River Hydraulics

Inhaltsverzeichnis

1. Frontmatter

2. Chapter 1. Hydraulic Design of Reservoir in Permeable Pavement for Mitigating Urban Stormwater

   Sanjeev Kumar Suman, Rajnish Kumar

   Abstract

   Green infrastructure stormwater control measures, such as permeable pavement systems, are common practices used for controlling stormwater runoff in a developed country. This paper focus on the permeable pavement as a measure of stormwater mitigation in urban area. A hydraulic design aspect of reservoir stone layer is offered along with solution for the study area. Hydraulic design of the stone reservoir storage area includes depth of reservoir layer, drawdown time and storage volume. The depth of stone reservoir is calculated using the minimum depth approach for a permeable pavement of a given specific region. Rajendra Nagar Patna as study area is considered for design calculation. The depth of reservoir layer is 471 mm corresponding to last three years average annual precipitation of 120 mm. This will store water 7963 m³ with draw down time of 57 h. Soil beneath reservoir layer having low-infiltration rate, hence required additional measure like drain pipe. In addition, proper maintenance is needed to keep pores of the pavement surface remain open. According to researchers, cost of the permeable pavement is 15–80% less than the other stormwater management measures. Increasing the amount of stormwater in-filtered can result in lower stream flow levels after storm events. Permeable pavement can be used to substantially reduce the volume of stormwater runoff.

3. Chapter 2. Analytical Expression for Measurement of Discharge Using Conical Obstruction in Small Rectangular Channels

   Ankur Kapoor, Aniruddha D. Ghare, Avinash D. Vasudeo

   Abstract

   Flow measurement in rectangular channels can easily be carried out using measuring flumes. The type of flume used in a particular application depends on the need for precision and cost. Traditional flumes such as cutthroat flumes are usually built with the channel itself by channel side convergence. Their construction or removal involves engineering work on the channel. The authors feel this as the limitation of the traditional flumes; as for similar sections of the network of channels, a new and independent construction of flume is required. The present study negates this drawback and proposes a particular kind of flume for flow measurement in rectangular irrigation channels in which the throat section of the flume is obtained with a cone shaped object, placed at the center of the rectangular channel. The limitation of a fixed structure can be overcome by using a mobile structure that works on the same principle and remains effective in similar situations. The present study involves the use of a cone shaped obstruction to restrict the flow in order to achieve critical condition. An analytical model is developed for discharge measurement in rectangular channels using the conical obstruction. The geometry of the channel at the location of the obstruction becomes complex due to the presence of cone shaped object. The study presents various comprehensive equations defining the flume geometry. The cone shaped obstruction is equipped with a gauge at its upstream side to measure the depth of flow upstream of the critical flow section. The reading of the gauge is directly related to the flow rate. The relation between upstream flow depth and rate of flow is obtained analytically using energy concept. An experiment is performed in the laboratory by observing flow depth after placing a cone in the rectangular channel under free flow condition. The experiment results validated the developed analytical model. The maximum error of the flow discharge obtained using the analytical approach was found to be 5.19 percent when compared with the actual flow rate. The proposed flume is appropriate for temporary use and can replace the traditional flumes for flow measurement in small conduits. The flume is a simple and affordable device for flow measurement which is easy to construct, carry, and mount. The cone is physically independent of the channel and can be used in different, similar sections of the network of channels. The unit can be quickly fixed and detached for momentary use in open channels. This flume can be used as a mobile device for momentary flow measurement in open channels under free flow condition.

4. Chapter 3. Efficient Numerical Algorithm for Flow Field Around Vertically Submerged Tandem and Aligned Circular Cylinders

   Abhijit Rout, Soni Parth Kaushikbhai, Arindam Sarkar

   Abstract

   A comparative analysis of the experimental and numerical results on flow fields around submerged tandem and aligned cylinders is presented. The flow characteristics were measured using Acoustic Doppler Velocimeter (ADV), and the cylinders were aligned 0 and 20° over horizontal plane rigid beds. The results are validated using steady numerical simulation using COMSOL 5.3. Experiments were conducted with two unsymmetrical cylinders of upstream cylinder diameter 3 cm and downstream cylinder diameter 7.5 cm, separated by 2.5 times the spacing i.e., 18.75 cm, under completely submerged conditions. A submergence ratio (depth of water to height of cylinder) of 1.4 was taken. A fully developed flow condition with an average flow velocity of 0.1165 m/s was ensured for both the arrangement. For numerical simulation, all the parameters and boundary conditions remain the same as experimental. The computational domain was limited around the cylinder to reduce the computational time. The horizontal distributions of time averaged three dimensional velocities at various radial loci on different horizontal planes have been plotted. Streamlines are plotted to study the flow features. The results collectively delineate the changes in the characteristics of the flow field at the wake of the upstream cylinder brought to effect by the presence of a larger downstream cylinder. A weak sheltering effect by the upstream cylinder on the downstream cylinder for 20^o angular alignment especially differentiates its flow field characteristics from that of the linear tandem arrangement of the cylinders at 0°.

5. Chapter 4. Experimental and Numerical Analyses of Boundary Shear Stress in Non-prismatic Compound Channel

   Laxmikant Das, Kishanjit Kumar Khatua, Bhabani Shankar Das

   Abstract

   As boundary shear stress is an important parameter in open channel flow so experiments are carried out in non-prismatic compound channel. These experimental channels comprising of rectangular main channel, two symmetrically disposed diverging flood plains. The boundary shear stress distribution cannot be determined easily as they depend upon the velocity field, the shape of the cross section, and the boundary roughness. Variation of shear on flood plain and main channel with respect to the relative flow depth and divergence angle has been demonstrated. The present experimental non-prismatic compound channel is having diverging flood plain. Here, experimentations were done with two water depth ratio (Dr) such as 0.4 and 0.5 and two diverging angle such as 5.93 and 9.83°. As a complementary study of the experimental research undertaken in this work, one numerical hydrodynamic tools, viz., three-dimensional CFD model (ANSYS—FLUENT) is applied to simulate the flow in non-prismatic compound channel. This study aims to validate ANSYS—FLUENT simulations of open channel flow by comparing the data observed in the hydraulics laboratory of the National Institute of Technology, Rourkela. In this study, I have used four turbulence models to validate the result up to the at most accuracy. The four models are as follows: LES, k-ɛ, k-ω, and SST. The experimental results were taken as the reference, and all the models simulation result of boundary shear stress is compared with it, among the four models LES was given the approximate result and was taken as the best model for the analysis of boundary shear stress for non-prismatic compound channel.

6. Chapter 5. Turbulence Flow Statistics Downstream of Grids with Various Mesh Sizes

   Pankaj Kumar Raushan, Santosh Kumar Singh, Koustuv Debnath

   Abstract

   An experimental approach was performed to examine the interaction between the rigid boundary and grid turbulence of different mesh sizes. Three unlike mesh sizes (M₁, M₂ and M₃) were used having a constant diameter (d) and cross-section. Variation of mean velocities in stream-wise and vertical direction, turbulent intensities, Reynolds shear stresses and turbulence kinetic energy at the different locations of the grid M₁, M₂ and M₃ are discussed. The time series of velocity was measured by an acoustic Doppler velocimetry (ADV). The measured data of velocity fluctuations were used to understand the variations of turbulent characteristics behind the grids with rigid boundary interaction.

7. Chapter 6. Review on Hydraulics of Meandering Rivers

   Jyotirmoy Barman, Jyotismita Taye, Bimlesh Kumar

   Abstract

   A meander is a bend in a sinuous watercourse or river. It consists of a series of turns with curvatures in alternate directions which are connected at the points of inflection or by short straight crossings (Dey). Scientists and researchers are studying the hydrodynamics, morphology, bed topography, etc. of meandering rivers for a very long time. The details of secondary flow become an integral part for some researchers while studying meandering rivers. The role of the centre region cell and the presence of the outer bank cell have also been investigated by many researchers and experts. The centre region cell or helical motion occurs due to unequal forces between centrifugal force and pressure force with flow near the surface directed towards the outer bank and that near the bed directed towards the inner bank. Many of them also tried to find the relation between outer bank circulation cell and bank shear stresses and how it affects bank erosion. Researchers and experts have worked to find out various parameters like mean flow, Reynolds shear stress, turbulent kinetic energy (TKE), etc. and their interactions in meander bends. A lot of field and laboratory experiments have been carried out with different conditions to understand the behaviour of meandering rivers.

8. Chapter 7. Prediction of Discharge Coefficient for Side Rectangular Weir Using Group Method of Data Handling (GMDH)

   Ali Shariq, Ajmal Hussain, Mujib Ahmad Ansari

   Abstract

   A side rectangular weir is used as a flow diversion structure, having spatially varied flow with decreasing discharge. They have various applications in the field of river, hydraulic, environmental and irrigation engineering. In this study, group method of data handling (GMDH) with two types of transfer function, namely quadratic polynomial one variable and quadratic polynomial two variable, were used to estimate the coefficient of discharge for sharp-crested side rectangular weir. On the basis of the F-test, it is found that the upstream Froude number is the most influencing parameter for the estimation of the coefficient of discharge. On the basis of dimensional analysis, it is observed that the coefficient of discharge depends on the ratio of the crest height to the length (P/L), ratio of breadth of the main channel to length (B/L), approach flow Froude number (F₁) and ratio of the upstream depth to length (y₁/L) of sharp-crested side rectangular weir. The coefficient of correlation (R = 0.93), average absolute deviation (AAD = 2.99) and mean absolute percentage error (MAPE = 3.078) show better performance of the present GMDH model. Finally, the results indicated that the GMDH model could provide more accurate predictions than those obtained by traditional regression models.

9. Chapter 8. Enhancement of Energy Dissipation Using Combination of Solid Roller Bucket and Type II Stilling Basin for Ogee Stepped Spillway

   P. B. Nangare, A. S. Kote

   Abstract

   One of the most critical factors in the design of a hydraulic system is the energy dissipation arrangement for high-velocity flow in an ogee spillway. The release of excess water from crest to toe of the ogee spillway generates a large amount of kinetic energy. This would result in scour and erosion on the spillway's downstream face. Many different forms of energy dissipators have been used for ogee spillways in the past. However, they have energy dissipation, scouring, and erosion issues. The aim of this study is to create a physical working model of an ogee stepped spillway with a combination of solid roller bucket and type II stilling basin as an energy dissipator for the Khadakwasla dam in Pune (India). Two sets of phase models for a design discharge of 2700 m³/s were used in laboratory experiments. The non-dimensional parameter (yc/h 0.8), nappe flow, and Froude number must be held within acceptable limits with 12 and 9 steps, respectively. The model results show that the 9-step model (Set 2) achieved 80.24% energy dissipation for a 4 m head with a controlled value of non-dimensional parameter up to 0.69, which is the highest energy dissipation among all sets of subject models. As a result of the current model analysis, it was discovered that the combination of a solid roller bucket and a type II stilling basin is the best energy dissipator for an ogee stepped spillway.

10. Chapter 9. Estimation of Coefficient of Discharge for Side Compound Weir Using the GMDH Technique

    Mujib Ahmad Ansari, Ajmal Hussain, Faisal Ahmad

    Abstract

    A sharp-crested side compound weir is a flow diversion structure provided in one or both sidewalls of a channel to spill/divert water from the main channel. It is widely used in irrigation, hydraulic and environmental engineering. The mechanism of flow through the compound side weir is complicated, and it is difficult to establish a model to accurately predict the coefficient of discharge. In this study, the group method of data handling network with quadratic polynomial, ratio and linear two-variable functions was used to predict the coefficient of discharge for side compound sharp-crested weir. The discharge coefficient of compound side weir has a high correlation with three dimensionless parameters including upstream Froude number (F₁), ratio of weighted crest height of side weir to crest length of side weir (\(P\)/L) and the ratio of upstream flow depth to crest length of side weir (y₁/L). Therefore, a new model for the determination of coefficient of discharge of side rectangular sharp-crested compound weir was developed. Results of the GMDH model were also compared with the available regression model, and it was found that GMDH results were better than that of the regression model. The performance of the present model is based on the coefficient of correlation (R = 0.8489), mean absolute percentage error (MAPE = 17.62) and average root means square error (RMSE = 16.10). On the basis of sensitivity analysis, it was found that (\(P\)/L) was the most effective parameter for the prediction of coefficient of discharge.

11. Chapter 10. Flow Distributions in a Compound Channel with Diverging Floodplains

    Bhabani Shankar Das, Kamalini Devi, Jnana Ranjan Khuntia, Kishanjit Kumar Khatua

    Abstract

    During flood, the flow distribution in main channel and floodplain is always an important factor for river engineer to model, accordingly, the measures can be taken in the floodplain area. Experiments on diverging compound channel show that the flow distribution in main channel and floodplains are found to be a function of four non-dimensional geometric and hydraulic parameters such as width ratio, relative flow depth, relative longitudinal distance and flow aspect ratio. This paper presents an empirical-non-linear-multivariable regression model by considering the aforementioned parameters to compute discharge distribution in diverging compound channels. The model is developed using discharge distribution data obtained from present laboratory experiments and with the published data of other researchers on diverging compound channels. The predictive strength of the developed regression model is validated using several major statistics. All deployed statistics have indicated that the developed model is highly significant. The outcome for all diverging compound channels resulted in minimum RMSE and MAPE values as 0.0092 and 4.35%, respectively, when the discharge is predicted using the developed multivariable regression model.

12. Chapter 11. Boundary Shear Stress Distributions in Compound Channels Having Narrowing and Enlarging Floodplains

    Kamalini Devi, Bhabani Shankar Das, Jnana Ranjan Khuntia, Kishanjit Kumar Khatua

    Abstract

    Compound channels are basically described as two stage open channels having main river and its adjoining floodplains. The momentum transfer phenomenon at the junction of main channel and floodplain is very crucial to be understood to estimate the discharge. The difference in water depth and roughness between the two zones generally causes momentum exchange at the interface. It is simple to quantify this momentum exchange for uniform flow conditions in river; however, for non-uniform flow condition the quantification is complex as the flow properties change in both longitudinal and lateral directions. Therefore, a study has been done on overbank flow with non-uniform flow condition, and stage discharge relationships are analyzed for accurate modeling. As natural rivers may have different configurations, so two different types of channels that are converging and diverging channels are considered and flow variables at different longitudinal positions are analyzed. Two discharge predicting models are developed which can be used for flow in natural rivers. These models depend on the non-dimensional forms of geometric and flow parameters and the percentage of the boundary shear forces carried by the adjacent floodplains. So it is required to analyze and estimate the boundary shear force distribution carried by main channel and non-prismatic floodplains before predicting flow. So, two different equations are proposed for percentage shear carried by converging and diverging floodplains. In addition, the developed models give simple ways for the quantification of percentage boundary shear force and provide accurate discharge result through non-prismatic channels. The predictions of the models are then compared with the models of other researchers. The prediction efficiency of the present model is found better than the models of previous researchers.

13. Chapter 12. Turbulence Characteristics in a Rough Open Channel Under Unsteady Flow Conditions

    Jnana Ranjan Khuntia, Kamalini Devi, Bhabani Shankar Das, Kishanjit Kumar Khatua

    Abstract

    The majority of open channel flows of interest to hydraulic engineers and hydrologists are unsteady. In unsteady flow cases, some aspects of flow (velocity, depth, viscosity, pressure, etc.) will be evolving in time. However, more numbers of issues identified with the unsteady flow have been roughly accepting as steady flow (for example, constant peak discharges in floodplains). Very few experimental investigations have been conveyed in previous literature to examine turbulence qualities in an open channel flow under unsteady flow states over rough beds. The present study investigates the vertical and horizontal fluctuating velocity profiles under unsteady flow states in a rectangular open channel. An experiment is conducted to observe the turbulence characteristics under unsteady flow conditions in a rough bed open channel for two different flow depths. One identical hydrograph is passed repeatedly through the rectangular flume with a fixed rough bed. The dense rough mat is used as a rough bed which replica of a dense grass bed. The flow patterns are investigated at both lateral and longitudinal positions over three different cross-sections by using a micro Pitot tube and Acoustic Doppler Velocimeter (ADV). For two given flow depths, the velocities on both the rising and falling limbs are observed and analyzed. Hysteresis effect loop between stage-discharge (h ~ Q) rating curve between the rising and falling limbs is illustrated. Turbulence characteristics, i. e., variations of lateral and vertical Reynolds stresses, are analyzed from measured fluctuation velocities.

14. Chapter 13. Study of Scour Near Pier of Gandhi Setu in Ganga River

    Binit Kumar, Vivekanand Singh

    Abstract

    In this paper, an attempt has been made to carry out the study of scour depth at one of the piers of the Gandhi Setu in Ganga River near Gaye Ghat, Patna. Different parameters of the different empirical equations have been calculated by collecting soil samples from the site and analyzed in the laboratory. Based on these parameters, the scour depth is calculated by using different empirical equations given by different researchers such as Shen et al., the Modified Laursen, Jain and Fischer and Lacey’s. The actual scour was also measured near one of the piers of Gandhi Setu in Ganga River at Patna, in-situ measurement using the rope attached with heavy weight. It was found that the scour depth measured manually matches satisfactorily with the scour depth computed using Lacey’s empirical formula.

15. Chapter 14. Optimisation of Hydraulic Design of Uri-II Dam Spillway, Jammu and Kashmir

    Vankayalapati S. Ramarao, M. R. Bhajantri

    Abstract

    Optimisation of hydraulic design of spillway involves verification of designs of various components of spillway which includes crest profile of spillway and bottom profile of breast wall, adequacy of spillway spans to pass the design flood, the sufficiency of divide walls and training walls, location of trunnion of gates, assessing the performance of energy dissipator, assessing the scour downstream of ski-jump bucket, design of pre-formed plunge pool, location of head regulator/power intake structure and upstream and downstream protection subjected to design floodwaters. Hydraulic model studies play a key role in optimising the designs of various components of the spillway as mentioned above. Hydraulic design of spillway of Uri-II dam was optimised in CWPRS, Pune, by conducting hydraulic model studies. Uri-II H.E.Project was envisaged as a run-of-the-river scheme on the River Jhelum in Uri Tehsil of Baramulla District of Jammu and Kashmir. It has a power generation capacity of 240 MW (4 units of 60 MW each) utilising a gross head of about 130 m. The project consists of a 52 m high and 173 m long concrete gravity dam with a 4.27 km long headrace tunnel (8.4 m diameter), a restricted orifice-type surge shaft (25 m diameter), two 5 m diameter steel-lined penstocks, four 3.5 m diameter bifurcated steel-lined penstocks, an underground powerhouse and a horseshoe shaped tailrace tunnel 3.77 km in length. The spillway is designed to pass design outflow flood of 4850 m³/s at FRL El. 1241 m and also to flush the sediment deposited in the reservoir into the river downstream. A breast wall spillway has been proposed with four low-level orifices of size 9 m wide × 11.4 m high (originally 12 m high) with crest level at El. 1217 m. The ski-jump bucket is provided for energy dissipation with invert at El. 1210.19 m and lip at El. 1213 m. The project was completed and all four units were commissioned and the 4th unit in July 2014. Hydraulic model studies enabled optimisation of various components of spillway by optimising the size of spillway spans and design of natural plunge pool and suggesting downstream hill slopes protection. Optimised hydraulic design was made by assessing the discharging capacity of the spillway, validating crest profile with pressures on the spillway surface, the performance of energy dissipation arrangement for the entire range of discharges, flow conditions in the reservoir upstream of the spillway and head regulator, flow conditions downstream of the spillway and head regulator and requirement of a natural plunge pool with expected scour levels. This paper provides detailed information on the hydraulic model studies carried out on the spillway and energy dissipator of Uri-II dam spillway, Jammu and Kashmir.

16. Chapter 15. Modification of Spillway Ski Jump Bucket Subjected to Higher Tail Water Levels

    Vankayalapati S. Ramarao, M. R. Bhajantri

    Abstract

    Spillways are provided to dispose off excess flood safely to downstream without causing excessive erosion. To dissipate the energy of flood, energy dissipators are provided for spillways. Ski jump buckets are one of the popular types of energy dissipators provided for spillways when the available tail water depths are very low, so that the clear ski jump forms and throws the flood away from the toe of the spillway, preventing the undermining of the spillway. However, depending upon the site conditions, ski jump buckets are provided where tail water levels are even at higher levels. In such typical conditions, submerged ski jump action occurs and the efficiency of energy dissipation arrangement may get reduced. As such, the performance of these designs is to be verified by conducting hydraulic model studies, since there are no exact codal provisions existing to have a flawless design. The optimization of ski jump bucket subjected to higher tail water levels can be done by studying its performance for various discharge conditions and making necessary modifications for getting clear ski jump action, without having hydraulic jump formation or submerged ski action in the bucket region which reduces energy dissipation and undermines spillway foundation. The submerged action of ski jump would also have an effect on the scour development downstream of the spillway and in the design of pre-formed plunge pool. A case study is presented in this paper where ski jump bucket of the spillway of Punatsangchhu-II H.E.Project, Bhutan, was optimized for coping up with prevailing higher tail water levels, by hydraulic model studies conducted on 1:70 scale geometrically similar physical hydraulic model in CWPRS, Pune.

17. Chapter 16. Prediction of Submerged Vegetated Flow in a Channel Using GMDH-Type Neural Network Approach

    Nekita Boraah, Bimlesh Kumar

    Abstract

    The study of flow in the vegetative channel is not new to existing concerns. The effect of vegetation in river systems with regards to its preservation is of much importance. The aquatic plants that thrive in water have been found to control the mean flow and turbulence of flow of river systems. Even the morphology of a channel can be affected by the submerged and emergent vegetation. The important parameter of any channel mainly velocity profile is influenced a lot due to the height and flexibility of submerged aquatic plants. This also impacts the transport of sediment in the channel. Apparently, the presence of plant life in a channel decreases the mean discharge and sediment load potential and leads to the accumulation of sediment in the channel due to additional drag produced by the presence of vegetation. Literature status reveals that the scope in this field is vast as not much has been contributed so far. Also, the studies mostly reveal the use of conventional methods to indicate the relationship between the different parameters. To develop models for relating the parameters and to predict future scope, soft computational techniques are used to simplify the otherwise complex equations. Studies indicate the use of neural networks in association with PSO techniques, also GA has been reported. This study has been conducted with the help of another soft-computing technique which analyses polynomial neural networks, Group Method of Data Handling (GMDH). This technique has been reported to be in extensive use in the field of hydraulics. This approach, as an advanced tool, has been modelled to predict the resistance due to flow–vegetation interaction in a submerged vegetated channel. The main aim of this approach is the development of an explicit model which optimises the parameters and predicts the unknown input–output mapping. The results generated by the model have been found to be sufficiently good. The model has been developed in the interest of predicting future outputs by capturing the related relationship of input–output mapping. It is designed so as to analyse the influence of various parameters on the velocity profile.

18. Chapter 17. Turbulent Flow Over a Train of K-Type Roughness

    Santosh Kumar Singh, Pankaj Kumar Raushan, Koustuv Debnath

    Abstract

    Detailed experimental investigations are reported in this paper to study the turbulent flow characteristics in wave-current flow over the bed-mounted ribs at equal spacing. Regular wave is generated by wave-maker at frequency f = 1 and 2 Hz which is installed at the entrance of the wave flume. The measurements were performed at the developed zone between the two consecutive ribs. The results show that mean stream-wise velocity changes significantly with the induced wave over turbulent current. Further, it is observed that the recirculation length changes slightly with a superposition of wave over current.