Dissertations/Theses - Department of Water Resources Engineering
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Item Forecasting Brahmaputra-Jamuna river flow from satellite data using artificial intelligence(Department of Water Resources Engineering (WRE), BUET, 2025-02-22) Asheque Mahmud, Md.; Jahan, Dr. NasreenBangladesh is a flood-prone country due to its low-lying geography, heavy monsoon rainfall, and frequent cyclones, particularly in the coastal and tidal regions. Severe flooding in recent decades has resulted in many causalities and food scarcity. As a result, reliable and timely flood forecasting and warning are recognized as crucial factors to decrease flood-related damage and human suffering. Unfortunately, the current flood forecasting system provides fairly accurate forecast for shorter lead times (upto 3 days) only (FFWC 2021). Therefore, improving medium to long-range flood forecasting with 5 to 10 day lead times has become essential for better flood preparedness in the country. The aim of this research was to explore the potential of artificial intelligence for medium-range flow forecasting with a 5-day lead time at the Bahadurabad station in the Brahmaputra basin, using data such as precipitation, precipitable water, soil moisture storage, and satellite-derived river water levels. Artificial Neural Network (ANN) and Support Vector Machine (SVM) were utilized for this purpose. This approach presents a promising alternative to traditional streamflow forecasting methods using a hydrologic model, with the results compared against the forecast from the Flood Forecast and Warning Centre (FFWC) of the Bangladesh Water Development Board. For both the ANN and SVM models, 70% of the available data was used for model training, 15% of data was used for model testing, and the rest of the data was used for independent validation. Various input data combinations (called ‘model scenarios’ here) are considered for the ANN and SVM models to simulate discharge. In addition, each data combination was tested using the currently available data, which has a 5-day latency, real-time data, and forecast data, as not all variables are yet available in real-time or forecasts, but are expected to be in the near future. The model that considers all input variables (scenario 01) and the model that uses a combination of water level, precipitation, and soil moisture as inputs (scenario 04) were found as the best models for both ANN and SVM. In this study, three models (Model A, Model B, and Model C) were developed to address data latency issues, considering different data availability scenarios. Model A uses ERA5 data, which currently has a 5-day latency period. Model B assumes the availability of real-time data (used ERA5 data ignoring latency). Model C simulates how discharge forecasts could be improved if reliable climate forecast data were available. The performances of the ANN and SVM methods demonstrated a comparable level of accuracy to the observed flow and, in some cases, surpasses the predictive accuracy of the FFWC model, which forecasts water levels that converted to flow via a rating curve. Here, the SVM methods generally outperformed the ANN methods. Specifically, for the SVM methods of Model A at which scenario A-01 achieved a Root Mean Square Error (RMSE) of 6802.82 m³/s, a coefficient of determination (R²) of 0.87, and a Nash–Sutcliffe Efficiency (NSE) of 0.87, while Model scenario A-04 resulted in a RMSE of 7236.50 m³/s, a R² of 0.85, and a NSE of 0.85. In case of evaluating the RMSE value by comparison in a percentage scale, it was observed that best SVM model scenario C-01 demonstrated an improvement of approximately 58.22% over FFWC Prediction of discharge via a rating curve. This research demonstrates that artificial intelligence, particularly SVM, offers a promising alternative to traditional flood forecasting methods, with improved accuracy in predicting flow at Bahadurabad station in the Brahmaputra basin. Its ability to utilize satellite-derived data enhances flood forecasting and contributes to more reliable predictions, which can significantly improve flood preparedness and risk management in Bangladesh.Item Distribution of suspended sediment transport between asymmetric bifurcated channels in mobile bed condition(Department of Water Resources Engineering (WRE), BUET, 2024-05-18) Aliur Rahman, Md.; Hossain, Dr. K.M. AhteshamBifurcations are a fundamental feature in alluvial rivers and estuarine systems, contributing to the complex dynamics of fluvial environments, alongside braiding, anabranching streams, and deltas. Despite extensive research, the distribution of flow and sediments at asymmetric bifurcations remains inadequately understood. To achieve in-depth understanding of flow and suspended sediment dynamics at asymmetric bifurcations, this study has been conducted in the Hydraulics and River Engineering Laboratory at the Department of Water Resources Engineering, BUET. The experimental investigation focuses on varying discharge rates and nose angles in asymmetric bifurcated channels to explore their influence on flow behavior and sediment distribution. In order to achieve the objectives of this study, a total of thirty-six experimental runs have been conducted comprising three distinct nose angles: nose type-1 [θ = (+) 3.5°], nose type-2 [θ = (-) 4.2°], and nose type-3 [θ = (-) 7.3°]. Each nose angle has been tested under three different upstream discharges (40 l/s, 50 l/s, and 60 l/s) with respective rate of sediment feeding. Throughout the experiments, key parameters such as discharge, flow velocity, water depth, bed level changes, and suspended sediment concentration have been measured at specific locations across the channel. Flow visualization has been also observed, particularly near the bifurcation. The results reveal that nose angle plays a vital role in suspended sediment distribution, with turbulence near the nose tip significantly increasing sediment in suspension. As the nose angle changes from positive to negative indicating flow area of nose tip or branch mouth opening narrower to wider of a bifurcated channel, the suspended sediment transport ratio increases for a given upstream flow discharge in that branch. Velocity variation patterns have been observed in relation to nose angle and discharge variation. Bed level changes indicates that erosion intensifies with increasing discharge, and the erosion-deposition pattern varies depending on the nose angles. The relationships among flow patterns, velocity variations, suspended sediment concentration, and bed level changes are examined with consideration of downstream boundary conditions. The bifurcation geometry, especially the branch mouth shape, plays a critical role in sediment dynamics. The nose angle is the significant factor that governs the distribution of sediment and discharge in river bifurcations. Nine nodal point relations of two bifurcated branches have been found for three different nose angles and three upstream discharges. The parameters of the nodal point relations, namely coefficient M and exponent k, reveal a defined pattern corresponding to variations in nose angle. However, these parameters do not demonstrate a significant linear correlation with variations in discharge. The suspended sediment transport ratio of the bifurcated channels is directly proportional to the discharge ratio and inversely proportional to the quasi-offtake bifurcated angle. These results have been compared with the relevant studies and found satisfactory. Nose angle is a vital factor in determining the distribution of suspended sediments between asymmetric bifurcated channels. Therefore, this study provides valuable insights into the interrelationship between suspended sediment transport and nose angle variations under asymmetric conditions, offering a deeper understanding of bifurcation dynamics in the fluvial systems.Item Development of water allocation mechanism for water stressed and abundance area under changing environmental condition(Department of Water Resources Engineering (WRE), BUET, 2023-09-16) Faisal Ahmed, Khan; Khan, Dr. Md. Sabbir MostafaWater is one of the most used (and abused) natural resources on the earth. Water resources are particularly vital for the Agriculture sector. Irrigation has been a determining factor in sustaining the self-sufficiency of Bangladesh in food grain production. In addition to the agriculture sector, domestic and industrial sectors have also been important consumptive water users. Water is a limited resource spatially and temporally. Therefore, this resource should be allocated among different sectors and users in an equitable and efficient way. This aspect of allocation of water is stated explicitly in SDG 6 on water and its sub-goals. Water management in Bangladesh and elsewhere is becoming more challenging due to growing demand and increasing conflict among users. The decision support tool, Water Evaluation and Planning System (WEAP) developed by Stockholm Environmental Institute (SEI) is increasingly being applied in managing water resources systems in diverse environments across the world. This study employed this toll for Gazipur and Manikganj districts, where the former area is water abundant and the latter is water stressed. Being the adjacent areas to the capital Dhaka, these districts are considered as commercially and industrially important area in Bangladesh. Water resources of this area is distributed unevenly over space and time (between and within years) making it a scarce resource in most places and situations. These districts are used to compare in respect of water resources availability, demands, unmet demands and managements. For water allocation, water demands of the different sectors for the base year 2016 and 2020 have been estimated. Water demands have been projected for the year 2030 and 2050. Water demand of domestic sector has been estimated for base year 2016, 2020 and for future years 2030 and 2050. Water demand of agricultural sector has been divided into crop water demand and livestock water demand. Crop sector water demand has been assessed using meteorological data by using FAO CROP WAT 8.0 software. Major crops like Boro and Wheat are considered for determining irrigation water requirements. Irrigation water requirements have been assessed for the year 2016, 2020 and projected for the year 2030 and 2050. Questionnaire survey has been conducted to find out water requirements of different type of industries and commercial units. Water demands of cattle, buffaloes, goat, fowl and duck have been determined separately. For surface water resources, river discharges have been simulated using seasonal autoregressive integrated moving average (SARIMA) model. For groundwater, output of groundwater study conducted by Bangladesh Agricultural Development Corporation (BADC) has been used. Upstream and downstream water quality of major rivers have been compared. Surface and groundwater quality have been compared with national and international standards. Using hydrological Tennant method, Environmental flow of all relevant rivers have been estimated. GIS shape file, all sectoral demands, surface water, groundwater data have been incorporated in the WEAP model for water allocation and simulated. Finally, five scenarios have been developed. First scenario has been considered water consumption by demanding sectors without any management in 2016, 2020, 2030 and 2050. Second scenario described regular growth of water demand by all sectors with effective water management. Third scenario described the regular growth of water demand by all sectors with effective water management but no growth of water demand in the industrial sector. Domestic demand site management 11.5 percent and increasing irrigation efficiencies up to 2 percent in 2030 and up to 4 percent in 2050 have been considered as management in water demanding sectors. No unmet water demand has been found in Manikganj in the first three scenarios. But unmet water demand was found for Gazipur. For Gazipur, another two scenarios have been formulated to elucidate water scarcity. Forth scenario has been formulated to replace intensively irrigated boro rice with low water demanding vegetables. Water management have been selected as like the third scenario. But still unmet water demand prevailed. So, the fifth scenario has been formulated to introduce with industrial water reuse increased up to 35 percent in 2030 and 55 percent in 2050. Scenario IV and V have been the modified situation of scenario III. So, finally, five scenarios have been formulated for the allocation of water in the study area. In the current trend without water management, water demand in Gazipur will increase up to 4.37 billion cubic meters (bcm) in 2030 and 7.52 bcm in 2050. Scenario I has been introduced with regular growth of water demand with no management and regulation. The unmet demand was projected to increase to 1.82 bcm in 2030 and 6.42 bcm in 2050. For scenario II, total water demand in Gazipur was projected as 1.82, 2.80, 4.37, and 7.52 bcm for 2016, 2020, 2030, and 2050 respectively. No unmet demand was found in 2016. But unmet demands were found 0.18, 1.42, and 5.71 bcm for 2020, 2030 and 2050, respectively. Scenario III for water scarce district Gazipur resulted in, total water demand 1.82, 2.80, 2.81, and 2.83 bcm for 2016, 2020, 2030, and 2050, respectively. No unmet demand was found in 2016. But the unmet demands were found 0.179, 0.207, and 0.264 bcm for 2020, 2030 and 2050 respectively. After considering three scenarios, unmet demands were found in the water scarce Gazipur district. Boro rice was found to be an intensively irrigated crop in the study area. The scenario IV has been developed to change the cropping pattern in the low flow dry season. This scenario replaced the boro rice from the cropping pattern and introduced vegetables in the dry season. Water demand in scenario IV for Gazipur resulted in 1.37, 2.36, 2.42, and 2.50 bcm for 2016, 2020, 2030, and 2050, respectively. The unmet demands were found to be 0.16, 0.11, and 0.936 bcm for 2020 and 2030 accordingly. Finally, scenario V for Gazipur has been formulated with higher water reuse in the industrial sector. There was no unmet water demand in the Gazipur district. For Manikganj, minimum water demand has been found at 481.20 million cubic meters (mcm) for scenario III in 2050, maximum water demand at 534.80 mcm for scenario I in 2020, which are the reasons for the decreasing trend of crop land. There was no unmet water demand for Manikganj for all scenarios. Industrial waste water reuse has been found as a good guideline for lowering water demands. District level restriction on new industries has been found successful for lowering water demands. Vegetable cultivation instead of rice cultivation has been found effective in lowering irrigation water demands. Finally, district specific water uses guidelines or micro level water policy have been found to be very useful in improving water scarcity.Item Monitoring water level, discharge and shoreline of Jamuna river using multi-satellite data(Department of Water Resources Engineering (WRE), BUET, 2024-10-23) Abdullah, Faruque; Jahan, Dr. NasreenIn a river-centric deltaic country like Bangladesh, an optimal and efficient management of water resources is a challenging task. This is further exacerbated by the lacking coverage and availability of the observation data, such as water level, discharge, and bathymetry. Traditional in-situ observation platforms are costly to install and maintain, and the data is often publicly inaccessible. This does not meet water resources management requirements, where timely and reliable information with high spatial and temporal coverage is preferable. Therefore, this study aims to address these challenges by designing a multi-satellite monitoring system that provides comprehensive, timely, and accessible data on key water resources components i.e. water level, discharge, shoreline, and floodplain bathymetry—thereby enhancing spatial and temporal coverage to meet the critical needs of water resource management in Bangladesh. The multi-satellite monitoring framework developed in this study integrates altimetry data from Sentinel-3A, Sentinel-3B, Jason-2/3, Synthetic Aperture Radar (SAR) data from Sentinel-1 and spectral data from Sentinel-2. A comprehensive, automated, near-real-time monitoring system is developed that can monitor water levels, discharge, shorelines, and floodplain digital elevation models (DEMs) and implemented over the Jamuna River. By leveraging the multi-satellite technique, the observation period of water level and discharge has been significantly improved from an average of 10 days with single satellites to 3.90 days and a continuous record has been developed for 2008 to 2022. Using SAR and multi-spectral imageries from Sentinel-1 and Sentinel-2 respectively, an automated shoreline extraction technique is applied to monitor the river shoreline and morphology in quasi near real-time. Such continuous monitoring provides an annual floodplain DEM, as well as a yearly assessment of river erosion-accretion. The dataset generated in this study has been validated based on in-situ observations at BWDB stations i.e. Bahadurabad (SW46.9L) and Kazipur (SW49A) showing good performances in monitoring water level and discharges. Multi-satellite water level monitoring shows an RMSE, MAE, average percent error and correlation coefficient values of 0.53 m, 0.36 m, 2.31% and 0.98 respectively while discharge estimations exhibited RMSE, MAE, average percent error and correlation coefficient of 4,738 m³/s, 2,997 m³/s, 23.69% and 0.95 respectively at Bahadurabad station. Analysis of the DEM reveals that the floodplains along the Jamuna river have been substantially changed over the last ten years, and the global bathymetry product does not reflect the current river topography (particularly the Chars). In addition, the erosion zone identified in the process matches well with secondary newspaper-based field conditions. By leveraging the improved temporal frequency provided by the multi-satellite data, the water level and discharge datasets developed in this study were able to effectively capture flood events. Additionally, continuous monitoring of the shoreline and floodplain using high-resolution satellite imagery provided highly detailed information on flood extents, enabling precise mapping and comprehensive assessment of the affected areas. This study concludes that multi-satellite remote sensing technique presented here can not only be a reliable operational tool for water resources management agencies in Bangladesh, but also can provide valuable and publicly accessible dataset to the broad water resource research community. Such up-to-date and accessible dataset should be useful for further advancing research on floods, morphological evolution, as well as for more informed decision-making.Item Laboratory study on sediment distribution of asymmetric Bifurcated river(Department of Water Resources Engineering (WRE), BUET, 2024-05-11) Balayet Hossain, MD.; Hossain, Dr. K. M. AhteshamBifurcation of a river is observed when a river following in a single stream separate into two or more separate streams. Factors involved in bifurcation are the geometry of the bifurcation (cross-sectional area, depth, width, nose angle), sediment characteristics, particle size, fall velocity, bed load, suspended load, etc. Several studies have been carried out on different aspects of channel bifurcation, e.g., dynamics, equilibrium configurations, the evolution of channel bed and bank, and modeling. This study aims to investigate the mutual effect of sediment discharge and flow discharge due to the variation of nose angle in an asymmetric bifurcated channel. Therefore, stepwise methodology has been formulated to achieve the objectives. Hence, an asymmetric bifurcated channel (main channel and two bifurcated channels) with fixed banks and mobile sand bed has been designed and constructed accordingly in the sand bed facility of the Hydraulics and River Engineering Laboratory, WRE, BUET, to conduct experimental runs. A total of thirty-seven runs have been performed for three different nose angles with three different upstream discharges (20l/s, 30l/s, and 40l/s) for varying water levels while feeding sediment into the flowing water. Data have been collected precisely and observation has been noted. The collected data have been analyzed and presented in different forms. The study reveals that accretion is dominant in the main channel and erosion is dominant in branch-1 and branch-2 of the bifurcated channel. It is found that high discharge mostly results in erosion in the channels, except for nose type 2 (at high discharge). It is evident from the results that the reduction of inflow area at the entrance nose to a certain amount is the major variable for the difference in sediment transport through bifurcated channels and also, sediment transport in the bifurcated channels is independent of upstream water discharge. It is found that for a particular discharge ratio, the sediment transport ratio is increased for nose angle variation from negative to positive. Also, the sediment transport ratio decreases for nose angle variation from positive to negative when a discharge is held constant. However, the sediment transport ratio increases for nose angle variation from positive to negative when a discharge is increasing. An empirical equation has been developed that shows the sediment ratio is proportional to the discharge ratio and inversely proportional to the quasi-offtake (bifurcation) angle. The coefficient M and exponent k increase with the increase of discharge. For a particular upstream discharge, M increases as the nose angle changes from negative to positive. When the nose angle is held constant, the value of exponent k in the nodal point relation increases as the discharge increases. It is expected that the outcome of the study will be helpful for the assessment of flow and sediment movement in bifurcated channels.Item Hydrodynamic modeling of Turag river to increase the draft for navigation(Department of Water Resources Engineering (WRE), BUET, 2023-06-20) Rafsan Jany, MD.; Zobeyer, Dr. A T M HasanThe Turag River provides an important riverine link with the Dhaka Metropolitan City. Other peripheral rivers such as Balu, Lakhya and Tongikhal are also important in maintaining circular water route and natural environment of the city. Through the ages, these rivers have been silted up and offtakes from the main source with the Jamuna have been almost disconnected. During the dry season causing obstructions to navigation in the surrounding rivers of Dhaka due to reduced drafts. To address this issue, a mathematical model-supported study has been taken to develop strategies for maintaining the required draft of the Turag River and ensuring a continuous navigation route around the city. The objective of this study is designed to assess the hydrodynamic parameters including water level, discharge and flow. For assessing the hydrodynamic condition, a 1D numerical model has been developed and simulated in HEC-RAS for the year 2017 and 2018. The model simulated stage hydrographs have been compared with observed stage hydrographs at station Mirpur SW302 of Turag river to calibrate and validate the model using Manning's roughness, n as the tuning parameter. Eventually, scenarios have been developed by dredging and checking the stability of dredged channel. The average percentage of lowering the existing bed level is 28.04%, and the average draft increased to 0.77 m. The model study indicates the necessity of lowering of existing bed by dredging about 67 Mm3. From dredged conditions, the longitudinal slope found 7 cm/km and the side slope for different cross-sections are approximately 1:2 to 1:3. To maintain the minimum draft at dry season for the BIWTA Class-III navigation route, some sections areas need to be dredged, and after that, BSTEM model analysis has been done for checking the stability of the dredged channel. It is hoped that the study will be helpful to assess hydrodynamic parameters and dredged Condition of the River for future Navigation of this route.Item Study on water demand and availability for purbachal new town using mathematical models(Department of Water Resources Engineering, BUET, 2023-08-29) Raiful Islam, Md.; Md. Abdul Matin, Dr.Purbachal New Town, a large-scale township project, has been reinitiated by the government to meet the increasing demand for population influx to the capital city, Dhaka. The development of new townships like Purbachal will add more pressure on the city's overall water supply. The present study has focused on predicting the future water demand and assessing the water availability for this newly planned township using mathematical models. By 2060, the total daily water demand for Purbachal will increase to 155 MLD, 193 MLD, and 251 MLD for the low, moderate, and high growth projections. Alongside the use of surface water, the study has explored alternative supply sources like rainwater harvesting and greywater reuse and achieved savings from demand site management for meeting the incurred water demand. The Geospatial Stormwater Management Model (GeoSWMM) quantifies rainwater harvesting as a low-impact development (LID) measure. The estimated yearly stormwater runoff is found to be 24476 million liters. Of these, 14432 million liters can be harvested from the rooftop area, which can meet up to 26% of the total water demand in a low-growth scenario. The current study has constructed different water demand and supply scenarios to examine the best possible combination of supply sources to minimize the difference between water demand and delivered supply. The Water Evaluation And Planning (WEAP) model is set up for 2020 and runs for the next 40 years using the projected water demand and available supply sources for the study area. The model result shows that the average unmet demand will increase to 24 MLD (16% of the total daily demand), 63 MLD (33% of the total daily demand), and 129 MLD (52% of the total daily demand) for the three-demand projection if none other than surface water is considered as a supply source. Seven other scenarios, each having three sub-scenarios (A, B, and C), have evaluated the impact of using alternative supply sources. The result shows that 45% utilization of total rainwater (Scenario 1B), 20% savings from demand site management (scenario 2C), or 25% of total demand covered by greywater reuse (scenario 3B) are found to be optimum for low growth demand. Combining 20% savings from demand site management and 30% of total demand by greywater reuse (Scenario 6C) is the optimum scenario for the moderate growth case. Besides, the combined use of 60% of total rainwater, 20% savings from demand site management, and 30% of total demand by greywater reuse (Scenario 7C) is the optimum scenario for the high growth case. These model results will open the path to effective decision-making and good water management for the Purbachal New Town despite having scope for further improvements.Item Evaluation of surface energy balance algorithm for land (SEBAL) model in the context of Bangladesh(Department of Water Resources Engineering (WRE), BUET, 2023-08-30) Dutt, Dipta Prahar; Jahan, Dr. NasreenSurface energy fluxes (also known as surface heat fluxes) consist of net radiation flux (Rn), soil heat flux (G), sensible heat flux (H), and latent heat flux (LE). Estimation of these fluxes is essential for climate modeling, disaster monitoring, plant water demand assessment, plant growth modeling, irrigation management and also in determining the large-scale atmosphere and ocean circulation patterns which eventually drive weather and climate. In situ measurements of these fluxes are expensive and available only over a limited number of field experiment sites. The Surface Energy Balance Algorithms for Land (SEBAL) is a well-known remote sensing-based model of estimating fluxes. Few studies have employed SEBAL in assessing heat fluxes in Bangladesh for few selected dates but none of them compared their results with any field measured data. This study aims at evaluating the performance of new automated version of SEBAL model to estimate energy fluxes in the context of Bangladesh. The SEBAL model has been set up for 2006 to 2012 using Landsat images of seven different wavelengths and climate data. Albedo, radiometric surface temperature, Soil-Adjusted Vegetation Index (SAVI) have been then computed from the pre-processed Landsat images. Net radiation (Rn) has been computed from downwelling solar radiation and land surface temperature obtained from Landsat thermal images. Then ground heat flux has beencomputed from Rn and Normalized Difference Vegetation Index. Sensible heat flux (H) is calculated as a function of observations such as wind speed, vegetation type and roughness and surface to air temperature differences. The hot and cold pixel necessary for H computation has been automatically calibrated. Then latent heat flux has been estimated as the residual in the surface energy balance. Necessary data have been collected from Asiaflux, United Stated Geological Survey (USGS), Bangladesh Meteorological Department (BMD) and Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2). Surface energy fluxes estimated from SEBAL model were then converted to daily fluxes and compared with the field measurements from an Eddy Covariance Tower located at an agricultural field of Bangladesh Agricultural University, Mymensingh. Estimated surface energy fluxes from SEBAL shows very good correlation with observed data of Eddy Covariance Tower at agricultural field. For net radiation, coefficient of determination (R2) and root mean squared error (RMSE) are 0.95 and 20.01 W/m2, respectively. Daily latent heat flux also shows good correlation with observed data. R2 and RMSE for latent heat flux are 0.75 and 18.45 W/m2, respectively. Temporal variation and mapping of surface energy fluxes for four types of land uses i.e., agricultural field, waterbody, urban area and forest area have been also been carried out. Net radiation reduces by 39.58%, 37.41%, 34.36% and 32.68% respectively for agricultural field, waterbody, urban area and forest area from summertime average to wintertime average from years 2006 to 2022. Latent heat flux also reduces by 48.44%, 50% and 0.01% respectively for agricultural field, waterbody and forest area from summertime average to wintertime average whereas LE increases by 19.18% for urban area over the years. Ground heat flux reduces by 61.22%, 76.57% and 104.14% for agricultural field, urban area and forest area respectively from summertime average to wintertime average over the years. Sensible heat flux reduces by 22.92% and 1.10% from wintertime average to summertime average for agricultural field and waterbody respectively whereas reduces by 47.85% and 82.72% from summertime average to wintertime average for urban area and forest area respectively. This study indicates that remote sensing-based surface energy balance algorithm, SEBAL can be a promising alternative to ground measurements of heat fluxes in the data-scarce regions.Item Mathematical modelling of stormwater drainage of the catchment of boalia khal including low impact development measures(Department of Water Resources Engineering, BUET, 2023-04-11) Abdur Rahman, Md.; Hasan Zobeyer, Dr. A T MDhaka city is one of the fastest growing megacities in the world and is facing a massive challenge to deal with rainfall-induced flooding. Severe storm events due to climate change and landuse changes are playing a key role in the acceleration of urban flooding. The main drivers of rainfall-induced flooding are fast & unplanned urbanization and incapacity of stormwater drainage systems to manage the peak runoff volume. The catchment of Boalia khal in the northeastern part of Dhaka city is one of those areas which face frequent flooding induced by intense rainfall during the pre-monsoon and monsoon periods. This study aims to obtain an optimum combination of Low Impact Development (LID) measures for stormwater management in the Boalia khal catchment area. This research focuses on investigating the influence of different individual LID (Rainwater Harvesting (RWH), Soak-Away Pits (SAPs), Porous Pavement (PP), Wetland Basin (WB)) and a combination of LID measures for the proposed drainage system to reduce the runoff volume, flood extent and pumping duration in the Boalia khal catchment area. A 1D-2D coupled drainage model was developed using the DHI MIKE URBAN interface. The design rainfalls were distributed using the Alternating Block Method. The drainage system of Dhaka city has been designed to handle a 1-day, 5-year rainfall event, while the pumps have been designed to cope with a 2-day, 5-year rainfall event. Consequently, the current systems are ill-equipped to deal with rainfall events that lead to urban floods, such as 1-day 10-year and 25-year occurrences. To assess the effectiveness of LID (Low Impact Development), this study conducted an analysis of various scenarios considering these different rainfall events. The peak water level is reduced by 8.4 cm at upstream of Boalia Khal and by 19.2 cm at downstream for a 25-year rainfall event after the application of low impact development measures. The combined (RWH-SAPs, PP and WB together) application of LID measures decreased the flood-affected area by 14% for a 10-year storm event and 15% for a 25-year storm event compared to without LID. Integrating RWH-SAPs and PP in the future drainage system may reduce pumping duration by up to 14%, equivalent to 3.0 hours. The addition of Wetland Basins alongside these LID measures can lead to a more substantial reduction of pumping duration up to 53%, i.e. 10 hours for a 10-year storm event.Thus, the application of porous pavement is effective for the reduction of flood extent and WBs are more effective for the reduction of pumping duration along with flood extent. To get optimum performance of wetland basins the invert level of the inlet control structure was set below the pump start level. It was found that climate change could lead to increased flood extents and longer pumping durations. However, the application of LID strategies mitigated these impacts, reducing flood extents and pumping durations under climate change scenarios.LID measures reduced the flooded area by 20% and average pumping duration by 43% for a 100-year storm event.Item Experimental investigation of local scour around two piers in tandem arrangements for different nose shapes(Department of Water Resources Engineering, 2023-07-22) Mukidul Islam, Md.; Mahalder, Dr. BadalA popular configuration for studying complex flow characteristics and local scour around groups of piers by using piers arranged in tandem configurations or side-by-side. Alongside factors such as pier spacing and median sediment size, the nose configurations of piers play a key role in influencing scour patterns, and subsequently, the flow characteristics around the piers. In this thesis, an experimental investigation was conducted to analyze the effects of pier nose shape and pier spacing on turbulent characteristics and scour depths around the piers.Three different shapesnamely, round nose, 600 nose angle, and 900 nose angle pierswere placed in both single and tandem arrangements. In the tandem arrangements, two identical piers were positioned at center-to-center (C/C) spacings of 3L, 6L, and 9L (where L represents the pier length) within two different sediment beds: Sand-A (d50 = 0.23 mm) and Sand-B (d50 = 0.89 mm). Three-dimensional instantaneous velocity was measured using an Acoustic Doppler Velocimeter (ADV). From the experiments, it was observed that the magnitude of turbulent intensity and turbulent kinetic energy between the piers was found to be higher for smaller center-to-center (C/C) spacing, attributed to increased interference from the rear pier. The turbulence structure was also influenced by the shape of the pier as the 900 nose angle piers exhibited the maximum turbulence intensity and turbulent kinetic energy.The Reynolds Shear Stress value near the bed was higher at the upstream of front pier. In contrast, at downstream of the pier, an oscillating (positive-negative) pattern was observed due to flow separation and vortex shedding. Analyzing the measured scour depths data, it was observed that for a single pier, the maximum scour depth was 19.61% higher around the round nose pier compared to the 600 nose angle pier, and 5.89% higher compared to the 900 nose angle pier. This difference was attributed to the comparatively blunter nose of the round nose pier, which led to an increase in the magnitude of the downflow as well as the formation of a horse-shoe vortex. The position of maximum scour depths also varied as for round nose pier; it was formed at the front of the pier. However, for the 600 nose angle and 900 nose angle piers, the maximum scour was observed at the frontal edge. The pier shape factorwas calculated as 0.88 for the round nose pier, 0.73 for the 600 nose angle pier, and 0.775 for the 900 nose angle pier. The smaller shape factors for the 600 nose angle and 900 nose angle piers were a result of their sharp leading edges. Experimental results also showed that the scour depth around the front pier always exceeded that around the rear pier. The highest scour depth around the front pier was recorded for 3 L C/C spacing compared with 6L and 9L C/C spacing attributed to the increased drag force of the front pier compared with other spacings. Notably, at a 9L C/C spacing, the scour depth around the front pier closely resembled that of a single pier configuration.Furthermore, it was observed that regardless of pier shape, the maximum scour depth was more pronounced for Sand-A in comparison to Sand-B. This observation was attributed to the formation of an armor layer at the base of the scour hole in Sand-A, which was influenced due to the accumulation of larger particles within the scour hole. Four existing scour depth predicting equations were used to compare predicted and observed scour depths around piers of different shapes. The results showed that the predictive equations consistently overpredicted scour depths. Among the four equations, Lacey's equation exhibited close values to the experimental results compared to the others.Lastly, a correction factor was introduced for incorporating the spacing between two piers in the CSU single pier equation, enhancing its ability to predict scour depths in tandem pier arrangements. Turbulence characteristics, as observed in the experimental results, were also compared with Computational Fluid Dynamics (CFD) model using ANSYS software. The simulated results exhibited patterns of turbulence characteristics similar to the experimental findings. However, the simulated results consistently overestimated the normalized streamwise velocity at mid-depth for all pier shapes. Furthermore, in all cases, the CFD simulations underestimated the normalized turbulent kinetic energy compared to the experimental findings. The findings of this study would be helpful in enhancing our understanding of the effects of pier nose shapes and spacing on turbulent flow characteristics and scour development around tandem piers.