Dissertations/Theses - Department of Water Resources Engineering
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Item Experimental study on hydraulic parameters and morphological behaviour of bank protection under oblique flow(Department of Water Resources Engineering (WRE), 2016-09-28) Sarkar, Sudip; Kulsum Navera, Dr.UmmeBraided river is one of the major river patterns of the alluvial river. It is a type of channel consisting of small branch channels with highgradient andsediment load separated by braid bars.This differentiation as well as further modificationof the channel originating oblique flow to the existing channel. This oblique flow has influenced to the flow hydraulics and morphological behavior of the affected braided channel. Discharge ratio and Obliqueangle between main and oblique flow channel have been observed asessentialparametersto investigate the dominant variables at the meeting point of these flow as well as downstream of combined channel. Time and flow dependent hydraulic parameters have been susceptible to erosion of bank protection works as well as the river bed itself. In the present study, a physical model has been carried out at River Research Institute (RRI), Faridpur, funded by Institute of Water Modelling (IWM), Dhaka to determine the hydraulic parameters and morphological behavior of bank protection work due to oblique flow. The basic variables such as discharge ratio and oblique flow angle have been considered in this research work.These two factors have influenced considerably to the hydraulic parameters as velocity distribution, scour depth and other related morphological parameters of the channel. There have been accomplishedtwenty-one (21) model run in this researchwork to fulfill the desired objectives.After a long trial and error process, the scale of the undistorted physical model has been selected as 1:50 but not to be done for bed material of the channel bed. In this study, there have been consideredthree oblique angles(200, 400,600).For each oblique angle, three different discharge ratios1.2,1.4,1.6 hasalso beentaken into account.For the design of bank protection works, stone boulders and geobag have been used at the right bank of the combined channel.It has been observed that velocity distribution and scouring pattern of the channel inclusive with the behavior of bank protective materialare beingclosely inter-related and influenced due to the presence of oblique flow.Item Effect of nearshore structures on reduction of wave energy along different locatons of coastline of Bangladesh(Department of Water Resources Engineering, 2019-09-28) Rahaman, Md.Tawhidur; Navera, Dr. Umme KulsumThe natural shape of Bangladesh coastal and marine areas is controlled by dynamic processes such as tides, wave actions, strong winds and it faces continuous land erosion and accretion. This study prioritizes the most vulnerable locations on the Bangladesh coast and finally selected the two most erosion-prone areas at the Cox Bazar coastline along the marine drive. Although there are few measures have been taken by the local authority using geotubes, tetrapods, and concrete block, but this does not stand appropriately against wave action; as a result, all previous measures are futile. This study is based on mathematical modeling to simulate the nearshore complex hydrodynamic and wave conditions. To analysis, the real-world nearshore scenarios, a two-dimensional model named Delft3D is used to set up the Bay of Bengal model. The coupled model is fully calibrated and validated to simulate the nearshore structures to examine the wave height, wave energy reduction rate with associated sediment transport patterns in the structures' vicinity. A series of Breakwater and Groins have been used at two different sites along the Cox Bazar coastline. The analysis shows that at site one, which is 1.7 km, Breakwaters are less capable of trapping sediment. The intervened series of Breakwater has a wave height reduction rate between 27 % - 53 %, wave energy reduction rate between 47%-78% and two of the Breakwater shows continuous erosion among three. On the other hand, series of Groin has wave height reduction rate between 9 % - 76 %, wave energy reduction rate between 17%-91%, and six groins shows continuous sedimentation within seven where one Groin shows continuous erosion. The analysis from site two, which is about 3 km shows, Groins are more capable of trapping sediment compare to Breakwater. The series of Breakwater at site two has a wave height reduction rate between 30 % -53 %, wave energy reduction rate 51% -78%, and all the eleven Breakwater shows continuous erosion; whereas, a series of Groin has wave height reduction rate between 15% - 53 %, wave energy reduction rate 51% -78%, and eleven groins show continuous sedimentation within thirteen where two Groin shows erosion. Moreover, the beach and sea view are also very important for the study areas, and Groins can be the best solution where no sand nourishment is required for long-term sustainability. This study is one of the first in Bangladesh to examine the nearshore structural intervention with Breakwater and Groin, can be used as a reference for field implementation or further research work.Item A Study on Fluvial Flood Hazard and Risk Assessment of Arial Khan River Floodplain under Future Climate Change Scenarios(Department of Water Resources Engineering, 2019-01-14) Roy, Binata; Khan, Dr. Md. Sabbir MostafaBangladesh is highly susceptible to flood due to its location at the confluence of the world’s three major basins– Ganges-Brahmaputra-Meghna (GBM) and hydro-meteorological and topographical characteristics of the basins. Increase in temperature and precipitation due to climate change will significantly increase the monsoon flow of the GBM rivers which may lead to more intense and frequent floods in Bangladesh in upcoming decades. In this study, the fluvial flood hazard and risk of Arial Khan River floodplain have been assessed for the predicted climate change scenarios of RCP 2.6 and RCP 8.5. A calibrated and validated SWAT model of GBM basins has been used to project the future flow magnitudes at Bahadurabad Transit (Brahmaputra River) and Hardinge Bridge (Ganges River) for RCP 2.6 and 8.5 scenarios. Using the flow magnitude of these stations as the upstream boundaries, a 1D HEC-RAS model has been set up for the Brahmaputra-Ganges-Padma River for generating future flow magnitude at Mawa of Padma River. Later, the discharge at the offtake of Arial Khan has been calculated establishing a linear regression equation between the Arial Khan and Padma River. Finally, a 1D-2D coupled model of Arial Khan River floodplain has been set up in HEC-RAS. This coupled model is calibrated and validated for Manning's roughness coefficient ‘n’ = 0.015-0.02 for the year of 2015 and 2017 respectively. After calibration and validation, the model is simulated for different periods of RCP 2.6 and RCP 8.5 scenarios: baseline (1976-2005), 2020s (2006-2035), 2050s (2036-2065) and 2080s (2066-2095). The model result shows that the total flood affected area is nearly 15% at the base condition which is increased to 30% and 47% approximately for the 2080s of RCP 2.6 and RCP 8.5 respectively. The hazard assessment reveals that at the base condition, 48%, 34% and 18% area are in the very low, low and high hazard zone respectively. It is increased to manifolds such as 21%, 27%, 34% and 18% in the very low, low, medium and very hazard zone respectively for the 2080s of RCP 2.6 and it became 22%, 26%, 34% and 18% in the low, medium, high and very high hazard zone respectively for the 2080s of RCP 8.5. Similar to hazard, risk assessment also shows that the very low and low risk zone will decrease and high and very high risk zone will increase significantly by the end of 21st century compared to the base period. Incorporation of vulnerability and exposure gives a complete different horizon to the overall assessment. It is found that some medium hazard zones have a high risk of flood damage due to its high exposure and vulnerability to flood while some high hazard zone falls into the low risk zone because of its low exposure and vulnerability. The overall flood assessment for different projections of RCP 2.6 and RCP 8.5 show that there is an increasing trend of the flood from baseline to 2080s, both for RCP 2.6 and RCP 8.5. From baseline to 2050s, the difference between RCP 2.6 and RCP 8.5 is slight. However, this variation becomes very drastic after the 2050s. The inundation pattern, hazard and risk extent increase manifolds in the 2080s of RCP 8.5 than those of RCP 2.6. So future climate change is going to have a terrible effect on the flood situation of Arial Khan River floodplain. The results found in this study provide useful information on projected changes of flood hazard and risk in the Arial Khan River floodplain over the next decades to a century. Additionally, this study will act as a guideline regarding how to incorporate the globalize climate change scenarios of a large basin to a small local river and its floodplain and find out localized flood hazard and risk maps under climate change scenarios.Item Hydrological modeling of Goranchatbari storm water drainage system using storm water management model(Department of Water Resources Engineering, 2018-03) Hossain, Md. Shahadat; Ali, Dr. Md. MostafaThroughout history urban floods have been one of the most severe naturalcatastrophes, which brought about loss of lives and huge economic losses inaddition to the influence on community activities and adverse effects on theenvironment. We have witnessed enormous flood events almost all over theworld, even in the early years of 21st century. The cruel lesson learnt is that wehave not coped well with floods in many over populated mega cities like Dhaka. Stormwater modeling has a major role in preventing issues such as flash floods and urban water-quality problems. However, in-detail modeling of large urban areas is time-consuming as it typically involves model calibration based on highly detailed input data. Stormwater models of a lowered spatial resolution would thus appear valuable if only their ability to provide realistic results could be proved. An urban inundation model, combining a storm sewer model SWMM and operations of Goranchatbari pumping station, has been developed to simulate inundation in urban areas due to storm water and outlet pumping station. The movement of water in the studied Goranchatbari watershed is characterized by two components, namely, the storm water flow component and the inundation component.SWMM is employed to solve the storm water flow component and to provide the flow hydrographs for surface runoff exceeding the capacity of the storm water. Drainage by pumping stations at outlets of the storm water system has also been taken into consideration. Rainfall frequency analysis of30 yr, 50yr and 100yr return periodswere conducted for Dhaka BMD and BWDB stations. The effect of rainfall due to climate change was incorporated in this SWMM drainage model to generate future scenarios of study area. The combined study is suitable for analysis of inundation on urban areas due to overflow of storm water and flooding caused by Climate Change. The parameters of the Goranchatbari model were calibrated by pumping water level and velocity verified for discrete storms with some internal khals system.The simulated SWMM model also validated with World Bank study inundation map prepared for actual event 2004. Simulated results applied to establish inundation maps to find out the flooded regions of study area due to waterlogging with different return periods. Simulated SWMM Model and inundation maps showed that the major drainage takes place at several locations of study area like Kalshi, Mirpur-10, Shewrapara and Kazipara which covering a huge study area from Mirpur-10 to Uttara with BauniaKhal to DigunKhal at retention pond. These area variations modify the features of both urban hydrology and hydraulics, and change the distribution of drainage network. It may lead to dual adverse effects in one specific region like Shewrapara, Kazipara which will risk of flooding on extreme rainfall. Therefore, finding appropriate solutions for these problems has been being a great challenge for the urban city like Dhaka.Item Assessment of shafique haor and sonamoral haor schemes against flash flood in greater Sylhet area(Department of Water Resources Engineering (WRE), BUET, 2019-09-30) Rifat Jahan.; Navera, Dr. Umme KulsumFlash flooding is one of the most recurring natural disaster over the northeastern region of Bangladesh. Haors are important areas for Boro cultivation as almost 80% of haor areas are covered by Boro rice. The farmers usually plant Boro crops in the floodplain in December and harvest from April to the first week of May. The Boro crop largely damage when flash flood occurs early May. For better water management and to facilitate crop production, Bangladesh Water Development Board (BWDB) has implemented about 118 schemes in the haor area to mainly protect Boro crop with some other functions like, drainage, irrigation, full flood protection. So, it is of utmost importance to understand and evaluate the performance of pre and post scenario of the implemented schemes against the flash flood frequency and Boro crop production. Therefore, a study has conducted to assessment the impact after implementation of the Flood Control, Drainage and Irrigation (FCDI) schemes against flash flood frequency and Boro crop production in greater Sylhet area. In this study, Shafique Haor scheme in Sylhet District and Sonamoral Haor scheme in Sunamganj District have been selected. To carry out the study, data of rainfall, discharge, water level, agricultural and Landsat satellite images have been collected from Bangladesh Meteorological Department (BMD), Bangladesh Water Development Board (BWDB), Center for Environmental and Geographic Information Services (CEGIS), Department of Extension (DAE) and United States Geological Survey (USGS) accordingly. In this study, hydrological and agricultural analyses have been carried out to assess the performance of Shafique Haor scheme and Sonamoral Haor scheme. Trend analysis, frequency analysis and Landsat satellite images analysis have been carried out under hydrological analysis. Under frequency analysis, Normal Distribution, Log-normal Distribution, Log-pearson type III and Gumbel’s Distribution have been considered. Normalized Difference Water Index (NDWI) has been calculated from the Landsat satellite images. In case of agricultural analysis, cropping pattern, cropping intensity, crop damage and crop production has been calculated. Impact has been assessed andsummarizedon changes in flash flood frequency and Boro crop production of Shafique Haor scheme and Sonamoral Haor scheme. In this regard, baseline has been created for pre-scheme scenario and post-scheme scenario for the identified indicators. Later, impact has been assessed by subtracting or comparing pre-scheme scenario status from post-scheme scenario status. It has been found that after implementation of the scheme interventions, risk of entrance of early flash floods reduced significantly. From the study, it has been also revealed that additional 5,466 ton and 1,327 ton crops have been produced in Shafique Haor scheme and Sonamoral Haor scheme accordingly during the post-scheme period. Therefore, Shafique Haor scheme and Sonamoral Haor scheme can be considered as complying with the objective to protect Boro crop from early flash floods and to facilitate crop productiItem Experimental study on the effect of permeable groyne on flow characteristics in a meandering channel(Department of Water Resources Engineering (WRE), BUET, 2018-12-18) Aflah Ornima.; Khan, Dr. Md. Sabbir MostafaGroynes are hydraulic structures that protect against bank erosion, maintain water level by deflecting flow direction, and ensure navigation safety. They can be used for flood control, land reclamation, and provision of navigable depth. In addition, their functions can be changed along with the goals of river works and the nature of the stream. Groynes are flow diversion structures, commonly used in river engineering especially at river bends to prevent bank erosion and control river meandering. Today, various types of groynes have been installed as pilot projects encouraging competent authorities proceed with such option in the wake of pertinent needs. One is impermeable another one is permeable. In this study, permeable groynes in meandering channel are used. The experimental study has been conducted in the open air facility of Water Resources Engineering Department, Bangladesh University of Engineering and Technology (BUET), Dhaka. Required data have been collected from 10 experimental runs in five different setups of the compound meandering channel. In each of those runs, velocities are measured at four cross-sections, and within each cross-section at four zones. Two depths of water (i.e. 20 cm and 15 cm) are considered in this study. Analyses are done for velocity distribution profile, velocity distribution coefficients (i.e. energy and momentum coefficients) and shear stress distribution. In the present study, studies are carried out on velocity distribution profiles, velocity distribution coefficients and shear stress distribution. For zone-wise distribution of mean velocity, 20 cm and 15 cm depths, set-up 2 (i.e. 3 groynes at L spacing, L = length of the groyne) is the best option among all the set- ups. For zones 2, 3 and 4, set-up 2 produces minimum velocities throughout the cross-sections although zone1 produced minimum velocities for set-up 4 (i.e. 3 groynes at 3L spacing) for 20 cm depth case. For cross-section-wise distribution for both 20 cm and 15 depths, set-up 2 is the best option among all the set- ups. Regarding energy coefficient, for 20 cm depth, hence set-ups 1 (single groyne), 3 (i.e. 3 groynes at 2L spacing) and 4 seem to be the preferred options. For 15 cm depth, set-ups 2 and 4 seem to be the preferred options regarding energy coefficient. Regarding momentum coefficient, for 20 cm depth, set-ups 1, 2, 3 and 4 seem to be the preferred options. For 15 cm depth, set-ups 2 and 4 seem to be the preferred options regarding momentum coefficient. Regarding shear stress distribution, set-up 2 seems to be the best option with the lowest values among all the zones for both 20 cm and 15 cm depths.Item Environmental flow assessment of Gorai- Madhumati- Kaliganga- Balaswar river system(Department of Water Resources Engineering (WRE), BUET, 2019-09-14) Tofail Islam, Mohammad; Navera, Dr. Umme KulsumEnvironmental flow (e-flow) in a river describes the quantity, quality and timing of water flow required to sustain minimum flow/ fresh water, estuarine ecosystem, the livelihoods and well-being of people that depend on these ecosystems. Bangladesh is already facing problem due to upstream withdrawal on Ganges River which caused the Gorai River (main tributary of Ganges in Bangladesh) almost dried up during low flow season. As a result, the demands for irrigation, navigation, industries and habitat suitability of fish species and other water users could not get the minimum water flow during the dry low flow season. Because of the reduced flow of water, the intrusion of saline water in the upstream has progressively made the south west region of the country vulnerable to increase salinity. In view of these river functions and problem, the assessment of environmental flow is essential. This research work has been carried out to assess the e-flow requirement of Gorai-Madhumati-Kaliganga-Balaswar River System which is a dominant river system in south-west region of Bangladesh. There are different methods have been used for determining e-flow in many countries around the world. To obtain the e-flow of Gorai-Madhumati-Kaliganga-Balaswar River System the methodology covers the hydrological methods such as Tennant Method, Flow Duration Method (FDC), Constant Yield Method (CYM), Hydraulic rating method (Weighted Perimeter Method), Habitat simulation method (PHABSIM), Holistic Method (Building Block Methodology). Fisheries such as Bacha, Ayeer, Golda, Carp Species and Salinity are the indicators for this research work. One-Dimensional mathematical model has also been set up by using HEC-RAS Modelling Tool for the condition of salinity to maintain the required e-flow through Gorai-Madhumati-Kaliganga-Balaswar River System. Historical flow data, Historical Water Level, Cross-sectional data and Salinity Data collected from Bangladesh Water Development Board (BWDB). The e-flow of Gorai and Madhumati River has been assessed by considering hydrological approaches and dominant fish requirement. Both of the Rivers, Dominant fish requirement is higher than hydrological approaches and the mean monthly flow is less than the required e-low during low flow season. In that case Gorai and Madhumati River must be maintained the minimum computed e-flow during low flow season for keeping the sustainable ecosystem. The flow demand for considering hydrological approaches and Dominant fish requirement in Kaliganga and Balaswar River is so called satisfactory; the mean monthly flow is higher than the required e-flow in both Kaliganga and Balaswar River. The existing salinity condition of Gorai and Madhumati River (upstream of Kamarkhali Bridge) has remained below 0.20 and 0.25 ppt respectively and the salinity level based on required e-flow has been remained the near to same. But Madhumati (downstream of Kamarkhali Bridge), Kaliganga and Balaswar River existing salinity condition has been remained from January to June is 1.2-5.2 ppt, 2.1-7.5 ppt and 5.5 to 8.2 ppt respectively and July to December 0.75-4 ppt, 1.2-6 ppt and 1.2-7 ppt respectively. The salinity level based on required e-flow of Madhumati, Kaliganga and Balaswar River from January to May has been remained around 0.3-1.80 ppt, 0.75-2.0 ppt and 1-2.5 ppt respectively and also from July to December has been remained below 1ppt.Item Study on monsoon flood hazard and vulnerability assessment of old-Brahmaputra river floodplain under climate change scenario(Department of Water Resources Engineering, 2019-03-24) Rahman, Afeefa; Khan, Dr. Md. Sabbir MostafaThis study is formulated to assess the monsoon flood hazard, vulnerability and risk of Old-Brahmaputra River and its surrounding floodplain for future climate change scenario of RCP 8.5 using numerical modeling approach. Firstly, a calibrated and validated hydrologic model of Brahmaputra river basin in HEC-HMS has been used to obtain the future flow magnitude for early (2020s), mid (2050s) and late century (2080s) for predicted climate data of RCP 8.5 scenario. Then the future flow at the Mymensingh of Old-Brahmaputra River has been obtained by conducting linear regression analysis considering the historical flow at Bahadurabad transit of Brahmaputra-Jamuna River as independent variable and the flow at Mymensingh of Old-Brahmaputra River as dependent variable. Then the study presents the simulation of flood flow of old Brahmaputra River and surrounding floodplain using HEC-RAS 1D-2D coupled hydrodynamic model. The 1D flow simulation was applied for the Old-Brahmaputra river channel and then integrated into 2D flow simulation incorporating the contribution of major tributaries and distributaries in the floodplain area using RAS Mapper. The developed hydrodynamic model is then calibrated and validated for Manning's roughness coefficient, n=0.014-0.017 for the year 2017 and 2016 respectively. To calibrate the inundation extent, flood inundation map obtained from simulation has been compared with the Sentinel-1 satellite image and flood map produced by FFWC on 16th August of 2017. Mean flood depth obtained in each upazilla under the study area has also been compared with the mean flood depth for the upazilla within the study area recommended by FFWC for 16th August of 2017 that provided satisfactory matching. Calibrated model was then simulated to obtain flood depth, flood flow velocity and inundation area of the years 1988, 1998, 2004, 2007, 2010, 2013, 2016 and 2017. Analysis results depicted that among the historical flood years, flood event of 1988 and 1998 were of devastating consequences comparing with others. Then the synthetic inflow hydrographs of Old Brahmaputra river generated for baseline, 2020s, 2050s and 2080s of RCP 8.5 scenario were fed into validated HEC-RAS model of Old Brahmaputra to generate the flood inundation depth, velocity and inundation area maps in the study area. The analysis results show an increasing trend of flood variables from baseline to 2080s. From baseline to 2080s, the total inundation area extended from 1975 km2 to 3923 km2 which is almost half of the study extent. Additionally, the mean flood depth and mean flood flow velocity are found to be increased as well. Thereafter, flood depth, velocity and inundation area have been incorporated with weightage obtained from PCA to calculate the flood hazard. The percentage area under different hazard zones for RCP 8.5 Scenario has been analyzed which shows that from baseline to 2080s the very low, low, medium and high and very high hazard zone changed from 25%, 36%, 36%, 3% and 0% to 5%, 36%, 40%, 14% and 5% highlighting significant increase of high to very high hazard zone. Thereafter, sensitivity, adaptive capacity, vulnerability and exposure have been estimated for the present and future socio-economic condition. Future population of each Upazilla was estimated using the logistic growth method. Selected indicators have been predicted for 2020s, 2050s and 2080s by trend analysis of the indicators of previous decades obtained from Population and Agricultural Census. Analysis on vulnerability maps highlights significant increase of moderate and high vulnerability zone from present to 2080s. Similarly, assessment of exposure for present and future highlights significant shift of few of the upazillas from high to very high exposure zones from present to 2080s. Thereafter, the flood risk is calculated for baseline and future multiplying flood hazard of each of the upazilla with the exposure and vulnerability of that particular unit. Risk assessment shows that all the upazillas are in the low to medium risk zone except Gaffargaon. Major part of the total study area may exist under the low to medium risk zone throughout the century. Thus, it can be interpreted that future climate change is going to have moderate impact on the flood situation of major portion of the old Brahmaputra River floodplain even if the wettest climate change scenario of RCP 8.5 is considered but there is an increasing trend of the flood from baseline to 2080s and the increment is significant after 2020s. It is hoped that the results would help floodplain management authorities in minimizing flood damage and loss of lives through technical approach.Item Assessment of hydro-morphological response of selected reach of the Jamuna river due to structural intervention using delft 3D model(Department of Water Resources Engineering, 2018-09-30) Hasan, Md. Zakir; Matin, Dr. Md. AbdulIn this study, an attempt has been made to analyze the hydro-morphological responses of the Jamuna River due to structural intervention in a selected reach by preparing a morphological model. The study reach covers from 30 km upstream of Bangabandhu Bridge (BB) to 20 km downstream of this bridge. A two-dimensional mathematical model has been developed using Delft3D and studied various options with structural intervention of groyne(s) along a selected reach in the right bank of the Jamuna River at the upstream of Sirajganj Hard Point (SHP). The model has been calibrated and validated against the data for the year 2012 and 2013 respectively. Then simulations have been done with seven different options consist of groynes with various number and spacing. The length of the groynes have been selected as about one-fourth of the channel width. The spacing and length ratio (S/L) of the groynes have been set as 1.0, 1.5 and 2.0 respectively for the option simulations. In order to quantify the response of the river hydrodynamics and morphology for various options at different locations, model results for the month of July have been assessed. All the model output have been presented and discussed. For the purpose of discussion and interpretation of model output, four points as the upstream of the structure (u/s), downstream of the structure (d/s), Sirajganj Hard Point (SHP) and Bangabandhu Bridge Site (BBS) have been taken into consideration. Model results show that at the upstream of the selected intervention, water level increases about 10.84% and for the downstream is 6.72%. This rise of water level may be for the afflux effect due to the structural intervention(s). The velocity and bed shear stress show decreasing tendency around the structures which indicates the attainment of siltation zone. The effects are considerable at the upstream and downstream of the groyne(s) and for the other two points (e.g. Sirajganj Hard Point and Bangabandhu Bridge Site) the effect is very little due to the long distance. From the velocity vectors and bank line velocities as well as bed shear stress, it can be decided that for this specific reach of the river, the maximum allowable spacing between the groynes is 2.0 times of its length. Otherwise the bank will be in vulnerable condition due to erosion. The bed level variation surrounding the groynes is considerable. The effect of groyne extends up to 1 km inside the river and 2 km laterally from either nose of the groyne. The maximum erosion is -5.25 m and deposition is +3.70 m along the length of the groyne. In case of lateral section (along the river) the values are -6.0 m and +4.0 m respectively. For the structures, the near bank velocity and bed shear stress become very small with the increasing number of intervention. Thus it can be said that to prevent the bank erosion, this types of structures with increasing numbers and different spacing provides satisfactory results. Overall, the model results show that it has the capacity to assess the hydro-morphological river responses for various options particularly at the vicinity of the interventions.Item Study on climate anomalies of Bangladesh using statistically downscaled climate projections for representative concentration pathways (RCPs) of IPCC fifth assessment report(Department of Water Resources Engineering, 2019-03-30) Rahaman, Ahmmed Zulfiqar; Ali, Dr. Md. MostafaBangladesh being the most vulnerable country to climate change necessitates generation of climate anomalies for the whole country due to inadequate researches on CMIP5 RCP scenarios, which are new GHGs emission trajectories over IPCC SRES scenarios. Statistical Downscaling Model for the country has been developed thus using SDSM for maximum temperature, minimum temperature, rainfall and solar radiation data of BMD and CanESM2 GCM predictors. Climate projections have been performed followed by analysis of climate anomalies, shifting of season and long term drought severity for future periods 2030s (2016-2045), 2050s (2046-2065) and 2080s (2066-2095). Both average maximum and minimum temperature has been found to be increased in future making southern part of Bangladesh hotter gradually. Indications of higher climate variability has been found from higher increase of average minimum temperature than average maximum temperature and fluctuations of seasonal rainfall variations. Changes in Indian monsoon circulation triggered by increased sea surface temperature and surface temperature is the prime cause of such inter-seasonal and inter-annual climate variability. Highest annual average maximum and minimum temperature increase are found to be 2.7⁰C in Khulna and 3.3⁰C in Satkhira respectively for 2080s under RCP8.5. Seasonal average maximum temperature increase is found higher in monsoon (4.5⁰C) and post-monsoon season (4.0⁰C) considering all scenarios. On the other hand, Bangladesh will face highest increment of average minimum temperature (5.2⁰C) in post-monsoon season. Mean annual average rainfall increase has been found 8%, 9% and 19% for 2030s, 2050s and 2080s respectively under RCP8.5, whereas maximum increase is found 11% for 2080s under RCP4.5. Pre-monsoon and monsoon average rainfall increase are found to be 10%-22% and 10%-16% respectively, whereas rainfall is found to be decreased 7%-8% in winter and 15%-17% in post-monsoon, making dry season drier. Highest average rainfall increase would be occurred on northern part of Bangladesh up to 33% in Dinajpur and on an average 24% in north-west region in 2080s considering three RCPs. Mean annual average solar radiation is found to be decreased for all RCPs except 2030s in RCP4.5 and RCP8.5. Although, change of mean annual average radiation is very less in between -0.1% to -0.4%, it can hamper future agriculture production. Season of rainfall has been found shifting towards pre-monsoon in the eastern portion of Bangladesh with relative to 1971-2000 decreasing monsoon rainfall occurrence except north-west and south-west regions of Bangladesh. Highest increase in occurrence of pre-monsoon rainfall is found to be 5%-6% in in north-eastern region, which clearly depicts that haor area of Bangladesh will be more prone to early rainfall as well as early flash floods in future period. Occurrence of severe and extreme meteorological long term drought will be increased almost all over Bangladesh in 2080s through decreasing occurrence of mild and moderate drought. Chance of increasing occurrence of severe drought is higher than extreme drought in both RCP4.5 and RCP8.5 scenarios. In most of the regions, occurrence of mild drought will be increased in 2050s and later decreased in 2080s for both RCPs. North-west region will remain drought prone in future. Occurrence of moderate, severe and extreme drought will be increased in far future up to 14%, up to 7% and up to 4% respectively considering RCP4.5 and RCP8.5. Duration of total drought occurrence will be decreased in 2050s, but will increase up to 8% throughout the country in 2080s considering both RCPs. Total duration of long term drought occurrence will be increased all over the western Bangladesh than other parts of the country with relative to 1981-2010. North-west region will face intensive severe drought spell than historical period. South west portion of Bangladesh will become prone to longer term drought with relative to 1981-2010. Total duration of drought occurrence will be decreased in eastern hill and north east regions. However, it is also clear that there is very insignificant correlation exist between overall rainfall pattern and long term drought over Bangladesh.