To dissipate energy a fall is provided in a canal. A fall which has gradual convex and concave curves for smooth transition of water and to reduce disturbance and impact is a:
ogee fall
Understanding Canal Falls and Energy Dissipation
Canal falls are essential hydraulic structures constructed in the course of a canal to lower the water level and dissipate the excess energy gained by the water due to a drop in elevation. Without energy dissipation, the high velocity water could cause severe erosion downstream of the fall, damaging the canal bed and banks.
Types of Canal Falls
Various types of canal falls are designed based on factors like the amount of drop, discharge, and soil conditions. Some common types include:
- Ogee fall
- Stepped fall
- Rapid fall
- Notch fall
- Vertical fall or Sarda fall
- Baffled chute fall
Analyzing the Specified Canal Fall Characteristics
The question describes a specific type of canal fall that uses "gradual convex and concave curves for smooth transition of water and to reduce disturbance and impact". Let's examine which of the options fits this description:
Ogee Fall Analysis
An ogee fall is characterized by an S-shaped profile. The upstream face is typically a convex curve, and the downstream face is a concave curve. This shape is specifically designed to guide the water smoothly over the crest and along the profile, minimizing turbulence and preventing cavitation. This smooth transition provided by the gradual convex and concave curves helps in efficient energy dissipation and reduces the impact on the downstream channel. This design is very effective for larger drops and higher discharges, similar in principle to spillways on dams.
Stepped Fall Analysis
A stepped fall consists of a series of steps. The water flows down these steps, and energy is dissipated through turbulence, splashing, and the formation of small hydraulic jumps on each step. While effective for energy dissipation, it does not utilize gradual convex and concave curves for a smooth transition in the manner described in the question; instead, it relies on abrupt drops.
Rapid Fall Analysis
A rapid fall is essentially a long sloping channel with a rough surface. Energy is dissipated by friction along the rough bed and banks as the water flows down the slope at supercritical velocity. It doesn't typically feature pronounced, specific convex and concave curves for transition like an ogee fall; its design is based on length and roughness.
Notch Fall Analysis
A notch fall uses a notch (like a trapezoidal, rectangular, or V-notch) to concentrate the flow, often also serving as a discharge measuring device. The drop is usually relatively small. While it dissipates some energy, its primary characteristic isn't the use of gradual convex and concave curves for a smooth S-shaped transition across a significant drop.
Conclusion
Comparing the descriptions, the canal fall that is specifically designed with gradual convex and concave curves to ensure smooth water transition and reduce disturbance and impact is the ogee fall. The S-shaped profile formed by these curves facilitates the flow over the fall efficiently while dissipating energy.
| Fall Type | Key Feature Described | Matches Question? |
|---|---|---|
| Ogee fall | Gradual convex and concave curves for smooth transition | Yes |
| Stepped fall | Series of steps causing turbulence | No |
| Rapid fall | Long, sloping rough channel | No |
| Notch fall | Uses a shaped notch; often for measurement | No |
Revision Table: Key Concepts of Canal Falls
| Term | Explanation | Purpose |
|---|---|---|
| Canal Fall | Structure to lower water level in a canal | Dissipate excess potential energy, control velocity, prevent erosion |
| Energy Dissipation | Converting kinetic/potential energy into heat/sound through turbulence, friction, etc. | Reduce erosive power of water flow |
| Ogee Curve | Combination of a convex curve followed by a concave curve (S-shape) | Guides water smoothly, minimizes negative pressure and turbulence |
Additional Information: Importance of Smooth Transition in Falls
Designing a fall with a smooth transition, like that achieved with the convex and concave curves of an ogee profile, is crucial for several reasons:
- Reduced Turbulence: A smooth flow path minimizes the formation of excessive turbulence, which can lead to energy losses and air entrainment.
- Prevention of Cavitation: Abrupt changes in profile or sharp angles can cause negative pressure regions, leading to cavitation (formation and collapse of vapor bubbles). Cavitation can severely damage the concrete structure. The smooth curves of an ogee fall help prevent this by maintaining positive pressure along the profile.
- Minimized Impact: Guiding the water smoothly reduces the direct impact energy on the downstream channel bed and banks, thereby reducing erosion.
- Efficient Flow: A well-designed ogee curve allows the water to flow efficiently over the fall without backing up excessively upstream.
Therefore, the use of gradual convex and concave curves is a sophisticated design feature aimed at optimizing hydraulic performance and structural integrity in canal falls.
Important Questions from Dams and Spillways
Which type of gate is generally used for low navigation dams?
The temporary all round enclosure which keeps the water away from the working area by using vertical barriers is called-
The heading up of water above its normal level while passing under the bridge is known as
The discharge passing over an ogee spillway, per unit length of its apex line is proportional to (Where H is head over the apex of its crest):
A gravity dam means:
