Velocity field and transverse dispersion in vegetated flows

In recent years aquatic vegetation has become more accepted and important in the river restoration schemes and preserving river ecology. The purpose of this thesis is to investigate the influence of emergent vegetation on velocity and turbulence fields in order to have a better understanding of the effect of vegetation on the transverse mixing processes. To achieve this objective, a series of experiments was conducted in an open channel flume with emergent rigid rods in both staggered and aligned arrangements. Detailed velocity, turbulence and dye tracer measurement were carried out for six vegetation densities relating to solid volume fractions (SVF) in the range 0.51 % to 7.79 %. In sparse vegetation (SVF < 10 %) as expected the normalised spatially-averaged longitudinal velocity reduces as the vegetation density increases with approximately 30 % to 50 % reduction when the solid volume fraction is doubled. Results indicated that in sparse vegetation, the normalised turbulence intensities increased with increasing solid volume fraction. The bulk drag coefficient increased with increasing vegetation density whilst decreased with increasing stem Reynolds number. The transverse mixing coefficient increases with both increasing vegetation density and stem Reynolds number. The current study showed that for sparse vegetation (SVF < 10%), the transverse mixing coefficient has a stronger correlation with turbulence intensity compared to transverse shear. Therefore indicating that within sparse vegetated flows, turbulence dominates over transverse shear in transverse mixing. In addition to that, transverse mixing also correlate better with double-averaged turbulence intensity compared to turbulent kinetic energy. This reflects that the turbulence in the longitudinal direction plays a greater contribution to the overall transverse dispersion than the contribution of the total turbulence in all three directions. Finally two vegetation transverse dispersions models proposed by other researcher for randomly distributed vegetation were tested against data from the current study. Both models were found to predict reasonably well

The stability of diaphragm wall for deep excavation

Rapid urbanisation and the increase in population has led to massive use of underground spaces, especially in the city. Before an underground structure is built, the use of retaining structure is crucial in order to prevent the excavation from failure. Diaphragm wall is a widely used retaining structure, particularly for deep excavation. A holistic understanding of the performance and its behaviour is essential to provide stability of the soil retained. A parametric study by using Plaxis2D has been conducted to determine the factors affecting the stability of diaphragm wall and the excavation sites in underground Mass Rapid Transit station of Hospital Kuala Lumpur (HKLX). The objectives of this study are to determine the effect of diaphragm wall stiffness, groundwater drawdown and the depth of wall for deep excavation. The stability is captured based on the lateral deflection of wall, bending moment, safety factor and ground movement near the diaphragm wall. From the study, it is found that the diaphragm wall with high stiffness can reduce wall deflection up to 20% with the addition of 49% bending moment and achieve a high factor of safety. Furthermore, groundwater drawdown is seen reducing lateral deflection of the wall up to 1.08% as well as increasing the factor of safety. Finally, decreasing wall depth reduces the wall deflection by 0.38% and also the basal heaving

Water salinity variability mapping for flooded paddy plots at Kuala Kedah, Malaysia

Salinity is an essential parameter in rice cultivation activity. It has a significant impact on paddy growth and also the yield of paddy. However, the level of salinity concentration in paddy plots depends on the surrounding conditions. The distance of the paddy area from the coastline, the temperature and intensity of rainfall should be considered in studies involving water quality. Additionally, the tide of events is also included in this study because of the position of the study area near the coastline. Therefore, this study was conducted to assess the level of salinity in two different rice cultivation seasons and describe the level of salinity concentration using a salinity variability map using the Inverse Distance Weighted (IDW) interpolation method. The data collection activities involved water sampling at 44 water inlets for each paddy plot in 30 hectares of the study area by referring to the Day After Sowing (DAS) as the paddy’s growth stage. These water samples were collected on 10 DAS, 40 DAS, and 60 DAS and subsequently tested using a portable conductivity meter namely EC500 Exstick II pH/Conductivity/Temperature Meter. Parallelly, georeference data which is latitude, longitude and elevation were gathered using Garmin GPSMAP 64s. Then, these data were analyzed using the IDW interpolation method in ArcGIS software and comes with salinity variability maps. The produced maps give an overview of the salinity concentration distribution by color scale range. Based on these salinity variability maps, the highest salinity concentration was recorded on 10 DAS and 60 DAS during Season 1 2019 and Season 2 2019, respectively for both tidal events. This result shows that the salinity concentration trend for both seasons is different due to the amount of rainfall received and the position of the paddy plot compared to the mean temperature factor

The application of open FOAM in modelling flow for vegetated channel

Vegetation plays an important role in the hydrodynamic behaviour of an open channel flow. This study attempted to investigate the flow characteristics of an emergent vegetated channel using Open-source Operations and Manipulation (OpenFOAM). InterFoam is an OpenFOAM solver used to model this simulation. It is one of the methods available to model free-flow surface flow. Results for flow velocity profile can be generated using ParaView software. This study used a constant inlet velocity of 0.0417 m/s. There are two sets of models including model L8 with a solid volume fraction (SVF) of 8% using 9 rigid dowels, and model 4S with SVF of 4% using 17 dowels within a 1.2 m2 study area. Dowels in L8 are arranged in linear formation compared to the 4S model in a staggered arrangement. The study found that in model 4S, the stem-scale vortices are developed individually after each dowel due to sparse staggered vegetation. Meanwhile, model 8L suggests oppositely the vortex is cramped from the closeness of the dowels. The shear layer is formed as the flow enters the vegetation patch at upstream and the instability causes the shear layer vortices between inside and outside the vegetation region. Both models agreed that as the flow moves downstream the vortices are greater and make the streamwise velocity region become slower. The vertical velocity profile acknowledges the shear layer patch-scale vortices have a greater influence on the flow of both models. The magnitude of turbulence intensity in lateral directions is bigger in model 4S than in model 8L. The influence of vortices shed by upstream cylinders has an increasing impact on the irregular shedding behaviour of downstream cylinders as plant density increases. In general, the TKE values of the Model 4S are higher than those of the Model 8L. Regardless of the solid volume percentage difference, the vegetation pattern between linear and staggered has an effect on the flow. Computational Fluid Dynamic (CFD) is indeed capable to solve complex hydrodynamic characteristic

Permodelan fizikal bagi kajian muara Sungai Langat

This study examines the sediment plume behaviour as it enters the sea. It uses the physical model and remote sensing techniques. This paper will only discuss the application of physical model in suspended sediment study at Sg. Langat estuary. Sg Langat estuary model was built according to Froude criterion. It was designed as a fixed bed using distorted scale model. Sg. Langat estuary model was characterized into wavelength (L), wave height (H), wave period (T), current velocity (V) and wave celerity (c). Prototype analysis was made using calculated data from physical model using upscale equation. It shows that, there exists a scale effect on wave height (H) data. Sediment plume dispersion simulation in physical model proved the importance of wave in sediment movemen

Teknik penderiaan jauh dalam kaji~ sedimen terampai di muara Sungai Langat

This study examines the sediment plume behaviour entering the sea using the physical model and remote sensing techniques. This paper will only discuss the application of remote sensing in suspended sediment study at Sg. Langat estuary. CIMEL radiance meter was used as a sensor to record optical data (digital count value or DN) from the simulation of the sediment plume dispersion in the model. This study observes the relationship between the DN obtained with the suspended sediment concentration. Results from correlation analysis show that the relation between DN and sediment plume concentration in the lab is most significant and strong at 0.85 μm wavelength, and the weakest relation is in the 0.45 μm wavelength. Small water particles from the wave generation were identified as one of the most important atmospheric disturbance to optical data, especially for shorter wavelength i.e. 0.45 μm. Beside that, water roughness and additional illumination from the 1000 watt spotlight also affect the DN values obtained. Water roughness has caused the increase in the DN value, while illumination from spotlight has caused a shift in the peak of spectral signature to longer wavelength, i.e. 0.85μ

Monitoring of three stages of paddy growth using multispectral vegetation index derived from UAV images

Paddy cultivation in Malaysia plays a crucial role in food production, with a focus on improving crop quality and quantity. With current national self-sufficiency levels ranging between 67 and 70%, the Malaysian government intends to produce higher-quality crops and boost agricultural production. However, the prominent paddy-producing state of Kedah has witnessed a decline in yields over the years. To address this, the study explores the effectiveness of unmanned aerial vehicles (UAVs) equipped with vegetation indices (VIs) for monitoring paddy plant health at various growth stages. Researchers acquired aerial imagery during two seasons in 2019, capturing three distinct growth stages: tillering (40 days after sowing), flowering (60 days after sowing), and ripening (100 days after sowing). These stages represent critical points in the paddy plant's life cycle. Agisoft Metashape software processed the images to extract VIs data. The study found that the Normalized Difference Vegetation Index (NDVI) and Blue Normalized Difference Vegetation Index (BNDVI) exhibited over 90% similarity. In contrast, the Normalized Difference Red Edge Index (NDRE), utilizing near-infrared and red-edge light reflections, demonstrated a unique relationship. NDRE outperformed NDVI and BNDVI with an R-squared value of 0.842, showcasing its superior accuracy, especially for dense crops like paddy plants sensitive to subtle changes in vegetation. In conclusion, this research highlights the potential of UAV-based VIs for effectively monitoring paddy plant health during different growth stages. The NDRE index, in particular, proves valuable for assessing dense crops, offering insights for precision agriculture and crop management in Malaysia

FLOOD FORECASTING MODEL USING EMPIRICAL METHOD FOR A SMALL CATCHMENT AREA

The two most destructive natural disasters in Malaysia are monsoonal and flash floods. Malaysia is located in the tropical area and received on average, around 2800 mm of rainfall every year. Due to this high amount, a reliable and timely flood forecasting system is necessary to provide early warning to minimize the destruction caused by flash flood. This study developed and checked the adaptability and adequacy of the flood forecasting model for 93 km2 catchment area, Kampung Kasipillay, in Kuala Lumpur. The Empirical Unit Hydrograph Model was used in this study and past rainfall data, water level and stagedischarge curve were used as inputs. A Rainfall-Runoff Model (RRM) which transforms the rainfall to runoff hydrograph, was developed using excel. Since some data, such as properties of the watershed, are not always complete and precise, some model parameters were calibrated through trial and error processes to fine-tune the parameters of the model to get reliable estimation. The simulated unit hydrograph model was computed in prior runs of the flood forecasting model to estimate the model parameters. These calibrated parameters are used as constant variables for flood forecasting model when the runoff hydrograph was regenerated. The comparison between the observed and simulated hydrograph was investigated for the selected flood events and performance error was determined. The performance error achieved in this study of 15 flood events ranged from -2.06% to 5.82%.e

Water budget-salt balance model for calculating net water saving considering different non-conventional water resources in agricultural process

Iraq is facing a dire water crisis due to the decrease in water quantities flow in Tigris and Euphrates Rivers. Due to population growth, several studies estimated the water shortage in 2035 to be 44 Billion Cubic Meter (BCM). Thus, Water Budget-Salt Balance Model (WBSBM) has been developed, applied and examined for the Euphrates River basin to compute the net water saving from Non-Conventional Water Resources (NCWRs). WBSBM includes 4-stages; the first is to identify the required data correspond to the conventional water resources in the study-area. The second stage is demonstrating the water-users activities. Thirdly, develop model through the proposed NCWR projects that reflect the required data. The final stage involves net water saving computation while applying all the NCWR projects simultaneously. The results obtained the optimal potential net water saving amount, which are 6.823 and 6.626 BCM/year in 2025 and 2035, respectively. In conclusion, the proposed WBSBM model has comprehensively examined different scenarios of utilizing NCWRs and has determined the optimal potential the net water saving amounts