Intakes, Conveyance and Hydropower Structures

Introduction and Context

Water-resource systems depend on structures that safely withdraw, convey, regulate and convert water energy. An intake transfers water from a reservoir, lake or river into a conveyance system. Tunnels, canals, pipelines and penstocks then deliver water to a treatment plant, irrigation command area or hydropower turbine. Surge tanks, forebays and powerhouses regulate hydraulic transients and convert potential energy into mechanical and electrical energy.

The design of these facilities is an integrated hydraulic, structural, geotechnical, mechanical, environmental and operational problem. A hydraulically efficient intake may be unacceptable if it admits sediment, debris or air. A high-head penstock may provide excellent energy conversion but impose excessive water-hammer pressures. Similarly, a powerhouse must be designed not only for turbine installation but also for excavation stability, flood protection, drainage, access, vibration control and safe operation.

This chapter develops the principles used to plan and evaluate these structures, with emphasis on professional design decisions and the interaction between steady and unsteady flow.

Learning Objectives

After studying this chapter, the reader should be able to:

1. Select and plan reservoir and river intakes for varying hydraulic and environmental conditions.

2. Estimate head losses in conveyance systems and assess hydraulic efficiency.

3. Explain the design and operation of tunnels, penstocks, forebays and surge tanks.

4. Evaluate water hammer and identify suitable surge-control measures.

5. Plan trash racks, gates, screens, sediment-exclusion and debris-handling systems.

6. Integrate hydraulic, structural, geotechnical, operational and environmental requirements in hydropower planning.

1. Functional Planning of a Water-Conveyance System

A typical hydropower waterway comprises:

• an intake structure;
• trash racks and gates;
• an approach channel, tunnel or canal;
• a desilting basin where required;
• a forebay or regulating reservoir;
• a penstock or pressure tunnel;
• a surge tank or surge chamber;
• turbines, generators and the powerhouse; and
• a tailrace returning water to the river.

The arrangement depends on topography, head, discharge, geology, sediment load, environmental constraints and the desired operating mode. Run-of-river schemes generally have limited storage and experience rapid discharge variation, whereas storage schemes can regulate seasonal inflow. Pumped-storage projects require waterways capable of flow reversal and repeated transient loading.

The principal design discharge is normally the turbine discharge or the design diversion discharge. Designers must also consider minimum ecological flow, flood discharge, shutdown flow, partial-load operation and future expansion. Hydraulic design should be based on a range of operating conditions rather than a single design point.

2. Intakes

2.1 Functions and types

An intake must admit the required discharge with acceptable velocity and head loss while excluding damaging debris, sediment, ice, air and floating material. It must also permit isolation, inspection, maintenance and emergency closure.

Common types include:

• Reservoir or tower intakes: vertical or inclined structures with openings at one or more levels. They are useful where reservoir water quality or operating level varies substantially.
• Dam intakes: openings incorporated into a concrete dam, usually connected to conduits or pressure tunnels.
• River diversion intakes: side intakes, frontal intakes, Tyrolean or bottom intakes, and weir-associated intakes.
• Shaft and inclined intakes: used where steep terrain or underground waterways make a surface structure unsuitable.
• Floating or submerged intakes: applicable where water levels vary widely or shoreline conditions are unstable.

Selection should reflect approach flow, sediment transport, debris regime, reservoir drawdown, seismicity, constructability and consequences of failure.

2.2 Hydraulic arrangement

An intake approach should produce a relatively uniform velocity distribution and avoid vortices, flow separation and excessive turbulence. Poor approach geometry can cause uneven trash-rack loading, air entrainment, sediment deposition and reduced turbine performance.

The gross power potential of a hydropower installation is

\[

P=\rho g Q H_g \eta

\]

where \(P\) is power (W), \(\rho\) is water density (kg/m³), \(g\) is gravitational acceleration (m/s²), \(Q\) is discharge (m³/s), \(H_g\) is gross head (m), and \(\eta\) is overall efficiency. The equation assumes steady discharge and represents the conversion of hydraulic energy into useful power. The net head used for turbine selection is obtained after subtracting intake, conveyance, valve, bend and other losses.

Approach velocity must be selected with reference to debris, fish protection, sediment and structural constraints. There is no universal velocity suitable for all intakes. Higher velocity reduces required opening area but increases losses, debris blockage risk and fish-injury risk. Criteria should therefore be taken from the governing authority, environmental permit and project-specific hydraulic model.

2.3 Trash racks and screens

Trash racks consist of regularly spaced bars supported by structural frames. Their purposes are to protect gates, turbines and pumps from logs, branches, ice and large debris. Important design variables are clear spacing, bar thickness, inclination, submergence, support spacing and cleaning method.

The rack loss is commonly expressed as

\[

h_r=K_r\frac{V_r^2}{2g}

\]

where \(h_r\) is head loss through the rack, \(K_r\) is a coefficient dependent on bar shape, spacing, inclination and blockage, and \(V_r subscript{ }\) is the velocity through the gross rack opening. The coefficient must be obtained from accepted empirical data or physical-model testing; it should not be assumed constant during blockage.

A rack-cleaning system may be manual, mechanical or hydraulic. Automatic raking is justified where debris loading is high, access is difficult or interruption of generation is costly. The design should include a safe debris-disposal route and provisions for detecting blockage through differential water-level or pressure measurements.

Fine screens may be installed for fish protection or turbine protection, but they cause greater head loss and require more frequent cleaning. Fish-friendly designs control approach velocity, avoid excessive turbulence and provide a safe bypass route.

2.4 Gates, valves and emergency closure

Gates provide isolation, regulation or emergency closure. Slide gates are common in low- and moderate-head conduits; fixed-wheel and wheel gates are suitable for larger openings and high heads. Butterfly and spherical valves are frequently used near turbines or in high-pressure penstocks.

An emergency closure device must be capable of stopping flow under specified failure conditions, including a penstock rupture or loss of turbine control. Closure time must be selected through transient analysis: rapid closure limits discharged water but can generate severe water hammer, whereas slow closure reduces pressure rise but may permit excessive runaway flow. Gate hoists, power supplies, brakes, interlocks and manual override systems are part of the safety design.

3. Conveyance Systems

3.1 Open channels and canals

Open channels are generally economical for low-pressure conveyance and moderate slopes. Their design requires consideration of flow capacity, freeboard, erosion, lining, seepage, sediment deposition and transitions. Uniform-flow calculations may use the Manning equation:

\[

Q=\frac{1}{n}AR^{2/3}S^{1/2}

\]

where \(Q\) is discharge, \(n\) is Manning roughness, \(A\) is flow area, \(R=A/P_w\) is hydraulic radius, \(P_w\) is wetted perimeter and \(S\) is energy slope. The equation is applicable primarily to gradually varied, uniform or near-uniform open-channel flow and should not be applied directly across gates, abrupt transitions or hydraulic jumps.

3.2 Tunnels

Tunnels are selected when terrain, environmental impact, alignment or head requirements make open waterways unsuitable. They may operate as free-surface tunnels or pressure tunnels. Pressure tunnels must be designed for internal pressure, external groundwater pressure, construction loads, transient loading and possible empty-tunnel conditions.

Key planning issues include geological mapping, exploratory drilling, rock-mass classification, groundwater control, lining type, ventilation, access, spoil disposal and construction method. A concrete lining may be required for hydraulic smoothness, watertightness, stability or protection against erosion. In competent rock, a shotcrete-and-rock-bolt system may provide primary support, with concrete lining added where hydraulic or durability requirements justify it.

Tunnel head loss can be estimated using Darcy–Weisbach friction:

\[

h_f=f\frac{L}{D}\frac{V^2}{2g}

\]

where \(h_f\) is friction head loss, \(f\) is the Darcy friction factor, \(L\) is conduit length, \(D\) is hydraulic diameter and \(V=Q/A\) is mean velocity. For a non-circular conduit, hydraulic diameter is conventionally \(D_h=4A/P\), where \(P\) is wetted perimeter. The Darcy factor depends on Reynolds number and relative roughness and may be obtained from the Colebrook–White relation or a suitable explicit approximation.

Local losses are represented by

\[

h_m=K\frac{V^2}{2g}

\]

where \(K\) depends on the particular entrance, bend, expansion, contraction, valve or outlet. All losses should be evaluated using the velocity in the relevant section.

3.3 Penstocks and pressure conduits

A penstock is a pressure conduit conveying water to turbines. It may be made of steel, reinforced or prestressed concrete, ductile iron, or a composite system. Selection depends on head, diameter, pressure, geology, internal corrosion, external buckling, fabrication and access.

Penstock design must address:

• internal pressure and longitudinal thrust;
• water-hammer pressure;
• dead weight and support reactions;
• thermal expansion and contraction;
• seismic effects;
• external vacuum and buckling;
• fatigue from repeated load cycles;
• corrosion and abrasion; and
• leakage containment and drainage.

Anchors resist longitudinal forces at bends, reducers, valves and changes in slope. Saddles support straight sections and permit controlled movement where appropriate. Expansion joints should be used only where their structural and sealing functions are clearly defined.

For a thin-walled cylindrical steel pipe under internal pressure, the approximate hoop stress is

\[

\sigma_h=\frac{pD}{2t}

\]

where \(p\) is internal pressure, \(D\) is internal diameter and \(t\) is wall thickness. This relation assumes a thin wall, uniform pressure and membrane action; it is not sufficient by itself for final penstock design because corrosion allowance, weld efficiency, buckling, external pressure, fatigue and stress concentrations must also be considered.

4. Water Hammer and Surge Control

4.1 Physical mechanism

Water hammer is the pressure change produced when flow velocity changes rapidly in a conduit. It results from fluid compressibility and pipe-wall elasticity. It can cause pipe rupture, support failure, excessive turbine pressure or sub-atmospheric pressure and collapse.

For a rapid change in velocity, the ideal Joukowsky pressure rise is

\[

\Delta p=\rho a\Delta V

\]

or, in head form,

\[

\Delta H=\frac{a\Delta V}{g}

\]

where \(\Delta p\) is pressure change, \(\Delta H\) is pressure-head change, \(a\) is wave velocity, and \(\Delta V\) is the change in mean velocity. The equation assumes a one-dimensional elastic wave and a sufficiently rapid change relative to the wave travel time. It provides a first estimate, not a complete design solution.

The wave travel time in a conduit of length \(L\) is approximately \(2L/a\) for a pressure wave to travel to a closure and return. If valve closure is slower than this characteristic period, the maximum pressure rise may be less than the ideal Joukowsky value. Actual systems require method-of-characteristics analysis when closure laws, branching, friction, turbine dynamics and surge devices are important.

4.2 Surge tanks

A surge tank is a free-surface chamber connected to a pressure tunnel or penstock. It absorbs or supplies water during changes in turbine discharge, thereby reducing pressure fluctuations. Types include simple surge tanks, restricted-orifice tanks, differential surge tanks and air-cushion chambers.

For an ideal simple surge tank, neglecting friction, the water-level motion follows the continuity relationship

\[

A_s\frac{dz}{dt}=Q_u-Q_t

\]

where \(A_s\) is tank area, \(z\) is tank water-level elevation, \(Q_u\) is inflow from the upstream conduit and \(Q_t\) is turbine discharge. The tank must be sufficiently large to limit oscillation, but an oversized tank increases cost and excavation. Stability, maximum and minimum water levels, overflow, access, drainage and freezing must be considered.

A restricted-orifice tank introduces energy dissipation and can reduce oscillation amplitude, but the restriction increases head loss and may delay response. Surge-tank design should be checked for load rejection, load acceptance, emergency shutdown and repeated operating cycles.

Other surge-control measures include controlled turbine closure, relief valves, bypass systems, air chambers, pressure-regulating chambers and appropriate conduit geometry. The selected measure should be assessed for reliability under loss of electrical power and control-system failure.

5. Forebays and Water-Level Regulation

A forebay is a regulating basin immediately upstream of a pressure conduit or penstock. It provides storage for short-term fluctuations, distributes flow among units and allows sediment or debris control before water enters the pressure system.

Forebay design includes inlet and outlet hydraulics, minimum submergence, anti-vortex measures, overflow capacity, emergency drawdown, bank stability, seepage control and sediment removal. The entrance to a penstock must avoid air-core vortices. Adequate submergence, smooth approach flow and anti-vortex devices are common remedies.

In cascade hydropower systems, the forebay may also coordinate upstream and downstream plant operation. Its operating rule should balance energy production, downstream environmental flow, spill prevention and ramp-rate restrictions.

6. Powerhouses and Energy Conversion

A powerhouse contains turbines, generators, governors, control systems, transformers, switchgear, drainage, ventilation and auxiliary equipment. It may be surface, underground, semi-underground or integrated with a dam.

The turbine type is selected mainly from net head and discharge. Pelton turbines are commonly used for high head and relatively low discharge; Francis turbines cover a broad intermediate range; Kaplan and propeller turbines are suited to low head and high discharge. Actual selection also depends on sediment concentration, operating range, cavitation characteristics, rotational speed and maintenance capability.

Net head is approximately

\[

H_n=H_g-\sum h_L

\]

where \(H_n\) is net head, \(H_g\) is gross head and \(\sum h_L\) is the sum of entrance, friction, bend, valve, trash-rack and other losses. The hydraulic efficiency of the waterway may be expressed as

\[

\eta_h=\frac{H_n}{H_g}

\]

provided both heads refer to the same datum and operating condition. Overall plant efficiency additionally includes turbine, generator, transformer and auxiliary losses.

Powerhouse planning must include flood levels, tailwater fluctuations, crane capacity, equipment transport, fire protection, escape routes, noise, vibration, drainage and access for replacement. Underground powerhouses require particular attention to rock stresses, groundwater inflow, ventilation and emergency egress.

7. Worked Example: Preliminary Penstock and Power Estimate

A hydropower scheme conveys \(Q=18\) m³/s through a 900 m long steel penstock of internal diameter 2.8 m. The gross head is 160 m. Assume Darcy friction factor \(f=0.020\), total minor-loss coefficient based on penstock velocity \(K=1.5\), water density \(\rho=1000\) kg/m³, \(g=9.81\) m/s² and overall turbine-generator efficiency \(\eta=0.88\). Estimate the friction loss, minor loss, net head and power.

The flow area is

\[

A=\frac{\pi D^2}{4}=\frac{\pi(2.8)^2}{4}=6.158\text{ m}^2

\]

Thus, the mean velocity is

\[

V=\frac{18}{6.158}=2.92\text{ m/s}

\]

The friction loss is

\[

h_f=0.020\left(\frac{900}{2.8}\right)\frac{(2.92)^2}{2(9.81)}

=2.77\text{ m}

\]

The minor loss is

\[

h_m=1.5\frac{(2.92)^2}{2(9.81)}=0.65\text{ m}

\]

Therefore, neglecting other losses for this preliminary estimate,

\[

H_n=160-2.77-0.65=156.58\text{ m}

\]

The power is

\[

P=1000(9.81)(18)(156.58)(0.88)

\approx24.3\text{ MW}

\]

This is a preliminary hydraulic estimate. Final design must include intake losses, tunnel losses, transient pressures, turbine performance over the operating range and all structural load cases.

8. Applied Case: Illustrative Mountain Hydropower Scheme

Background

An illustrative 120 MW mountain hydropower project uses a reservoir intake, a 6 km headrace tunnel, a surge tank and two steel penstocks supplying Francis turbines. The river carries high sediment loads during monsoon floods and floating logs during storms.

Problem

Initial planning proposed a large fixed trash rack and rapid turbine closure to protect the turbines during grid failure. Hydraulic review predicted high rack blockage during storms and a pressure rise exceeding the allowable penstock design pressure during load rejection.

Analysis

A physical model and one-dimensional transient model were used together. The model examined approach flow, vortex formation, rack blockage, turbine closure laws and surge-tank oscillations. Sediment sampling showed that fine sediment could pass the rack and cause turbine abrasion, while large debris was the principal rack hazard. Geological investigation also indicated fractured rock near the proposed surge-tank location.

Approach and solution

The final arrangement included a larger intake opening, inclined mechanically cleaned trash racks, a debris boom upstream, a sediment-exclusion basin and an abrasion-resistant turbine runner coating. A restricted-orifice surge tank was relocated to stronger rock. Turbine closure was staged rather than instantaneous, and a bypass system was provided for emergency pressure control. The penstock was divided into anchored sections, with detailed fatigue and seismic checks.

Outcome

The revised design reduced normal hydraulic losses, limited predicted transient pressure to the allowable envelope and improved availability during debris seasons. The project also adopted online monitoring of rack differential head, penstock pressure, vibration and sediment concentration.

Learning points

The case demonstrates that intake, sediment, transient and structural decisions cannot be separated. Physical modelling is valuable where three-dimensional approach flow or debris behaviour is uncertain, while numerical transient modelling is essential for testing multiple operating scenarios. Monitoring and maintainability should be incorporated during initial design rather than added after commissioning.

9. Design Verification, Risk and Contemporary Practice

A professional design should use staged verification:

1. establish hydrology, sediment and debris design data;

2. define normal, abnormal and emergency operating cases;

3. calculate steady hydraulic losses;

4. perform transient analysis using realistic valve and turbine characteristics;

5. verify structural, geotechnical and seismic load cases;

6. test complex intake or junction arrangements physically or with validated computational-fluid-dynamics models; and

7. prepare inspection, maintenance, emergency-action and instrumentation plans.

Computational-fluid-dynamics models can identify recirculation, vortices and non-uniform velocity, but their results depend on mesh quality, turbulence modelling, boundary conditions and validation. Artificial intelligence can assist in debris-image classification, predictive maintenance and anomaly detection from pressure and vibration data. It should support—not replace—hydraulic judgement, independent checking and safety-critical protection systems.

Climate change introduces uncertainty in flood magnitude, drought duration, sediment yield, wildfire debris and temperature. Design reviews should therefore examine nonstationary hydrology, operating flexibility, ecological flow, reservoir drawdown and adaptation options. Regulatory requirements commonly address dam safety, occupational safety, environmental flows, fish passage, water quality, sediment management, navigation and cultural heritage. Compliance must be demonstrated through documented criteria and auditable decisions.

Challenges and Limitations

Important limitations include uncertainty in extreme hydrology, incomplete geological information, empirical loss coefficients, scale effects in physical models, uncertain debris blockage and changes in turbine operation over the project life. Designs based only on average conditions may fail during low-level vortices, flood debris, emergency closure or partial-load operation.

Economic optimisation must not reduce essential safety margins. Lower diameter may reduce capital cost but increase energy losses and water-hammer severity. Larger surge tanks may improve operational stability but increase excavation and environmental impacts. Decisions should consider life-cycle cost, reliability, failure consequences, maintainability and environmental performance rather than initial cost alone.

Best-Practice Checklist

• Define the full range of hydraulic and operational conditions.
• Separate gross head, net head and transient pressure envelopes.
• Use validated coefficients for racks, entrances, bends and valves.
• Provide safe isolation and emergency closure.
• Design debris removal and sediment management as operational systems.
• Check both positive pressure and vacuum conditions.
• Coordinate hydraulic, structural, geotechnical and mechanical designs.
• Validate complex flow arrangements with physical or numerical modelling.
• Include instrumentation, inspection access and emergency procedures.
• Reassess hydrology, sediment and climate risks during periodic safety reviews.

Chapter Summary

Intakes must admit water efficiently while controlling debris, sediment, air and fish-related impacts. Their geometry, trash racks, gates and cleaning systems strongly influence reliability. Conveyance systems may consist of channels, tunnels or pressure conduits; their design requires hydraulic-loss calculations together with geotechnical, structural and operational verification. Penstocks must resist internal pressure, water hammer, external buckling, seismic effects, fatigue and corrosion.

Water hammer results from rapid velocity changes and can be initially estimated using the Joukowsky relation, but final design generally requires transient analysis. Surge tanks, controlled closure, bypasses, relief valves and air chambers reduce transient risk. Forebays regulate short-term flow and prevent air entrainment before water enters penstocks. Powerhouses integrate turbines, generators and safety systems, and plant output depends on net head and overall efficiency.

Successful projects use integrated modelling, realistic operating scenarios, physical verification where necessary, maintainable debris and sediment systems, reliable monitoring and compliance with safety and environmental requirements. Contemporary practice increasingly combines digital monitoring and data analytics with established hydraulic and structural engineering judgement.

Key Terms

Intake: Structure that withdraws water from a reservoir, river or lake.

Trash rack: Bar screen that excludes large debris from a waterway.

Forebay: Regulating basin immediately upstream of a pressure conduit or penstock.

Penstock: Pressure conduit conveying water to a turbine.

Headrace: Conveyance system carrying water from an intake toward the powerhouse.

Tailrace: Channel or tunnel returning turbine discharge to the river.

Gross head: Elevation difference before subtracting hydraulic losses.

Net head: Head available at the turbine after hydraulic losses.

Water hammer: Pressure transient caused by rapid change in conduit velocity.

Joukowsky relation: First-estimate relation between velocity change and pressure-wave magnitude.

Wave velocity: Speed at which a pressure disturbance travels through water and conduit walls.

Surge tank: Chamber that absorbs or supplies water during flow transients.

Hydraulic loss: Energy head dissipated by friction and local disturbances.

Darcy friction factor: Dimensionless factor used to calculate conduit friction loss.

Minor loss: Local head loss caused by entrances, bends, valves or transitions.

Cavitation: Formation and collapse of vapour cavities caused by low pressure.

Anchor block: Structural element resisting longitudinal pressure-conduit forces.

Powerhouse: Facility containing turbines, generators and associated equipment.

Approach velocity: Velocity immediately upstream of an intake screen or rack.

Load rejection: Rapid reduction of turbine-generator electrical load.

Review Questions

Short Answer Questions

1. State four principal functions of an intake.

2. Distinguish between gross head and net head.

3. What is the purpose of a surge tank?

4. Define water hammer and identify its principal cause.

5. Why are anchor blocks provided in penstock systems?

Long Answer Questions

1. Explain the hydraulic and operational design considerations for a reservoir intake with trash racks and gates.

2. Discuss the selection, design and verification of tunnels and penstocks for a high-head hydropower project.

3. Derive or explain the applicability of the Darcy–Weisbach and local-loss equations in a conveyance system.

4. Explain the causes of water hammer and compare surge tanks, controlled closure, bypasses and relief valves as mitigation measures.

5. Describe the integrated planning requirements of a powerhouse, including hydraulic, structural, geotechnical, mechanical, safety and environmental considerations.

Analytical / Application Questions

1. A penstock conveys 12 m³/s through a 2.0 m diameter, 600 m long pipe. If the Darcy friction factor is 0.022, calculate the mean velocity and friction head loss. State the assumptions used.

2. A 150 m long pressure conduit has a wave velocity of 1000 m/s, and the flow velocity changes by 2.5 m/s during emergency closure. Estimate the ideal pressure change using the Joukowsky relation and discuss why the actual value may differ.

3. A proposed intake experiences frequent rack blockage during floods. Develop an engineering decision framework comparing increased rack area, mechanical cleaning, upstream debris exclusion and operational shutdown, including hydraulic, economic, environmental and safety criteria.

Multiple Choice Questions with Answers

Question 1

Which structure primarily absorbs or supplies water during rapid changes in turbine discharge?

A. Forebay

B. Surge tank

C. Tailrace

D. Trash rack

Correct Answer: B. Surge tank

Question 2

In the equation P = ρgQHη, H represents which quantity when estimating useful hydropower output?

A. Gross reservoir volume

B. Net hydraulic head

C. Pipe diameter

D. Wave velocity

Correct Answer: B. Net hydraulic head

Question 3

The Darcy–Weisbach equation is primarily used to estimate:

A. Friction head loss in a conduit

B. Turbine rotational speed

C. Reservoir evaporation

D. Trash-rack bar spacing

Correct Answer: A. Friction head loss in a conduit

Question 4

According to the Joukowsky relation, pressure change is directly proportional to:

A. Pipe length only

B. Change in flow velocity and wave velocity

C. Reservoir area only

D. Turbine efficiency only

Correct Answer: B. Change in flow velocity and wave velocity

Question 5

What is the principal purpose of a trash rack?

A. Increase turbine head

B. Exclude damaging large debris

C. Measure reservoir storage

D. Dissipate all water-hammer energy

Correct Answer: B. Exclude damaging large debris

Question 6

For a fixed gross head and discharge, reducing conveyance losses will generally:

A. Reduce net head

B. Increase net head and potential power

C. Increase sediment concentration automatically

D. Eliminate the need for gates

Correct Answer: B. Increase net head and potential power

Question 7

Which turbine is generally associated with high head and relatively low discharge?

A. Pelton

B. Kaplan

C. Propeller

D. Axial-flow pump

Correct Answer: A. Pelton

Question 8

A penstock anchor block is mainly designed to resist:

A. Longitudinal hydraulic forces

B. Atmospheric humidity

C. Fish migration

D. Reservoir evaporation

Correct Answer: A. Longitudinal hydraulic forces

Question 9

For a conduit carrying 18 m³/s through an area of 6 m², the mean velocity is:

A. 0.33 m/s

B. 3 m/s

C. 12 m/s

D. 108 m/s

Correct Answer: B. 3 m/s

Question 10

Which condition most directly increases the risk of air-core vortex formation at a penstock entrance?

A. Adequate submergence and uniform approach flow

B. Insufficient submergence and strong circulation

C. A smooth downstream tailrace

D. Low generator efficiency

Correct Answer: B. Insufficient submergence and strong circulation