Plastic Grass Research Articles

Hydraulic resistance of artificial vegetation patches in aligned and staggered configurations

ABSTRACT The paper reports the results of laboratory experiments to investigate the effect of vegetation patch mosaics on hydraulic resistance. Experiments were run for seven levels of vegetation coverage with square patches of flexible plastic grass in aligned and staggered configurations and a wide range of hydraulic conditions. Hydraulic resistance was substantially higher for staggered than aligned configurations, particularly for intermediate ranges of vegetation coverage. The results indicate that hydraulic resistance differs between regimes of isolated roughness flow, wake interference flow, and skimming flow. Two types of models are proposed to predict hydraulic resistance (i.e. Manning’s coefficient n) for aligned and staggered configurations, one as a function of the nondimensional spatially-averaged hydraulic radius and another as a function of relative submergence and surface area blockage factor. To account for the effects of vegetation patch alignment, an additional factor α is introduced. This work provides comprehensive datasets and models that can be used to improve the prediction of hydraulic resistance in open-channel flows with vegetation patches.

Questing behavior of adult Amblyomma americanum (L.) in a laboratory setting</p >

Tick-borne diseases are on the rise globally; however, information is lacking about tick questing behavior. In this laboratory study, we explored tick preferences for stem type (plastic grass, wooden, and metal), questing height, and head orientation. Using 60 Amblyomma americanum adults over three 72-hour replicates, we determined that 21.7% of ticks quested at any given time and that ticks exhibited a strong preference to quest with their heads oriented downwards, irrespective of stem type. Individual ticks tended to quest on only one stem in this study, and a maximum of three. Nonetheless, ticks appeared to prefer questing on wooden and plastic grass stems over metal stems. We did not find an effect of time of day on tick questing rates. Increased understanding of tick questing behavior can improve vector control efforts.

Flow velocity characteristics at a confluent channel with and without flexible vegetation

The interaction between confluence and vegetation is important for understanding the rules of flood control and ecological restoration. To this end, artificial flexible plastic grass was used in a 90° confluent open channel to simulate the ambient conditions of the natural state, and three-dimensional velocities were measured by an acoustic Doppler velocimeter. The velocities of different spatial distribution in different conditions were analysed. The results showed that the existence of vegetation will change the velocity's horizontal distribution and the velocity decreases greatly because of the vegetation. The vegetation reduces the deflection angle of the 90° confluence flow intersection. Under the influence of the vegetation, the flow direction can be restored to the main flow direction more quickly after confluence. Vegetation is the main factor causing the flow velocity reduction in the upstream, whereas in the vicinity of the confluence the influence of vegetation on the velocity will change with the intensity of the turbulence in the region. The influence range of the vegetation on the vertical velocity was found to be double the average height of the vegetation. The vertical velocities changes greatly near the average height of the vegetation.

Artificial lawns: Environmental and societal considerations of an ecological simulacrum

The replacement of living lawns with synthetic (plastic) grass seems to be on the increase in cities. This paper presents some environmental and societal considerations relating to the installation of artificial lawns to encourage research of the phenomenon at this early stage of emergence. After first discussing the development of ‘third generation’ synthetic grasses that have made artificial lawns more appealing, it then considers how the replacement of living lawns with plastic grass represents a potentially concerning step towards ecological simulation, or the replacement of real ecosystems with simulacra that address cultural desires but remove nature altogether. The paper then examines some of the possible environmental and societal impacts that may result from the replacement of living lawns with their artificial counterparts, and concludes with the presentation of a research framework for investigation of the emerging artificial urban lawnscape.

Compound channel flow with a longitudinal transition in hydraulic roughness over the floodplains

Flows in a compound open-channel (two-stage geometry with a main channel and adjacent floodplains) with a longitudinal transition in roughness over the floodplains are experimentally investigated in an 18 m long and 3 m wide flume. Transitions from submerged dense vegetation (meadow) to emergent rigid vegetation (wood) and vice versa are modelled using plastic grass and vertical wooden cylinders. For a given roughness transition, the upstream discharge distribution between main channel and floodplain (called subsections) is also varied, keeping the total flow rate constant. The flows with a roughness transition are compared to flows with a uniformly distributed roughness over the whole length of the flume. Besides the influence of the downstream boundary condition, the longitudinal profiles of water depth are controlled by the upstream discharge distribution. The latter also strongly influences the magnitude of the lateral net mass exchanges between subsections, especially upstream from the roughness transition. Irrespective of flow conditions, the inflection point in the mean velocity profile across the mixing layer is always observed at the interface between subsections. The longitudinal velocity at the main channel/floodplain interface, denoted $$U_{int}$$ , appeared to be a key parameter for characterising the flows. First, the mean velocity profiles across the mixing layer, normalised using $$U_{int}$$ , are superimposed irrespective of downstream position, flow depth, floodplain roughness type and lateral mass transfers. However, the profiles of turbulence quantities do not coincide, indicating that the flows are not fully self-similar and that the eddy viscosity assumption is not valid in this case. Second, the depth-averaged turbulent intensities and Reynolds stresses, when scaled by the depth-averaged velocity $$U_{d,int}$$ exhibit two plateau values, each related to a roughness type, meadow or wood. Lastly, the same results hold when scaling by $$U_{d,int}$$ the depth-averaged lateral flux of momentum due to secondary currents. Turbulence production and magnitude of secondary currents are increased by the presence of emergent rigid elements over the floodplains. The autocorrelation functions show that the length of the coherent structures scales with the mixing layer width for all flow cases. It is suggested that coherent structures tend to a state where the magnitude of velocity fluctuations (of both horizontal vortices and secondary currents) and the spatial extension of the structures are in equilibrium.

Soccer vs. running training effects in young adult men: which programme is more effective in improvement of body composition? Randomized controlled trial.

The aims of this study were: 1) To determine the effects of a 12-week recreational soccer training programme and continuous endurance running on body composition of young adult men and 2) to determine which of these two programmes was more effective concerning body composition. Sixty-four participants completed the randomized controlled trial and were randomly assigned to one of three groups: a soccer training group (SOC; n=20), a running group (RUN; n=21) or a control group performing no physical training (CON; n=23). Training programmes for SOC and RUN lasted 12-week with 3 training sessions per week. Soccer sessions consisted of 60 min ordinary five-a-side, six-a-side or seven-a-side matches on a 30-45 m wide and 45-60 m long plastic grass pitch. Running sessions consisted of 60 min of continuous moderate intensity running at the same average heart rate as in SOC (~80% HRmax). All participants, regardless of group assignment, were tested for each of the following dependent variables: body weight, body height, body mass index, percent body fat, body fat mass, fat-free mass and total body water. In the SOC and RUN groups there was a significant decrease (p < 0.05) in body composition parameters from pre- to post-training values for all measures with the exception of fat-free mass and total body water. Body mass index, percent body fat and body fat mass did not differ between groups at baseline, but by week 12 were significantly lower (p < 0.05) in the SOC and RUN groups compared to CON. To conclude, recreational soccer training provides at least the same changes in body composition parameters as continuous running in young adult men when the training intensity is well matched.

Assessing the dye‐tracer correction factor for documenting the mean velocity of sheet flow over smooth and grassed surfaces

AbstractIn the investigation of overland flow hydraulics, mean flow velocity (V) is frequently estimated using the measured surface flow velocity (Vs) multiplied by a correction factor, α. In total, 291 tests were performed in a flume with three beds [smooth glass (GL), sandpaper (SD), and plastic grass (GR)] to investigate α under submerged and non‐submerged flows, and Vs was observed using dye‐tracer method whilst V was calculated by the measured water depth and flow rate. For GL with 5.2% slope and 100 &lt; Re &lt; 5000 [Reynolds number (Re)], α ranged from 0.35 to 0.79, with an average of 0.54. For SD with slopes ranging from 2.6% to 25.9% and 300 &lt; Re &lt; 1200, α varied from 0.18 to 0.48 with an average of 0.32. Raindrop impacts decreased α for GL at 5.2% slope, but the effect diminished for SD as the slope increased. The α‐values less than the theoretical value of 0.67 in laminar flows may be attributed to the greater spatial variability in overland flow compared with channel flow. For GR with non‐submerged flows and Re &lt; 4200, α varied inversely with sediment concentration (SC) at 5.2% slope but was only slightly related to SC at steep slopes of 15.6% and 25.9%. The α‐values were approximately 0.8 for turbulent flows and even greater than 1.0 under high flow discharges. This finding may relate to sheet flow disturbance and retarded surface velocity due to the protruding scattered grass stems. For each surface, α varied positively with Re; α was inversely related to slope for SD but positively related to slope for GR. There was a positive relation between h and α for GL and SD but a negative relation for GR, which highlights the importance of flow inundation status to α. The inundation ratio (h/Δ) is a promising indicator for predicting α; thus, further investigations using different submerged and non‐submerged surfaces are required to predict α effectively based on (h/Δ). Copyright © 2015 John Wiley &amp; Sons, Ltd.

Application of Roughening with the Grass Cushions in the Hydraulic Model of Comprehensive Harness of Qian'an Reach of Luan River

Restricted by such factors as the size of test area, amount of work and water depth of model, hydraulic models are often made into distorted patterns, whereas the distorted models demand for roughening usually. The hydraulic model of comprehensive harness of Qian'an Reach of Luan River requires big roughness that general roughening technologies cant meet, so the plastic grass cushions were introduced. The preliminary experiment in flume, the preliminary experiment of the comprehensive model and the verification experiment of the comprehensive model proved the feasibility of the technology of roughening with the grass cushions in hydraulic model tests.

Sediment Trapping from Hyperconcentrated Flow as Affected by Grass Filter Strips

To evaluate the effect of vegetative filter strips on sediment trapping, the spatial distribution of deposited sediment, and the size distribution of deposited particles from hyperconcentrated flows, a simulated grass filter strip experiment was conducted with plastic grass using an adjustable slope steel flume. The simulated vegetation cover was 36%, and the inflow sediment concentrations applied were 147, 238, 320, and 429 kg m−3. The sediment concentration in the outflow, and the sediment particle size were determined. The results showed that the grass filter strips trapped most of the sediment from inflow at low sediment concentration. The deposition efficiency decreased with increasing sediment concentration, being 55.2% and 15.7% in the 147 and 429 kg m−3 sediment treatments, respectively. Most of the deposited sediments were distributed in the upper flume. In addition, the grass filter strips mainly trapped the coarse sediment (particle size > 10 μm).

Awards Season: Science Through the Eyepiece

Awards Season: Science Through the Eyepiece

Carcinus maenas (Crustacea: Brachyura): Influence of artificial substrate type and patchiness on estimation of megalopae settlement

Settlement patterns of decapod crustaceans are influenced by size, shape and nature of substrates, as well as by species-specific behaviour patterns. Hog's hair filter material is one of the most commonly used artificial substrates in the study of settlement rates. However, the use of hog's hair collectors in settlement studies poses several problems: movement restriction of settled animals, relatively long and complicated laboratory processing time, and cost and decreasing availability. Despite widely used, no consistent investigation has focused on the influence of size and shape of hog's hair collectors on rates of benthic settlement. A first experiment was set to investigate the effects of collector patchiness on settlement abundances of Carcinus maenas megalopae. Benthic hog's hair collectors of different sizes were deployed intertidally in the lower Mira Estuary. Settlement was addressed as ind collector − 1 and ind m − 2 in relation to collector' surface area and perimeter:area ratio. Results showed that collector patchiness significantly influenced settlement response of C. maenas megalopae, which differed according to settlement intensity and measure. Megalopae settlement responded to lower scales of habitat patchiness at high than at low intensity. Settlement as ind collector − 1 generally increased, while as ind m − 2 generally decreased, with increasing collector' surface area (decreasing perimeter:area ratio). A second experiment investigated the efficiency of plastic grass, as a new type of artificial surface, in estimating settlement patterns of C. maenas megalopae, and compared it with that of hog's hair. Collectors of both types were deployed daily and intertidally in the lower Mira Estuary. Settlement showed the same pattern and intensity on both collector types. Plastic grass collectors constitute a good alternative to those of hog's hair, possessing several advantages over them.

Flow Patterns in Compound Channels with Vegetated Floodplains

Understanding the hydraulics of flow in a compound channel with vegetated floodplains is very important for determining the stage-discharge curve and for supporting the management of fluvial processes. In this paper, the flow patterns over different types of vegetation, such as tree, shrub, and grass, are described, based on an experimental study. For vegetation on the floodplain, the authors choose plastic grass, duck feathers, and plastic straws as model grass, shrubs, and trees, respectively. A 3D acoustic Doppler velocimeter was used to measure the local flow velocities for different types of vegetation on the floodplain, and the total discharge and flume slope were measured independently. In the cases of nonvegetated floodplains, all measured streamwise velocity distributions followed the logarithmic distribution, but for vegetated floodplains, they followed an S-shaped profile, exhibiting three zones. For all cases, the fluctuating velocity followed a normal distribution. The influence of different types of vegetation on the distributions of the secondary currents, turbulence intensities, and Reynolds shear stresses were also analyzed.

Epibenthic invertebrates of natural and constructed marshes of San Diego Bay

To aid in assessing the functioning of a constructed salt marsh and the acjacent natural marsh, we conducted a one-year study of epibenthic invertebrates using a new sampling method. Invertebrates were trapped in litter bags (5-mm mesh) filled withSpartina foliosa; these were compared with bags containing other substrates (plastic grass,Typha, andScirpus, all of which trapped fewer individuals thanSpartina-filled bags. A total of 168Spartina-filled bags trapped 43,531 individuals over 8 sampling dates. Invertebrate abundances differed by season, elevation, cover ofSpartina, and marsh type. There were more invertebrates trapped in fall than in winter; there were more in the lower than higher elevation, and in the natural marsh, there were twice as many invertebrates in areas with ⋝80% cover ofSpartina than with ⋜20% cover. The strongest pattern was with marsh type. Natural, fully vegetated marsh had 2—3 times as many individuals as the sparsely-vegetated, 4-year-old constructed marsh. Overall, the most abundant species was a larval dipteran,Pericoma sp., which was up to 9 times more abundant in the natural marsh. An anemone,Diadumene franciscana, was virtually restricted to the natural marsh. However, the more open constructed marsh had significantly moreHemigrapsus oregonensis crabs and more exotic mussels (Musculista senhousia). The invertebrate assemblage in the 4-year-old marsh was not equivalent to that of the natural marsh. Both marshes had 37 species, but species lists were 46% similar for all sites and dates combined, and relative abundances were 67% similar. Coarser sediment, lower organic matter, and sparse vegetative cover were potential causes of significantly lower abundances in the constructed marsh.

The decomposition of litter in grasslands of northern Mexico: a comparison between arid and non-arid environments

The mass loss of grass litter was studied in two climatically contrasted zones: the Bolson de Mapimi (Chihuahuan Desert, annual rainfall 271 mm) and La Michilia (Western Sierra Madre pine–oak forest, annual rainfall 788 mm). Plastic grass litter bags were placed on the ground and collected periodically over 29 months, dried, weighed and analysed for carbon and nitrogen. The dry mass data were fitted to time, rainfall and temperature as independent variables, using differential equation models that assume constant or variable decomposition rates. The overall velocity of decomposition was strongly correlated with the proportion of leaves and stems in the initial litter. In La Michilia, decomposition rates decreased as the litter disappeared. Weight loss was found to be associated more with temperature and rainfall than with time, and the C:N ratio decreased strongly as decomposition progressed. In Mapimi, on the other hand, decomposition rates did not decrease so strongly as litter disappeared; time was found to be an adequate predictor of mass loss, and the C:N ratio was more constant. It is concluded that abiotic factors (physical weathering) are responsible for a large portion of the mass loss of grass litter in arid environments.

Floodplain Sedimentation: A Preliminary Investigation of Contemporary Deposition within the Lower Reaches of the River Culm, Devon, UK

Within a 13 km reach of the lower course of the River Culm, Devon, UK, the river has a well-developed flood-plain which is frequently inundated at times of high flow. Detailed records of suspended sediment load obtained from upstream and downstream gauging stations indicate that approximately 28% of the upstream load may be deposited within this reach. Direct measurements of floodplain sedimentation using ‘plastic grass’ sediment traps evidence both macro-and microscale spatial variations in deposition which can be related to the duration of inundation, the topography of the floodplain surface and the flow velocity of the inundating water. Rates of deposition have been estimated from conveyance losses and these have been compared with data obtained from the sediment traps. Average rates of approximately 490 g m-2 (0.49 mm year-1) are indicated. A comparison of the characteristics of storm and floodplain sediment indicated that conveyance losses are associated with a preferential loss of the coarser fractions, although appreciable deposition of the clay fraction also occurs.