Vegetation In Open Channel Research Articles

Determining longitudinal dispersion coefficients for submerged vegetated flow

Prediction of the physical transport and mixing of pollutants or other soluble material is crucial for effective river management. Although well established methods exist which describe mixing processes in open channel flow, the presence of vegetation has a significant impact on mixing and few existing techniques account for this. To date, existing models which predict longitudinal dispersion coefficients in vegetated open channel flow have been derived and verified based on experiments conducted in simulated vegetation. This paper presents observations of longitudinal dispersion coefficients in a channel featuring living vegetation and tests against both an existing and a newly proposed model for longitudinal dispersion coefficient in submerged vegetated open channel flow. A model based on a mathematical technique of predicting dispersion in plain shear flow is shown to be capable of predicting longitudinal dispersion coefficients to within 20%.

Bulk Flow Resistance in Vegetated Channels: Analysis of Momentum Balance Approaches Based on Data Obtained in Aging Live Vegetation

Previous work has sought to investigate flow resistance caused by vegetation in open channels. However, many existing flow resistance models are based on data from artificial plant mimics in laboratory channels and are untested with live, aging vegetation and may neglect some of the key effects. This paper presents results from a study using two types of live vegetation grown within a laboratory channel. A series of flow resistance tests were conducted over a time period sufficient to observe changes caused by growth. The effects of the vegetation on bulk flow resistance are presented and discussed. The results are compared with predictions made by existing practical momentum balance based models for flow through emergent vegetation, and new empirical relationships are presented. The work shows that momentum balance methods can provide an accurate prediction of flow depth in live vegetation provided that the relationship between bulk drag coefficient and flow is known. This relationship has been shown to ...

Predicting the impact of vegetations in open channels with different distributaries’ operations on water surface profile using artificial neural networks

Most of the open water irrigation channels in Egypt suffer from the infestation of aquatic weeds, especially the submerged ones that cause numerous hydraulic problems for the open channels themselves and their water distributaries such as increasing water losses, obstructing water flow, and reducing channels’ water distribution efficiencies. Accurate simulation and prediction of flow behavior in such channels is very essential for water distribution decision makers. Artificial neural networks (ANN) have proven to be very successful in the simulation of several physical phenomena, in general, and in the water research field in particular. Therefore, the current study aims towards introducing the utilization of ANN in simulating the impact of vegetation in main open channel, which supplies water to different distributaries, on the water surface profile in this main channel. Specifically, the study, presented in the current paper utilizes ANN technique for the development of various models to simulate the impact of different submerged weeds’densities, different flow discharges, and different distributaries operation scheduling on the water surface profile in an experimental main open channel that supplies water to different distributaries. In the investigated experiment, the submerged weeds were simulated as branched flexible elements. The investigated experiment was considered as an example for implementing the same methodology and technique in a real open channel system. The results showed that the ANN technique is very successful in simulating the flow behavior of the pre-mentioned open channel experiment with the existence of the submerged weeds. In addition, the developed ANN models were capable of predicting the open channel flow behavior in all the submerged weeds’cases that were considered in the ANN development process

Hydraulic resistance of some selected vegetation in open channel Flows

AbstractVegetation in rivers has important roles in improving and restoring river environment. Other than it adds high aesthetic value to revetments, that it can be used as a levee protection in environmental friendly way. In open channel hydraulics, vegetation often causes changes in the flow resistance, usually resulting in the increase of flood stage. Both experimental and numerical researches have been conducted on flow resistance of vegetation in open channels, however, the researches were based mostly on the vegetation found in the region where the researches were conducted, and this restricts the generality of the results.In this study, three Korean natural vegetations, Zoysia matrella (Korean zoysia), Pennisetum alopecuroides (L.) Spreng. (Korean native vegetation) and Phragmites communis Trin. (Korean reed) were used in flume tests on the effect of vegetation in the channel on flow resistance. ‘n‐VR’ retardance curves were developed for each grass. All the grasses were tested under unmown conditions. Z. matrella was tested under fully submerged condition and other two were tested under both submerged and un‐submerged conditions.Resistance coefficient, expressed as Manning's n, converged to about 0.027 (total roughness) for Z. matrella as VR increased. Resistance coefficients for other plants were found affected by the states of the plants, that is, whether they were ‘green’ or ‘dormant’. Generally, resistance coefficients are higher when plants are ‘green’ than when they are ‘dormant’. This is because the resistance coefficient is influenced by the leaf elements of vegetation on the river flow in addition to the stem of vegetation. The interaction between the bending part of vegetation and the water surface can also increase the resistance coefficient. In terms of water depth, P. communis Trin were found more affected on the resistance coefficients compared to Z. matrella and P. alopecuroides (L.) Spreng. Copyright © 2008 John Wiley & Sons, Ltd.

Characteristics of Flow Resistance in Open Channels With Non-Submerged Rigid Vegetation *

The flow resistance factors of non-submerged rigid vegetation in open channels were analyzed. The formulas of drag coefficient C D and equivalent Manning's roughness coefficient n d were derived by analyzing the force of the flow of non-submerged rigid vegetation in open channel. The flow characteristics and mechanism of non-submerged rigid vegetation in open channel were studied through flume experiments.

STUDY ON TURBURENCE STRUCTURES IN PARTLY VEGETATED OPEN-CHANNEL FLOWS WITH A PARTICLE-IMAGE VELOCIMETRY (PIV)

The importance of vegetated zone in rivers has recently been recognized not only for river management but also for water flow environment. From this point of view, some researchers have investigated vegetated open-channel flows to clarify turbulent structures such as mean velocity profiles and turbulence intensity distributions.In this study, images of very small 75μm diameter particles uniformly scattered in vegetated open-channel flows were taken using a CCD camera and 2W Argon-Ion laser slit illumination. Instantaneous velocities at many points in the laser slit plane were obtained from these continuous two images of particles. This new method is called the “Particle-Image Velocimetry (PIV)”, and seems to be very powerful to investigate coherent vortices in space and time, because simultaneous velocities at every point can be obtained easily. It was found that the density of vegetation effects on structures such as instantaneous vectors and vorticities.

Turbulence Characteristics of Vegetated Open-Channel Flows

Turbulence Characteristics of Vegetated Open-Channel Flows

Experimental Study on Turbulent Structures of Partly Vegetated Open-channel Flows

Vegetation in rivers decreases the flow capacity and therefore has been removed from river basin. However, the importance of vegetated zone in rivers has recently been recognized not only for river management but also for water flow environment. Turbulent structures of vegetated open-channel flows and the associated sediment transport are investigated by some researchers.In this study, turbulent measurements in partly vegetated open-channel flows were accurately conducted by using a fiber-optic laser Doppler anemometer (FLDA). Basic turbulent structures such as mean velocity and turbulence were experimentally obtained and discussed as comparing compound open-channel flows.