scholarly journals Laboratory study of the effects of flexible vegetation on solute diffusion in unidirectional flow

2021 ◽  
Vol 33 (1) ◽  
Author(s):  
Sha Lou ◽  
Hao Wang ◽  
Hongzhe Liu ◽  
Guihui Zhong ◽  
Larisa Dorzhievna Radnaeva ◽  
...  
Keyword(s):  
Solute Transport ◽  
Flow Velocity ◽  
Diffusion Coefficients ◽  
Submerged Vegetation ◽  
Vegetation Density ◽  
Longitudinal Diffusion ◽  
Vegetation Height ◽  
Rigid Vegetation ◽  
Flexible Vegetation ◽  
Inflow Discharge

Abstract Background Flexible vegetation is an important part of the riverine ecosystem, which can reduce flow velocity, change turbulence structure, and affect the processes of solute transport. Compared with the flow with rigid vegetation, which has been reported in many previous studies, bending of flexible vegetation increases the complexity of the flow–vegetation–solute interactions. In this study, laboratory experiments are carried out to investigate the influence of flexible vegetation on solute transport, and methods for estimating the lateral and longitudinal diffusion coefficients in the rigid vegetated flow are examined for their applications to the flow with flexible vegetation. Results The experimental observations find that vegetation can significantly reduce flow velocity, and the Manning coefficient increases with increasing vegetation density and decreases with inflow discharge. Under all the cases, the vertical peak of the solute concentration moves towards the bottom bed along the flow, and the values of vertical peak concentration longitudinally decreases from the injection point. The lateral diffusion coefficients Dy increase with vegetation density, while the longitudinal diffusion coefficients DL are opposite. Both Dy and DL increase with the inflow discharge. To estimate the Dy and DL in the flow with flexible vegetation, an effective submerged vegetation height considering vegetation bending is incorporated in the methods proposed for flow with rigid vegetation (Lou et al. Environ Sci Eur 32:15, 2020). The modified approach can well predict the diffusion coefficients in the experiments with the relative errors in the range of 5%–12%. Conclusions The methods proposed in this study can be used to estimate the lateral and longitudinal diffusion coefficients in flows through both rigid and flexible vegetations using the effective submerged vegetation height.

Numerical Study on Wave Attenuation of Tsunami-Like Wave by Emergent Rigid Vegetation

2021 ◽  
pp. 1-28
Author(s):  
K. Qu ◽  
G. Y. Lan ◽  
S. Kraatz ◽  
W. Y. Sun ◽  
B. Deng ◽  
...  
Keyword(s):  
Solitary Waves ◽  
Wave Energy ◽  
Wave Attenuation ◽  
Tsunami Wave ◽  
Numerical Study ◽  
Wave Model ◽  
Indian Ocean Tsunami ◽  
Vegetation Density ◽  
Rigid Vegetation ◽  
Total Wave

The extreme surges and waves generated in tsunamis can cause devastating damages to coastal infrastructures and threaten the intactness of coastal communities. After the 2004 Indian Ocean tsunami, extensive physical experiments and numerical simulations have been conducted to understand the wave attenuation of tsunami waves due to coastal forests. Nearly all prior works used solitary waves as the tsunami wave model, but the spatial-temporal scales of realistic tsunamis differ drastically from that of solitary waves in both wave period and wavelength. More recent work has questioned the applicability of solitary waves and been looking towards more realistic tsunami wave models. Therefore, aiming to achieve more realistic and accurate results, this study will use a parameterized tsunami-like wave based on wave observations during the 2011 Japan tsunami to study the wave attenuation of a tsunami wave by emergent rigid vegetation. This study uses a high-resolution numerical wave tank based on the non-hydrostatic wave model (NHWAVE). This work examines effects of prominent factors, such as wave height, water depth, vegetation density and width, on the wave attenuation efficiency of emergent rigid vegetation. Results indicate that the vegetation patch can dissipate a considerable amount of the total wave energy of the tsunami-like wave. However, the tsunami-like wave has a higher total wave energy, but also a lower wave energy dissipation rate. Results show that using a solitary instead of a tsunami-like wave profile can overestimate the wave attenuation efficiency of the coastal forest.

scholarly journals Riparian Vegetation Density Mapping of an Extremely Densely Vegetated Confined Floodplain

Hydrology ◽  
2021 ◽  
Vol 8 (4) ◽  
pp. 176
Author(s):  
István Fehérváry ◽  
Tímea Kiss
Keyword(s):  
Riparian Vegetation ◽  
Woody Species ◽  
Submerged Vegetation ◽  
Vegetation Types ◽  
Vegetation Density ◽  
Vegetation Zone ◽  
Density Mapping ◽  
Vegetation Zones ◽  
Branch Density ◽  
Vegetation Patches

The most crucial function of lowland-confined floodplains with low slopes is to support flood conveyance and fasten floods; however, obstacles can hinder it. The management of riparian vegetation is often neglected, though woody species increase the vegetation roughness of floodplains and increase flood levels. The aims are (1) to determine the branch density of various riparian vegetation types in the flood conveyance zone up to the level of artificial levees (up to 5 m), and (2) to assess the spatial distribution of densely vegetated patches. Applying a decision tree and machine learning, six vegetation types were identified with an accuracy of 83%. The vegetation density was determined within each type by applying the normalized relative point density (NRD) method. Besides, vegetation density was calculated in each submerged vegetation zone (1–2 m, 2–3 m, etc.). Thus, the obstacles for floods with various frequencies were mapped. In the study area, young poplar plantations offer the most favorable flood conveyance conditions, whereas invasive Amorpha thickets and the dense stands of native willow forests provide the worst conditions for flood conveyance. Dense and very dense vegetation patches are common in all submerged vegetation zones; thus, vegetation could heavily influence floods.

scholarly journals Exploring the contributions of vegetation and dune size to early dune development using unmanned aerial vehicle (UAV) imaging

2017 ◽  
Vol 14 (23) ◽  
pp. 5533-5549 ◽  
Author(s):  
Marinka E. B. van Puijenbroek ◽  
Corjan Nolet ◽  
Alma V. de Groot ◽  
Juha M. Suomalainen ◽  
Michel J. P. M. Riksen ◽  
...  
Keyword(s):  
Unmanned Aerial Vehicle ◽  
Vegetation Type ◽  
Grass Species ◽  
Surface Model ◽  
Maximum Height ◽  
Vegetation Density ◽  
Vegetation Height ◽  
Erosion Processes ◽  
Aerial Vehicle ◽  
Vegetation Characteristics

Abstract. Dune development along highly dynamic land–sea boundaries is the result of interaction between vegetation and dune size with sedimentation and erosion processes. Disentangling the contribution of vegetation characteristics from that of dune size would improve predictions of nebkha dune development under a changing climate, but has proven difficult due to the scarcity of spatially continuous monitoring data. This study explored the contributions of vegetation and dune size to dune development for locations differing in shelter from the sea. We monitored a natural nebkha dune field of 8 ha, along the coast of the island Texel, the Netherlands, for 1 year using an unmanned aerial vehicle (UAV) with camera. After constructing a digital surface model and orthomosaic we derived for each dune (1) vegetation characteristics (species composition, vegetation density, and maximum vegetation height), (2) dune size (dune volume, area, and maximum height), (3) degree of shelter (proximity to other nebkha dunes and the sheltering by the foredune). Changes in dune volume over summer and winter were related to vegetation, dune size and degree of shelter. We found that a positive change in dune volume (dune growth) was linearly related to initial dune volume over summer but not over winter. Big dunes accumulated more sand than small dunes due to their larger surface area. Exposed dunes increased more in volume (0.81 % per dune per week) than sheltered dunes (0.2 % per dune per week) over summer, while the opposite occurred over winter. Vegetation characteristics did not significantly affect dune growth in summer, but did significantly affect dune growth in winter. Over winter, dunes dominated by Ammophila arenaria, a grass species with high vegetation density throughout the year, increased more in volume than dunes dominated by Elytrigia juncea, a grass species with lower vegetation density (0.43 vs. 0.42 (m3 m−3) week−1). The effect of species was irrespective of dune size or distance to the sea. Our results show that dune growth in summer is mainly determined by dune size, whereas in winter dune growth was determined by vegetation type. In our study area the growth of exposed dunes was likely restricted by storm erosion, whereas growth of sheltered dunes was restricted by sand supply. Our results can be used to improve models predicting coastal dune development.

Cost-effectiveness of two monitoring strategies for the great crested newt (Triturus cristatus)

2010 ◽  
Vol 31 (3) ◽  
pp. 403-410 ◽  
Author(s):  
Jérôme Pellet ◽  
Madeleine Kröpfli ◽  
Patrick Heer
Keyword(s):  
Large Scale ◽  
Cost Effective ◽  
Amphibian Conservation ◽  
Submerged Vegetation ◽  
Vegetation Density ◽  
Triturus Cristatus ◽  
Monitoring Strategies ◽  
Cost Effective Method ◽  
Crested Newt ◽  
Monitoring Protocols

AbstractDesigning cost-effective monitoring protocols is a fundamental prerequisite for amphibian conservation. Here, we report a comparison of flashlight survey and trapping (with and without light sticks as trap baits) in order to determine flashlight detectability and trap detectability of great crested newts (Triturus cristatus). Twelve ponds were surveyed in Switzerland where T. cristatus had been known to occur. We measured covariates affecting both flashlight detectability and trap detectability. Newt flashlight detectability using 20 min long flashlight surveys was on average ± SE = 39% ± 10%). Flashlight detectability was mostly influenced by surface and submerged vegetation density, as well as by water temperature. Newt trap detectability during one night using six funnel traps per pond was on average±SE = 41%±10%. Trap detectability was mainly affected by trap position in the pond, with traps lying on the pond floor being more likely to attract newts. The use of light sticks did not enhance the trap detectability. Estimates of flashlight detectability and trap detectability were used to define how many times the sites have to be visited to be 95% certain of not missing T. cristatus in ponds where they are present. In both cases multiple visits (7 flashlight surveys or 6 trapping sessions) have to be performed. Flashlight surveys are the most easily applied and most cost-effective method to use in large scale programs.

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