Flow characteristics in different densities of submerged flexible vegetation from an open-channel flume study of artificial plants

The arid desert ecosystem is very fragile, and the change of its river discharge has a direct impact on irrigation and natural environment. River discharge attenuation coefficients is a key index to reveal the stability of desert river ecosystem. However, due to the harsh conditions in desert areas, it is difficult to establish a hydrological station to obtain data and calculate the attenuation coefficients, so it is urgent to develop new methods to master the attenuation coefficients of rivers. In this study, Taklamakan desert river was selected as the research area, and the river discharge of the desert river were estimated by combining low-altitude UAV and satellite remote sensing technology, so as to calculate the attenuation status of the river in its natural state. Combined with satellite remote sensing, the surface runoff in the desert reaches of the Hotan River from 1993 to 2017 were estimated. The results showed that the base of runoff attenuation in the lower reaches of the Hotan River is 40%. Coupled UAV and satellite remote sensing technology can provide technical support for the study of surface runoff in desert rivers within ungauged basins. Using UAV and satellite remote sensing can monitor surface runoff effectively providing important reference for river discharge monitoring in ungauged catchments.

https://www.mdpi.com/2073-4441/11/12/2633/pdf

Low Altitude Unmanned Aerial Vehicles (UAVs) and Satellite Remote Sensing Are Used to Calculated River Discharge Attenuation Coefficients of Ungauged Catchments in Arid Desert

Experimentation on submerged flow over flexible vegetation patches with downward seepage

Flowing water bodies often have plants that differ greatly in size and type, which interfere with fluid flow structure. Although there are studies describing vegetation–flow interactions in ideal laboratory conditions, their practical application is sometimes still difficult. This paper presents results of research involving laboratory simulations channel flow and the effects upon its structure as it passes through a combined layer of submerged and emerged vegetation in an open-channel flume. Instantaneous time-average velocity and turbulence at various locations were measured with a 3D acoustic Doppler velocimeter. The experimental results showed that the mean velocity profiles can be divided into three layers: bottom, middle and upper. The velocity profiles show the flow structure was complex variable over time creating mixing velocity layers associated with inflection points and velocity spikes. Turbulence intensity urms, vrms, wrms was nearly invariant for the flow depth at the bottom layer in most locations within the vegetation area. Maximum turbulence intensity occurred within the middle layer and migrated vertically as frontal width of the plant increased. Maximum turbulence intensity fluctuated at the velocity mixing layer where there is significant momentum exchange. The Manning's vegetation roughness coefficient n(v) due to vegetation resistance increased with vegetation density as expected. In all, the results show flow structure varies substantially at the stem section and at the canopy top of submerged vegetation. These analytical findings will be useful in understanding river channel hydraulic transport and mixing processes and useful in river engineering applications and modelling. Copyright © 2013 John Wiley & Sons, Ltd.

An open‐channel flume study of flow characteristics through a combined layer of submerged and emerged flexible vegetation

The effect of hydraulic resistance on the downstream evolution of the water surface profile h in a sloping channel covered by a uniform dense rod canopy following the instantaneous collapse of a dam was examined using flume experiments. Near the head of the advancing wavefront, where h meets the rods, the conventional picture of a turbulent boundary layer was contrasted to a distributed drag force representation. The details of the boundary layer around the rod and any interferences between rods were lumped into a drag coefficient Cd. The study demonstrated the following: In the absence of a canopy, the Ritter solution agreed well with the measurements. When the canopy was represented by an equivalent wall friction as common when employing Manning's formula with constant roughness, it was possible to match the measured wavefront speed but not the precise shape of the water surface profile. However, upon adopting a distributed drag force with a constant Cd, the agreement between measured and modeled h was quite satisfactory at all positions and times. The measurements and model calculations suggested that the shape of h near the wavefront was quasilinear with longitudinal distance for a constant Cd. The computed constant Cd(≈0.4) was surprisingly much smaller than the Cd(≈1) reported in uniform flow experiments with staggered cylinders for the same element Reynolds number. This finding suggested that drag reduction mechanisms associated with unsteadiness, nonuniformity, transient waves, and other flow disturbances were more likely to play a role when compared to conventional sheltering effects.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018WR023889

Resistance to Flow on a Sloping Channel Covered by Dense Vegetation following a Dam Break

Manning’s ‘n’ co-efficient for flexible emergent vegetation in tandem configuration

The dynamic pressures exerted on a vertical wall due to cnoidal waves have been investigated in presence and absence of model vegetation on its seaside. The pressures were measured at 3 different elevations along the wall. Tests were conducted with waves of constant height of 0.11m, with its period was varying between 5 and 20secs, thus covering a wide range of Ursell parameter varying between 18 and 700. The model vegetation was positioned adjacent to the wall on its seaside. All the vegetal characteristics including their rigidity are carefully modelled. The peak pressures (pmax) were extracted from the measured time series and are presented in a dimensionless form as a function of parameters governing the characteristics of waves and plantation. Two types of configurations of the green belt with the individual stems of vegetation fixed in tandem and staggered arrangement were considered for the tests. The study indicates that the staggered arrangement of plantation is more effective in attenuating the ...

https://journals.sagepub.com/doi/pdf/10.1260/1759-3131.2.3.169

L. Noarayanan

Papers

Manning’s ‘n’ co-efficient for flexible emergent vegetation in tandem configuration

Role of Vegetal Configuration on the Pressures Due to Cnoidal Waves on a Wall