Effects Of Water Level Variations Research Articles

Impact of Water Level Variation on Mechanical Properties of Porous Concrete

This paper investigates porous concrete and the influence of water level variations and porosity on the mechanical, physical, and hydraulic properties of porous concrete. The effect of different void percentages and various water levels on the properties of porous concrete was studied. Fabricated specimens with targeted porosities of 20% and 25% were subjected to a series of tests to evaluate their compressive strength, hydraulic conductivity (permeability), and porosity. The permeability of the specimens was assessed using a falling head permeameter to ensure effective water percolation. Porosity was quantified through a volumetric method, providing insights into void content. Both cubical and cylindrical specimens were used for all tests, along with compression tests under both air-dried and oven-dried conditions. The results showed that the maximum compressive strength occurred under oven-dried conditions for both cubical (7.05 MPa, 5.58 MPa) and cylindrical (8.36 MPa, 4.81 MPa) specimens, with 20% and 25% porosities, respectively. The compressive strength was found to be low in air-dried samples and increased with higher water levels, peaking at the 40% water level. Furthermore, the porosity exhibited a significant correlation with the reduction in density, affecting the mechanical properties. For the cylindrical and cubical samples, the dry density decreased by 16.03 kg/m3 and 20.85 kg/m3 and the permeability increased by 0.41 mm/s and 0.84 mm/s, respectively, for every 1% increase in porosity. The results showcased the effect of water level variation on porous concrete properties as well as its promising ability to infiltrate water. This promotes the development of sustainable pavement systems by minimizing surface runoff and aiding groundwater recharge.

Centrifuge Model Test Study on the Mutual Effect of Water Level Variation and Excavation on the Deformation and Failure of Slopes

The stability level and deformation characteristics of slopes are influenced by the mutual effect of various loads. Slopes often experience a coupling application of water level variation and excavation. A series of centrifuge model tests were carried out to observe the response of slopes under different sequences of water level variation and excavation. An image-based measurement system is used to measure the full displacement field of slopes, analyze the failure sequence of tests, and clarify the failure mechanism of slopes under different sequences. The loading sequence significantly influences the deformation and failure characteristics of the slope. It has been proven that slip surfaces form from the bottom to the top of slopes. The safety limit of the slope is greater under the water level variation-excavation sequence than under the opposite sequence. The slope deformation appears in a limited region that expands during the test. The influence mechanism of water level variation is analyzed, and it is found that water level variation increases the deformation in an area near the slope surface under excavation conditions. The failure mechanism of the slope under excavation and water level variation can be illustrated by significant coupling processes of deformation localization and local failure. The inversion of the loading sequence changes the location of deformation localization and thus induces variation in the position of the slip surface.

Effects of water level variations on survival, morphological phenotype and responsiveness of tadpoles to phytohemagglutinin

To investigate the responses of morphological and physiological characteristics in tadpoles of Pelophylax nigromaculatus to various water levels, a total of 480 tadpoles with similar sizes were treated with rapid, moderate and slow desiccation. Both the metamorphosis duration and average metamorphosis survival rate of specific developmental stages were counted. Their body and internal organ sizes, as well as the responsiveness to phytohemagglutinin (PHA-P) of froglets were measured after complete metamorphosis. The results showed that the metamorphosis duration of tadpoles in the control group was the longest. The average metamorphosis survival rate of different treatment groups ranged from 72.5% to 90.8%, which was the highest in the control group and the lowest in the rapid desiccation group. Body weight (BW) and body length (BL) of froglets in control and slow desiccation groups were significantly higher than those of moderate or rapid desiccation groups. Body width, ratio of BW to BL, carcass wet weight and the wet weight index of lung and fat body were the lowest in rapid desiccation group. There was no significant difference in the wet weight index of heart, spleen, kidneys and digestive organs, as well as the length index of different segments of whole digestive tract between groups. The maximal response value of froglets to PHA-P appeared at 3 h after injection in different treatments, which was significantly higher in moderate and slow desiccation groups than the control group. There was no significant difference between rapid desiccation group and any other groups. The tadpoles of P. nigromaculatus might accelerate the metamorphosis developmental process to cope with desiccation stress, accompanying with decreased atrophic body size and weakened cell-mediated immunity, which would harm tadpoles to successfully land.

Simulation of the water level influence on the difference within the water-tube tiltmeter in Shuangyang Lake

This article analyzes the relationship between the water level and the water-tube tilting in Shuangyang lake, based on the differential deformation features reflected by the NS and EW components of the water-tube tiltmeter. The results show a good spatiotemporal consistency between the variation of water level and the NS tilt component, which is considered to be affected by the magnitude and duration of the water level variation in Shuangyang Lake. The article uses Landsat remote sensing image data to extract the water boundary of Shuangyang Lake, and takes advantage of the finite element numerical simulation method to build three-dimensional models for different geological structural conditions of the Shuangyang seismostation. The simulation results show that when the underground medium is granite, the effect of water level variation on the vertical displacement of the surface is non-directional. With a 50-m soil layer in Model 2, the simulated NS tilt variation is equivalent to the actual observed water-tube tiltmeter NS component when the water level variation is 0.44 m and 0.8m. When the variation of water level reaches 2.0m, the simulation result of the NS component is 79.6 ​ms, which is slightly larger than the observed result of 60.32 ​ms. However, the simulation results show that the variation of the EW component is significantly smaller than that of the NS one. Due to the fact that the Shuangyang lake is long in the NS direction and short in the EW direction, the existence of the soil layer tends to generate ground deformation along the NS direction in the vicinity of the lake after the increase of water level, thereby resulting in the difference of the ground deformation in the two directions.

Long-term hydrogeophysical monitoring of the internal conditions of river levees

To evaluate the vulnerability of the earthen levee of an irrigation canal in San Giacomo delle Segnate, Italy, a customized electrical resistivity tomography (ERT) monitoring system was installed in September 2015 and has been continuously operating since then. Thanks to a meteorological station deployed at the study site, we could investigate the relationship between the inverted resistivity values and different parameters, namely air temperature, rainfall and water level in the canal. Air temperature seems to have a minor but not negligible influence on resistivity variations, especially at shallow depth. A model of soil temperature versus depth was used to correct resistivity sections for air temperature variations through the different seasons. Changes of the water level in the canal and rainfall significantly affect measured resistivity values. At the study site, the most important variations of resistivity are related to saturation and dewatering processes in the irrigation periods. Although we explored the effect of drawdown procedures on resistivity data, this process, causing rapid variations of resistivity values, is still not completely understood because the canal is rapidly emptied during rainfall events. Therefore, the effect of variations of the water level in the canal on levee resistivity cannot be distinguished from the effect of rainfalls. To study the effect of water level variations alone, we considered the beginning of the irrigation period when the dry canal is gradually filled and we observed a smooth trend of resistivity changes. The effect of rainfall on the data was studied during different periods of the year and at different depths of the levee so that the resistivity variations could be evaluated under different conditions. To convert the inverted resistivity sections into water content maps, an empirical and site-dependent relationship between resistivity and water content was obtained using core samples. Water content data can then be used for the implementation of stability analysis using custom modeling. This study introduces an efficient technique to monitor earthen levees and to control the evolution of seepage and water saturation in pseudo-real time. Such a technique can be exploited by Public Administrations to reduce hydrogeological risks significantly.

A practical scheme of vibration monitoring and modal analysis for caisson breakwater

In this study, a practical vibration analysis approach to obtain the dynamic characteristics of an in-situ caisson breakwater under the ambient wave load is presented. Firstly, a scheme of vibration monitoring and modal analysis is designed for the caisson breakwater. The limits of vibration monitoring on the caisson system is examined based on sensor placement and excitation source. An output-only modal analysis approach which combines the time-domain stochastic subspace identification method and the frequency domain decomposition method is designed to estimate modal parameters from wave-induced ambient vibration signals. Secondly, in-situ tests on a real caisson breakwater are described. Acceleration signals recorded under ambient wave-induced excitation are experimentally analyzed for a few caisson units under sea-level variation. Finally, experimental modal analyses are performed on the measured acceleration signals to evaluate the practicality of the proposed scheme. The numerical modal analysis of the caisson-foundation system was also conducted to support the experimental mode identification result. Relative modal responses of three adjacent caisson units are analyzed to estimate relative differences in dynamic characteristics due to their structural conditions. Also, the effect of water-level variation on modal parameters such as natural frequencies, modal damping and mode shapes is analyzed from the in-situ vibration records of a single caisson unit.

Lateral variability of subtidal flow at the mid‐reaches of a macrotidal estuary

AbstractTransverse variations of tidal and subtidal flow were investigated in a macrotidal and convergent estuary. This was accomplished by combining data analysis of current velocities and water density with numerical modeling at the mid‐reaches of the Gironde Estuary (France). Nonlinear mechanisms responsible for overtide generation and hence subtidal flows were found to vary across the estuary and from neap to spring tides. Subtidal flows were driven by a combination of internal asymmetry, tidal advective accelerations, nonlinear effects of water level variations, quadratic friction, and river discharge. The quarter‐diurnal overtide band (D4) in the flow was generated by internal asymmetry and tidal advective accelerations during neap tide. The ratio of quarter‐diurnal to squared semidiurnal bands (D4/D22) was largest (>0.3) in sections of the channel showing subtidal outflow. River discharge increased from neap to spring tides causing a subsequent increase of seaward subtidal currents. During spring tide, D4 was generated by tidal advective accelerations and quadratic friction combined with river discharge, rather than by internal asymmetry. The sixth‐diurnal overtide (D6) in the flow was comparable to D4 for both neap and spring tides. Largest D6/D23 ratios were found in the shallowest cross‐channel locations during both neap and spring tides.

Effects of salinity and wet–dry treatments on C and N dynamics in coastal-forested wetland soils: Implications of sea level rise

Forested wetlands dominated by baldcypress (Taxodium distichum) and water tupelo (Nyssa aquatica) are commonly found in coastal regions of the southeastern United States. Global climate change and in particular sea level rise will alter the frequency and magnitude of wet/dry periods and salinity levels in these ecosystems. Soil microcosm experiments were set up to identify the effects of water level variations (0.4–3.0 g-water g-soil−1) and salinity changes (0, 1 and 5 ppt of NaCl) on greenhouse gas emissions (CH4, CO2, and N2O) and dissolved organic carbon (DOC) characteristics from forested wetland soils. Our results indicate that, the effect of water level was much greater than salt intrusion on C and N cycling. Wet–dry treatments significantly decreased DOC production and total CH4-C loss, aromatic and humic-like substance compounds in DOC were increased in both flooding and wet–dry treatments after 60-d incubation. The molecular weight (MW) of DOC, as indicated by E2/E3 ratio and spectral slope, after flooding treatments was higher than that in wet–dry treatments. A first order kinetic model showed there was a positive linear correlation (r2 = 0.73) between CO2 emission rate and DOC concentration which indicated that CO2 was mainly generated from DOC. An exponential kinetic model was applied to describe the correlation between CH4 emission rate and DOC concentration (r2 = 0.41). This study demonstrates that an increase in salinity, and in particular variations in wet–dry cycles, will lead to changes in the formation of climate-relevant greenhouse gases, such as CH4, CO2, and N2O.

Investigating effect of water level variation and surface tension crack on riverbank stability

During high flow season, the rise and fall of river water level could induce riverbank instability and threaten structural safety of flood-protection facilities on floodplains. Through a flume experiment, this paper investigates the influences of three factors (namely, drawdown rate of river stage, initial water elevation, and riverbank slope angle) on riverbank stability due to the fall of river water level. From the laboratory experiments it was observed that tension crack appeared in all riverbank failure cases and all failure patterns were of planar type. Moreover, this paper presents a riverbank stability analysis model that explicitly incorporates the integral effect of all forces acting upon the failure plane and tension crack. The prediction accuracy of the proposed model is examined by using experimental data obtained in this study and field data of the Hotophia Creek in the USA and the Sieve River in Italy. A comparison of model simulation results with and without considering tension crack clearly indicates the importance and necessity of including tension crack for achieving good accuracy in riverbank stability simulations. For practical application of the improved riverbank stability model, two empirical formulas for estimating tension crack location and failure plane angle were examined and modified to enhance their appropriateness in riverbank stability simulation. Finally, the improved model with the modified empirical formulas was verified to show its good prediction in riverbank stability analysis.

Effects of Toshka Pumping Station Operations on Power Quality and Stability of Electrical Grid

Toshka is a large water pumping stations in Egypt. This station contains 21 units (18+3 Extentions) each 12MW. At a full capacity the full power consumptions can reach 200MW. The electrical feeding system for the stations contains; transformer, substations and Overhead transmission line (its long 300km), so the operations of the stations causes some problem for the electrical grid due to large value of power consumptions. In this paper, some problems were studied during the operations of the station. Effect of starting time on the station running and current consuming were studied. Also the effect of water level variations on the suctions side in Nasser Lake, speed changing, and power quality of the grid on the power consumptions. It was focused on the voltage and current variations, and the flicker occurred during the station operation. Finally the effects of number of harmonic filters used depending on the power rating of the unit, and effective short circuit ratio (ESCR) values on the stability of the electrical grid during the full load operations. The analyses of the results are obtained from actual measurement on the stations using modern power quality analyzers during different cases of operation are explained. This study is more useful for studying the problem occurred on the electrical grid during running of Toshka Stations, as it’s a large station in Egypt and has special design, at different cases and conditions of operation.

Long-term assessment of best cathode position to maximise microbial fuel cell performance in horizontal subsurface flow constructed wetlands

The cathode of microbial fuel cells (MFCs) implemented in constructed wetlands (CWs) is generally set in close contact with water surface to provide a rich oxygen environment. However, water level variations caused by plants evapotranspiration in CWs might decrease MFC performance by limiting oxygen transfer to the cathode. Main objective of this work was to quantify the effect of water level variation on MFC performance implemented in HSSF CW. For the purpose of this work two MFCs were implemented within a HSSF CW pilot plant fed with primary treated domestic wastewater. Cell voltage (Ecell) and the relative distance between the cathode and the water level were recorded for one year. Results showed that Ecell was greatly influenced by the relative distance between the cathode and the water level, giving an optimal cathode position of about 1 to 2cm above water level. Both water level variation and Ecell were daily and seasonal dependent, showing a pronounced day/night variation during warm periods and showing almost no daily variation during cold periods. Energy production under pronounced daily water level variation was 40% lower (80±56mWh/m2·day) than under low water level variation (131±61mWh/m2·day). Main conclusion of the present work is that of the performance of MFC implemented in HSSF CW is highly dependent on plants evapotranspiration. Therefore, MFC that are to be implemented in CWs shall be designed to be able to cope with pronounced water level variations.

Water level effect on herbaceous plant assemblages at an artificial reservoir-Lago Azul State Park, Southern Brazil.

This study presents the effect of water level variation on the assemblages of herbaceous species in Mourão I Reservoir, Lago Azul State Park, Southern Brazil. The structure and distribution of populations was examined in February (dry period) and April (rainy period), 2011, in two transects. These transects started at the forest edge towards the center of the lake. The end of the transect coincided with the end of the plants within the lake. On every two meters along of the transects we sampled a wooden square of 0.25 m(2) for species biomass analysis.The macrophyte stand was composed entirely of emergent species. Considering the periods, most species were less frequent in the rainy period (April), but Ipomea ramosissima (Poir.) Choisy, Commelina nudiflora L., Eleocharis acuntagula (Roxb.) Schult. and Verbena litorales (Kunth.) had their frequency increased during this period, probably due to their resistance. The influence of flood as measured by the NMDS point out that both before and after the flood, there are plots with distinct compositions and biomass. The water level variation affects the dynamics of plant composition and structure in marginal areas of the Reservoir.

Effects of groundwater level variations on the nitrate content of groundwater: a case study in Luoyang area, China

Most researchers usually adopt laboratory experimental methods when studying the effects of water level variations on the concentrations of pollutants. In this study, the data from routine monitoring sites in the city of Luoyang, China, are collected and analyzed to verify the results of previous laboratory experiments and to examine whether variations in the water level affect the concentration of pollutants in different locations, particularly that of nitrates. Statistical studies conducted between 2007 and 2011 show a significant variation in the groundwater depth in the Luoyang area. This depth variation clearly affected the groundwater environment in the soil system. This study uses field data to investigate the effects of water table fluctuation on the nitrate content of groundwater. Hydrogeological information and land management data are collected from five monitoring points in Luoyang. The significance of and correlation between the environmental indicators of groundwater depth and soil–water systems are then analyzed using SPSS and Origin software. The results show that the redox potential (Eh) and nitrate nitrogen content are strongly correlated with groundwater depth. Significantly negative correlations were found between nitrate nitrogen and ammonium nitrogen concentration, between Ehand ammonium nitrogen concentration, and between pH and nitrate nitrogen concentration. These results indicate that water table fluctuation affects the soil–water physicochemical properties and further exerts a significant effect on nitrate movement across soil sola.

Water level and fish-mediated cascading effects on the microbial community in eutrophic warm shallow lakes: a mesocosm experiment

Information on the effects of water level changes on microbial planktonic communities in lakes is limited but vital for understanding ecosystem dynamics in Mediterranean lakes subjected to major intra- and inter-annual variations in water level. We performed an in situ mesocosm experiment in an eutrophic Turkish lake at two different depths crossed with presence/absence of fish in order to explore the effects of water level variations and the role of top-down regulation at contrasting depths. Strong effects of fish were found on zooplankton, weakening through the food chain to ciliates, HNF and bacterioplankton, whereas the effect of water level variations was overall modest. Presence of fish resulted in lower biomass of zooplankton and higher biomasses of phytoplankton, ciliates and total plankton. The cascading effects of fish were strongest in the shallow mesocosms as evidenced by a lower zooplankton contribution to total plankton biomass and lower zooplankton:ciliate and HNF:bacteria biomass ratios. Our results suggest that a lowering of the water level in warm shallow lakes will enhance the contribution of bacteria, HNF and ciliates to the plankton biomass, likely due to increased density of submerged macrophytes (less phytoplankton); this effect will, however, be less pronounced in the presence of fish.

Water level effects on breaking wave setup for Pacific Island fringing reefs

AbstractThe effects of water level variations on breaking wave setup over fringing reefs are assessed using field measurements obtained at three study sites in the Republic of the Marshall Islands and the Mariana Islands in the western tropical Pacific Ocean. At each site, reef flat setup varies over the tidal range with weaker setup at high tide and stronger setup at low tide for a given incident wave height. The observed water level dependence is interpreted in the context of radiation stress gradients specified by an idealized point break model generalized for nonnormally incident waves. The tidally varying setup is due in part to depth‐limited wave heights on the reef flat, as anticipated from previous reef studies, but also to tidally dependent breaking on the reef face. The tidal dependence of the breaking is interpreted in the context of the point break model in terms of a tidally varying wave height to water depth ratio at breaking. Implications for predictions of wave‐driven setup at reef‐fringed island shorelines are discussed.

Time-History Response Analysis of Jacket Offshore Platform due to Water Level Variation and Safety of Structural Members

Jacket structures are designed for a specific water level (LAT). One of the important issues about these structures is the water level rise. For example, the level of water in the Caspian Sea has risen by 2.5m in the last fifteen years and is continuing to rise. The aim of this study is to investigate the behavior of one typical shallow or medium water jacket platform (a four-leg steel jacket platform in 55m water depth) under water level rise and to evaluate utilization factor of different element at different elevations. In this paper the finite element method (ANSYS) was used for the purpose of modeling of the structure. This paper discusses the effect of water level variation acting on the jacket structure and illustrates subsequent results of the stress utilization within the structure elements. The results of time history analysis show that the initial design water depth (before water level rise) has a basic role on the subsequent behavior of structural elements.

Comparative effects of water level variations on growth characteristics of Myriophyllum aquaticum

Wersal RM & Madsen JD (2011). Comparative effects of water level variations on growth characteristics of Myriophyllum aquaticum. Weed Research 51, 386–393.Summary Myriophyllum aquaticum is a non‐native aquatic plant that has invaded a range of habitats in the United States and Europe. Myriophyllum aquaticum reduces native species richness at local scales, water quality, habitat quality for fish and wildlife and impacts on human uses. Despite the submersed leaf form, M. aquaticum is not typically a weed problem as water level increases, although little data exist describing basic biological and ecological mechanisms affecting growth. The objective of this study was to quantify changes in M. aquaticum growth as water levels increase from 0 (representing shoreline habitat) to 137 cm under controlled mesocosm conditions. Total biomass at 0 cm was 96% greater than plants grown at a depth of 137 cm. Biomass of emergent shoots, stolons and roots were also greater when M. aquaticum was grown at the 0 cm water level. Submersed shoot biomass was on average 99% greater between 37 and 77 cm. Submersed shoots comprised a small fraction, 0.1–12% of total biomass, depending on water level. Total plant length was 25% greater when plants were grown at water levels from 0 to 77 cm, compared with plants grown at 97, 117 or 137 cm. Nuisance growth is dependent upon plants emerging from the water column; as water levels increase, this becomes more difficult for plants, as a result of the reduced photosynthetic ability of submersed leaves. These results can be used to identify optimal areas for M. aquaticum growth and possibly predict areas of new infestations.

The effect of water level variations on production-destruction processes in the Mozhaisk Reservoir

The results of many-year studies of production destruction processes in the Mozhaisk Reservoir are used to examine their specific features in extremely dry years. It is shown that the processes of organic matter formation and destruction in the reservoir are more active when water level is low. Variations in the intensity of production-destruction processes in all phases of synoptic cycle are analyzed (during cooling, cold, heating, and warm). Changes in weather conditions are shown to be accompanied by phytocenosis restructuring. Fine-cell phytoplankton forms are shown to dominate in phytocenosis composition when water level in the reservoir is extremely low.

Spatial variations of tidal water level and their impact on the exposure patterns of tidal land on the central Jiangsu coast

The exposed area of intertidal zone varies with tidal water level changes. If intercomparisons of satellite images are adopted as a method to determine geomorphological changes of the intertidal zone in response to accretion or erosion processes, then the effect of water level variations must be evaluated. In this study, two Landsat TM images overpassing the central Jiangsu coastal waters on 2 January and 7 March 2002, respectively, were treated by the changing detection analysis using Image Differencing and Post-classification Comparison. The simultaneous tide level data from four tide gauge stations along the coast were used for displaying the spatial variations of water levels and determining the elevations of waterlines. The results show that the spatial variations of water levels are highly significant in the central Jiangsu coastal waters. The huge differences of tidal land exposure patterns between the two imaging times are related mainly to the spatial variations of tidal water levels, which are controlled by the differences in tidal phases for different imaging times and the spatial variations of water level over the study area at each imaging time. Under complex tidal conditions, e.g., those of the central Jiangsu coastal waters, the tide-surge model should be used to eliminate effectively the effects of water level variations on remote sensing interpretation of geomorphological changes in the intertidal zone.

Field Observation of Infiltration Flow in a Sand Spit at the Mouth of Nanakita River

Development of sand spit can frequently be observed at river mouths in Japan due to predominant action of waves as compared with flushing by river discharge. Progress of river mouth closure may cause reduction in flow through a river opening, resulting in increase in infiltration flow through a sand spit at a river entrance. However, there have been quite few investigation on this type of flow, although there have been many on coastal aquifer. In the present study, results of field observation of infiltration flow in a sand spit at the mouth of Nanakita River are described. Comprehensive numerical simulation is also performed to investigate the effect of water level variation in the mouth on the strength of infiltration flow.