Vegetation obstructions

Hydraulics and hydrology are another field of study, where we meet structures interacting with a flow. Water flows in natural or artificial conduits with vegetation or with artificial obstructions have obtained a considerable attention of researchers over past 50 years. The main question arisen initially was a reduction in the water discharge associated with vegetation that was estimated to be from 20% to 70%. Prof. V.N. Goncharov stated in his book of 1962 that there were no tools, at that time, to perform such calculations of flows. 

As for the terrestrial vegetation, the difficulty appeared here concerns to the problem of the estimate of the vegetation stiffness that may be also called the density of the obstruction layer (the canopy). In the field measurements of Bennovitsky [53, 54], the natural vegetation (the reed) provided the blockage 7,40, and 120 plants on m2. In the measurements of Nepf [463], the blockage of plants was 330 plants/m2. Another measure for the canopy density, the frontal area per unit volume s, 1 /m, has been more universal. Its typical vertical distribution is shown in Fig. 1.7, [463],... 

Figure 1.9 Typical velocity distributions measured in the horizontal-plane problem by Ben-novitsky [56] (a) relative obstructed cross section a>veg/a>0 = 0.19, and (b) a>veg/a>0 = 0.45. Line markings 1 - border of the vegetated area 2 - velocity distribution if vegetation is absent 3 -flume symmetry line.

It has been few years only since hydraulics began the implementation of methods used by meteorologists for modeling the flows obstructed by vegetation. A more close exchange between both sciences seems to be very useful. 

In this Eulerian theoretical approach, a number of obstructions is considered as a continuous medium, or even media. They may have their own motion, for example, the waving of leafs in the case of vegetation canopy. In the case of droplets, their motion in the vertical direction and along the wind can be described by the following momentum equation for each size r ... 

Both of the above types of canopy are characterized by a very small fraction of the total canopy volume, so that canopy modelers can generally neglect this volume not occupied by the fluid. The same concept relates to many other types of obstructed geometries such as droplet layers, Sections 1.4 and 3.2, windmills, Section 1.4 and bubble flows, Section 7.5. Despite their diversity, many of these flows may, nevertheless, be united by the fact that one needs to account for both the internal decelerated flow within the obstructed geometry and for the external free flow over it. Field experiments in natural forests or in agricultural canopies, in wind tunnels with simulated forests of urban settlements and in water flumes with simulated aquatic vegetation have discovered many common features of these flows. These features are formalized in mathematical models. 

Bennovitsky, E.L., and Gayev, Ye.A. (2004) Analysis of flows trough vegetated beds. Flow and transport processes in complex obstructed geometries, Abstracts of NATO Advances Study Institute PST.ASI.980064, Kyiv, Institute of Hydromechanics NASU, May 4-15, 2004. 

Flow and Transport Processes in Complex Obstructed Geometries from Cities and Vegetative Canopies to Engineering Problems Kyiv, Ukraine 4-15 May 2004... 

The NATO Advanced Study Institute Flow and Transport Processes in Complex Obstructed Geometries from cities and vegetative canopies to engineering problems was held in Kyiv, Ukraine in the period of May 4- 15, 2004. This book based on the papers presented there provides an overview of this new area in fluid mechanics and its applications that have developed over the past three decades. The subject, whose origins lie both in theory and in practice, is now rapidly developing in many directions. 

Although lack of vitamin K is rare, because it is present in green leafy vegetables and synthesized by intestinal bacteria, it may occur with a combination of poor diet and long-term use of antibiotics. Deficiency may also occur because of malabsorption secondary to other conditions such as coeliac disease, or due to lack of bile secretion as in obstructive jaundice. 

In this study, the base factor of Manning s n formula expressed in Eq. (2), n was tested for each water depth and condition on bare flume bottom. The adjustment factors nj and n2 were considered to be zero. The adjustment factor n3 for obstruction roughness were considered as the steel bars contribution and tested before each set of test for every flow depth, flow velocity and stem density of vegetation. The correction factor for meandering channels m5 was considered to be zero. Thus Eq. (2) can be written as ... 

Driver passed where view of road ahead was obstructed by hill, curve, vegetation, traffic, adverse weather conditions, etc. 

Traffic density, merging traffic, and visual distractions are factors of the environment related to vehicle accidents. Trees, bushes, and buildings that obscure intersections and people or vehicles emerging from driveways and yards are environment conditions, too. Community zoning ordinances often control setback of buildings, vegetation, fencing, and other obstruction from roadways to help assure visibility. 

On-road cycle lane partially obstructed by vegetation... 

I off-road cycleways obstructed by street furniture/vegetation. 

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