(SEM VIII) THEORY EXAMINATION 2018-19 ANALYSIS AND DESIGN OF HYDRAULIC STRUCTURE

SECTION A – Detailed Explanation
 

Section A consists of short-answer type questions, but “short” does not mean writing one-line definitions. In university exams, even 2-mark questions should contain a proper definition, working principle, purpose, and practical importance.
 

Let us understand each topic properly.

Regulation Work
 

Regulation works are hydraulic structures constructed to control the flow of water in canals and rivers. The main purpose of these works is to regulate discharge, maintain required water level, and ensure safe distribution of water. Examples include canal regulators, head regulators, and cross regulators. These structures prevent excessive velocity, reduce erosion, and help in systematic irrigation distribution. Without regulation works, water flow becomes uncontrolled, leading to damage and inefficient irrigation.

Bed Bars
 

Bed bars are structural members provided in weirs and barrages to strengthen the floor against uplift pressure and seepage forces. When water flows over a hydraulic structure, seepage develops beneath the floor. Bed bars help in increasing resistance against sliding and uplift pressure. They act as reinforcement elements and improve structural stability.
 

Syphon Aqueduct
 

A syphon aqueduct is a type of cross-drainage work where the canal passes below the drainage channel, and the drainage water flows under pressure. It is constructed when the drainage bed level is higher than the canal bed level. The structure ensures that canal water and drainage water do not mix. It is commonly used in flat terrains where level differences create crossing conflicts.
 

Silt Excluder
 

A silt excluder is a device constructed near the headworks of canals to prevent entry of excessive silt into the canal system. Rivers carry suspended sediments, and if they enter canals, they reduce carrying capacity and cause maintenance issues. The excluder diverts silt-laden bottom layers back to the river while allowing relatively clear water into the canal.
 

Flood Routing
 

Flood routing is the process of determining how a flood wave moves through a reservoir or river channel. It helps engineers predict peak discharge at downstream points and design spillways accordingly. Flood routing is important in reservoir planning because it determines storage requirements and dam safety.

Demand Curve
 

In hydroelectric plants, the demand curve represents variation of load with time. It helps in planning installed capacity and determining load factor, plant factor, and utilization factor. The shape of the demand curve influences power plant design.

Keys and Water Stops

Keys are projections provided at joints in concrete structures to improve resistance against sliding. Water stops are flexible materials embedded in joints to prevent leakage. In hydraulic structures, leakage control is extremely important, and water stops ensure water tightness.

Controlled Spillway

A controlled spillway is provided with gates that regulate discharge. Unlike uncontrolled spillways, gated spillways allow operators to adjust flow depending on reservoir level. This improves flood management efficiency.

Surge Tank

A surge tank is a protective structure in hydroelectric power plants. It absorbs sudden pressure fluctuations (water hammer) caused by rapid turbine shutdown. It prevents damage to penstocks and maintains steady flow conditions.

SECTION B – Detailed Conceptual + Numerical Understanding

Section B contains analytical and design-based questions.

Canal Fall

A canal fall is constructed when ground slope is steeper than canal slope. Without a fall, water would flow at excessive velocity causing erosion. A fall safely reduces water level and maintains controlled velocity. Factors affecting location include soil type, discharge, topography, and economic considerations.

Khosla’s Theory

Khosla’s theory is used for analyzing seepage under hydraulic structures. Unlike Bligh’s theory, which considers creep length, Khosla’s theory uses potential flow concepts. It determines uplift pressure distribution and exit gradient.

The design procedure involves:

Calculating floor length and depth of sheet piles.

Determining uplift pressure at key points.

Checking exit gradient against safe limit (usually 1/7 or 0.18).

Providing sufficient floor thickness to resist uplift.

Safety against piping is critical in weir design.

Divide Wall

A divide wall separates under-sluices from the main weir portion. It prevents cross-currents and protects structure from scouring. Proper length and depth are required to prevent erosion near foundations.

Gallery in Dam

Galleries are internal passages in dams used for inspection, grouting, drainage, and instrumentation. They help monitor seepage and structural health. Without galleries, internal inspection becomes impossible.

Hydroelectric Scheme

Hydroelectric plants are classified as run-of-river, storage, and pumped storage plants. In numerical problems, installed capacity, load factor, plant factor, and utilization factor are calculated.

Load factor indicates how efficiently plant capacity is used.

SECTION C – Major Design & Stability Analysis

Section C is the most important and highest scoring part. Answers must be descriptive, formula-based, and logically structured.

Weir Theory and Failure

A weir is constructed across rivers to raise water level for irrigation diversion. Failures occur due to:

Piping (undermining due to seepage)

Scouring

Sliding

Overturning

Proper foundation design prevents these failures.

Bligh’s Theory

Bligh’s creep theory assumes seepage follows the contact between floor and subsoil. Total creep length must be greater than C × H, where C is creep coefficient and H is head difference.

Although simple, it does not account for pressure distribution accurately.

Reservoir Planning

Reservoirs are classified as storage, balancing, and flood control reservoirs. Storage zones include dead storage, live storage, and flood storage.

Proper geological and hydrological investigations ensure dam safety.

Masonry Dam Stability

In masonry dam analysis, forces considered include:

Weight of dam                                                             Water pressure

Uplift pressure

Checks required:                                                          Overturning safety

Sliding safety

Maximum and minimum stresses at toe and heel

Principal stress must remain within permissible limits.

Spillway and Ogee Design

Spillways release excess flood water safely. Ogee spillway profile matches lower nappe of flowing water.

Discharge formula:
Q = Cd L H^(3/2)

Effective crest length must consider pier and abutment contraction.