecological integrity of running waters

Using selected examples of recent research, this paper illustrates the role of abiotic components within running-water ecosystems. The important role of temperature is acknowledged but the paper focuses on another key driver: physical stability, defined in relation to hydrological (frequency, duration and timing of inundation) and substratum parameters (channel dynamics, bedform and sediment size). The importance of this driver is illustrated by reference to four spatial scales. At the scale of the bedform, surface-water and groundwater interactions play an important role not least in driving energy exchanges and determining the temperature dynamics within the ecologically important surface layer of the bed sediments. At the reach scale, bedform development, channel form dynamics, and associated changing hydraulic conditions determine both benthic and riparian community patterns. At the catchment scale, new research has shown that the processes responsible for the formation of islands and divided channels play important roles in the functioning of fluvial hydrosystems. Finally, at the regional scale, the flow regime modified by the geomorphological history of the river over at least the past 16 000 years explains ecological patterns. The integration of hydro-geomorphological knowledge from all four scales of analysis is shown to be fundamental for understanding the ecological characteristics of running waters and for managing ecological integrity.

Periphyton development in three valley segments of a New Zealand grassland river: test of a habitat matrix conceptual model within a catchment

We monitored water nutrient concentrations, periphyton biomass, and periphyton cellular nutrient concentrations in run and riffle habitats at sites representative of headwater, mid-catchment and lowland valley segments of a grassland river for two years, and community composition on four occasions during this period, to determine how these communities varied spatially and temporally as a function of downstream changes in hydraulic conditions, flood disturbance regimes and enrichment. Predictions of community biomass and structure were tested under a proposed habitat matrix conceptual model for periphyton. Discharge increased and valley segment slope decreased in a downstream direction as expected from geomorphic models of catchment processes. However, site-specific depths and velocities did not change systematically down the river. Water nutrient concentrations suggested a change from nitrogen limitation of primary production at the headwater site to phosphorus limitation at the lowland site. This was associated with a downstream increase in stream nitrate concentrations, but not phosphorus. However, cellular nutrient concentrations and instream nutrient bioassays suggested either N limitation, or weak N and P limitation, at all sites. In runs, mean monthly chlorophyll-a did not vary significantly (P>0.05) among the three sites, but it did in riffles. The differences in community biomass between run and riffle habitats were more significant than differences among sites. Periphyton community structure in the runs was similar among valley segments during a period of frequent flood disturbances, but during a period of infrequent disturbances communities in the headwater sites were dominated by filamentous cyanobacteria whereas in the mid-catchment and lowland sites they were dominated by nitrogen-fixing cyanobacteria and diatoms. Major differences in community structure occurred in riffles among the sites. Riffle communities at the headwater site were dominated by filamentous cyanobacteria and diatoms, whereas at the mid-catchment and lowland sites filamentous green algae and diatoms were dominant, possibly a result of increased nitrate concentrations progressing downstream. Overall; a downstream gradient in nitrate enrichment appeared to control biomass and community composition of the riffle communities, but not the run communities. Strong grazer activity in runs during more hydrologically stable periods at the lowland site appeared to override any response to nutrients and maintained biomass at low levels. Periphyton biomass and community composition was predicted more accurately from the habitat matrix conceptual model based on local habitat factors than by expected downstream gradients in hydraulic conditions and enrichment.

Transport equivalence of cassiterite and its application to stream sediment surveys for heavy minerals

Accumulation of heavy minerals, such as gold and cassiterite, on stream beds is a well-known phenomenon that results from differences in the rates of transport of the heavy minerals and the sediment as a whole. These accumulations can be both an advantage and a disadvantage to exploration geochemical surveys. Hence, it would be beneficial to be able to recognize such accumulations and, if necessary, correct for them. This, however, requires an improved understanding of the sedimentology of heavy minerals in fluvial channels. In this study we use pit-traps to determine relative rates of transport and estimate transport equivalent sizes of cassiterite and sediment on a coarse sand-gravel stream bed in Malaysia. Results show that for grain sizes finer than about 180 μm (80 mesh ASTM) cassiterite grains have the same average transport rate as sediment grains roughly three times larger. This information can be used to identify and correct geochemical data for Sn anomalies resulting from accumulations of cassiterite that develop on the stream bed in response to the high density of cassiterite and changing hydraulic conditions. In principle the same methodology should be applicable to other heavy minerals.

Hydraulic influences on periphyton and benthic macroinvertebrates: simulating the effects of upstream bed roughness

1. Hydraulic conditions, periphyton biomass and invertebrate communities were compared on artificial substrates exposed to a range of upstream roughness conditions across an area of uniform current velocity and depth in a gravel‐bedded river. The effect of river bed roughness was simulated by installing roughness elements upstream of artificial substrates.2. Increasing upstream roughness reduced the average near‐bed velocity above the substrates and increased short‐term variability in velocity (i.e. turbulence).3. Periphyton chlorophyll a density showed a general decline with near‐bed velocity and was significantly lower on the substrates exposed to the river bed reference and 0 mm roughness treatments than the 110 mm roughness elements. Chlorophyll a was also negatively correlated with the abundance of larger collector‐browsing invertebrates. This indicates that effects of the changes in hydraulic conditions on invertebrates may have contributed to the observed treatment effects on periphyton.4. Invertebrate abundance and diversity declined with increasing upstream roughness. Filter‐feeders, collector‐browsers and predatory invertebrates all declined in abundance with increasing upstream roughness, but the effect was strongest for filter‐feeders. Eight of the nine most common taxa showed significant treatment effects. The orthoclad chironomid, Eukiefferiella sp., was not influenced strongly by upstream roughness, but its abundance was correlated significantly with periphyton biomass.

Prediction of Bed-Load Transport by Desert Flash Floods

A number of predictive bed-load sediment transport equations are rated against a unique set of field data collected by automatic slot samplers during flash floods in a desert wadi. The Meyer-Peter and Müller equation is shown to perform well, providing a median ratio of calculated to observed ( C /O) bed-load flux of 1.18. The Bagnold equation is shown to underpredict considerably, with a median C /O of 0.44. The Parker equation performs better, though it still underpredicts with a median C /O of 0.78. The apparent success of the Meyer-Peter and Müller formula is attributed to the ready supply of sediment to the channel system in desert and semidesert environments. This ensures that the channel bed remains unarmored, in contrast to supply-limited, armored, perennial rivers of humid zones. It also ensures that bed-load flux responds to changing hydraulic conditions in a comparatively simple fashion.

Radon as a natural groundwater tracer in the chalk aquifer, UK

The radon concentration in the groundwater of the Chalk, SE England, a fissured aquifer, was measured at 16 sites over a period of 15 months to assess its potential as a natural groundwater tracer. Each site demonstrated appreciable radon concentration variation over this period, apparently in response to changes in hydraulic conditions within the aquifer. Further interpretation will concentrate on a three-component model for the groundwater and its dissolved radon in the fissures of the Chalk.

Modeling Soil Erosion by Overland Flow: Application Over a Range of Hydraulic Conditions

Modeling the erosion of cohesive soils on slopes where shallow overland flow is dominant requires practical and useable equations that rely upon key parameters: F, the fraction of excess stream power available for mechanical work, and, J, the specific energy of entrainment. Data from a series of rainfall simulator experiments were used to evaluate the consistency of F and J for two contrasting soil types across a range of hydraulic conditions. A summary of the conceptual model together with key equations used in the analyses of data is given. Parameter evaluation and the implications of using inappropriate sediment concentrations and/or assuming spatially uniform flow when rills are present are discussed. The two soils studied were a cracking clay (vertisol) and a slightly dispersive sandy clay loam (aridisol). From detailed information on rill dimensions and frequency, calculated values of F were found to be relatively insensitive to changes in hydraulic conditions for turbulent flow conditions. Its value was approximately 0.1 for both soil types. Parameter J was also reasonably consistent when rill dimensions and frequency were used in the analyses. The F and J values were more scattered by assuming spatially uniform flow across a surface when rills were present.

Quasi-3D modelling of suspended sediment transport by currents and waves

A quasi-3D model for suspended sediment transport based on an asymptotic solution of the convection-diffusion equation is developed for currents and waves. The influence of waves on the sediment concentration is included through the diffusion analogy and the boundary condition near the bed. The flow velocity profile is assumed to have a logarithmic shape. An extensive sensitivity analysis concerning the influence of wave and current parameters on the suspended adjustment phenomenon shows that the presence of waves considerably enlarges the suspended load and its adjustment time and length scales. Validity analysis of the quasi-3D formulation results in restrictions for the suspension parameter (modified for waves) and for the time and length scales of changes in hydraulic conditions. The presence of waves eases all the above restrictions and thus enlarges the validity area of the model considerably. The model is compared with 2DV and 3D numerical solutions of the convection-diffusion equation with good agreement and verified with existing measurements.

Effect of Short-Term and Long-Term Changes in Hydraulic Conditions on Nitrifying Biofilm

Hydraulic conditions affect the biofilms used in the treatment of very low concentration of pollutants. Effect of hydraulic conditions on nitrifying biofilm grown under a NH4-N concentration of about 1 mg/l (substrate-limiting condition) was investigated in a cylindrical reactor (ø40 cm × 46 cm (working height)). Velocity and turbulence at 4 mm from the wall of the reactor mixed by paddles were measured by a hotfilm anemometer. Nitrifying biofilm was grown on the wall of the reactor at a base hydraulic condition with average turbulent intensity of 6.6 cm/s. Turbulent intensity was reduced for a period of three to four times the hydraulic retention time and the resulting flux was measured at the end of this period (short-term). This short-term effect of turbulent intensity on specific flux (NH4-N flux/NH4-N concentration in bulk water) varied with turbulent intensity according to a power law of turbulent intensity in agreement with the theoretical expression derived for filamentous biofilms under turbulent conditions. When turbulent intensity was changed and kept at the changed value for several days (long-term), filamentous type biofilm with higher substrate flux was observed at high turbulent intensities but colony-type biofilms under low turbulent intensities showed reduced mass transfer.

Simulation of Run-Off from the Greenland Ice Sheet for Planning Hydro-Electric Power, Ilulissat/Jakobshavn, West Greenland

Simulations of run-off from the Greenland ice sheet were made as part of a feasibility study for provision of hydroelectric power for Ilulissat/Jakobshavn, West Greenland. The aims were to see if the available short series of run-off measurements are typical of those under present climatic conditions, and to assess possible changes in run-off likely to be caused by gross changes in drainage pattern on the ice sheet. Specific run-off was calculated from climatological data, whilst run-off volumes were calculated by integrating specific run-off over the area of the ice sheet. There have been substantial year-to-year variations in run-off, but the 6 year measurement period is reasonably representative of present climatic conditions. Run-off could be reduced by 21% as a result of changes in hydraulic conditions on the ice sheet without this having a significant effect on the economy of the planned hydro-electric power station.

Applied Glacier Research for Planning Hydro-Electric Power, Ilulissat/Jakobshavn, West Greenland

Glaciological investigations were carried out on the Greenland ice sheet to help develop plans for a hydro-electric power station to supply energy to Ilulissat/Jakobshavn. The investigations required research on supraglacial and subglacial melt-water drainage in order to delineate water-drainage basins. This involved repeated detailed photogrammetric mapping, radio echo-sounding, hot-water drilling, and mathematical modelling of subglacial drainage. Repeated mappings combine to show an overall stability in the supraglacial drainage pattern, while model calculations for the subglacial conditions show a limited sensitivity in the predicted drainage areas to changes in hydraulic conditions. The investigations provide the basis for setting safer limits for planning hydro-electric power in the area, and give a general understanding of glacier hydrology for a continuous ice cover such as the Greenland ice sheet.