Constant Water Level Research Articles

Geostatistical analysis of field hydraulic conductivity in compacted clay

Hydraulic conductivity(K) of fractured or porous materials is associated intimately with water flow and chemical transport. Basic concepts imply uniform flux through a homogeneous cross-sectional area. If flow were to occur only through part of the area, actual rates could be considerably different. Because laboratory values ofK in compacted clays seldom agree with field estimates, questions arise as to what the true values ofK are and how they should be estimated. Hydraulic conductivity values were measured on a 10×25 m elevated bridge-like platform. A constant water level was maintained for 1 yr over a 0.3-m thick layer of compacted clay, and inflow and outflow rates were monitored using 10×25 grids of 0.3-m diameter infiltration rings and outflow drains subtending approximately 1×1 m blocks of compacted clay. Variography of inflow and outflow data established relationships between cores and blocks of clay, respectively. Because distributions of outflow rates were much less and bore little resemblance to the distributions of break-through rates based on tracer studies, presence of macropores and preferential flow through the macropores was suspected. Subsequently, probability kriging was applied to reevaluate distribution of flux rates and possible location of macropores. Sites exceeding a threshold outflow of 100×10−9 m/s were classified as outliers and were assumed to probably contain a significant population of macropores. Different sampling schemes were examined. Variogram analysis of outflows with and without outliers suggested adequacy of sampling the site at 50 randomly chosen locations. Because of the potential contribution of macropores to pollutant transport and the practical necessity of extrapolating small plot values to larger areas, conditional simulations with and without outliers were carried out. Simulated scenarios based on all available data compared well with conditional simulations based on randomly chosen locations.

Paedomorphosis in Ambystoma Talpoideum: Effects of Density, Food, and Pond Drying

The expression of metamorphosis and paedomorphosis in the salamander Ambystoma talpoideum was examined in a three—factor experiment using artificial ponds. This experiment was designed to measure simultaneously the effects of initial larval density, food level, pond drying regime, and their interactions on the percentage of individuals metamorphosing or becoming paedomorphic. A higher percentage of individuals metamorphosed from drying low—density, and high—food ponds than from constant water level, high—density, and low—food ponds. A higher percentage of individuals became paedomorphic in constant water—level and low—density ponds than in drying and high—density ponds. Food level had no effect on the expression of paedomorphosis. Initial density, food level, and drying regime all had significant effects on the mean snout—vent length of larvae in ponds. The percentage of paedomorphic individuals in a pond was positively correlated with mean snout—vent length in the population. Analysis of covariance using snout—vent length as the covariate removed density and food level effects on the percentage of metamorphic individuals but did not remove the effects of drying regime. Use of snout—vent length as covariate in an analysis of covariance for the percentage of paedomorphic individuals failed to remove significant effects of density or drying regime. Only initial density affected the survival of larvae. The factors manipulated in this experiment affected the expression of paedomorphosis both directly through the physical environmental conditions that they created and indirectly through the growth and body size of larvae. These results suggest that differences in environmental factors among populations can affect the life—history pathways of individuals and lead to a predominance of paedomorphosis in permanent aquatic habitats with favorable growth environments.

Phenotypic Variation in Metamorphosis and Paedomorphosis in the Salamander Ambystoma talpoideum

Phenotypic variation in metamorphosis and paedomorphosis in the salamander Ambystoma talpoideum was examined to determine its environmental or genetic basis. Eight artificial ponds were maintained, four at each of two environmental treatments: constant water level, to simulate fish free permanent breeding ponds, and gradual drying out, to simulate temporary breeding ponds. Two populations of salamanders were used, derived from two breeding ponds having different frequencies of paedomorphosis. The water level in the drying treatment was lowered during the last 10 wk of the experimental period with no apparent differences in water chemistry parameters between treatments and only a slight change in water temperatures during the last 2 wk. The quality of the growth environment for larvae, as measured by body size and survivorship, was the same in the four experimental treatments. The frequency of metamorphosis was significantly higher in the drying treatment that under constant water level, and also differed between populations. The frequency of paedomorphosis was significantly different between populations but not between water level treatments. The effects of water level were potentially confounded by those of water temperature, density of larvae, and amount of food. Population differences in the frequency of metamorphosis and paedomorphosis could potentially represent genetic differences resulting from the different selective regimes that individuals encounter in breeding ponds varying in drying frequency. However, phenotypic plasticity and nongenetic maternal effects cannot be dismissed without further experimentation.

Tolerance ofSphagnumto water level

Four species of Sphagnum which occur on ombrotrophic mires were grown at different levels above the water table. In one experiment the species were grown at constant water levels in a bog pool and, in another, at fluctuating water levels in a transplant experiment. A general trend was found of decreasing photosynthetic capacity with increasing height above the water table. This indicates that the hollow species (S. balticum and S. tenellum) are unable to tolerate the hummock sites, whereas the hummock species (S. fuscum and S. rubellum) could well survive the environmental conditions of the hollows but are absent because of biotic factors.

Subirrigation System Control for Water use Efficiency

ABSTRACT Afield experiment and a computer simulation analysis were conducted to evaluate the water requirements of subirrigation under three methods of system control. First year results from the field experiment indicate that irrigation water requirements can be reduced by controlling the system such that the midpoint water table depth is allowed to fluctuate within certain limits. A simulation model based on numerical solutions to the Boussinesq equation was developed to allow comparison between the control methods using historical weather records. Several simulations were conducted for each control method to optimize the set points for starting and stopping subirrigation for the given method. Using the optimum set points, the simulations predicted a decreased irrigation requirement when the midpoint water table depth was allowed to fluctuate. The irrigation requirement was decreased by an average of 6.7% over constant water level control for five years of simulations. Much larger differences could have occurred had the set points not been optimized. That is, there is potentially more difference in irrigation water requirements for different set points within a given control method than between two different control methods. The results indicate that there is a good potential for reducing irrigation requirements of subirrigation. A slight modification in the way in which subirrigation systems are currently controlled can result in decreased subirrigation water usage.

Cracking in feedwater pipework of light water reactors: Causes and remedies

The present paper deals with cracking in ferritic pipework of light water reactor (BWR) feedwater systems whose causes are unsuitable design and manufacture and, at least occasionally, unsuitable water quality. Thus in two BWR plants in the German Federal Republic large circumferential cracks have been found in the circumferential welds in the main feedwater pipelines immediately adjacent to the reactor pressure vessel, and in a further BWR large longitudinal cracks have been found in pipe bends of the reactor water purification pipework connected to the main feedwater pipelines. The piping regions near the reactor pressure vessel feedwater nozzles represent a boundary region of varying thermodynamic states of the pressurised water. The reactor pressure vessel is heated to saturation temperature by the radioactive decay heat, and then cooler water, and sometimes (during start-up) cold water is injected into the reactor pressure vessel in order to maintain a constant water level about 2 m above the upper edge of the feedwater nozzles. In order to improve the state of knowledge regarding the stressing conditions under prevailing operating conditions, extensive strain and temperature measurements have been carried out. The results of these measurements carried out in several BWRs confirm the occurrence of rapid temperature changes in the feedwater pipework in the regions where it connects to the reactor pressure vessel, leading to varying stresses which at times reach the plastic region. These processes are triggered by special operating states such as start-up and shut-down or hot standby operation with feedwater flows smaller than 6% relative to normal operation under full load.

Dispositif experimental pour l'etude de divers impacts sur la faune benthique d'un cours d'eau

An experimental device was built to study, under semi-natural conditions, the effects of various substances on benthic communities of streams. The three main parts of the system are a head box, a mixing device and five channels. They are completed by a water-catchment and treatment system at the end. The water is supplied by gravity from a small dam built on a brook while a weir on the back side of the head box insures a constant water level and consequently a constant discharge of water in the experimental channels. Chemical substances to be tested are added at the exit of the head box and are mixed with the water in five inclined scales equipped with alternate triangular steps. The bottom of the channels is filled with gravel which is placed in small plastic baskets allowing reproducible and undisturbed samples to be taken. The results of the colonization by benthic organisms show that the longitudinal gradient which exists at the beginning of the experiments decreases rapidly and becomes non-significant after six weeks. Statistically the colonization is identical for the five channels and consequently any channel could be chosen as a control. The qualitative composition of the benthic communities in the channels and in the brook are very similar even though chironomids and mayflies are more abundant and caddisflies less numerous in the channels.

Methods of confining oil in unlined caverns in aquifers: Water table maintenance by well recharge

One of the methods of petroleum storage is using unlined caverns located below the water table of an aquifer. The water pressure will exceed the oil pressure in the cavern, water will penetrate the cavern, and the oil will be confined. In order to prevent excessive lowering of the water table and to maintain a prescribed constant water level it is necessary, in most cases, to inject water into the aquifer. The influence of rock properties and of flow geometry on the rates of water flow into the cavern and on the shape of the phreatic surface were studied. The equations of flow were solved by a numerical method, and the results were presented in a dimensionless form.

Hydraulic Considerations in Declining-Rate Filtration

Flow control through granular filters is an important factors in filter performance in both water and wastewater treament. Declining-rate filtration plants operate without effluent rate control devices on each filter. All the filters in the plant operate at the same water level and the same head loss. Therefore, the cleanest filter operates at the highest filtration rate and the dirtiest filter operates at the lowest rate. The filters decline in rate as each filter is backwashed in succession. Declining-rate filtration plants produce better water quality and require less head loss than constant-rate or constant water level filters. The design of declining-rate plants has been hampered by the absence of rational approaches to several hydraulic questions which are answered in the paper as follows: What total head loss is required? How can excessive filtration rates be prevented without the use of rate controllers? How can the water level variations in the filter be predicted and how are they affected by the number of filters in the plant? How does the plant respond to imposed load variations—

Design and Testing of a Microlysimeter for Wetland Rice1

AbstractAssessment of water loss as transpiration and evapotranspiration for each hour or for each day in the field is difficult because the available methods are either very expensive or inaccurate. This paper introduces a simple, sensitive, and accurate microlysimeter for wetland rice (Oryza sativa L.) fields.The microlysimeter was designed and tested to measure transpiration and evapotranspiration in wetland rice fields. It consists of a poly‐vinyl‐chloride cylinder, sealed at the lower end and connected to a water reservoir/manometer through flexible tubing. A constant water level is maintained in the microlysimeter with a Mariotte system and water loss from the reservoir/manometer is measured. Total water loss as evaporation from free water surface in the cylinder and transpiration from canopy was measured as evapotranspiration. To measure transpiration, the cylinder was covered to stop evaporation from free water surface in the cylinder.The microlysimeters were laboratory‐calibrated and compared in the field with large square tanks. Water use pattern as evapotranspiration per unit land area was essentially the same with both the units. The microlysimeter is accurate even for time intervals as short as 1 hour and can be fabricated locally.

Morphology and movements of nearshore sediments in a non-tidal environment, K0ge Bugt, · Denmark

On a non-tidal, medium- to fine-grained sandy coast, the morphology and material budget in the littoral zone - primarily on the nearshore terrace and the shoreface - have been analysed ori the basis of 65 detailed maps surveyed in a permanent grid for a period of two months. Simultaneously, records were made of wind, water, and waves. The map drawings and the calculations of variations in sediment volumes were made by EDP. The investigations showed that the nearshore bar might be built up during high as well as low waterle­vels, initiated either by a small breakpoint bar or a swash bar. The observed nearshore bar moved landward up to 30 cm per hour during periods with onshore winds and during constant water-levels and/or constant wind speeds. Analyses of the material budget showed that variations in volume ( down to minus 1 m) were mainly due to profile adjustments. Especially noteworthy was that, after a gale, the quantities of sediments supplied were larger than those removed from the area during the gale. Furthermore, it was demonstrated that the total quantity of material of the inshore and the beach by and large remained constant in spite of obvious occurrences of nearshore bars migrating towards the coastline during the investigation period. Only an extraordinary gale situation was able to add permanent material to the barrier.

Effects of Soil Water Levels on Components of Growth and Yield in Peas1

Abstract Greenhouse grown peas (Pisum sativum L. cv. Alaska) were irrigated at 4 levels with constant water conditions and with 2 water levels varied at 3 physiological stages of growth. At constant water levels total dry matter, seed yield, seed size, number of seeds per plant, plant height, watering level, and water used were positively related. Number of nodes per plant remained constant in all treatments but internode length varied in relation to water level and scheduling. Maintaining a high watering level during pod filling or flowering resulted in highest seed yields. Plant height was significantly reduced with decreasing water levels for constant water regimes At variable water regimes taller plants were evident when water was high during flowering to early pod filling.

Transient analysis of phreatic aquifers lying between two open channels

The unsteady state flow of water through an unconfined aquifer can be represented by the Boussinesq equation. The nonlinear term involving the highest derivative in this equation was approximated by a linear term, and the resulting approximate Bossinesq equation was linearized to a Fokker‐Planck equation by the method of functional transformation. Solutions to the problem of groundwater flow through phreatic aquifers lying between (1) constant water level boundaries and (2) variable water level boundaries were obtained from the general solution of the Fokker‐Planck equation for constant and variable rates of recharge and withdrawal. Variable rates of recharge and withdrawal were approximated by periodic step functions which represented two different rates, one each for both rainy and dry seasons. Variable water levels in the open channels were approximated by step functions, and the initial condition was represented by straight line segments. An analytical solution of the approximate Boussinesq equation was compared with the finite difference solution of the original Boussinesq equation. The difference between the two solutions was almost negligible, and therefore the applicability of the analytical solutions to groundwater resource management was established. The effect of variable water level boundaries on groundwater dynamics was studied by performing a sample calculation.

Reservoir Mechanism

The physical problem dealt with in this article is the unsteady groundwater flow in an isotropic, nonhomogenous aquifer of limited horizontal extent and arbitrary boundary shape. The unsteady ground-water level is described by a differential equation which is solved by the Galerkin finite element method, combined with orthogonal eigenfunctions. Unlike many numerical procedures the physical properties of the aquifer are not lost. Boundary conditions are provided by nature in the form of watertight rocks, rivers, lakes or any kind of constant water level in hydraulic contact with the aquifer, or given boundary inflow or outflow.

The use of Stigeoclonium subsecundum (chlorophyceae) as a bioassay organism II. The use of stigeometers in a continuous flow system

A continuous flow algal bioassay system using Stigeoclonium subsecundum attached to glass slides (stigeometers) was developed. An artificial stream was constructed so that the algal biomass on each stigeometer could be increased to a specific level prior to the bioassay. Battery jars, in which the stigeometers were placed on vertical glass rods were used for the bioassay. A continuous flow of water entered the battery jar through a stopcock and left by means of a siphon outlet system which also maintained a constant water level in the battery jar. A paddle located in the center of the battery jar and connected to a variable speed motor produced a current of water over the stigeometers. Dechlorinated tap water was used to maintain the growth of the attached algae in both the artificial stream and in the battery jars. A one week limit was set as the maximum length of time a bioassay could be conducted. This was due to the extremely fast growth of the algal mat in the battery jars exposed to a current of 0.75 m s −1. Zoospores released by the attached filaments and sampled by concentrating the battery jar effluent also because difficult to count after one week. The flexibility of this type of algal bioassay system was also discussed.

Inexpensive Constant Water Level Device for Flow-Through Aquariums

Inexpensive Constant Water Level Device for Flow-Through Aquariums

Factors influencing clustering in the intertidal snail Cerithium moniliferum

The snail Cerithium moniliferum Kiener at Heron Island (southern end of the Great Barrier Reef) clusters at outgoing tide and disperses at incoming tide. In containers with a constant water level, but exposed to the normal day and night rhythm, the snails cluster and disperse rhythmically for up to several days. Graphical simulation and spectral analysis, preceded by first difference filtering, showed two components, one corresponding to the tidal, and the other to the diurnal rhythm. Snails kept under continuous light also exhibit a two-component rhythm of clustering and dispersal. In containers with high (40 cm) water level and under continuous light or normal day and night rhythm, the two-component rhythm may—for some unknown reason—be replaced by long fluctuations of dispersal, with clustering occurring in the afternoon only in snails kept under normal alternation of day and night. Snails kept for 24 h in dryness prior to putting them into containers with water, remain clustered (sometimes with an initial dispersal “shock”) for a long time, with subsequent slow fluctuations of clustering and dispersal, probably induced by the light conditions. Factors contributing to clustering and dispersal are: (1) increased rate of dropping from container walls at outgoing tide; (2) lack of locomotory activity at low tide; (3) negative geotaxis at incoming tide; (4) positive geotaxis at outgoing tide; (5) attraction of snails by other snails (positive chemotaxis) throughout the rhythm. Sudden exposure to light increases the rate of dropping from the container walls and may be a contributing factor to stronger clustering during the day. Factors 1–4 show endogenous periodicities.

Effects of root medium and watering on transpiration, growth and development of glasshouse crops

The effect of adding clay, moisture and the compaction on the physical properties of peat as well as the effect on transpiration and growth of tomato plants were investigated during short term laboratory experiments. The effect of 6, 12, and 20 cm peat height in beds with constand water level were investigated in a 5 months tomato crop. Admixture of clay reduced the porosity of the peat. Adding the clay at moderate pressure (10, 100 g cm-2) decreased the amount of large pores (equivalent to pores emptied at pF 2.0) and to an increase of smaller pores (equivalent to pores emptied in the pF intervals 2.0–4.2). The reduction in the amount of large pores was greater with admixture of montmorillonite than with a soil clay. An increase of the soil clay content from 50 to 70 per cent had an insignificant effect on the amount of large pores. Increasing the moisture content of the peat resulted in that fewer pores were emptied at pF 1.3. At a pressure of 1000 g cm-2 the decrease of large pores was more marked for pure peat than for mixtures of peat and soil clay. Increasing the pressures from 10 to 100 g cm-2 had only a slight effect. For a mixture of peat and montmorillonite a linear relationship was found between the clay content and bulk density, while a curvilinear relationship existed for a mixture of peat and soil clay. In short term laboratory experiments with tomato seedlings transpiration and growth rate were at a maximum at a pF equivalent to 20–30 per cent airfilled pores. In a glasshouse experiment with tomatoes an increase was recorded in yield, size of fruit, leaf area and total dry matter production with increasing peat heights above a constant water level. The experimental results showed that porous root media, such as peat, should be treated to counteract the existence of zones having sub-optimal air content by use of sub-irrigation. re]19730227

Ein naturgemäßes Verfahren zur Bekämpfung von Stechmücken (Diptera: Culicidae)1

AbstractA natural method for controlling mosquitoes (Diptera, Culicidae). The application of “poisonous substances” in pest control means a measure contradicting natural conditions. However, the conversion of the natural environment into a human environment — a process which cannot be stopped — would also have to be counted under this heading unless it will be possible to recall, or develop intentionally, measures for landscape development, for shaping the human environment as such that eventually will not have destructive but rather constructive effect, i.e. that take effect within the context of life. This means that the living conditions of the pests concerned will have to be designed to be less favourable for them while a sound landscape structure is maintained. For all long time, drainage has been considered as one of the most elegant measures to resolve mosquito problems. Drainage can be formed, however, only in situations where, due to human interference, the groundwater level has not yet decreased to a critical degree. And where could we still afford a reduction beyond the present level? The life of mosquitoes is closely interrelated with water levels in their habitat. Together with the hydrologic conditions of a given region which in turn depend on climate, a superordinate entity is formed. In this case, control of a mass development of mosquitoes as a pest that does not affect the environment, is achieved by a corresponding adjustment of hydrologie conditions. A uniform water supply to mosquito breeding areas and maintenance of an approximately constant water level over the year will eliminate the risk of a mass development of mosquitoes of the genus Aëdes meaning pests at our geographical latitude, because flooding (which cannot take place any more) will be required for the eggs deposited at dry sites; otherwise, the larvae which are aquatic could not hatch.

RESERVOIR MECHANISM

The physical problem dealt with in this article is the unsteady ground-water flow in an aquifer of limited horizontal extent and arbitrary boundary shape. The unsteady ground-water level is described by a differential equation, the solution of which includes the solution of an eigen-value problem by a numerical method. Boundary conditions are provided by nature in the form of watertight rocks, rivers, lakes or any kind of constant water level in hydraulic contact with the aquifer. The run-off is found to behave as a sum of flows through infinitely many linear reservoirs, corresponding to the eigen-functions. The resulting equations for ground-water level and run-off discharge are sums of convolution integrals of the infiltration, an easy process to handle in a digital computer. Finally, the mathematical model derived is used to analyse the inflow into a water reservoir in Iceland from a nearby lava field, and the runoff is compared with flow data.