16.1.2. Department of Civil Engineering

Good morning all of you. Today let us discuss on open channel flow. This is the last class on open channel flow. As we discuss about the specific energy and today we will solve a few problems as well as we will discuss about hydraulic jump and the best hydraulic cross sections what is required for designing a canal structures.

In this introduction, the professor sets the stage for the day's lecture on open channel flow, indicating that the session will cover several important concepts including specific energy, hydraulic jump, and the design of hydraulic cross sections for canals. Open channel flow is the flow of liquids, usually water, over a surface that is not confined within a pipe or a channel.

Think of a river flowing over rocks. This is similar to open channel flow where the water navigates around obstacles, and engineers must understand how to design structures like bridges and dams to manage this natural flow.

So as I told in previous classes that the mostly we are following it Saint-Gilles and Mela books and some part of Hanif Chaudhary books or the F.M. White this is as you know it very simple chapters with lot of assumptions we design this open channel flow, flow under a sluice gate, spillway, many civil engineering structures. So we try to design based on this open channel flow.

In this part, the professor references key textbooks that provide foundational theories and models for designing open channel flows. These resources emphasize the simplicity and assumptions made in open channel flow analysis, which allows for easier calculations when dealing with structures like sluice gates and spillways.

Imagine planning a park with small streams and ponds. Civil engineers use principles from these books to ensure the water flows efficiently through the park, preventing flooding and ensuring that the plants and animals in the park thrive.

The basic concept what we use is we will talk about that the conservations of mass and energy equations. So these two equations as we consider for the one-dimensional flow that is what we have simplified it one-dimensional incompressible okay steady flow.

The fundamental principles of open channel flow are based on the conservation of mass and energy. These equations help engineers understand how fluid moves through channels by simplifying the flow into one dimension, assuming that the fluid is incompressible and that the flow is steady.

Think of pouring water from a bucket into a sloped gutter. The volume of water (mass) you pour affects how fast and far it flows (conservation of mass), and you can visualize how much energy is needed to push that water down the slope (conservation of energy).

The basic idea to know it, the flow depth variations in open channels, the velocity variations, how the velocity changes it, how much of energy losses, okay. losses is happening it because of the flow and mostly it is governed by the gravity forces and the frictional forces as I discussed earlier.

Open channel flow involves understanding how variations in depth affect velocity and energy losses. Gravity pulls the water downward while friction with the channel surface slows it down. Both these forces shape how water behaves in the channel.

Imagine water flowing down a slide. At the beginning, it’s steep (like a deep channel), and the water moves quickly; as it flattens out (like a shallow channel), the water slows down due to increased friction with the surface.

Subcritical flow means when you have a flow proud number lesser than 1. ... When you have the flow proud number is equal to 1 that is the conditions we have when you have the critical flow. ... Supercritical flow where the flow proud numbers is greater than 1.

In open channel flow, flow conditions are categorized into three types based on the Froude number: subcritical, critical, and supercritical. A Froude number less than 1 indicates tranquil, subcritical flow; equal to 1 indicates critical flow where wave speed matches flow speed; and greater than 1 indicates supercritical flow, characterized by rapid, turbulent movement.

Think of a river. In slow moving sections (subcritical), you see calm waters. Near a waterfall (critical), everything rushes down quickly, and after the drop (supercritical), the water splashes over rocks and creates turbulent waves.

... when you have a the critical flow that means the flow proud number is equal to 1. This is what is a recap what we discussed in the last 2 classes. Also we are going to discuss about best hydraulic sections...

The hydraulic jump is a phenomenon that occurs when supercritical flow transitions to subcritical flow, causing a sudden increase in flow depth and a decrease in flow velocity. This transition creates turbulence and energy loss, which can be observed in rivers downstream of dams.

Consider a water slide ending in a pool. When the sliding water splashes into the pool, it creates waves and turbulence. This is similar to a hydraulic jump; the transition from fast to slow flow creates a visual and energetic disturbance.

Let us come back to the hydraulic charms how does it forms it. If you look it that if you have a more or less the horizontal surface okay more or less you have a horizontal surface and you have a sluice gate okay it is a gate operating it...

Designing best hydraulic cross sections involves optimizing the shape of the channel to minimize resistance, reduce construction costs, and maximize flow efficiency. Channel shapes can vary from rectangular to trapezoidal, each with different advantages depending on the flow conditions.

Think of designing a race track for water balloons. Choosing a shape that allows balloons to flow quickly without bumping into walls or slowing down is crucial for a good race. Likewise, engineers must choose the right design for channels to ensure smooth and efficient water flow.

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