Determination Of Hydraulic Roughness Coefficient Of Some Vegetated Species
Need help with a related project topic or New topic? Send Us Your Topic
DOWNLOAD THE COMPLETE PROJECT MATERIAL
Determination Of Hydraulic Roughness Coefficient Of Some Vegetated Species
ABSTRACT
A field study was conducted on three selected grasses, Spear grass (Imperata cylindrica), Guinea grass (Panicum maximum), and Bahama grass (Cynodon dactylon), to determine the hydraulic roughness coefficient (Manning’s n), the effect of bed slope (0.2%, 0.3%, and 0.4%) on the n-value, and to select the most suitable vegetation for erosion control based on the results.
This experiment’s setup consists of 12 trapezoidal open channels that are 5m long, 0.12m wide at the top, and have a maximum flow depth of 0.03m. The experiment was conducted at various flow depths of 0.001m, 0.002m, 0.003m, 0.004m, and 0.005m. The vegetation height varied with the slope, and all grasses were examined in an unsubmerged situation.
The discharge was estimated using the timed gravimetric method, so Manning’s equation may be used to calculate the hydraulic roughness coefficient (n). The n-value ranges for Spear grass, Guinea grass, and Bahama grass were 0.020-0.046, 0.031-0.111, and 0.034-0.198, respectively, at all three slopes.
Bahama grass has the greatest Manning’s n, which can be linked to its extensive root system and creeping behaviour. Linear correlations were established between Manning’s number (n) and degree of submergence (Y/H), Reynolds number (Re and VR), vegetation density, flow depth, and drag coefficient (Cd).
It was discovered that for each slope, the degree of submergence grows as the Manning’s n drops, Reynolds number and VR increase as the Manning’s n falls, and flow depth increases as the Manning’s n declines.
Except for Guinea and Bahama grass, vegetation density rises with Manning’s n at a constant flow depth. For all plants, the Reynolds number increases while the drag coefficient Cd decreases as the flow depth increases.
Chapter One: Introduction
1.1 Background of Study
Soil erosion is recognised as the leading source of environmental degradation in most developing countries. It appears to be the worst natural calamity, particularly in Nigeria (Onwuka et al., 2012).
Soil erosion is simply the process by which soil particles (sediments) are detached, transported, and deposited by erosion forces such as water and wind. It can be caused by both natural (water and wind) and human forces (for example, man removing the protective cover of flora).
Surface erosion processes include rain splashing, sheet washing, rilling, and gullying, which are all forms of water erosion. Climate, vegetation, soil type, terrain, and farming activities all have an impact on water-induced erosion. Erosion is acknowledged to pose a major hazard to human life. In agriculture, it affects production by removing or washing plant nutrients and organic debris.
According to Ogunlela and Makonjuola (2000), water erosion can be controlled in two ways: (1) by reducing the erosive capacity of the flowing water through structural measures (e.g., check dams) and (2) by increasing the soil’s resistance relative to the erosive capacity of the flowing water through vegetation cover.
Vegetation can be used to control erosion because of its buttress and expansive root systems, which contribute to increased erosion resistance. According to Greenway (1987), roots strengthen the soil, increasing its shear strength, and keep soil particles at the ground surface, reducing its susceptibility to erosion.
Maintaining vegetation cover is critical to preventing bare soil erosion. By deflecting the impact of raindrops, vegetation reduces soil particle dissociation and movement.
Vegetation can be thought of as a preventative measure against erosion. Chow (1959) observed that the presence of grasses/vegetation reduces energy and retards flow.
The vegetation in the channel influences the flow across the channel, and the level of influence is determined by the vegetation’s properties as well as the flow parameters. The vegetation features include the vegetation species, degree of submergence (submerged or not), density, distribution, and flexibility.
The flow characteristics include the flow area, depth, and side walls of the channel. The main influence of vegetation in the channel is flow velocity; vegetation tends to enhance roughness, flow resistance, or retardance.
This property that vegetation provides to resist flow is known as Manning co-efficient of roughness, n, also known as retardance co-efficient. The n-value is determined by a variety of factors, including the size and shape of the soil grains on the channel (soil type), type of vegetation, size and shape of channel, change of season, presence of obstruction, and so on.
All of these factors are interdependent (Chow, 1959). According to Ree and Palmer (1949), the ability of vegetation to resist flow is determined by the ratio of flow depth to vegetation height. According to Rodney et al. (2011), the roughness coefficient fluctuates depending on the vegetation season.
1.2 Statement of Problem
Many researchers have engaged in this field of inquiry, yielding differing results from various plants. Various models and formulae have been devised to predict the flow resistance of vegetation.
However, this appears to be unreliable because different vegetation have different characteristics (for example, the height of the vegetation affects flow resistance, but it is reduced by the bending of the vegetation), which affects the hydraulic roughness coefficient, n (n-values), and these vary from place to place and time to time. As a result, their numbers fluctuate on a regular basis.
1.3 AIM AND OBJECTIVES OF THE STUDY
The purpose of this study is to investigate the suitability of some Nigerian grasses (Spear grass (Imperata cylindrica), Guinea grass (Panicum maximum), and Bahama grass (Cynodon dactylon) for erosion control by collecting a wide range of data demonstrating the relationship between flow characteristics and vegetation characteristics in order to determine the hydraulic roughness coefficient, n (n-value). The study’s particular aims are as follows:
To determine the selected vegetation’s suitability for erosion control.
To assess the flow retardance of each of these plant covers or grasses.
To investigate the impact of bed slope on the hydraulic roughness coefficient.
1.4 Justification for Study
The project will seek to tackle soil erosion by employing vegetation for erosion control to slow the velocity of flow on the open channel, so resolving one of the primary engineering difficulties associated with soil and water conservation in order to sustain crop productivity.
This is feasible due to the effect of plant on soil, which resists flow but varies depending on the vegetation. This study was able to produce or develop results that can be used by engineers in the design of channels, highways, and bridges, as well as farmers in selecting vegetation with a higher hydraulic roughness coefficient to control erosion on their farmlands by reducing flow erosivity.
1.5 SCOPE OF THE STUDY
The purpose of this study is to determine the hydraulic roughness coefficient, n, of some plants in order to select vegetation capable of controlling erosion.
1.6 Significance of the Study
The purpose of this study is to get results on the hydraulic roughness coefficient, n, of various grasses and to identify those with the ability to resist flow based on their vegetative features.
Need help with a related project topic or New topic? Send Us Your Topic