Degree Of Submergence Research Articles

An Experimental Study on the Effect of Distance and Sheltering Area of a Group of Linearly Arranged Sacrificial Piles on Reducing Local Scour around a Circular Bridge Pier under Clear-Water Conditions

One of the major problems associated with bridge piers is ensuring their safety against local scouring caused by the erosive action of flow. Numerous countermeasures have been developed and tested to solve this problem, among which sacrificial piles are highly recognized due to their high performance, economy, durability, and ease of construction. Several factors affect the performance of sacrificial piles, such as their number, size, degree of submergence, and geometric arrangement parameters. In this study, the performance of a group of linearly arranged cylindrical sacrificial piles in reducing local scour around a circular bridge pier was investigated by varying the number of piles (or sheltering area) and distance between piles and the pier under clear-water conditions. Three values of distance between piles and the pier and three values of sheltering area (or number of piles) were tested. The efficiencies of sacrificial piles in different configurations were presented in terms of the percentage reduction in maximum scour depth at an unprotected pier under the same hydraulic conditions. The results of this experiment show that when linearly arranged sacrificial piles are placed close to the pier (at distance D; D is the pier diameter), an increase in the number of piles (or sheltered area) results in an increased scour depth, and when placed far from the pier (2D and 3D), an increase in the number of piles results in a decrease in scour depth around the pier. In addition, for 40% and 60% sheltering conditions, scour depth increased with an increase in the spacing between piles and the pier, while for 80% sheltering conditions, optimum protection was observed at a distance of 2D. Overall, two piles placed at distance D provided optimum protection with a scour depth reduction of 41.6%, while minimum protection was recorded when the same were placed at a spacing of 3D from the pier (25.5%).

Determination of Hydraulic Roughness Coefficients of Some Vegetated Species in Awka, Nigeria

In this study, selected types of grasses were studied to determine their hydraulic roughness coefficient and to select the most suitable grass for erosion control. The experiments were performed in twelve trapezoidal open channels measuring 5 m x 0.12 m x 0.03 m at different flow depths (0.001m, 0.002m, 0.003m, 0.004m and 0.005m) and at varying bed slope (0.2%, 0.3%, and 0.4%). Overall, Bahama grass showed the highest Manning’s n-value due to its deep root system and creeping nature. For each slope, the degree of submergence, Reynolds number, and flow depth increases as Manning’s n decreases. As the flow depth increases, the Reynolds number increased while the drag coefficient, Cd decreases.

Hydraulic characteristics of the Parshall flume entrance wingwall: Numerical simulation and test

AbstractThe Parshall flume is a common open channel water‐measuring facility that is widely used in hydrological monitoring, agricultural irrigation and municipal water supply. In engineering applications, there is no clear requirement for the form of the wingwalls connecting the channel and Parshall flume. Therefore, it has different effects on flow measurement accuracy, flow velocity distribution and hydraulic characteristics. To standardize its construction requirements, a wingwall form with high flow measurement accuracy is evaluated. Computational fluid dynamics (CFD) numerical simulations and hydraulic experiments have shown the influence of different wingwalls on hydraulic characteristics. The governing test parameters include wingwall forms, incoming flow and degree of submergence. By measuring water surface fluctuation, streamline distribution and flow measurement error, the effects of different wingwall forms on flow measurement accuracy and hydraulic characteristics were evaluated. The results showed that the fluctuation of the water surface is affected by the boundary conditions. Layout I has the highest flow measurement accuracy and has an arc‐shaped wingwall with a radius of 1.5 m. By comparing the results of the tests and simulations, the average error is 3%. The results showed that the hydrodynamic model of the Parshall flume can provide a theoretical basis for the design and development of the measurement structure in the future.

Flow and wake characteristics associated with large wood to inform river restoration

Wood is an integral part of a river ecosystem and the number of restoration projects using log placements is increasing. Physical model tests were used to explore how the wood position and submergence level (discharge) affect wake structure, and hence the resulting habitat. We observed a von-Kármán vortex street (VS) for emergent logs placed at the channel center, while no VS formed for submerged logs, because the flow entering the wake from above the log (sweeping flow) inhibited VS formation. As a result, emergent logs placed at the channel center resulted in ten times higher turbulent kinetic energy compared to submerged logs. In addition, both spatial variation in time-mean velocity and turbulence level increased with increasing log length and decreasing submergence level. Submerged logs and logs placed at the channel side created a greater velocity deficit and a longer recirculation zone, both of which can increase the residence time in the wake and deposition of organic matter and nutrients. The results demonstrate that variation in log size and degree of submergence can be used as a tool to vary habitat suitability for different fish preferences. To maximize habitat diversity in rivers, we suggest a diverse large wood placement.

Effect of various flow, sediment and geometrical parameters on partially or fully submerged deck scour

The effect of various parameters of flow, sediment and geometric features of the bridge on the depth and shape of the scour hole occurred underneath a bridge deck model without a pier was investigated by a series of experiments conducted in a flume under partially and fully submerged flow and clear water conditions. The experiments were performed with factors such as approach flow depth, discharge, sediment size, degree of submergence, girder location and depth. A total of 112 experiments were conducted for both partially and fully submerged flow conditions. The experimental data showed that the partially submerged flow increased the maximum depth of scour hole and affected the shape of the scour hole more when compared to the fully submerged flow. It was also noted that parameters that directly affected flow structure in the bridge opening such as girder height might significantly increase the maximum depth of scour hole. Effect of the distance between a single girder and the bridge edge was also tested by using three different girder location and it was found that as the distance increased, the depth of the scour hole decreased and the location of the maximum scour depth moved with the girder to where the contraction in the flow area occurred.

Pressure flow and weir scour beneath a bridge deck

In this study, a series of experiments in a flume was conducted to investigate the maximum scour hole depth that occurred due to the vertical contraction of the flow underneath a bridge deck model without a pier. The bridge model was tested under pressurized and weir type of flows governed by clear water conditions. Various parameters of flow, sediment, and geometric features of the bridge, such as approach flow depth, discharge, sediment size, girder depth and degree of submergence were varied to investigate their effects on the maximum depth of scour hole. A total of 102 experiments were conducted and two empirical equations were developed separately for pressure and weir flow types with the use of experimental data. Effects of the aforementioned parameters on the scour hole were also analyzed and discussed.

Small unmanned aerial model accuracy for photogrammetrical fluvial bathymetric survey

Fluvial systems offer a challenging and varied environment for topographic survey, displaying a rapidly varying morphology, vegetation assemblage and degree of submergence. Traditionally theodolite or GPS based systems have been used to capture cross-section and breakline based topographic data which has subsequently been interpolated. Advances in survey technology has resulted in an improved ability to capture larger volumes of information with infrared terrestrial and aerial LiDAR systems capturing high density (<0.02 m) point data across terrestrial surfaces. The rise of Structure from Motion (SfM) photogrammetry, coupled with small unmanned aerial vehicles (sUAV), has potential to record elevation data at reach scale sub decimetre density. The approach has the additional advantage over LiDAR of seeing through clear water to capture bed detail, whilst also generating ortho-rectified photographic mosaics of the survey reach. However, data accuracy has yet to be comprehensively assessed. Here we present a survey protocol for sUAV deployment and provide a reach scale comparison between a theodolite and SfM sUAV survey on the River Sprint, Kendal, the River Ehen at Egremont, England and the Afon Elwy, at Llanfair Talhaiarn, Wales. Comparative analysis between theodolite survey and SfM suggest similar accuracy and precision across terrestrial surfaces with error lowest over solid surfaces, increasing with vegetation complexity. Submerged SfM data, captured bed levels generally to within ±0.25 m with only a weak relationship recorded between error and flow depth. Significantly, associated error when linked to channel D50 highlights the ability of unmanned aerial vehicles to capture accurate fluvial data across a range of river biotopes and depths to 2.4 m.

Effect of 2014 massive flood on well water qualities: A case study on Kelantan River basin, Malaysia

AbstractThe effect of physical and biological qualities of wells after submergence was assessed following December 2014 flood in Kelantan. Studies were carried out on a total of 65 wells from 13 stations around Kelantan River basin in which the wells’ water were sampled for pH, total dissolved solid (TDS), turbidity and microbial contamination. About 95% of the well showed to be contaminated, 7 out of 65 samples (11.1%) showed TDS values &gt;400 μS·cm−1; and 19 samples (29.2%) recorded turbidity beyond 7.0 NTU. Statistical non-parametric tests carried out on independent groups showed that the status of well contamination was neither determined by both degree of submergence nor by the geographical location. Also the physico-chemical parameters are independent of flood inundation. However, TDS and turbidity values changed based on geographical location, at p &lt; 0.05. Well from estuary recorded higher TDS (241.2 μS·cm−1 ±159.5 SD) and turbidity (8.04 NTU ± 6.53 SD) compared to those from inner basin (TDS at 156.3 μS·cm−1± 88.9 SD; turbidity at 2.90 NTU ± 2.46 SD), respectively. The flood water had played significant role in the transmission of existing contaminant, and most of the wells were unsafe for drinking. We concluded that the degree of flood submergence does not necessarily determine the severity of the well contamination in Kelantan, but the existing contamination may exacerbate further the potential risk during post flood period.

Assessing methods for estimating roughness coefficient in a vegetated marsh area using Delft3D

A Delft3D-FLOW model was used to simulate tidal flow in Davis pond marsh in Louisiana, USA. The study area is a freshwater marsh consisting of one main channel and floodplain. Vegetation-induced flow resistance greatly influences tidal flow dynamics in the marsh. This study evaluated eight approaches to estimate vegetation roughness, including two constant Manning's n values, four empirical relations for calculating n, and two methods for calculating Chezy's C values originally embedded in the Delft3D model. Simulated results of water surface elevation (WSE) were compared with the corresponding field observation at eleven stream gauges in the study area. We concluded that the roughness coefficient for vegetated area varies with time as flow depth changes. Among the selected empirical relations for the vegetation roughness, the ones accounting for the effect of the vegetation frontal area and the degree of submergence have closely matched the measurements.

Effects of river width changes on flow characteristics based on flume experiment

The rapid changes in flow pattern due to varying channel widths will make significantly impact on the hydraulic structures and evolutions of open channel. To better understand the impact of varying width, a flume experiment with adjustable width and a depth-averaged two-dimension numerical model were used to analyze the variations of flow parameters. Our experimental results showed that flow velocity gradually increased with decreasing water depth in converging region, and decreased with increasing water depth in diverging zones. It was also found that the turbulence intensity laws in three directions were not agreed with the theoretical relationships proposed by Nezu and Nakagawa in 1993 in straight open channel flows. The flow in the channel with varying width may change from the supercritical flow to the subcritical flow as a function of Froude number. Our numerical simulations with different flow rates showed that most of the hydraulic jumps in diverging region were submerged jump and the degree of submergence increased with increasing flow rate in gradual channel transition. When the flow rate increased, the range of supercritical flow rapidly decreased and the flow changed from the supercritical condition to the subcritical condition in diverging sections.

Three-Dimensional Hydrodynamic Simulation of Tidal Flow through a Vegetated Marsh Area

AbstractSimulation of tidal flow in an estuarine marsh area is challenging because of resistance from spatially and temporally varied vegetation. This study simulated the tidal flow in the Davis Pond marsh area near New Orleans, Louisiana, using an open source program. To quantify the time-varying roughness coefficient, four empirical equations for calculating Manning’s roughness coefficient were incorporated into the program in addition to two options offered by the program to calculate the Chezy’s coefficient and one option to use the modified momentum equations and the k−ϵ turbulence model. Results showed that the time-varying roughness coefficient equations accounting for both the degree of submergence and the vegetation frontal area gave the closest matches with the observed data.

Flow adjustment at the leading edge of a submerged aquatic canopy

[1] This paper describes the transition from open channel flow to flow over submerged vegetation using velocity measurements collected with acoustic Doppler velocimetry (ADV) and particle-image velocimetry (PIV). Submerged canopies were constructed from arrays of rigid circular cylinders of height h in water of depth H. Both the canopy density, described by the frontal area per volume (a), and degree of submergence (H/h) were varied. Flow adjustment occurs in three stages. First, velocity begins to decelerate upstream of the canopy, due to a high-pressure region generated at the canopy leading edge, and continues to decelerate within the canopy, due to canopy drag. Rapid flow deceleration within the canopy creates strong vertical flux out through the top of the canopy that extends over a length proportional to the canopy drag length scale, (CDa)−1, with CD being the canopy drag coefficient. Second, a mixing layer develops at the canopy interface, with the stress at the top of the canopy initially increasing, but eventually reaching a constant value. At this point, the flow within the canopy is fully developed. The length scale for mixing-layer development is related to canopy drag (CDa) and the depth ratio (H/h). In the third stage, the boundary layer above the mixing layer adjusts to the channel boundary conditions. A model is developed to predict the adjustment of vertically averaged velocity within the canopy. Measurements confirm that the flow adjustment is not dependent on canopy length.

Flow resistance models for flexible submerged vegetation

Summary This paper investigates the variation of hydraulic roughness parameters with flow depth for submerged flexible vegetation. In an experimental study flexible grass canopies are used to examine the impact of stem height, grass type and degree of submergence on the flow resistance properties. Results reveal that Manning’s n roughness coefficient increases with decreasing flow depth reaching an asymptotic constant at lower levels of vegetation submergence. Data suggest that the value of the constant is dependent on the vegetation height and the vegetation properties. Currently the n - UR method underpredicts the Manning’s n and the data from this study extends the USDA method for lower bed slopes and for smaller UR values. The vegetal drag-Reynolds number model is extended for submerged flexible grass linings of differing heights and types. Similar values of the vegetative characteristic number k are evaluated as from previous studies yet for contrasting vegetation types. The vegetal drag coefficient value was found to be strongly correlated to the vegetation height, and follows a power law relationship. The exponent value was found to be independent of the vegetation characteristics.

Supercritical sewer flows at a combining junction: A model study of the Edworthy trunk junction, Calgary, Alberta

An experimental study on supercritical sewer flows at a junction chamber was conducted using a physical model for the Edworthy trunk sewer in Calgary, Alberta. This model study showed that a junction chamber with a small angle of two combining inflows helps to retain kinetic energy of the flow and reduces the water level in the surcharged chamber, thus avoiding the occurrence of fountains. The behavior of the supercritical junction flow in the chamber was investigated. Transition of flow regimes in the chamber was studied and three flow regimes were identified: regime I features shock waves in open-channel flow in the chamber; regime II is characterized by surcharge flow in the chamber and orifice flow in the outlet pipe; and regime III is associated with pipe-full flow in the outlet pipe following the surcharged chamber. It was found that regime II could be the most critical condition for the consideration of water level in a surcharged chamber. A theoretical analysis of regime II flow was carried out, and the degree of submergence in the chamber can be satisfactorily predicted for given inflow conditions. The effects of a rounded entrance of the outlet pipe and the benching in the junction chamber were also evaluated experimentally. Key words: sewer hydraulics, supercritical flow, energy loss, junction manhole.

Comparative Characterization of the Pigment Complex in Emergent, Floating, and Submerged Leaves of Hydrophytes

The content of chlorophylls (Chls) and carotenoids was studied in the leaves of 42 species of boreal aquatic plants with different degree of submergence (emergent, floating, and submerged) and isopalisade, dorsoventral, and homogenous types of mesophyll structure. Hydrophytes were shown to have a low Chl content (1–2 mg/g fr wt) and low Chls/carotenoids ratio (2.3–3.5) as compared to terrestrial plants. The pigment content per dry wt unit and unit leaf area was dependent on the type of mesophyll structure. It was a consequence of the changes in the parameters of leaf mesophyll structure characterizing the density of photosynthetic elements. In a sequence emergent → floating → submerged forms, the content of Chls and carotenoids decreased, and the photosynthetic capacity decreased due to a reduction in the chloroplast number per unit leaf area. Adaptation of submerged leaves to low illumination and slow CO2 diffusion changed the functional properties of chloroplasts. An increase in the pigment content in the chloroplasts of submerged leaves (7 × 10–9 mg Chl, 2 × 10–9 mg carotenoids) as compared to emergent and floating leaves was accompanied by a decline in the photosynthetic capacity per Chl comprising 1.6 mg CO2/(mg Chl h) versus 3.9 and 3.8 mg CO2/(mg Chl h) in emergent and floating leaves, respectively.

Submergence-induced damage of photosynthetic apparatus in Phragmites australis

Phragmites australis colonises new areas by seedling establishment after drop down of water levels and exposure of mud flats. Seedlings may subsequently be subjected to submergence resulting from fluctuations of the water level. Seedling survival depends on tolerance to total or partial submersion. In particular, the response to short submergence periods may be related to the tolerance of green tissues. Three-month-old plants were partially or totally submerged in tanks for 2–17 days, and subsequently re-exposed to the air. The effects of submergence on photosystem II (PSII) activity and pigment contents and the reversibility of changes were analysed at the level of individual leaves. Pigment contents decreased during submergence and failed to recover following a return to non-submerged conditions. PSII photochemical efficiency was affected by submergence and exhibited varying recovery levels depending on duration and degree of submergence. Emerged leaves of partially submerged plants displayed an increase in both photochemical efficiency in the light adapted state and in pigment content, whereas submerged leaves of the same plants were negatively affected and did not recover. The effects of short-term stress were found to be reversible. Over longer periods, partially submerged reed favoured top emerged leaves at the expense of submerged ones, thus suggesting short-term avoidance of anoxia rather than tolerance.

Multinuclear Magnetic Resonance Analysis of Two Humic Acid Fractions from Lowland Rice Soils

To determine the effects of intensive cropping of tropical lowland rice (Oryza sativa L.) and the associated long-term soil submergence on chemical properties of soil organic matter, we used solid-state 13C and 15N and solution 31P nuclear magnetic resonance (NMR) spectroscopy to analyze the labile mobile humic acid (MHA) and the more recalcitrant calcium humate (CaHA) fractions extracted from a series of soils supporting several long-term field experiments in the Philippines. The soils varied mainly in degree of submergence and cropping intensity, ranging from a rainfed rice field without soil submergence to irrigated double- and triple-cropped fields in which soil remains submerged almost all year long. As reported previously, all analyses associated increasing intensity of rice cropping with larger proportions of less humified material in the MHA and CaHA, such as diester phosphorus (P), amide nitrogen (N), and phenolic carbon (C). We established significant correlations between proportions of various spectral areas as well as between some spectral areas and other humic acid (HA) properties such as visible light absorption and free radical concentration (positive indices of humification) and hydrogen (H) concentration (negative index of humification). For example, spectral proportions of heterocyclic N were positively, and proportions of amide N and phenolic C negatively, correlated with visible light absorption and free radical concentration, and each of these spectral proportions had an opposite sign when correlated with H concentration. The correlations of N-alkyl C proportions were the strongest with these properties and with other functional group proportions.

Multinuclear Magnetic Resonance Analysis of Two Humic Acid Fractions from Lowland Rice Soils

To determine the effects of intensive cropping of tropical lowland rice (Oryza sativa L.) and the associated long-term soil submergence on chemical properties of soil organic matter, we used solid-state 13C and 15N and solution 31P nuclear magnetic resonance (NMR) spectroscopy to analyze the labile mobile humic acid (MHA) and the more recalcitrant calcium humate (CaHA) fractions extracted from a series of soils supporting several long-term field experiments in the Philippines. The soils varied mainly in degree of submergence and cropping intensity, ranging from a rainfed rice field without soil submergence to irrigated double- and triple-cropped fields in which soil remains submerged almost all year long. As reported previously, all analyses associated increasing intensity of rice cropping with larger proportions of less humified material in the MHA and CaHA, such as diester phosphorus (P), amide nitrogen (N), and phenolic carbon (C). We established significant correlations between proportions of various spectral areas as well as between some spectral areas and other humic acid (HA) properties such as visible light absorption and free radical concentration (positive indices of humification) and hydrogen (H) concentration (negative index of humification). For example, spectral proportions of heterocyclic N were positively, and proportions of amide N and phenolic C negatively, correlated with visible light absorption and free radical concentration, and each of these spectral proportions had an opposite sign when correlated with H concentration. The correlations of N-alkyl C proportions were the strongest with these properties and with other functional group proportions.

Streamwise oscillations of a cylinder in steady current. Part 2. Free-surface effects on vortex formation and loading

A cylinder in a steady current beneath a free surface is subjected to oscillations in the streamwise direction. Techniques of high-image-density particle image velocimetry and instantaneous force measurement provide the relationship between the instantaneous, global flow patterns and the unsteady loading on the cylinder.The existence of locked-on states for the fully submerged cylinder is addressed in the companion study of Cetiner &amp; Rockwell (2001). The present investigation shows that it is possible to generate distinctly different locked-on states of vortex formation, provided the cylinder is located immediately beneath the free surface. As a consequence, the time-dependent transverse force is phase-locked to the cylinder motion. In the event that a finite gap exists between the cylinder and the free surface, however, instantaneous, jet-like flow through the gap acts to destabilize such locked-on states. Lissajous representations of the forces demonstrate the degree of phase-locking or, in some cases, a loss of lock-on and associated phase drift. Moreover, the degree of submergence of the cylinder beneath the free surface has remarkable consequences for the magnitudes of positive and negative spikes of the time-dependent force signatures, as well as the averaged spectra of the transverse force. In turn, these alterations of the unsteady transverse force are accompanied by substantial changes of the averaged in-line and transverse forces.Vortex systems can exist at locations both upstream and downstream of the cylinder. They are due to vorticity from the cylinder surface and/or the free surface. The space–time development of the entire system of vorticity concentrations is interpreted in terms of the time histories of the relative velocity of the cylinder and the instantaneous forces on the cylinder. In turn, these features of the vorticity field are related to critical points near the free surface, deduced from topologies of the corresponding velocity and streamline patterns. Despite the fact that changes in the patterns of vorticity and the corresponding topologies occur in conjunction with large fluctuations of the transverse force coefficient, the dimensionless strength of the vortices is below the threshold for which distinguishable, localized deformations of the free surface occur.

Structure of the Photosynthetic Apparatus in Leaves of Freshwater Hydrophytes: 1. General Characteristics of the Leaf Mesophyll and a Comparison with Terrestrial Plants

The structure of photosynthetic elements was investigated in leaves of 42 boreal plant species featuring different degrees of submergence (helophytes, neustophytes, and hydatophytes). The mesophyll structure types were identified for all these species. Chlorenchyma tissues and phototrophic cells were quantitatively described by such characteristics as the sizes of cells and chloroplasts in the mesophyll and epidermis, the abundance of cells and chloroplasts in these tissues, the total surface area of cells and chloroplasts per unit leaf area, the number of plastids per cell, etc. The hydrophytes typically had thick leaves (200–350 μm) with a well-developed aerenchyma; their specific density per unit area (100–200 mg/dm2) was lower than in terrestrial plants. Mesophyll cells in aquatic plants occupied a larger volume (5–20 × 103μm3) than epidermal cells (1–15 × 103μm3). The number of mesophyll cells per unit leaf area was nearly 1.5 times higher than that of epidermal cells. Chloroplasts were present in the epidermis of almost all species, including emergent leaves, but the ratio of the chloroplast total number to the number of all plastids varied depending on the degree of leaf submergence. The total number of plastids per unit leaf area (2–6 × 106/cm2) and the surface of chloroplasts per unit leaf area (2–6 cm2/cm2) were lower in hydrophytes than in terrestrial plants from climatically similar habitats. The functional relations between mesophyll parameters were similar for hydrophytes and terrestrial plants (a positive correlation between the leaf weight per unit area, leaf thickness, and the number of mesophyll cells per unit leaf area), although no correlation was found in hydrophytes between the volume of mesophyll cells and the leaf thickness. Phototrophic tissues in aquatic plants contributed a larger fraction to the leaf weight than in terrestrial plants, because the mechanical tissues were less developed in hydrophytes. The CO2assimilation rates by leaves were lower in hydrophytes than in terrestrial plants, because the total surface area of chloroplasts per unit leaf area is comparatively small in hydrophytes, which reduces the conductivity for carbon dioxide diffusion towards the carboxylation sites.