Structure and Working of Check Dams

STRUCTURE AND WORKING OF CHECK DAMS

The word 'dam' carries a connotation that has always reminded me of a massive towering structure built over a gushing river. However, there is another kind of dam, implemented in regions such as Rajasthan: the check dam. Unlike their larger counterparts, checks dams are designed stop water to enable it to perculate into the ground to recharge the acquirers. Rajasthan, with its arid climate and frequent droughts, has been a pioneer in the use of check dams for many years. Over the last few years, through government programs and community efforts, traditional water conservation techniques like johads (small earthen check dams) have been revitalized. 

Typically constructed in areas of steep terrain, Check dams, also known as gully plugs are small barriers built across natural drainage channel to capture and store runoff water. Essentially, in a small catchment area, the small dams store extra water flow during monsoon rains. The impounded water is forced into the ground by the pressure that is created in the catchment area, thereby raising the groundwater levels. 

 

Depending on the scale of the check dam both temporary and permanent check dams can be built. On the grassroot level natural materials such as stone, sand, logs and natural available are used for the purpose of constructing a temporary check dam. For a larger scale project, materials such as cement, bricks and sandbags could be utilized to accommodate the needs of 2-3 villages, establishing a self-sustaining permanent check dam. 

             

             

The design of a check-dam is both simple and ingenious. Although check-dams can vary in shape, size and materials, the basic structural elements remains the same. 

1. Foundation- The base must be structurally stable sound to withstand the pressure of the running water. It is generally built using either stone or concrete. 

2. Body- The main part of the dam is constructed using locally available materials such as stones, bricks, concrete or even wood. The body of the dam is typically built to a height that will effectively slow down the water flow without causing excessive backwater flooding. In Rajasthan, without a government's permit, the maximum height allowed is 3m. The cross-section is usually trapezoidal, with the wider base providing stability.

3. Spillway- This is an overflow structure that allows excess water to flow over the dam safely without damaging it during periods of heavy rainfall. 

4. Silt trap- A section is designed t†o capture silt and debris carried by the water, preventing them from clogging the spillway or reducing the dam's effectiveness.

The design of check dams varies based on the specific requirements of the site, including the topography, water flow, and available materials. 

 1) Site selection- The two main factors taken into consideration are topography and the geology of the site. Preferably, choosing a site with with a natural drainage path or a downward sloping hill leading to a catchment area. Additionally, the site should have a stable foundation typically consisting of bedrock or well- compacted soil to support the structure. 

2) Materials available- To reduce the cost of construction, the usage of locally available materials is advisable.  Investing in high quality materials ensures the overall durability and justifies the investment in the long run.  

3) Analysing in the long run- 

i) High Evaporation Rates: By using surface covers or creating shaded areas by planting trees, dams can be designed to minimise the loss of water through transpiration. 

ii) Sediment Load: Maintenance checks including regular de-silting is crucial considering the sandy nature of the Rajasthan and the potential for high sediment load. 

iii) Community Involvement: By engaging the local communities in the construction and maintenance process, long term sustainability and effectiveness can be ensured.