Experiment # 1

“To establish steady uniform flow conditions in laboratory flume and to determine the Chezy’s constant “C” & Manning’s roughness coefficient “n””.

Apparatus

1. S-6 Tilting laboratory flume with manometer, slope adjusting scale and flow arrangement.
2. Hook gauge (to measure depth of water)

Related Theory

Flume

It is a channel supported above the ground level. Steady uniform flow

Open Channel Flow

In this type of flow, flow takes place under the action of gravity & the water surface is open to air ex:- canals, rivers. Steady uniform flow

Pipe Flow

In this type of flow, flow takes place under Pressure & the whole inner surface is wet generally. ex:_ flow in water supply pipes & drainage pipes. Steady uniform flow

Steady Flow

In this type of flow in which flow properties (discharge, velocity etc ) remains same with respect to time at a particular section. Steady uniform flow

Unsteady Flow

In this type of flow in which flow properties (discharge, velocity etc ) does not remain same with respect to time at a particular section. ex river flow. Steady uniform flow

Uniform Flow

In this type of flow in which flow properties (discharge, velocity etc ) remains same with respect to distance. ex:- flow through a pipe of uniform diameter is steady uniform flow.

Steady Uniform Flow

In this type of flow in which flow properties (discharge, velocity etc ) remains same with respect to distance as well as  with respect to time. ex:- flow through a pipe of uniform diameter is steady uniform flow. Steady uniform flow

Steady Non Uniform Flow

In this type of flow in which flow properties (discharge, velocity etc ) remains same with respect to time but change with respect to distance. ex:- Constant flow through a pipe of varying diameter is steady non uniform flow. Steady uniform flow

Unsteady Uniform Flow

In this type of flow in which flow properties (discharge, velocity etc ) remains same with respect to distance but change with respect to time. ex:- flow through a pipe of uniform diameter but pumping rate is different. Steady uniform flow

Unsteady Non Uniform Flow

In this type of flow in which flow properties (discharge, velocity etc ) does not remain same with respect to distance as well as with respect to time. ex:- Flow in natural channels. Steady uniform flow

Assumptions of an Ideal Fluid

1) Fluid is non viscous.
2) Fluid is incompressible.
3) Fluid motion is steady.

Chezy’s Formula

The Chezy formula can be used to calculate mean flow velocity in conduits and is expressed as
v = c (R S)^1/2
where
v = mean velocity (m/s, ft/s)
c = the Chezy roughness and conduit coefficient
R = hydraulic radius of the conduit (m, ft)
S = slope of the conduit (m/m, ft/ft)
This formula is only suitable for Lined channels.

Manning’s Formula

V=(1/n)*R^(2/3)*S^(1/2)

where:
V is the cross-sectional average velocity (ft/s, m/s)
n is the Gauckler–Manning coefficient (independent of units)
R is the hydraulic radius (ft, m)
S is the slope of the water surface or the linear hydraulic head loss (ft/ft, m/m)
(S = hf/L)
This formula is for unlined channels. Steady uniform flow

Relationship b/w Chezy’s & Manning’s Formula

Procedure

1) Measure the channel width and length.
2) Adjust suitable value of slope.
3) For constant value of slope, vary the discharge and find the depth of flow of water.

Precautions

1) Tip of the hook gauge should just touch the water.
2) Take piezometric Readings when flow is ready.
3) Take more then three readings. Steady uniform flow

Observations & Calculations

Comments

The values of Mannings roughness coefficient should decrease generally with the increase in discharge but in our case first they decrease and then they increase. Similarly the values of  Chezy’s constant should increase with the discharge but in our case they are increasing and then decreasing. This can be due to any experimental mistake or inappropriate way of taking readings. The water depth in the flume was also not uniform everywhere , may be the reading was taken at the point of higher depth. Some values of mannings coefficient depending on the material are given as under. Steady uniform flow