TO DETERMINE THE VALUE OF MANNINGS ROUGHNESS COEFFICIENT FOR UNIFORM FLOW

TITLE:

TO DETERMINE THE VALUE OF MANNINGS ROUGHNESS COEFFICIENT FOR UNIFORM FLOW

OBJECTIVES:

1. To study the change in manning roughness Coefficient by varying discharge.

2. To determine the manning roughness coefficient.

APPARATUS REQUIRED:

1. Glass sided tilting flume, 

2. Point gauge,

3. Differential manometer.

THEORY:

The type of flow in which the dependent flow variables such as depth,velocity, discharge,etc remain constant over a given length of the channel is called uniform flow. The chezy equation for an uniform open channel flow is given by:

 `v=C root(2)(RS_0)`

As per mannings test, we have,

`C=1/nR^(2/3)S_0^(1/2)`

Thus, `v=1/nR^(2/3)S_0^(1/2)`

Where,

`v=`average velocity of flow

`n=`Mannings roughness constant.

`R=`hydraulic radius

`S_0=`Bed slope

TITLE:

TO DETERMINE THE VALUE OF MANNINGS ROUGHNESS COEFFICIENT FOR UNIFORM FLOW

OBJECTIVES:

1. To study the change in manning roughness Coefficient by varying discharge.

2. To determine the manning roughness coefficient.

APPARATUS REQUIRED:

1. Glass sided tilting flume, 

2. Point gauge,

3. Differential manometer.

THEORY:

The type of flow in which the dependent flow variables such as depth,velocity, discharge,etc remain constant over a given length of the channel is called uniform flow. The chezy equation for an uniform open channel flow is given by:

 `v=C root(2)(RS_0)`

As per mannings test, we have,

`C=1/nR^(2/3)S_0^(1/2)`

Thus, `v=1/nR^(2/3)S_0^(1/2)`

Where,

`v=`average velocity of flow

`n=`Mannings roughness constant.

`R=`hydraulic radius

`S_0=`Bed slope

PROCEDURES:

1. The sluice gates at the discharge end of the channel was raised.

2. The hydraulic bench pump was then started and the water was allowed to flow.

3. When the flow conditions had become stable, the flow rate and the depth of flow was measured.

4. The above procedure was repeated for different discharge.

OBSERVATIONS:

Total Volume is $=400*510*200mm^3$

$=0.0408 m^3$

length,$L=4.5 \ m$

Bed slope,`S_0=0.03/4.5=0.0066`

Width,`B=0.37`

CALCULATIONS:

RESULTS:

Thus the meaning constant varies between `0.0077` to `0.108` and the average value is found to be `0.072`.

CONCLUSIONS:

The following conclusions can be notified:

1. The coefficient of roughness is reduced when the discharge increases for a particular slope and bed.

2. The slope of channel and bed roughness are the main factor affecting the value of coefficient of roughness.

3. For the same bed roughness, the increase in discharge will not have more effect on coefficient of roughness.