This chapter is based on the book Hydraulics of Spillways and Energy Dissipators By Rajnikant M. Khatsuria, This lecture slide describes the design of Overflow and Ogee spilways for Masters Students in Hydraulic Engineering
PracticalProfileofSpillwaY
When the profile for the crest of the ogee spillway is plotted over the triangular profile the section of a gravity dam (non-overflow section) ,it is found that it goes beyond vie downstream face of the dam , thu requiring thickening of the section for the spillway .
However,this extra concrete can be saved by shifting the curve of the nappe in a backward direction until this curve becomes tangential to the downstream face of the dam .
Design of spillway
Design an ogee spillway for concrete gravity dam, for the following data :
(1) Average river bed level = 100.0 m
(2) R.L. of spillway crest =204.0 m
(3) Slope of d/s face of gravity dam = 0.7 H : 1 V
(4) Design discharge = 8000 cumecs
(5) Length of spillway = 6 spans with a clear width of 10 m each.
(6) Thickness of each pier = 2.5 m
If h/Hd is greater than 1.7 than high spillway so effect of velocity is neglected
The co-ordinates from x = 0 to x = 27.4 m are worked out in the table below :
Topics:
1. Reservoir Classification
2. Investigations
3. Selection of Site for Reservoir
4. Zones of Storage
5. Storage Capacity and Yield
6. Mass Inflow Curve & Demand Curve
7. Calculation of Reservoir Capacity
8. Reservoir Sedimentations
9. Life of Reservoir
10. Selection of Dam
PracticalProfileofSpillwaY
When the profile for the crest of the ogee spillway is plotted over the triangular profile the section of a gravity dam (non-overflow section) ,it is found that it goes beyond vie downstream face of the dam , thu requiring thickening of the section for the spillway .
However,this extra concrete can be saved by shifting the curve of the nappe in a backward direction until this curve becomes tangential to the downstream face of the dam .
Design of spillway
Design an ogee spillway for concrete gravity dam, for the following data :
(1) Average river bed level = 100.0 m
(2) R.L. of spillway crest =204.0 m
(3) Slope of d/s face of gravity dam = 0.7 H : 1 V
(4) Design discharge = 8000 cumecs
(5) Length of spillway = 6 spans with a clear width of 10 m each.
(6) Thickness of each pier = 2.5 m
If h/Hd is greater than 1.7 than high spillway so effect of velocity is neglected
The co-ordinates from x = 0 to x = 27.4 m are worked out in the table below :
Topics:
1. Reservoir Classification
2. Investigations
3. Selection of Site for Reservoir
4. Zones of Storage
5. Storage Capacity and Yield
6. Mass Inflow Curve & Demand Curve
7. Calculation of Reservoir Capacity
8. Reservoir Sedimentations
9. Life of Reservoir
10. Selection of Dam
Reservoir Planning: Introduction; Investigations for reservoir planning; Selection of site for a reservoir; Zones of storage in a reservoir; Storage capacity and yield; Mass inflow curve and demand curve; Calculation of reservoir capacity for a specified yield from the mass inflow curve; Determination of safe yield from a reservoir of a given capacity; Sediment flow in streams; Life of reservoir; Reservoir sediment control; flood routing. Various types of Spillways and design.
WEIRS VERSUS BERRAGE
TYPES OF WEIRS
COMPONENT PARTS OF A WEIR
CAUSES OF FAILURE OF WEIRS & THEIR REMEDIES
DESIGN CONSIDERATIONS
DESIGN FOR SURFACE FLOW
DESIGN OF BARRAGE OR WEIR
Topics:
1. Types of Diversion Head Works
2. Weirs and Barrages
3. Layout Diversion Head Works
4. Causes of Failures of Weirs and Barrages on Permeable Foundations
5. Silt Ejectors and Silt Excluders
spillway,types of spillways,
Design principles of Ogee spillways ,Spillway gates. Energy
Dissipaters and Stilling Basins Significance of Jump Height Curve and Tail Water Rating
Curve,
USBR and Indian types of Stilling Basins.
ENERGY DISSIPATORS
stilling basin
A stilling basin is defined as a structure in which a hydraulic jump used for energy dissipation is confined either partly or entirely.
Certain auxiliary devices such as chute blocks, sills, baffle walls, etc. are usually provided in the stilling basins to reduce the length of the jump and thus to reduce the length and the cost of the stilling basin.
Moreover, these devices also improve the dissipation action of the basin and stabilize the jump.
Chute Blocks :
These are triangular blocks with their top surface horizontal. These are installed at the toe of the spillway just at upstream end of the stilling basin.
They act as a serrated device at the entrance to the stilling basin. They furrow the incoming jet and lift a portion of it ab0ve the floor.
These blocks stabilise the jump and thus improve its performance, these also decrease the length of the hydraulic jump.
Basin Blocks or Baffle Blocks or Baffle Piers :
These are installed on the stilling basin floor between chute blocks and the end sill. These blocks also stabilise the formation of the jump.
Moreover, they increase the turbulence and assist in the dissipation of energy.
They help in breaking the flow and dissipate energy mostly by impact. These baffle blocks are sometimes called friction blocks.
Sills and Dentated Sills :
Sill or more preferably dentated sill is generally provided at the end of the stilling basin.
The dentated sill diffuses the residual portion of the high velocity jet reaching the end of the basin. They, therefore, help in dissipating residual energy and to reduce the length of the jump or the basin.
particular location of these blocks mainly depends upon the initial Froude number (F1) and the velocityof the incoming flow. The stilling basins are usually rectangular in plan. These aremade up of concrete.
[A] U.S.B.R. Stilling basins :
[B] Indian Standards Basins :
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
Type I basin (F1 between 2.5 to 4.5)
Provide chute blocks and end sill
Length of basin = 4.3 y2 to 6.0 y2
Width of chute block = y1
Spacing = 2.5 y1
Height of chute block = 2y1
Length of chutes = 2y1
U.S.B.R. Type-II basin for F1 greater than 4.5 and v1 less than 15 m/sec.:
U.S.B.R. Type-Ill basin for F, greater than 4.5 and V1 greater than 15 m/sec :
Chutes and dentated sills provided
Baffle is not provided because of –velocity is high and cavitation is possible.
[B] Indian Standards Basins :
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
IS Type-Ill basin is usually provided with a sloping apron for the entire len
This chapter is based on the book Hydraulics of Spillways and Energy Dissipators By Rajnikant M. Khatsuria ,concerned with the general procedure of an overall design. An evaluation of the basic data should be the first step in the preparation of the design. This includes the topography and geology as well as flood hydrography, storage, and release requirements.
Reservoir Planning: Introduction; Investigations for reservoir planning; Selection of site for a reservoir; Zones of storage in a reservoir; Storage capacity and yield; Mass inflow curve and demand curve; Calculation of reservoir capacity for a specified yield from the mass inflow curve; Determination of safe yield from a reservoir of a given capacity; Sediment flow in streams; Life of reservoir; Reservoir sediment control; flood routing. Various types of Spillways and design.
WEIRS VERSUS BERRAGE
TYPES OF WEIRS
COMPONENT PARTS OF A WEIR
CAUSES OF FAILURE OF WEIRS & THEIR REMEDIES
DESIGN CONSIDERATIONS
DESIGN FOR SURFACE FLOW
DESIGN OF BARRAGE OR WEIR
Topics:
1. Types of Diversion Head Works
2. Weirs and Barrages
3. Layout Diversion Head Works
4. Causes of Failures of Weirs and Barrages on Permeable Foundations
5. Silt Ejectors and Silt Excluders
spillway,types of spillways,
Design principles of Ogee spillways ,Spillway gates. Energy
Dissipaters and Stilling Basins Significance of Jump Height Curve and Tail Water Rating
Curve,
USBR and Indian types of Stilling Basins.
ENERGY DISSIPATORS
stilling basin
A stilling basin is defined as a structure in which a hydraulic jump used for energy dissipation is confined either partly or entirely.
Certain auxiliary devices such as chute blocks, sills, baffle walls, etc. are usually provided in the stilling basins to reduce the length of the jump and thus to reduce the length and the cost of the stilling basin.
Moreover, these devices also improve the dissipation action of the basin and stabilize the jump.
Chute Blocks :
These are triangular blocks with their top surface horizontal. These are installed at the toe of the spillway just at upstream end of the stilling basin.
They act as a serrated device at the entrance to the stilling basin. They furrow the incoming jet and lift a portion of it ab0ve the floor.
These blocks stabilise the jump and thus improve its performance, these also decrease the length of the hydraulic jump.
Basin Blocks or Baffle Blocks or Baffle Piers :
These are installed on the stilling basin floor between chute blocks and the end sill. These blocks also stabilise the formation of the jump.
Moreover, they increase the turbulence and assist in the dissipation of energy.
They help in breaking the flow and dissipate energy mostly by impact. These baffle blocks are sometimes called friction blocks.
Sills and Dentated Sills :
Sill or more preferably dentated sill is generally provided at the end of the stilling basin.
The dentated sill diffuses the residual portion of the high velocity jet reaching the end of the basin. They, therefore, help in dissipating residual energy and to reduce the length of the jump or the basin.
particular location of these blocks mainly depends upon the initial Froude number (F1) and the velocityof the incoming flow. The stilling basins are usually rectangular in plan. These aremade up of concrete.
[A] U.S.B.R. Stilling basins :
[B] Indian Standards Basins :
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
Type I basin (F1 between 2.5 to 4.5)
Provide chute blocks and end sill
Length of basin = 4.3 y2 to 6.0 y2
Width of chute block = y1
Spacing = 2.5 y1
Height of chute block = 2y1
Length of chutes = 2y1
U.S.B.R. Type-II basin for F1 greater than 4.5 and v1 less than 15 m/sec.:
U.S.B.R. Type-Ill basin for F, greater than 4.5 and V1 greater than 15 m/sec :
Chutes and dentated sills provided
Baffle is not provided because of –velocity is high and cavitation is possible.
[B] Indian Standards Basins :
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
1. Horizontal apron - Type-I
2. Horizontal apron - Type-II
3. Sloping apron - Type-Ill
4. Sloping apron - Type-IV
IS Type-Ill basin is usually provided with a sloping apron for the entire len
This chapter is based on the book Hydraulics of Spillways and Energy Dissipators By Rajnikant M. Khatsuria ,concerned with the general procedure of an overall design. An evaluation of the basic data should be the first step in the preparation of the design. This includes the topography and geology as well as flood hydrography, storage, and release requirements.
unit 4 vsem cross drainage works & srturcture water resource engineering Siph...Denish Jangid
unit 4 vsem cross drainage works & srturcture water resource engineering types of CDW Siphon Aqueduct Determination of Maximum Flood Discharge selection of cross drainage works Fluming of Canal Necessity (Merits) of Cross Drainage Works
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
TECHNICAL TRAINING MANUAL GENERAL FAMILIARIZATION COURSEDuvanRamosGarzon1
AIRCRAFT GENERAL
The Single Aisle is the most advanced family aircraft in service today, with fly-by-wire flight controls.
The A318, A319, A320 and A321 are twin-engine subsonic medium range aircraft.
The family offers a choice of engines
Quality defects in TMT Bars, Possible causes and Potential Solutions.PrashantGoswami42
Maintaining high-quality standards in the production of TMT bars is crucial for ensuring structural integrity in construction. Addressing common defects through careful monitoring, standardized processes, and advanced technology can significantly improve the quality of TMT bars. Continuous training and adherence to quality control measures will also play a pivotal role in minimizing these defects.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
Cosmetic shop management system project report.pdf
Lecture 1 free overfall and ogee
1. Addis Ababa Science and
Technology
College of Architecture and Civil
Engineering
HYDRALUCIS STRUCURES I
CENG 6605
Mesay Daniel (PhD)
Fitsum Tesfaye (PhD)
3. Spillway
• The principal function of a spillway is to pass down the
surplus water from the reservoir into the downstream river.
• After a spillway control device and its dimensions have
been selected, the maximum spillway discharge and the
maximum reservoir water level should be determined by
flood routing.
• Cost estimates of the spillway and the dam should be
made.
• Comparisons of various combinations of spillway capacity
and dam height for an assumed spillway type, and of
alternative types of spillways allow selection of an
economical spillway type.
5. Selection of Spillway Size and Type
General Considerations
• All pertinent factors of hydrology, hydraulics, design, cost, and
damage should be considered.
• In this connection and when applicable, consideration should be
given to such factors as:
– the characteristics of the flood hydrograph
– the damages that would result if such a flood occurred without the
dam
– the damages that would result if such a flood occurred with the dam
in place
– the damages that would occur if the dam or spillway were breached,
– the effects of various dam and spillway combinations on the probable
damages upstream and downstream of the dam
– the relative costs of increasing the capacity of spillway
– the use of combined outlet facilities to serve more than one function
7. Design of Ogee Spillways
General
• The ogee or overflow spillway is the
most common type of spillway.
• It has a control weir that is ogee or S-
shaped.
• It is a gravity structure requiring
sound foundation and is preferably
located in the main river channel,
although there are many spillways
located on the flanks in excavated
channels due to foundation
problems.
• The structure divides naturally into
three zones: the crest, the rear
slope, and the toe.
• Because of its high discharge
efficiency, the nappe-shaped profile
is used for most spillway control
crests.
8. Design of Ogee Spillways contd.
General
• The application of the theory of flow through spillways is
based largely upon empirical coefficients, so the designer
should deal with maximum and minimum values as well as
averages, depending upon the design objective.
• To be conservative, the designer should generally use
maximum loss factors in computing discharge capacity, and
minimum loss factors in computing velocities for the design
of energy dissipators.
• As more model and prototype data become available, the
range between maximum and minimum coefficients used
in design should be narrowed.
9. Design of Ogee Spillways contd.
Basic Considerations
• A spillway is sized to provide the required
capacity, usually the entire spillway design
flood, at a specific reservoir elevation.
• This elevation is normally at the maximum
operating level or at a surcharge elevation
greater than the maximum operating level.
10. Design of Ogee Spillways contd.
Hydraulic analysis of a spillway usually involves
four conditions of flow:
1. Subcritical flow in the spillway approach, initially
at a low velocity, accelerating, however, as it
approaches the crest.
2. Critical flow as the water passes over the
spillway crest.
3. Supercritical flow in the chute below the crest.
4. Transitional flow at or near the terminus of the
chute where the flow must transition back to
subcritical.
11. Design of Ogee Spillways contd.
Basic Considerations contd.
• When a relatively large storage capacity can be obtained above the
normal maximum reservoir elevation by increasing the dam height,
a portion of the flood volume can be stored in this reservoir
surcharge space and the size of the spillway can be reduced.
• The use of a surcharge pool for passing the spillway design flood
involves an economic analysis that considers the added cost of a
dam height compared to the cost of a wider and/or deeper spillway.
• When a gated spillway is considered, the added cost of higher
and/or additional gates and piers must be compared to the cost of
additional dam height.
12. Shape for Uncontrolled Ogee Crest
• Crest shapes have been studied extensively in
the Bureau of US Reclamation Hydraulics
Laboratories.
• For most conditions the data can be
summarized according to the form shown on
in next slide, where the profile is defined as it
relates to axis at the apex of the crest.
14. Shape for Uncontrolled Ogee Crest contd.
• That upstream portion from the origin is defined as
either a single curve and a tangent or as a compound
circular curve.
• The downstream portion is defined by the equation:
𝑦
𝐻 𝑜
= −𝐾
𝑥
𝐻 𝑜
𝑛
in which 𝐾 and 𝑛 are constants whose values depend
on the upstream inclination and on the velocity of
approach.
The following figure gives values of these constants for
different conditions.
15.
16. Shape for Uncontrolled Ogee Crest
contd.
• The approximate profile shape for a crest with a
vertical upstream face and negligible velocity of
approach is shown in the following figure.
• The profile is constructed in the form of a
compound circular curve with radii expressed in
terms of the design head, 𝐻 𝑜.
• This definition avoids the need for solving an
exponential equation; furthermore, it is
represented in a form easily used by a layman for
constructing forms or templates.
17.
18. Shape for Uncontrolled Ogee Crest
contd.
• For ordinary design conditions for small
spillways where 𝑃 ≥ 0.5𝐻 𝑜, this profile is
sufficiently accurate to avoid seriously
reduced crest pressures and does not
materially alter the hydraulic efficiency of the
crest.
• When the 𝑃 < 0.5𝐻 𝑜 on the crest, the profile
should be determined from the given
exponential formula.
19. Shape for Uncontrolled Ogee Crest
contd
• US Army Corps of Engineers, WES (1952) has
developed several standard shapes, designated as WES
standard spillway shapes, represented on the
downstream of the crest axis by the equation:
𝑋 𝑛
= 𝐾𝐻 𝑜
𝑛−1
𝑌
Where
𝑋 and 𝑌 are coordinates of crest profile with origin at the
highest point of the crest.
𝐻 𝑜is the design head including velocity head of the approach
flow.
𝐾 and 𝑛 are parameters depending on the slope of the
upstream face.
21. Shape for Uncontrolled Ogee Crest
contd
• In the revised procedure developed by WES using the data of USBR,
the upstream quadrant was shaped as an ellipse with the equation:
𝑋2
𝐴2
+
𝑌2
𝐵2
= 1
Where
𝐴 = Semi-major axis (functions of the ratio of approach depth to
design head)
𝐵 =Semi-minor axis (-do-)
• And the downstream profile conformed to the equation
𝑋1.85
= 𝐾𝐻 𝑜
0.85
𝑌
where 𝐾 is a parameter depending on the ratio approach depth and
design head.
22. Shape far Uncontrolled Ogee Crest contd
• The design curves suggested by WES are
reproduced as shown the following slide.
• For 𝑃 𝐻 𝑜 = 2, 𝐴 and 𝐵 become constant with
values of 0.28𝐻 𝑜 and 0.164 0.16𝐻 𝑜
respectively.
23.
24. Spillway Discharge
• The ogee crest spillway is basically a sharp-crested weir with the
space below the lower nappe filled with concrete.
• The shape of such a profile depends upon the head, the inclination
of the upstream face of the overflow section, and the height of the
overflow section above the floor of the entrance channel (which
influences the velocity of approach to the crest).
• The discharge over a spill-way crest is limited by the same
parameters as the weir, and determined by the following:
𝑄 = 𝐶𝐿 𝑒 𝐻𝑒
3/2
𝑄= discharge
C= Coefficient of discharge
𝐿 𝑒=effective length
𝐻𝑒=Specific energy above the crest center
25. Spillway Discharge contd.
• The discharge coefficient is influenced by a
number of factors:
o Height of spillway above stream bed or depth of
approach,
o relation of the actual crest shape to the ideal nappe
shape,
o upstream face slope,
o downstream apron interference,
o down stream submergence, and
o Ratio of actual total head to the design head,
26. Spillway Discharge contd.
• The height of spillway, 𝑃 above stream bed or
approach channel affects the velocity of approach
which in turn affects the coefficient of discharge,
𝐶.
• With increase in 𝑃 the velocity of approach
decreases and the 𝐶 increases.
• Model tests indicate that the 𝐶 becomes fairly
constant when P > 3.0𝐻 𝑜, where 𝐻 𝑜 is the
design head including the head due to velocity of
approach.
27. Pier and Abutment Effects
• Where crest piers and abutments are shaped to cause
side contractions of the overflow, the effective length,
𝐿 𝑒, is less than the net length of the crest, 𝐿.
• The effect of the end contraction may be taken into
account by reducing the net crest length as follows:
𝐿 𝑒 = 𝐿 − 2(𝑁𝐾𝑝 + 𝐾𝑎)𝐻𝑒
Where: 𝑁 is number of pier
𝐾𝑝is pier contraction coefficient
𝐾𝑎is abutment contraction coefficient
𝐻𝑒 is actual head on the crust
28. Pier and Abutment Effects contd.
• 𝐾 𝑝 is affected by:
o the shape and location of the pier nose,
o the thickness of the pier,
o the design head, and
o the approach velocity.
• For conditions of design head, 𝐻 𝑜 ,
o For square-nosed piers with corners rounded on a
radius equal to about 0.1 of the pier thickness, 𝐾𝑝 =
0.02
o For round-nosed piers, 𝐾𝑝 = 0.01
o For pointed-nose piers,𝐾 𝑝 = 0.00
29. Pier and Abutment Effects contd.
• 𝐾𝑎 is affected by:
o the shape of the abutment,
o the angle between the upstream approach wall and the axis of the
flow,
o the head in relation to the design head, and
o the approach velocity.
• For conditions of design head, 𝐻 𝑜 ,
o For square abutments with headwall at 90o to direction of flow: , 𝐾 𝑎 =
0.2
o For rounded abutments with headwall at 90oto direction of flow, when
0.15𝐻 𝑜 ≤ 𝑟 ≤ 0.5𝐻 𝑜, 𝐾a = 0.1
o 𝐾 𝑝 = 0.00
o For rounded abutments with radius larger than 0.5𝐻 𝑜and head wall is
placed not more than 45o to direction of flow, 𝐾 𝑎 = 0.00
30. Effect of Approach Velocity
• Another factor influencing the discharge
coefficient of a spillway crest is the depth in the
approach channel relative to the design head
defined as the ratio 𝑃 𝐻 𝑜,
• As 𝑃 decreases relative to the design head, the
effect of approach velocity becomes more
significant.
• These coefficients are valid only when the ogee
is formed to the ideal nappe shape; that is, when
𝐻𝑒 𝐻 𝑜 = 1
31.
32.
33. Effect of Heads Different from Design
Head
• A wider ogee shape will result in positive
pressures along the crest contact surface,
thereby reducing the discharge.
• With a narrower crest shape, negative
pressures along the contact surface will occur,
resulting in an increased discharge.
34.
35. Effect of Upstream Face Slope
Increase in slope
increases coefficient Increase in slope
variable change in
coefficient
36.
37. Effect of D/S Apron Interference and
D/S Submergence
• When the water level below an overflow weir
is high enough to affect the discharge, the
weir is said to be submerged.
• The vertical distance from the crest of the
overflow to the downstream apron and the
depth of flow in the downstream channel, as
it relates to the head pool level, are factors
that alter the discharge coefficient.
38. Effect of D/S Apron Interference and
D/S Submergence contd.
• Five distinct characteristic flows can occur below an overflow crest,
depending on the relative positions of the apron and the
downstream water surface:
1. flow can continue at supercritical stage;
2. a partial or incomplete hydraulic jump can occur immediately
downstream from the crest;
3. a true hydraulic jump can occur;
4. a drowned jump can occur in which the high-velocity jet will follow
the face of the overflow and then continue in an erratic and
fluctuating path for a considerable distance under and through the
slower water; and
5. no jump may occur-the jet will break away from the face of the
overflow and ride along the surface for a short distance and then
erratically intermingle with the slow moving water underneath.
41. Uncontrolled Ogee Crests Designed for
less than Maximum Head
• Use of a smaller design head results in increased discharges for the
full range of heads.
• The increase in capacity makes it possible to achieve economy by
reducing either the crest length or the maximum surcharge head.
• The subatmospheric pressures on a nappe-shaped crest do not
exceed about one-half the design head when the design head is not
less than about 75 percent of the maximum head.
• For most conditions in the design of spillways, these negative
pressures will be small, and they can be tolerated because they will
not approach absolute pressures that can induce cavitation.
• Care must be taken, however, in forming the surface of the crest
where these negative pressures will occur.
• The negative pressure on the crest may be resolved into a system of
forces acting both upward and downstream. These forces should be
considered in analyzing the structural stability of the crest structure.
43. Sub atmospheric crest
pressures
All other conditions remaining
the same, pressures along the
side of the crest piers are
always lower than those along
the center line of the span.
WES suggest that the maximum
negative pressure on the crest
should be restricted to (-6m) of
water and that the crest profile
be designed for a head
𝐻 𝑜 = 0.309𝐻𝑒_𝑚𝑎𝑥
1.2186
(in ft
units).
44. Determination of Design Head
• Hager (1991) has generalized the results of studies of various
research workers as follows:
• The absolute minimum of crest pressure, 𝑃 𝑚𝑖𝑛
𝑃 𝑚𝑖𝑛
𝐻𝑒
= 𝛾(1 − 𝜒)
Where
𝜒 =
𝐻𝑒
𝐻 𝑜
𝐻𝑒 = Operating head
𝐻0 = Design head, and
𝛾 = Coefficient of proportionality
= 1 for WES profile with 45 downstream slope
= 0.9 for WES profile with 30 downstream slope
45. Determination of Design Head contd.
• The location of zero bottom pressure, 𝑋0 from crest axis
𝑋 𝑜
𝐻 𝑜
= 0.9𝑡𝑎𝑛𝛼(
𝐻𝑒
𝐻 𝑜
− 1)0.43
Where 𝛼 is the downstream slope.
The coefficient of discharge
𝐶 𝑑 =
2
3 3
1 +
4𝜒
9 + 5𝜒
In the equation 𝑄 = 𝐶 𝑑 ∗ 𝑏(2𝑔𝐻3
)0.5
Or
𝐶 𝑑 =
1
3
1 +
4𝜒
9+5𝜒
in the equation 𝑄 = 2/3𝐶 𝑑 ∗ 𝑏(2𝑔𝐻3
)0.5
46. Determination of Design Head contd.
• The limiting operating head, 𝐻𝐿for a given crest
profile is governed by the magnitude of the
minimum pressure on the crest which could
induce cavitation.
• Theoretically, this pressure is the vapour
pressure, 𝑃𝑣 , Inserting 𝑃𝑣 in place of 𝑃 𝑚𝑖𝑛and
𝐻𝐿in place of 𝐻𝑒in equation slide 52 yields:
𝐻𝐿 =
𝑃𝑣
𝛾(1 − 𝜒)
47. Determination of Design Head contd.
• Cavitation is also dependent on the air
content and particularly on the local
turbulence level and smoothness of the flow
surfaces.
• Considering the uncertainties of these factors,
Abecasis (1970) assumed a minimum pressure
of -7.6 m for incipient cavitation.
48. Downstream Slope or Rear Slope
• The downstream slope is made tangential to the crest profile with
the angle of the slope generally determined by requirement of
structural stability.
• Slopes are usually in the range of 0.6H:1V to 1.1H:1V.
• The rear slope together with sidewalls constitutes the discharge
channel leading the flow from the crest to the energy dissipator.
• Because of the acceleration of the flow and the gradual increase in
the velocity, extreme care is required to ensure that the profile of
the discharge channel, both in elevation and plan, strictly conforms
to the design profile.
• Also, the specified tolerances of surface finish is to be adhered to,
as otherwise cavitation damage can be inflicted if flow velocity
exceeds 25 m/s.
49. Water Surface Profile
• Water surface profiles in the crest region of standard
spillway profiles, including the effects of piers and
abutments, have been given in WES
• The generalized relationship for a freely overflowing
spillway without piers, etc. is:
𝑆 = 0.75 𝜒1.1
−
1
6
𝑋
Where S =
𝑠
𝐻 𝑜
𝑠 =Vertically measured flow depth
X =
𝑥
𝐻 𝑜
𝑥 =Longitudinal coordinate and −2 < 𝑋 < 2
50. Spillway Toe
• The spillway toe is the junction between the
discharge channel and can be design as the
energy dissipator component.
• Its function is to guide the flow passing down the
spillway and smoothly in the energy.
• A toe curve is made up of a circular arc,
tangential to both the rear slope and the apron.
• A minimum radius of 3 times the depth of flow
entering the toe is recommended.
51. Spillway Toe contd.
• The pressures on the floor and sidewalls in the region
of the curvature increase due to centrifugal action.
• The resulting pressure is the summation of the
hydrostatic pressure and the centrifugal pressure, given
by:
𝑃
𝛾
= 𝑌(1 +
𝑉2
𝑔𝑅
)
• Where
• 𝑌 is the Depth of flow at the toe
• 𝑉 is the mean velocity at the toe
• 𝑅 is the radius of the toe curvature
52. Gate-Controlled Ogee Crests
• Releases for partial gate openings for gated
crests occur as orifice flow.
• With full head on a gate that is opened a small
amount, a free discharging trajectory will
follow the path of a jet issuing from an orifice.
53. Gate-Controlled Ogee Crests contd.
• Releases for partial gate openings for gated crests
occur as orifice flow.
• With full head on a gate that is opened a small
amount, a free discharging trajectory will follow
the path of a jet issuing from an orifice.
• For a vertical orifice the path of the jet can be
expressed by the parabolic equation:
−𝑦 = 𝑥𝑡𝑎𝑛𝜃 +
𝑥2
4𝐻𝑐𝑜𝑠2 𝜃
where 𝐻 is the head on the center of the opening.
54. Gate-Controlled Ogee Crests contd.
• If subatmospheric pressures are to be avoided along the
crest contact, the shape of the ogee downstream from the
gate sill must conform to the trajectory profile.
• Gates operated with small openings under high heads
produce negative pressures along the crest in the region
immediately below the gate if the ogee profile drops below
the trajectory profile.
• Tests showed the subatmospheric pressures would be equal
to about one-tenth of the design head when the gate is
operated at small openings and the ogee is shaped to the
ideal nappe profile for maximum head 𝐻𝑜.
55.
56. Gate-Controlled Ogee Crests contd.
• The trajectory profile (rather than the nappe) may
be adopted to avoid subatmospheric pressure
zones along the crest.
• Where the ogee is shaped to the ideal nappe
profile for maximum head, the subatmospheric
pressure area can be minimized by placing the
gate sill downstream from the crest of the ogee.
57. Discharge Over Gate-Controlled Ogee
Crests
• The discharge for a gated ogee crest at partial
gate openings will be similar to flow through an
orifice and may be computed by the equation:
𝑄 = 𝐶𝐷𝐿 2𝑔𝐻
where:
𝐻 = head to the center of the gate opening
(including the velocity head of approach),
𝐷 = shortest distance from the gate lip to the crest
curve, and
𝐿 = crest width.
61. Deign of Overfall Spillway
• An overfall spillway
can be gated or
ungated and
provided for flow
over an arch or
buttress dam.
62. Deign of Overfall Spillway contd.
• The main concern in the design of free jet
spillways is either the deep scour just
downstream of the dam (as in the case of a
deflected jet) or impact forces on the stilling
basin floor at the foot of the dam (with a free
falling jet).
• The free jet falls from straight drop spillway
also known as the box inlet drop spillway
which is simply a rectangular box.
63. Deign of Overfall Spillway contd.
Design Considerations
• The choice of the type of discharge structure—
whether to have a free over-fall over a crest or a
deep-seated bottom outlet—depends largely on
the volume of flood to be disposed, width of the
gorge, and the characteristics of the rock forming
the gorge and riverbed.
• With free over-fall over the top, the jet would fall
very near the base of the dam where a concrete-
lined stilling basin would be necessary to prevent
undermining.
64. Deign of Overfall Spillway contd.
• The hydraulic characteristics are
defined as follows:
o The crest structure and discharge
rating are similar to those for the
overflow spillway.
o The flow normally leaves this
structure shortly below the crest.
o The exit structure is normally some
variation of a flip-bucket.
o The flip-bucket radius, 𝑅 for an
overfall spillway is at least 5𝑑, where
𝑑 is the flow depth at the bottom of
the bucket.
65. Deign of Overfall Spillway contd.
Overflow Crest
• Overflow crest profiles on the top of arch dams
have to be adjusted with overhangs either on the
upstream, downstream, or on both sides, since
the width available at the top is seldom adequate
to base an overflow profile.
• A standard ogee profile or parabolic profile is
suitable with the required overhang.
• Generally, three types of profiles are used:
66. Profiles terminating such that the overflow jet is directed to fall on
the concrete apron for the entire range of discharges.
Overflow profile ( Beznar dam, Granada)
67. Overflow profile with nappe splitters (Palawan dam, Rhodesia).
Profiles with nappe splitters to effect aeration of the jet and
spreading over larger area.
69. Deign of Overfall Spillway contd.
• The radius is usually undersized to minimize the size of the
overhang, which can destabilize the top of a thin-arch dam.
• However, the radius should be sufficient to fully—deflect a
significant flood.
• The bucket exit angle is selected to throw the jet to a suitable
location in the tailrace.
• The trajectory can be estimated by:
𝑦 = 𝑥𝑡𝑎𝑛𝜃 −
𝑥2
3.6𝐻𝑐𝑜𝑠2 𝜃
where:
𝑦 = 𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝑏𝑢𝑐𝑘𝑒𝑡 𝑙𝑖𝑝
𝑥 = ℎ𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝑏𝑢𝑐𝑘𝑒𝑡 𝑙𝑖𝑝
𝜃 = 𝑏𝑢𝑐𝑘𝑒𝑡 𝑒𝑥𝑖𝑡 𝑎𝑛𝑔𝑙𝑒, and 𝐻 = 𝑑𝑒𝑝𝑡ℎ +
𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 ℎ𝑒𝑎𝑑 𝑎𝑡 𝑡ℎ𝑒 𝑏𝑢𝑐𝑘𝑒𝑡 𝑙𝑖p.
71. Deign of Overfall Spillway contd.
• The energy from an overfall spillway is normally
dissipated by a plunge pool, which can be lined or
unlined.
• If unlined, the scour and the scour rate will be based
on both flow and geology.
• The scour hole development is usually
indeterminate.
• However, the terminal scour depth for a uniformly
erodible material can be estimated from the
following empirical formula (Coleman, 1982; USBR,
1987)
illustrates the comparative costs for different combinations of spillway and dam, and indicates a combination that results in the least total cost.
To do such comparison it needs so many flood routing tasks, spillway layouts and spillway and dam estimates.
Cost of ungated spillway is higher than gated spillway until the maximum reservoir water surface reaches about 3004 feet . After that point the cost is less that the cost of gated spillway.
The maximum water surface from the ogee crest and the gate crest are compared here.
The discharge capacity is compared when the gates are opened
Ho=He
Show in the separate file
Show the reproduced curves
Discharge coefficients for vertical-faced ogee crest. Design of small dams page 370
The statements are correct.
Correct the discharge equation
Where He_ max is the maximum operating head.
Arch dams of height exceeding 200 m are not unusual and some dams while in planning or construction will be about 300 m in height