check dam

Check Dam ( Erosion Control ) : 2 Types, Design, Functions, Advantages & Disadvantages

 

A check dam is a linear structure constructed perpendicular to concentrated flows across the waterway to control erosion by reducing the velocity of the flow. 

✔ Check dam retains flood water and traps sediment. It is best to use when the drainage area is 10 acres or less.

✔ Construction of the check dam is relatively inexpensive and easy. 

✔ Check dam materials may include fiber logs (e.g., wattles), rock, sand bags, triangular sediment dikes, concrete, steel, and prefabricated systems or other materials.

✔ Check dam consists of an embankment and spillway. Some check dam consists of the only embankment. 

Straw/hay bales and silt fences should not be used for check dam applications, as they are not intended for concentrated flow areas.

✔ At the beginning of construction,  a water body would be formed behind the check dam, gradually the water body will be filled with sediment deposits.

The area formed by the deposit is usually used as farmland because it plays an important role in the grain production in that region.

Check dam is generally used in concentrated flow areas but not in-stream or channel. It can either be the permanent or temporary barrier that prevents erosion and promote sedimentation by slowing flow velocity.

 

 


 

  1. Purpose  

The main purpose of a check dam is to reduce the velocity of the flow to control erosion, not to collect sediment, although sediment collection is an added benefit.

 


 

  2. Types of Check Dam  

 

i. Based on Purpose

 

a. Temporary Check Dam

These check dams are constructed for a limited time.

Generally; rocks, logs, and sand bags are utilized for the construction of temporary check dams.

 

b. Permanent Check Dam

These dams are constructed permanently.

These dams are generally constructed utilizing concrete or steel or rock or a composite of two or more materials.

 

i. Based on Materials Used

 

a. Concrete Check Dam

Check dam

 

b. Rock Check Dam

rock check dam

 

c. Rubber Check Dam

Rubber Check dam

 

d. Fiber Log Check Dam

Fiber Log Check Dam

 

e. Silt Dike Check Dam

Silt Dike Check Dam

 

f. Sand Bag Check Dam

sand bag check dam

 


 

  3. Functions of Check Dam  

A check dam is pre-designed and constructed to meet the following concept:-

1. To reduce the velocity of the water.

2. Raise the bed level and reduce the slopes in a gully by silting up and trapping the silt.

3. Support the unstable side slopes.

4. Promote the water percolation in the soil and conserve water for plant growth and also for the stability of banks.

 


 

  4. Design Consideration of Check Dam  

Design consideration includes the following points:-

check dam

 

1. Site selection

a. The site should be wide enough to provide high runoff.

b. The spillway has to be large enough with sufficient freeboard to take the expected maximum runoff. (concrete mortared rock dam must not exceed 8 m in height whereas the log crib dam must not exceed 2 m. The  spacing of a dam for 2 m height in a 20-degree channel will be 12 m.)

c. It should be made at a straight and firm stream bed. It should not be made on a curve and junction of gullies or streams.

d. The foundation of the check dams should rest on base rock.

e. The selection of the site is also restricted by the height of the structure. If the elevation difference between the 2 sides is too high, 1 or more sides have to be selected in between so that structural height will be limited.

 

2. Spacing

The spacing of check dams should be so placed that, the line joining the top of the lower check dam and the bottom of the successive upper check dam gives the gradient.

This gradient will give a non-erosive velocity of flow. This gradient is known as a compensation gradient.

For general practice, the compensation gradient is taken as 3 to 5% of the slope. The horizontal distance between successive check dams is given by:

b=h*100/(So-Se)

where,

b=spacing between two check dams

h=Height of check dam up to the notch

So=Existing bed slope in percentage

Se=Establishing slope of the bed in percentage

 

3. Number

The number of check dams required is determined from the following formula:

number of check dams =(a-b)/H

where,

a=total vertical distance between first and last dam

b=Se*d’/100

d’=horizontal distance between first and last dam

H=average height

 


 

  5. Design  – Example  

We have provided this design example in PDF Format for your ease. Download it and grab the knowledge.

Download Example Download

 


 

  6. Hydrological Aspect   

Runoff estimate

The rational formula is the most commonly used method for the estimate of runoff.

The peak rate of runoff is calculated by using the following rational formula;

Q=CIA/360

Where,

Q=Rate of runoff

C=Catchment coefficient or the coefficient of runoff

I=Intensity of runoff

A=Catchment area

 


 

  7. Advantages of Check Dam  

Some advantages of this dam are:

a. It provides an irrigation facility.

b. It reduces flow velocity and helps in the protection of river banks.

c. Economical than other dam types.

d. It is simple to construct the check dam. So, no requirement for advanced machines and technologies.

e. It helps in flood & erosion control.

f. It facilitates the production of electricity on a small scale.

 


 

  8. Disadvantages of Check Dam  

Some disadvantages of this dam are:

a. It causes a rise in the groundwater table.

b. Affects aquatic lives.

c. It has a limited life span and strength.

d. Depending on the type of check dam installed, removal may be costly.

e. Requirement of maintenance mainly after heavy rainfall.

 

Read Also: Earthen Dam