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Erbil polytechnic university
Technical engineering college
Civil engineering department
Spillway
Group G (6)
1-Ziyad Asaad
2-Paywand Shakir
3-Mohammed Jalal
4-Ahmad Karim
5-Ismail Mukhlis
Supervisor :
Dr. Bassil Y. Mustafa
Mr. Alend W. Abdulrazaq
Introduction
 Spillways in storage and detention dams
serve to release excess floodwater,
preventing overflow. They include various
types like irrigation canals, power canals,
and feeder canals, managing flows beyond
diversion works like weirs and barrages.
Ogee-style spillways, illustrated in Bhakra
and Hirakud dams, are
common.Functioning as safety valves,
spillways are crucial for dam safety.
Inadequate capacity or design flaws can
lead to dam collapses, especially in earthen
and rockfill structures.
Ahmed Karim
Types Of Spillways
1. Vertical Drop type Spillway
2. Ogee (overflow) Spillways
3. Chute (Open Channel or Trough) Spillways
4. Conduit and Tunnel Spillways
5. Drop Inlet (Shaft or Morning Glory) Spillways
6. Culvert Spillway
7. Siphon spillways
8. Side channel spillway
9. Stepped spillway
Ahmed Karim
Vertical Drop type Spillway
 Vertical drop type spillways are crucial for efficient
water flow control in dams and reservoirs, utilizing
a vertical wall or chute to harness the potential
energy created by the height difference between
water levels and downstream discharge points.
These spillways operate solely on gravity,
eliminating the risk of mechanical failure and
reducing maintenance needs. Their simplicity,
reliability, and cost-effectiveness make them
advantageous, particularly in new dam projects.
Ahmed Karim
Ogee (overflow) Spillways
 The ogee spillway, illustrated in Fig. 3 (a) and Fig. 3 (b), features a control weir with
an ogee or S-shaped profile. The upper curve closely conforms to the lower nappe
of a ventilated sheet falling from a sharp-crested weir, ensuring smooth flow over
the crest. By preventing air access to the underside, the flow glides over the crest
with high efficiency at designed head discharges. The profile below the upper
curve extends tangent, supporting the sheet's face and directing flow onto the
apron of a stilling basin or spillway discharge channel.
Ahmed Karim
Ahmed Karim
Chute (Open Channel or Trough) Spillways
 A chute, open channel, or trough-type spillway conveys discharge from a reservoir
to a downstream river through an open channel, positioned along a dam abutment
or through a saddle. This spillway type, regardless of the control device regulating
flow, is commonly termed a chute spillway
Ahmed Karim
Drop Inlet (Shaft) Spillways
 Drop inlet spillways, also known as shaft spillways, are hydraulic structures
designed to safely discharge excess water from reservoirs or dams. Utilizing a
unique design with a vertical shaft or concrete structure resembling a funnel, they
facilitate efficient energy dissipation and hydraulic jump, ensuring controlled water
discharge.
Paywand Shakir
Culvert Spillway
 A culvert spillway is a crucial part of water management systems, controlling excess
water flow to prevent flooding and ensure smooth passage. Its effectiveness
depends on size, shape, and maintenance, with shapes ranging from circular to
rectangular.
Paywand Shakir
Siphon spillways
 A siphon spillway is a type of spillway in which surplus water is disposed to
downstream through an inverted U shaped conduit. It is generally arranged inside
the body or over the crest of the dam . In both types of siphon spillways, air vents
are provided at the bent portion of the upper passageway to prevent the entrance
of water when the water level is below the normal poll level. Whenever the level
rises above normal pool level, water enters into the conduit and is discharged to
the downstream of the channel by siphonic action
Paywand Shakir
 Side channel spillway is similar to chute spillway but the only difference is the crest
of side channel spillway is located on one of its sides whereas crest of chute
spillway is located between the side walls. In other words, the water spilling from
the crest is turned to 90 degrees and flows parallel to the crest of side channel
spillway unlike in chute spillway. Side channel spillways are preferred over chute
spillways when flanks of sufficient width are not available, usually to avoid heavy
cutting. The angle of turn of water flow after passing weir crest can also be kept
between 00 and 900.
Side channel spillway
Paywand Shakir
Stepped spillway
 A stepped spillway is a water control structure with terraces designed to dissipate water energy, preventing
erosion and ensuring stability. Its key advantage lies in efficiently handling high flow rates by creating small
waterfalls that reduce velocity and sediment transport downstream. Cost-effectiveness is another benefit,
making it a preferred choice in budget-constrained projects compared to more complex spillway
types.Beyond practical advantages, a stepped spillway can enhance aesthetics with visually appealing
cascading waterfalls. However, challenges include ensuring proper step design to handle expected flow
rates, avoiding issues like excessive erosion or inadequate energy dissipation. Stepped spillways are a
popular and cost-effective solution for controlling water flow in dams and reservoirs, preventing erosion,
and offering aesthetic appeal, contributing to project success.
Paywand Shakir
Selection of Spillway Size and Type
 In determining the optimal combination of storage and spillway capacity for
handling the selected inflow design flood, a comprehensive evaluation of
hydrological, hydraulic, design, cost, and damage factors is essential.
Considerations include the characteristics of the flood hydrograph, potential
damages with and without the dam, impacts of dam or spillway breaches, and the
effects on damages both upstream and downstream. Factors such as the relative
costs of increasing spillway capacity and the potential use of combined outlet
facilities for multiple functions should also be taken into account.Hydrological and
hydraulic considerations play a crucial role in determining the type and size of a
spillway. Service outlet releases may be considered during the inflow design flood,
provided they are available and feasible in flood situations. Overall, a thorough
assessment of these factors guides the decision-making process to ensure the
effective and safe operation of the dam and spillway system.
muhammad Jalal
Type of Selection of Spillway Size
1. Hydrological Considerations
2. Hydraulic Considerations
muhammad Jalal
 Routing the incoming peak flood through the reservoir upstream of the dam is
essential, with higher storage capacity resulting in a lower routed flood peak that
the spillway must accommodate. An economic analysis is crucial to determine the
optimal combination of storage capacity and spillway size for cost-effective
spillway and associated structures like energy dissipaters.
muhammad Jalal
Hydraulic Considerations
 The hydraulic design of various spillway prevent structural failure, and minimize
maintenance costs. Detailed hydraulic design should adhere to relevant codes
provided in the references. Key aspects of hydraulic design include:
1. Fixing the crest level
2. Design of waterway
3. Design of spillway profile
4. Design of energy dissipation device
5. Design of aeration device
6. Design of anti-vortex device
muhammad Jalal

7. Design of control gates and their operation
 8. Design of outlet works
 9. Reservoir operation schedule
 10. Desalting of reservoirs
These considerations collectively contribute to the effective and safe
functioning of spillways, promoting structural integrity and reducing the need
for extensive maintenance. Following established codes ensures compliance
with industry standards in the hydraulic design process.
muhammad Jalal
Example
1. Design an ogee spillway with the following data.
Height of spillway crest above river bed =100m
Design discharge = 12000m3 Number of spans = 6
Clear distance between piers =15m
Thickness of pier =3m
Slope of downstream face of the overflow section = 0.8:1
Assume any data if required.
Solution:
Clear water way (L') =clear d/ce b/n piers * number of span = 6x15=90m
Assuming Cd = 2.30, (value ranges b/n 2.1- 2.5)
From Q= CdLeHe3/2
Q=2.30x90xHe3/2
Ziyad Asaad
12000= 2.30x90x He3/2 He= 15.43m.
Check effect of height of spillway/approach velocity: Model tests have shown that the effect of approach
velocity is negligible when the height of the spillway above the streambed is equal to or greater than 1.33 Hd
(P ≥ 1.33 Hd)
P/Hd= 100/15.43=6.48,
P/He = 6.48>1.33, effect on Cd is negligible.
Thus, the velocity of approach is small and He≈Hd=15.43m
Effect of actual head: if the design head is equal to the actual head, (He/Hd) ratio is 1.0 and therefore, there
is no effect on Cd.
Effect of upstream slope: Assumed to be vertical, hence no effect on Cd.
Effect of downstream apron: In this case, d+hd=100+15.43=115.43m.
(ℎd+ d)/He= 115.43/15.43 = 7.48 > 1.70 ,hence no effect on Cd.
Effect on end construction: Let us assume Kp=0.02 and Ka=0.20.
Therefore, effective length
Le = L' -2(NKp +Ka )(He)
= 90.0 − 2(5×0.02 +0.2)×15.43= 80.74
Q=CdLeHe3/2
12000 = 2.30 80.74 He3/2
He= 16.59m
Ziyad Asaad
Substituting this value of He is equation of effective length,
= 90 − 2(5 × 0.02 + 0.2) 16.59 = 80.05
Substitute on Discharge equation,
12000=2.30x80.05xHe3/2
He=16.7m
Let’s take the design head (He) of 16.70m.
Downstream profile: X n = KHd n-1y
Velocity of approach=
𝑄
𝐴
=
12000
(90+5×3)×(100+16.70)
= 0.98𝑚/𝑠
Head due to approach velocity is given by:
𝐻𝑎 =
𝑉2
2𝑔
=
(0.98)2
19.62
= 0.05𝑚 𝑠𝑚𝑎𝑙𝑙 𝑎𝑛𝑑 𝑛𝑒𝑔𝑙𝑖𝑔𝑖𝑏𝑙𝑒
Hd ≈ He
For a given upstream vertical condition i.e. vertical face, K=2.0, and n=1.850.
X n =KHd n-1 y
Ziyad Asaad
x1.85=2.00x (16.70)0.85y=21.895y
Y= 0.0457(x) 1.85....................................................………………d/s profile
Before determining the various co-ordinate of d/s we shall determine the tangent point.
The d/s slope is given 0.8H:1V
For d/s face of the overflow section,
𝑑𝑦
𝑑𝑥
=
1
0.8
= 1.25
From equation, Y= 0.0457(x)1.85, differentiating WRT x
𝑑𝑦
𝑑𝑥
= 1.85 × 0.0457(𝑥)0.85
= 0.0845(𝑥)0.85
Combining the two equations,
0.0845x0.85 =1.25 x= 23.80m.
The tangent point of the profile is at a distance of 23.8m from the origin.
X 0 1 2 3 4 5 6 7 8 9 10 11 12
Y=
0.0457(x)
1.85 0.000 0.046 0.165 0.349 0.594 0.897 1.257 1.672 2.141 2.662 3.235 3.859 4.533
13 14 15 16 17 18 19 20 21 22 23 23.8
5.25
7
6.02
9
6.85
0
7.71
9
8.63
5
9.59
8
10.60
7
11.66
3
12.76
5
13.91
2
15.10
5
16.09
1
Ziyad Asaad
For upstream profile:
the curve should go up to the point given by: 0.27Hd= 0.27*16.7 = 4.509 , substitute the value
of Hd resulting the equation below,
𝑌 =
0.724 𝑥 + 0.27𝐻𝑑
1.85
𝐻𝑑
0.85 + 0.126𝐻𝑑 − 0.4315𝐻𝑑
0.375
(𝑥 + 0.27𝐻𝑑)0.625
y= 0.06614 (x+4.509)1.85+2.1042-1.2402(x+4.509)0.62 upstream profile
x(m)
0 -1 -2 -3 -4 -4.509
y(m) 0 0.0609
24
0.2630
56
0.641
91
1.3099
76
2.1042
Ziyad Asaad
2. The crest level of dam spillway has been kept at 723.70m while the maximum level in the
reservoir is to be 734.50m calculate the maximum discharge through the overflow spillway,
when the flow takes place through 5 units of 12.2m width each at the crest of the spillway.
Solution:
Assume pointed nose piers and rounded abutments (Kp = Ka= 0)
Effective length of spillway crest
Le= L`-2 (N*kp+Ka) He
L`=5*12.2= 61m
Maximum flood rise over the crest, H = 734.5-723.70 = 10.8m
Neglecting velocity of approach and taking C=2.2
Le = 61-2(4*0+0)10.8=61m
Q = CLe H3/2
Q = 2.2*61*10.83/2=4763 m3/s
If square nosed piers and square abutments are assumed: (Kp = 0.02, Ka= 0.2)
Le= 61-2(4*0.02+0.2)10.8=54.952m
Q= 2.2*54.952*10.83/2= 4291m3/s
Ziyad Asaad
Conclusion
 In conclusion, spillways stand as vital components within water management
systems, offering a dependable method for releasing surplus water from dams and
reservoirs, averting overtopping and potential failures. Beyond their primary
function, spillways are instrumental in flood control and contribute significantly to
the sustainable management of water resources. Given the ongoing challenges
posed by climate change and population growth, the critical role of spillways in
effective water management remains paramount.
Ismail Mokhlis
1. Straight drop spillway is suitable for arch dams and for small drops.
2. Ogee spillway is the most commonly used spillway for its high
dischargingefficiency.
3. Chute spillway can be provided in any type of foundation.
4. Side channel spillways are hydraulically less efficient.
5. Shaft spillway becomes undesirable where a discharge more than the
designcapacity is to be passed.
6. siphon spillway is an automatically operated type spillway.
Ismail Mokhlis
(i) IS:6934 “Recommendations for Hydraulic Design of High Ogee overflow Spillways” by Bureau of
Indian Standards, New Delhi
(ii) IS:5186 “Criteria for Design of Chute and side Channel Spillways” by Bureau of Indian Standards,
New Delhi
(iii) IS:6966 “Criteria for Hydraulic Design of Barrages and Weirs” by Bureau of Indian Standards, New
Delhi
(iv) “Design of Small Dams” by U.S.B.R., Oxford and IBH Publishing Co.
(v) “Engineering for Dams” Vol. 1, Wiley Eastern Pvt. Ltd. New Delhi by Creager, Justin & Hinds,
(vi) “Morning-Glory Shaft Spillways Prototype Behavior”, by Bradley, J.N., Trans. ASCE, Vol. 121, 1956
(vii) “Hydraulics of Closed Conduit Spillways- Part I – Theory and its application University of
Minnesota, Saint Anthony Falls Hydraulic Laboratory, Technical Paper No. 12, series B, January 1952,
revised February 1958
References

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"Exploring the Essential Functions and Design Considerations of Spillways in Water Management and Hydraulic Engineering Projects"

  • 1. Erbil polytechnic university Technical engineering college Civil engineering department Spillway Group G (6) 1-Ziyad Asaad 2-Paywand Shakir 3-Mohammed Jalal 4-Ahmad Karim 5-Ismail Mukhlis Supervisor : Dr. Bassil Y. Mustafa Mr. Alend W. Abdulrazaq
  • 2. Introduction  Spillways in storage and detention dams serve to release excess floodwater, preventing overflow. They include various types like irrigation canals, power canals, and feeder canals, managing flows beyond diversion works like weirs and barrages. Ogee-style spillways, illustrated in Bhakra and Hirakud dams, are common.Functioning as safety valves, spillways are crucial for dam safety. Inadequate capacity or design flaws can lead to dam collapses, especially in earthen and rockfill structures. Ahmed Karim
  • 3. Types Of Spillways 1. Vertical Drop type Spillway 2. Ogee (overflow) Spillways 3. Chute (Open Channel or Trough) Spillways 4. Conduit and Tunnel Spillways 5. Drop Inlet (Shaft or Morning Glory) Spillways 6. Culvert Spillway 7. Siphon spillways 8. Side channel spillway 9. Stepped spillway Ahmed Karim
  • 4. Vertical Drop type Spillway  Vertical drop type spillways are crucial for efficient water flow control in dams and reservoirs, utilizing a vertical wall or chute to harness the potential energy created by the height difference between water levels and downstream discharge points. These spillways operate solely on gravity, eliminating the risk of mechanical failure and reducing maintenance needs. Their simplicity, reliability, and cost-effectiveness make them advantageous, particularly in new dam projects. Ahmed Karim
  • 5. Ogee (overflow) Spillways  The ogee spillway, illustrated in Fig. 3 (a) and Fig. 3 (b), features a control weir with an ogee or S-shaped profile. The upper curve closely conforms to the lower nappe of a ventilated sheet falling from a sharp-crested weir, ensuring smooth flow over the crest. By preventing air access to the underside, the flow glides over the crest with high efficiency at designed head discharges. The profile below the upper curve extends tangent, supporting the sheet's face and directing flow onto the apron of a stilling basin or spillway discharge channel. Ahmed Karim
  • 7. Chute (Open Channel or Trough) Spillways  A chute, open channel, or trough-type spillway conveys discharge from a reservoir to a downstream river through an open channel, positioned along a dam abutment or through a saddle. This spillway type, regardless of the control device regulating flow, is commonly termed a chute spillway Ahmed Karim
  • 8. Drop Inlet (Shaft) Spillways  Drop inlet spillways, also known as shaft spillways, are hydraulic structures designed to safely discharge excess water from reservoirs or dams. Utilizing a unique design with a vertical shaft or concrete structure resembling a funnel, they facilitate efficient energy dissipation and hydraulic jump, ensuring controlled water discharge. Paywand Shakir
  • 9. Culvert Spillway  A culvert spillway is a crucial part of water management systems, controlling excess water flow to prevent flooding and ensure smooth passage. Its effectiveness depends on size, shape, and maintenance, with shapes ranging from circular to rectangular. Paywand Shakir
  • 10. Siphon spillways  A siphon spillway is a type of spillway in which surplus water is disposed to downstream through an inverted U shaped conduit. It is generally arranged inside the body or over the crest of the dam . In both types of siphon spillways, air vents are provided at the bent portion of the upper passageway to prevent the entrance of water when the water level is below the normal poll level. Whenever the level rises above normal pool level, water enters into the conduit and is discharged to the downstream of the channel by siphonic action Paywand Shakir
  • 11.  Side channel spillway is similar to chute spillway but the only difference is the crest of side channel spillway is located on one of its sides whereas crest of chute spillway is located between the side walls. In other words, the water spilling from the crest is turned to 90 degrees and flows parallel to the crest of side channel spillway unlike in chute spillway. Side channel spillways are preferred over chute spillways when flanks of sufficient width are not available, usually to avoid heavy cutting. The angle of turn of water flow after passing weir crest can also be kept between 00 and 900. Side channel spillway Paywand Shakir
  • 12. Stepped spillway  A stepped spillway is a water control structure with terraces designed to dissipate water energy, preventing erosion and ensuring stability. Its key advantage lies in efficiently handling high flow rates by creating small waterfalls that reduce velocity and sediment transport downstream. Cost-effectiveness is another benefit, making it a preferred choice in budget-constrained projects compared to more complex spillway types.Beyond practical advantages, a stepped spillway can enhance aesthetics with visually appealing cascading waterfalls. However, challenges include ensuring proper step design to handle expected flow rates, avoiding issues like excessive erosion or inadequate energy dissipation. Stepped spillways are a popular and cost-effective solution for controlling water flow in dams and reservoirs, preventing erosion, and offering aesthetic appeal, contributing to project success. Paywand Shakir
  • 13. Selection of Spillway Size and Type  In determining the optimal combination of storage and spillway capacity for handling the selected inflow design flood, a comprehensive evaluation of hydrological, hydraulic, design, cost, and damage factors is essential. Considerations include the characteristics of the flood hydrograph, potential damages with and without the dam, impacts of dam or spillway breaches, and the effects on damages both upstream and downstream. Factors such as the relative costs of increasing spillway capacity and the potential use of combined outlet facilities for multiple functions should also be taken into account.Hydrological and hydraulic considerations play a crucial role in determining the type and size of a spillway. Service outlet releases may be considered during the inflow design flood, provided they are available and feasible in flood situations. Overall, a thorough assessment of these factors guides the decision-making process to ensure the effective and safe operation of the dam and spillway system. muhammad Jalal
  • 14. Type of Selection of Spillway Size 1. Hydrological Considerations 2. Hydraulic Considerations muhammad Jalal
  • 15.  Routing the incoming peak flood through the reservoir upstream of the dam is essential, with higher storage capacity resulting in a lower routed flood peak that the spillway must accommodate. An economic analysis is crucial to determine the optimal combination of storage capacity and spillway size for cost-effective spillway and associated structures like energy dissipaters. muhammad Jalal
  • 16. Hydraulic Considerations  The hydraulic design of various spillway prevent structural failure, and minimize maintenance costs. Detailed hydraulic design should adhere to relevant codes provided in the references. Key aspects of hydraulic design include: 1. Fixing the crest level 2. Design of waterway 3. Design of spillway profile 4. Design of energy dissipation device 5. Design of aeration device 6. Design of anti-vortex device muhammad Jalal
  • 17.  7. Design of control gates and their operation  8. Design of outlet works  9. Reservoir operation schedule  10. Desalting of reservoirs These considerations collectively contribute to the effective and safe functioning of spillways, promoting structural integrity and reducing the need for extensive maintenance. Following established codes ensures compliance with industry standards in the hydraulic design process. muhammad Jalal
  • 18. Example 1. Design an ogee spillway with the following data. Height of spillway crest above river bed =100m Design discharge = 12000m3 Number of spans = 6 Clear distance between piers =15m Thickness of pier =3m Slope of downstream face of the overflow section = 0.8:1 Assume any data if required. Solution: Clear water way (L') =clear d/ce b/n piers * number of span = 6x15=90m Assuming Cd = 2.30, (value ranges b/n 2.1- 2.5) From Q= CdLeHe3/2 Q=2.30x90xHe3/2 Ziyad Asaad
  • 19. 12000= 2.30x90x He3/2 He= 15.43m. Check effect of height of spillway/approach velocity: Model tests have shown that the effect of approach velocity is negligible when the height of the spillway above the streambed is equal to or greater than 1.33 Hd (P ≥ 1.33 Hd) P/Hd= 100/15.43=6.48, P/He = 6.48>1.33, effect on Cd is negligible. Thus, the velocity of approach is small and He≈Hd=15.43m Effect of actual head: if the design head is equal to the actual head, (He/Hd) ratio is 1.0 and therefore, there is no effect on Cd. Effect of upstream slope: Assumed to be vertical, hence no effect on Cd. Effect of downstream apron: In this case, d+hd=100+15.43=115.43m. (ℎd+ d)/He= 115.43/15.43 = 7.48 > 1.70 ,hence no effect on Cd. Effect on end construction: Let us assume Kp=0.02 and Ka=0.20. Therefore, effective length Le = L' -2(NKp +Ka )(He) = 90.0 − 2(5×0.02 +0.2)×15.43= 80.74 Q=CdLeHe3/2 12000 = 2.30 80.74 He3/2 He= 16.59m Ziyad Asaad
  • 20. Substituting this value of He is equation of effective length, = 90 − 2(5 × 0.02 + 0.2) 16.59 = 80.05 Substitute on Discharge equation, 12000=2.30x80.05xHe3/2 He=16.7m Let’s take the design head (He) of 16.70m. Downstream profile: X n = KHd n-1y Velocity of approach= 𝑄 𝐴 = 12000 (90+5×3)×(100+16.70) = 0.98𝑚/𝑠 Head due to approach velocity is given by: 𝐻𝑎 = 𝑉2 2𝑔 = (0.98)2 19.62 = 0.05𝑚 𝑠𝑚𝑎𝑙𝑙 𝑎𝑛𝑑 𝑛𝑒𝑔𝑙𝑖𝑔𝑖𝑏𝑙𝑒 Hd ≈ He For a given upstream vertical condition i.e. vertical face, K=2.0, and n=1.850. X n =KHd n-1 y Ziyad Asaad
  • 21. x1.85=2.00x (16.70)0.85y=21.895y Y= 0.0457(x) 1.85....................................................………………d/s profile Before determining the various co-ordinate of d/s we shall determine the tangent point. The d/s slope is given 0.8H:1V For d/s face of the overflow section, 𝑑𝑦 𝑑𝑥 = 1 0.8 = 1.25 From equation, Y= 0.0457(x)1.85, differentiating WRT x 𝑑𝑦 𝑑𝑥 = 1.85 × 0.0457(𝑥)0.85 = 0.0845(𝑥)0.85 Combining the two equations, 0.0845x0.85 =1.25 x= 23.80m. The tangent point of the profile is at a distance of 23.8m from the origin. X 0 1 2 3 4 5 6 7 8 9 10 11 12 Y= 0.0457(x) 1.85 0.000 0.046 0.165 0.349 0.594 0.897 1.257 1.672 2.141 2.662 3.235 3.859 4.533 13 14 15 16 17 18 19 20 21 22 23 23.8 5.25 7 6.02 9 6.85 0 7.71 9 8.63 5 9.59 8 10.60 7 11.66 3 12.76 5 13.91 2 15.10 5 16.09 1 Ziyad Asaad
  • 22. For upstream profile: the curve should go up to the point given by: 0.27Hd= 0.27*16.7 = 4.509 , substitute the value of Hd resulting the equation below, 𝑌 = 0.724 𝑥 + 0.27𝐻𝑑 1.85 𝐻𝑑 0.85 + 0.126𝐻𝑑 − 0.4315𝐻𝑑 0.375 (𝑥 + 0.27𝐻𝑑)0.625 y= 0.06614 (x+4.509)1.85+2.1042-1.2402(x+4.509)0.62 upstream profile x(m) 0 -1 -2 -3 -4 -4.509 y(m) 0 0.0609 24 0.2630 56 0.641 91 1.3099 76 2.1042 Ziyad Asaad
  • 23. 2. The crest level of dam spillway has been kept at 723.70m while the maximum level in the reservoir is to be 734.50m calculate the maximum discharge through the overflow spillway, when the flow takes place through 5 units of 12.2m width each at the crest of the spillway. Solution: Assume pointed nose piers and rounded abutments (Kp = Ka= 0) Effective length of spillway crest Le= L`-2 (N*kp+Ka) He L`=5*12.2= 61m Maximum flood rise over the crest, H = 734.5-723.70 = 10.8m Neglecting velocity of approach and taking C=2.2 Le = 61-2(4*0+0)10.8=61m Q = CLe H3/2 Q = 2.2*61*10.83/2=4763 m3/s If square nosed piers and square abutments are assumed: (Kp = 0.02, Ka= 0.2) Le= 61-2(4*0.02+0.2)10.8=54.952m Q= 2.2*54.952*10.83/2= 4291m3/s Ziyad Asaad
  • 24. Conclusion  In conclusion, spillways stand as vital components within water management systems, offering a dependable method for releasing surplus water from dams and reservoirs, averting overtopping and potential failures. Beyond their primary function, spillways are instrumental in flood control and contribute significantly to the sustainable management of water resources. Given the ongoing challenges posed by climate change and population growth, the critical role of spillways in effective water management remains paramount. Ismail Mokhlis
  • 25. 1. Straight drop spillway is suitable for arch dams and for small drops. 2. Ogee spillway is the most commonly used spillway for its high dischargingefficiency. 3. Chute spillway can be provided in any type of foundation. 4. Side channel spillways are hydraulically less efficient. 5. Shaft spillway becomes undesirable where a discharge more than the designcapacity is to be passed. 6. siphon spillway is an automatically operated type spillway. Ismail Mokhlis
  • 26. (i) IS:6934 “Recommendations for Hydraulic Design of High Ogee overflow Spillways” by Bureau of Indian Standards, New Delhi (ii) IS:5186 “Criteria for Design of Chute and side Channel Spillways” by Bureau of Indian Standards, New Delhi (iii) IS:6966 “Criteria for Hydraulic Design of Barrages and Weirs” by Bureau of Indian Standards, New Delhi (iv) “Design of Small Dams” by U.S.B.R., Oxford and IBH Publishing Co. (v) “Engineering for Dams” Vol. 1, Wiley Eastern Pvt. Ltd. New Delhi by Creager, Justin & Hinds, (vi) “Morning-Glory Shaft Spillways Prototype Behavior”, by Bradley, J.N., Trans. ASCE, Vol. 121, 1956 (vii) “Hydraulics of Closed Conduit Spillways- Part I – Theory and its application University of Minnesota, Saint Anthony Falls Hydraulic Laboratory, Technical Paper No. 12, series B, January 1952, revised February 1958 References

Editor's Notes

  1. Supervisor : Dr. Bassil Y. Mustafa Mr. Alend W. Abdulrazaq
  2. Vertical Drop type Spillway Ogee (overflow) Spillways Chute (Open Channel or Trough) Spillways Conduit and Tunnel Spillways Drop Inlet (Shaft or Morning Glory) Spillways Culvert Spillway Siphon spillways Side channel spillway Stepped spillway
  3. Hydrological Considerations Hydraulic Considerations
  4. Type of Selection of Spillway Size Hydrological Considerations Hydraulic Considerations
  5. The hydraulic design of various spillway prevent structural failure, and minimize maintenance costs. Detailed hydraulic design should adhere to relevant codes provided in the references. Key aspects of hydraulic design include: Fixing the crest level Design of waterway Design of spillway profile Design of energy dissipation device Design of aeration device Design of anti-vortex device
  6. 7. Design of control gates and their operation 8. Design of outlet works 9. Reservoir operation schedule 10. Desalting of reservoirs These considerations collectively contribute to the effective and safe functioning of spillways, promoting structural integrity and reducing the need for extensive maintenance. Following established codes ensures compliance with industry standards in the hydraulic design process.
  7. Straight drop spillway is suitable for arch dams and for small drops. Ogee spillway is the most commonly used spillway for its high dischargingefficiency. Chute spillway can be provided in any type of foundation. Side channel spillways are hydraulically less efficient. Shaft spillway becomes undesirable where a discharge more than the designcapacity is to be passed. siphon spillway is an automatically operated type spillway.