Check dams

Check dams- a strategy to check siltation and sedimentation from catchment areas into nearby water bodies. Its mode of action, types, advantages and disadvantages.

1. CHECK DAMS Submitted to: Submitted by: Dr. R.N.Ram Ujjwala Upreti Head of Department. PhD. II Sem.(41776) Fisheries Resource Management Aquaculture.

2. What are check dams? A check dam also called ditch check, is a small sometimes temporary dam constructed across a waterway, drainage ditch or swale. Typically check dams are constructed of rock with mixed vegetation, and retain some porosity allowing for water to leak through the stones and vegetation. It counteracts erosion by reducing water flow velocity causing sediment traps. Materials used in construction of check dams- Rocks Sand bags Fiber logs Cement concrete and other materials.

3. Functioning of check dams Placed in a waterway/ditch Interrupts water flow & flattens gradient Reduces water velocity Low erosion & trap sediments Note :- Main function is to lower the velocity of water, infiltration sedimentation are added benefits.

4. Types of check dams 1. Rock check dams It is made up of well graded stones consisting of a mixture of rock sizes, typically 1.5-12 inches for best results. These are constructed 4-5 feet wide at the bottom and 1.5-2 feet wide at the top. 1.5-2 feet high, with side slopes no steeper than 2:1 in ratio.

5. 2. Sand bag check dams- Sand bags made up of weather resistant and tightly woven geotextile fabric material sufficient to prevent leakage of filler material. Height 1.5-2 feet, with side slopes in ratio 2:1 End of bag is tightly abutted and overlapped to direct flow of water away from joints.

6. 3. Gabion check dams A gabion is a cage which has a cubic shape filled with stony material in a metal grating keeping the stones together and stops them moving under the pressure of water. The technique of gabion check dam consist of binding different cages together to form a gabion unit. Stony material is mixture of rocks varying in size from 1.5-12 inches in diameter.

7. Types of check dams: Concrete check dam Check dam made up of other material (rubber)

8. Design considerations Site - The drainage area should be less than 10 acres. Waterway should be on a slope <50% and a minimum depth to bedrock of 2 feet. Size - Height of check dam should be 2-3 feet. Centre of dam should be at least 6 inches less than its edges. Spacing - Spacing is needed to be done in order to reduce water velocity, erosion and protect the channel between dams. The dams should be spaced such that the toe of the upstream check dam is equal to the elevation of the down stream's check dam crest.

9. Check dam constructed across a swale/channel

10. Advantages Highly effective practice to reduce flow velocity in channels and waterways. Contrasting to big dams have faster implementation timeline and are cost effective. Hampers establishment of grass linings in channels and drainage ditches. Their implementation will not displace people or communities nor will they destroy natural resources if careful design considerations are undertaken. Simple to construct, do not rely on advanced technology.

11. Limitations Not appropriate in channels that drain area of more than 10 acres. Not appropriate in channels that are already grass-lined unless erosion is expected, as installation may damage vegetation. Promotes sediment trapping which can be re-suspended during high storms or after removal of the check dams. Become more difficult to establish on steep slopes as velocity is higher and thereby the distance between dams must be shortened.

12. Conclusion Check dams are highly efficient in lowering the velocity of flowing water across the channel. Economic in use, with a need of proper maintenance. Check dams are continuously used in rural areas or areas where latest technology cannot be applied or supplied immediately. However these are very useful and constructed in many parts of the country but cannot be used for larger drainage channels of more than 10 acres, besides there is always need of large dams for large scale projects.