This study investigates the complex flow structure generated by riparian emergent vegetation along the edge of floodplain. Detailed velocity and boundary shear stress measurements were carried out for various arrangements of emergent rigid cylindric rods of 3 mm, 6 mm and 9 mm diameters and for three different rod densities. In addition, the impact of foliage on the flow field was assessed during a series of experiments where brushes were used instead of smooth rods. The results of these new experiments are first presented. In addition to the laboratory data, field data was obtained through Acoustic Doppler Current Profiler measurements for two flood events in a stretch of the river Rhône that can be approximated to a straight compound channel with vegetated banks. The analysis of the flow structure highlights the presence of strong secondary circulation and increased vorticity on the river banks. The rods on the edge of the floodplain increase significantly flow resistance, reducing velocity and decreasing boundary shear stress. Flow rate was seen to decrease with increasing vegetative density for all cases except when foliage was added. This suggests that an optimum threshold density, for which a smaller density would lead to an increased flow rate might exist. Wakes trailing downstream of the vegetation stem, planform coherent structures advected between the main channel and the floodplain, and eddying motion in the flow due to enhanced turbulence anisotropy are among the defining patterns observed in the studied compound channel flows with one line of emergent vegetation along the edge of the floodplain. The Shiono and Knight Method (SKM) was modified in order to account for the increased turbulence activity due to the rods. The drag force term was introduced in the same way as in the work of Rameshwaran and Shiono (2007). However, a new term was added to the transverse shear stress term in the form of an Elder formulation, incorporating a friction drag coefficient which can be derived from the experimental data. In this proposed version, the advection term was set to zero. Another version of the SKM, similar to Rameshwaran and Shiono (2007), was also tested with the addition of a local drag friction only applied in the rod region. The proposed SKM version without the advection term was favored as it can be more closely related to the experimental data and to physical processes. Finally, the capabilities of Telemac-2D were tested against the experimental data for various turbulence models. The Large Eddy Simulation turbulence model highlighted some unsteady flow patterns that were observed during experiments, while satisfactorily predicting the lateral velocity and boundary shear stress distributions.

The growth patterns of emergent vegetation can be a useful indicator for factors affecting lake health. However, field data to characterize emergent vegetation at many reservoirs may not be available or may be limited to small, isolated areas. We present a case study using remotely sensed data from the Landsat satellite to generate data to represent emergent vegetation in the near-shoreline and tributary delta areas of Malheur Lake, Oregon. We selected late June images for this study as vegetation is relatively mature in late June and visible, but has not completely grown-in providing a better indication of vegetation coverage in satellite images. We investigated the correlation of vegetation coverage (an indicator of emergent vegetation) with lake area on the day of the satellite collection, average daily maximum temperatures for April, May, June, and July, and average daily precipitation in June, all parameters that could affect vegetation. To estimate historic emergent vegetation extent, we computed the Normalized Difference Vegetation Index (NDVI) for 30 years of Landsat satellite images from 1984 to 2013. Around Malheur Lake we identified eight regions-of-interest (ROI): three inlet areas, three wet-shore areas (swampy areas), and two dry-shore areas (less swampy areas). For each ROI we generated time-series data to quantify the emergent vegetation as determined by the percent of area covered by pixels with NDVI values greater than 0.2. We measured lake area by computing the Modified Normalized Difference Water Index (MNDWI) and computing the area by summing the pixels that indicated water. We compared NDVI time-series values with the time series for lake area, June precipitation, and maximum daily temperatures for April, May, June, and July to determine if these parameters were correlated. Correlation would imply that emergent vegetation was influenced by the parameter. We found that correlations of vegetative extent in any of the eight ROIs with the selected parameters were minimal, indicating that there are other factors besides the ones chosen that drive emergent vegetation levels in Malheur Lake. This study demonstrates that Landsat data have sufficient spatial and temporal detail for quantification and description of ecosystem changes and thus offer a good source of information to understand historic trends in reservoir health. We expect that future work will explore other potential drivers for emergent vegetation extent, such as carp populations in Malheur Lake which are known to affect emergent vegetation. Carp were not considered in this study as we did not have access to data that reflect carp numbers over this 30 year period.

No description available.

Salt marshes are important habitats that provide many ecosystem services, but they are susceptible to the impacts of sea level rise (SLR), often resulting in emergent vegetation loss. In areas with enough sediment input, marshes can keep pace with SLR by gaining elevation or through upland migration. However, salt marshes in areas with limited sediment input, such as the Grand Bay National Estuarine Research Reserve, often cannot keep pace with sea level rise. Additionally, the rate of SLR is increasing making it more difficult for marshes to keep pace. To assess the short-term response of marsh vegetation to sea level rise, percent cover, stem density, and elevation, data from 2016 to 2020 in four different marsh elevation zones were analyzed in this study. Results demonstrated that the four marsh elevation zones are responding disparately to SLR. These findings indicate that it is imperative to implement restoration plans to account for site variability to conserve these vital habitats.

Better understanding of the role of vegetation in the transport of fluid and pollutants requires improved knowledge of the detailed flow structure within the vegetation. Instead of spatial averaging, this study uses discrete measurements at multiple locations within the canopy to develop velocity and turbulence intensity profiles and observe the changes in the flow characteristics as water travels through a vegetation array simulated by rigid dowels. Velocity data were collected with a one dimensional laser Doppler velocimeter (LDV) under single layer emergent and submerged flow conditions, and through two layers of vegetation. The effects of dowel arrangement, density, and roughness are also examined under the single layer experiments. The results show that the velocity within the vegetation array is constant with depth and the velocity profile is logarithmic above it. The region immediately behind a dowel, where the vorticity and turbulence intensity are highest, is characterized by a velocity spike near the bed and an inflection point near the top of the dowel arrays. With two dowel layers, the velocity profile in the region behind a tall dowel exhibits multiple inflection points and the highest turbulence intensities are found there. / Master of Science

Yes / This review paper addresses the structure of the mean flow and key turbulence quantities in free-surface flows with emergent vegetation. Emergent vegetation in open channel flow affects turbulence, flow patterns, flow resistance, sediment transport, and morphological changes. The last 15 years have witnessed significant advances in field, laboratory, and numerical investigations of turbulent flows within reaches of different types of emergent vegetation, such as rigid stems, flexible stems, with foliage or without foliage, and combinations of these. The influence of stem diameter, volume fraction, frontal area of stems, staggered and non-staggered arrangements of stems, and arrangement of stems in patches on mean flow and turbulence has been quantified in different research contexts using different instrumentation and numerical strategies. In this paper, a summary of key findings on emergent vegetation flows is offered, with particular emphasis on: (1) vertical structure of flow field, (2) velocity distribution, 2nd order moments, and distribution of turbulent kinetic energy (TKE) in horizontal plane, (3) horizontal structures which includes wake and shear flows and, (4) drag effect of emergent vegetation on the flow. It can be concluded that the drag coefficient of an emergent vegetation patch is proportional to the solid volume fraction and average drag of an individual vegetation stem is a linear function of the stem Reynolds number. The distribution of TKE in a horizontal plane demonstrates that the production of TKE is mostly associated with vortex shedding from individual stems. Production and dissipation of TKE are not in equilibrium, resulting in strong fluxes of TKE directed outward the near wake of each stem. In addition to Kelvin–Helmholtz and von Kármán vortices, the ejections and sweeps have profound influence on sediment dynamics in the emergent vegetated flows.

In 2011 Manitoba experienced an extreme flood. The operation of the Assiniboine River Diversion resulted in the addition of approximately 1.72 million cubic decameters of water to Lake Manitoba and an increase in water levels to 1.5 m above normal. Although this event resulted damage to farmland and many local homes, it also provided me the unique opportunity to utilize previously impractical methods of bathymetric and substrata distribution analysis in the adjoining Delta Marsh. Combined with satellite imagery taken in 2011 I was able to classify the vegetation classes within the study area and explore the relationship between vegetation distributions and water depth as well as those between water depth and substrata distribution. A seed bank study was carried out to explore the diversity of viable seeds in the area. In addition, satellite imagery taken in 2009 was used to evaluate the effects of the flood event experienced in 2011. / October 2015

Marsh vegetation is widely considered to offer protection against coastal storm damage, and vegetated flow has thus become a key area of hydrodynamic research. This study investigates the utility of simulated Spartina alterniora marsh vegetation as storm protection using an ADV measurement technique, and is the first to apply jet self-similarity analysis to characterize the overall mean and turbulent flow properties of a three-dimensional axisymmetric jet through a vegetated array. The mean axial flow of a horizontal axisymmetric turbulent jet is obstructed by three configurations of staggered arrays of vertical rigid plant stems. The entire experiment is repeated over five sufficiently high jet Reynolds number conditions to ensure normalization and subsequent collapse of data by nozzle velocity so that experimental error is obtained. All self-similarity parameters for the unobstructed free jet correspond to typical published values: the axial decay coefficient B is 5:8 +/- 0:2, the Gaussian spreading coefficient c is 85 +/- 5, and the halfwidth spreading rate eta_(1/2) is 0:093 +/- 0:003. Upon the introduction of vegetation, from partially obstructed to fully obstructed, B falls from 5:1+/- 0:2 to 4:2 +/- 0:2 and finally 3:7 +/-0:1 for the fully obstructed case, indicating that vegetation reduces axial jet velocity. Cross-sectionally averaged momentum for the unobstructed free jet is M=M0 = 1:05 +/- 0:07, confirming conservation of momentum. Failure of conservation of momentum is most pronounced in the fully obstructed scenario – M=M0 = 0:54 +/- 0:05. The introduction of vegetation increases spreading of the impinging jet. The entrainment coefficient alpha for the free jet case is 0.0575; in the fully obstructed case, alpha = 0:0631. Mean advection of mean and turbulent kinetic energy demonstrates an expected reduction in turbulence intensity within the vegetated array. In general, turbulent production decreases as axial depth of vegetation increases, though retains the bimodal profile of the free jet case; the fully vegetated case, however, exhibits clear peaks behind plant stems. Turbulent transport was shown to be unaffected by vegetation and appears to be primarily a function of axial distance from the jet nozzle. An analysis of rate of dissipation revealed that not only does the cumulative effect of upstream wakes overall depress the magnitude of spectral energy density across all wavenumbers but also that plant stems dissipate large anisotropic eddies in centerline streamwise jet flow. This study, thus, indicates that sparse emergent vegetation both reduces axial flow velocity and has a dissipative effect on jet flow. Typically, however, storm surge does not exhibit the lateral spreading demonstrated by an axisymmetric jet; therefore, the results of this study cannot conclusively support the claim that coastal vegetation reduces storm surge axial velocity.