Dissertations/Theses - Department of Water Resources Engineering

Browse

Filters

2004 - 200922010 - 20143

Settings

Subject: search.filters.subject.River bank protection-Bangladesh

Search Results

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Hydrodynamic simulation of the river Jamuna
    (Department of Water Resources Engineering, 2004-08) Mohammad Mostafa Ali; Bhuiyan, Dr. Muhammed Ali
    This research deals with the morphological analysis of Jamuna river using finite element method. RMA2, a hydrodynamic model and SED2D, a sediment transport model, have been used to simulate the morphology of the Jamuna. Models have been applied using SMS (Surface-water Modeling System) environment, which gives the pre- and post- processing options for input and output data. The finite element mesh has been developed using LANDSAT image of the Iih November 2000. Initial bed elevations for the nodes of the mesh have been composed from the scattered survey data of April 2001 by BIWT A. Once the mesh and bathymetry have been obtained, the models are ready thereby to incorporate boundary conditions, initial conditions and material properties. The hydrodynamic model developed in this study has been satisfactorily calibrated and validated against the observed water surface elevations at Aricha for 2001 and 2002, respectively. Sediment model has also been calibrated using measured bathymetry by BIWTA with the simulated bathymetry of 23rd August 2001. The model has been validated with the measured bathymetry of November 2002 and November 2003. Sediment rates at Baruria have been generated from the SED2D model and compared with the FAP-24 data (FAP, 1996). Results reveal that erosion takes place in the outer bend of the meandering Eastern anabranch. In Western ana branch, severe deposition has been observed near the confluence due to backwater effect of Jamuna-Ganges flow. Velocity reduction in the confluence significantly diminishes their sediment transport capacity, and hence inducing deposition. Three morphological years have shown much similar type of erosion/deposition patterns, which occur mainly in August and September of each year. An investigation, using surveyed bathymetries from 1996 to 2003, shows that the 1998 flood initiates drastic changes in its Western anabranch near Nagarbari, which indeed may have an impact on the shifting of flow more towards left bank at Naradaha. These observations of measured data are further substantiated by the results obtained from the present simulation models. To find a suitable location for ferry ghat and also for a sustainable navigable channel, three options have been investigated. Existence of a deep pocket near Naradaha motivates this study to take those options and among them Option 2, which is a dredging option in the upstream channel connecting upper segment of the deep pocket, has appear to show very little deposition compared to other options. Thus the option in question presents a prospective alternative for developing a sustainable ferry route.
  • Thumbnail Image
    Item
    Assessment of morphological aspects and bank protection works of the river Surma
    (Department of Water Resources Engineering, 2004-08) Tauhid-Ur-Rahman, Md.; Abdul Matin, Dr. Md.
    Realizing the gravity of the changed hydro morphological characteristics of the hilly river, Surma, this study has been conducted to investigate the morphological characteristics, sediment transport phenomena and also to analyze the design parameters of the implemented bank protection works of this river at Sylhet. Mainly, cross sectional properties at 24 selected sections of the river Surma for the years 1970, 1989, 1991 and 1999 were analyzed. It is observed that sedimentation is portrayed in the period 1972-73 to 1981-82 whereas erosion can be illustrated in the period from 1981-82 to 1991-92. Sedimentation dominates over a period often years before reaching a peak of erosive activity in 1999. In addition, it has been found that the river had turned into wider and shallower up to 1989. After that, it changed into comparatively narrower and shallower for the last decade (I989 to 1999). Variation of width in successive years shows that the section no. S-18 and S-38 experienced the sudden rise and fall during the 30 years period. In addition, the maximum rise in calculated mean bed level is happened at section no. S-42 (I 3.13 m) whereas the maximum fall in mean bed is found at section no. S- 18 (0.82m in 1991) and S-3 (0.46m in 1989). Due to the deposition of huge sediment load (about 3.00 MT/year), the river has lost its normal carrying capacity about 27% and flash flood visits almost every year inundating the surrounding lands and towns. Discharge carrying capacity and sediment concentration of 14 cross sections of the river Surma starting from S-29 (Sylhet) to S-42 (Lubachara) have been estimated under bankful conditions, using a simplified resistance equation and a sediment predictor. Results indicate that the section no. S-31 has the highest discharge carrying capacity (973.22 cumecs) whereas section no. S-41 has the lowest of that (133.55 cumecs) among all the selected sections. In this regard, it can be mentioned that the bankful discharge of Surma at Sylhet is 1373.33 cumecs. Superimposition of satellite images shows that the change of planform of this river is not significant over the last five years period (I 997 -2002). Sediment load of the Surma river has been computed with the help of three well known sediment predictors such as Engelund-Hansen's equation, Ackers-White's equation and van Rijn's equation for the years 1975, 1989 and 1999 at the station Sylhet and were compared with the values of the measured sediment load of those years. The observed annual sediment load at Sylhet was 2.77 6MT, 3.121 MT and 3.0971 MT for the year 1975,1989 and 1999 respectively. However, the average annual sediment load predicted from Engelund-Hansen's equation is 0.727 MT, from Ackers White's equation is 1.818 MT and from van Rijn's formula is 0.828 MT. Comparison shows that out the three sediment predictors Ackers White's formula is found to be well suited against the observed data of the river, Surma. The implemented bank protection works starting from Kazirbazar to Mollapara at Sylhet City has been also considered for this present study. Depending on the assembled field data and information, hydraulic design parameters of the bank protection works were evaluated in terms of effectiveness, suitability and sustainability.
  • Thumbnail Image
    Item
    Experimental study on flow behaviour around launching apron
    (Department of Water Resources Engineering, 2010-01) Ehsanul Haque, Md.; Hossain, Dr. M. Monowar
    Launching apron is widely used at the toe of all riverbank protection works. Use of launching apron around revetment is very popular for protection of structures against scour failure. A systematic experimental investigation was conducted to study the flow behaviour around launching apron in a laboratory channel situated in the Hydraulics and River Engineering Laboratory of the Department of Water Resources Engineering, BUET. Since launching apron is a measure to limit scour in sand bed for riverine structures, initially the investigation incorporated flow behaviour and then the scour study were observed. The extent of aerial coverage of launched apron was determined during the test runs in connection with the study. Before the test runs, few trial runs were conducted initially to gather information on flow behaviour and scour using fixed as well as mobile bed with a view to visualizing some idea about the size of apron materials. Afterwards necessary test runs were conducted. Each test was run for 8 hours to maintain uniformity among the tests. Sixty test runs were conducted in total of which 24 test runs were conducted using fixed bed and 36 test runs were conducted using mobile bed. For fixed bed bank slopes of 1:1.25,1: 1.5 and 1:2 were used. For mobile bed also the same three bank slopes were utilized. Three discharges of 40 lis, 50 lis and 60 lis were used for test runs. The apron materials fabricated using sand-cement were of sizes 3mm, 4mm, 5mm and 6 mm. Geobags were also used as apron materials which was prepared by filling with sands inside properly sewn cloths and weighing approximately 1 gm. These materials were placed on the toe of sloping revetment. Test runs were conducted for specified conditions and measurement were taken. The study was made under clear-water condition and the channel bed formed ripples during test runs, while mobile bed test runs were conducted. Test runs were conducted for different apron setting configuration and velocities were measured using a programmable 2-D electromagnetic liquid velocity meter. The flow behavior was analyzed critically by examining the measured data on velocity. The flow field analys~s were conducted by examining the variation of stream wise velocity and changes along vertical direction. The study showed that presence of apron at the toe of revetment caused a change in the velocity distribution near bed. In most of the cases, shifting away of maximum velocity was observed that caused shifting of maximum discharge flux away from the revetment. Analysis of velocity contour also revealed this trend of shifting maximum velocity away from the revetment. It was found that, when apron material was laid around a structure, the apron behaved like a submerged extension of the revetment. It was also observed that, launching apron was protecting the revetment structure in two ways - one was by forming a protective layer on the sloping face of the developed scour hole and the other was by forcing the scour hole to be formed away from the structure for mobile bed tests. Scour depth was found to vary with velocity variation of flow and an increasing tendency of scour depth has been observed with increasing flow intensity. It was found that placing of apron in different arrangement not only reduced the maximum scour depth but also had changed the deposition pattern around revetment. Attempts were made to establish non-dimensional relationship between relative scour depths with projected area of apron provided. Using data obtained for different test arrangements regression analyses were performed to derive expressions. These expressions are expected to be useful for practical applications .
  • Thumbnail Image
    Item
    Experimental study on placement of toe protection elements of river bank protection works under live bed condition
    (Department of Water Resources Engineering, 2014-05) Tanzim Ahmed; Abdul Matin, Dr. Md.
    Bank protection works are essentially important parts of river training works. In recent times, out of all types of river training structures, bank revetments works are common in Bangladesh. The purpose of bank revetments is to prevent bank erosion as a structural measure. They have to be designed to resist the current and wave and to protect the river bed and river bank against erosion. Toe scour is probably the most frequent cause of failure of riprap revetments. This is true not only for riprap, but also for a wide variety of protection techniques. A flexible toe protection in the form of a falling apron finds many applications in Bangladesh. For designing of bank protection works in perennial rivers, where low water level prevails, the construction works have always been a difficult task. Placing of underwater apron materials requires a considerably higher skill, equipment demand and standard and practical approaches. Such scenarios become more challenging as the channel bed composed of sand. In the sand bed channel flowing under equilibrium condition may be considered as live bed channel. The present study has been undertaken to investigate experimentally two important aspect of underwater construction such as the placing behavior and incipient condition of toe protection elements under live bed condition. The experiments are conducted in the Hydraulics and River Engineering Laboratory of Water Resources Engineering Department, BUET. Three types of CC block and five types of geobag have been used to conduct fifteen experimental runs with two different hydraulic conditions to investigate placing behavior. For the incipient condition experimentation, four types of CC block and five types of geobag have been used to conduct nineteen experimental runs with various conditions. The measured data have been used to obtain various relationships at the incipient condition of the toe protection elements. Experimental results are analyzed to develop relationships between shear velocities, depth averaged velocity, relative depth, turbulent intensity, depth factor, boundary Reynolds number and Shield’s number. Developed empirical relationships can be used to predict the shear velocity, depth averaged velocity, turbulent intensity and depth factor at incipient condition for selected types and sizes of toe protection elements. The proposed relationships are also compared with the equations available in previous studies. Comparisons show that the predictive capacity of the proposed xviii relationships is found to be satisfactory. Both CC block and geobag shows greater shear velocity and shear stress in case of live bed than that of fixed bed. Shear velocity on a live bed is about 2% greater than that of fixed bed for CC Block. For geobag shear velocity is about 8% greater on a live bed than that of fixed bed. The shear stress on live bed for CC block and geobag is about 4% and 16% greater than fixed bed respectively. However, a comparison has been made between underwater and dry bed toe protection to observe the incipient parameters. It is suggested that the designer should consider the hydraulic parameters which should be commensurate with underwater constructional aspects. Therefore, this study will be helpful in designing of toe protection in case of underwater construction in real life practice.
  • Thumbnail Image
    Item
    Experimental Study on Settling Behavior of Toe Protection Elements of River Bank Protection Works
    (Department of Water Resources Engineering, 2011-12) K. M. Ahtesham Hossain Raju; Abdul Matin, Dr. Md.
    River bank erosion has always been a challenging problem in Bangladesh. Conventional method of designing erosion protection structures are governed by the hydraulic loads resulting from currents and waves. The effectiveness of design of protection works mainly depends on its constructional aspects. The appropriate method of construction depends on mechanism of settling behavior of protection elements. In practice, toe protection elements are dumped into flowing water and settle somewhere on the river bed to form an apron. But the placement of elements at designated positions is difficult to ensure. The present study has been undertaken to investigate experimentally two important aspect of underwater construction such as the settling behavior and threshold condition of toe protection elements. The experiments are conducted to determine the fall velocity in a square shaped settling column of 30 cm X 30 cm X 130 cm and in the large tilting flume of the Hydraulics and River Engineering Laboratory of Water Resources Engineering Department, BUET. Sixteen different sizes of elements ranging from 1.6 cm X 1.6 cm X 1.3 cm to 4.1 cm X 4.1 cm X 2.7 cm have been used to conduct 64 experimental runs with the discharges range from 0.033 m3/s to 0.203 m3/s. During experimentation various observations are made and the measured data are used to obtain various relationships for the settling behavior of the toe protection elements. Experimental results are analyzed to develop relationships between the relative size and flow parameters. Developed empirical relationships can be used to predict the settling velocity, horizontal settling distance and incipient condition for selected types and sizes of toe protection elements. The proposed relationships are also compared with the equations available in previous studies. Comparisons show that the predictive capacity of the proposed relationships is found to be satisfactory i.e. for fall velocity prediction equation, the error is 3.91% for CC block and 2.38% for geobags. To estimate settling distance results show that the developed equation also performed better compared to Zhu et al. (2004). Also verification of the proposed equation has been done using the independent set of laboratory data and result shows satisfactory agreement with an error of 3.80%. It is hoped that the outcome of the present study can be used as a tentative guideline for under water construction of toe protection elements in river bank protection works.