Open Channel Flow

presented by Umut Türker

What is open channel flow? Open channel flow is a flow which has a free

surface and flows due to the gravitational effect

What is open channel flow? Open channel hydraulics, a subject of great

importance to civil engineers, deals with flows having a free surface in channels constructed for

water supply, irrigation, drainage, and hydroelectric power generation; in sewers, culverts, and tunnels

flowing partially full; and in natural streams and rivers.

What is open channel flow? An open channel is a duct in which the liquid flows

with a free surface. This is in contrast with pipe flow in which the liquid

completely fills the pipe and flow under pressure.

What is open channel flow? The flow in a pipe takes place due to difference of

pressure (pressure gradient), whereas in open channel it is due to the slope of the channel bed

(i.e.; due to gravity)..

What is open channel flow? In pipe flow:

The hydraulic gradient line (HGL) is the sum of the elevation and the pressure head (connecting

the water surfaces in piezometers).The energy gradient line (EGL) is the sum of the

HGL and velocity head.The amount of energy loss when the liquid flows

from section 1 to section 2 is indicated by hL.

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What is open channel flow?

What is open channel flow? In open channel flow :

The hydraulic gradient line (HGL) corresponds to the water surface line (WSL); the free water

surface is subjected to only atmospheric pressure which is commonly referred to as the

zero pressure reference in hydraulic engineering practice.

What is open channel flow? In open channel flow :

The energy gradient line (EGL) is the sum of the HGL and velocity head.

The amount of energy loss when the liquid flows from section 1 to section 2 is indicated by hL.

For uniform flow in an open channel, this drop in the EGL is equal to the drop in the channel bed.

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What is open channel flow?

What is open channel flow?

Based on their shape, an open channel can be prismatic or non-prismatic:

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What is open channel flow?

Prismatic channels:a channel is said to be prismatic when the cross section is uniform and the bed slope is constant.

What is open channel flow?

Non-prismatic channels:when either the cross section or the slope (or

both) change, the channel is referred to as non-prismatic. It is obvious that only artificial channel

can be prismatic.

What is open channel flow? The most common shapes of prismatic channels are rectangular, parabolic, triangular, trapezoidal

and circular.

Types of open channelsCanal

FlumeChute

DropCulvert

Open Flow Tunnel

What is Canal? Canal is a long and mild-sloped channel built in the

ground

Coachella canal, USA

What is Flume? Flume is a channel usually supported on or above

the surface of the ground to carry water

Box flume, California, 1916

USA

What is Chute? Chute is a channel having steep slope.

Gilbbesjavri, Northern Finland

What is Drop? Drop is similar to chute, but the change in elevation

is affected in a short distance

East Boulder River, USA

What is Culvert? Culvert is a covered channel flowing partly full,

which is installed to drain water through highway and railroad embankments.

A road to home,Anywhere

What is Open flow tunnel? Open-Flow Tunnel is a comparatively long covered

channel used to carry water through a hill or any obstruction on or in the ground.

Urfa tunnels in Turkey, for Southern Anatolian Project,

Diameter, 7.62-mLength, 2x26.4-km

Discharge, 80-m3/sec

Classification of open surface flow

Open Channel Flow can be classified according to the variation by TIME and SPACE

Steady and unsteady flow occurs with respect to TIME variance

Uniform and nonuniform flow occurs with respect to SPACE variance

Classification of open surface flow

Variation in time:Steady flow, velocity and depth does not change

with timeUnsteady flow, velocity and depth change with

time

Classification of open surface flow

Variation in space:Uniform flow, velocity and depth same at each

different cross-section

Non-uniform flow, velocity and depth vary between cross-sections

Classification of open surface flow

In steady flows, all the characteristics of flow are constant with time.

In unsteady flows, there are variations with time

Classification of open surface flow

In uniform flow, all characteristics of flow are same along the whole length of flow. velocity, V1 = V2 and flow area,

A1 = A2

In uniform channel flow, water surface is parallel to channel bed.

Classification of open surface flow

In non-uniform flow, characteristics of flow vary along the whole length of the channel.

By non-uniform flow, we mean that the velocity varies at each section of the channel.

In the non-uniform flow, the energy grade line is not parallel to the bed of the channel.

Classification of open surface flow

Non-uniform flow can be caused by:

Differences in depth of channel Differences in width of channel

Differences in the nature of bed Differences in slope of channel

and Obstruction in the direction of flow.