Select the option that is appropriate regarding the following two statements labelled Assertion and Reason.
Assertion: Check dams of low height are constructed across the tributaries of rivers at different stages to arrest the sediments in the catchment area.
Reason: Check dams serve the purpose of detention reservoirs and keep all the sediments in suspension.

Question

Select the option that is appropriate regarding the following two statements labelled Assertion and Reason.

Assertion: Check dams of low height are constructed across the tributaries of rivers at different stages to arrest the sediments in the catchment area.

Reason: Check dams serve the purpose of detention reservoirs and keep all the sediments in suspension.

Prepp Team · Accepted Answer

Analyzing Check Dams and Sediment Control

Let's carefully examine the given Assertion and Reason regarding the function of check dams, especially concerning sediment management in catchment areas.

Understanding the Assertion

The Assertion states:

Assertion: Check dams of low height are constructed across the tributaries of rivers at different stages to arrest the sediments in the catchment area.

This statement describes a common and effective practice in soil and water conservation. Check dams are small, temporary or permanent barriers built across gullies, small streams, or tributaries. Their primary purpose is to slow down the flow of water and trap sediment, thus reducing erosion and improving soil stability in the upstream catchment area. Building them at different stages (intervals) along a tributary helps manage water flow and sediment incrementally. The mention of "low height" is also characteristic of many check dams, distinguishing them from larger dams built for water storage or power generation.

Based on standard soil and water conservation principles, this Assertion is true.

Understanding the Reason

The Reason states:

Reason: Check dams serve the purpose of detention reservoirs and keep all the sediments in suspension.

Let's break down the Reason:

Check dams serve the purpose of detention reservoirs: This part is true. By slowing down water flow and temporarily holding water behind them, check dams act as small detention or retention structures, helping to manage runoff.
...and keep all the sediments in suspension: This part is false. The main mechanism by which check dams control sediment is by reducing the velocity of the flowing water. When water velocity decreases, the sediment it is carrying (which was in suspension or being transported along the bed) loses energy and settles out of the water. Check dams are designed precisely to *promote* sediment deposition, not keep it in suspension. Keeping sediment in suspension means it continues to be carried downstream, which is the opposite of what check dams aim to achieve in terms of sediment control.

Therefore, the Reason contains a false statement about how check dams handle sediment.

Conclusion on Assertion and Reason

The Assertion is true because low-height check dams are constructed across tributaries to arrest sediments in the catchment area.
The Reason is false because while check dams act as detention reservoirs, they cause sediment to settle (deposit), they do not keep all sediment in suspension.

Given that the Assertion is true and the Reason is false, we need to select the option that reflects this.

Comparing this conclusion with the given options:

Option 1: Assertion is true but Reason is false. (Matches our conclusion)
Option 2: Both Assertion and Reason are true and reason is the correct explanation of assertion. (Incorrect, Reason is false)
Option 3: Both Assertion and Reason are true but Reason is not the correct explanation of Assertion. (Incorrect, Reason is false)
Option 4: Both Assertion and Reason are false. (Incorrect, Assertion is true)

Thus, the appropriate option is that the Assertion is true but the Reason is false.

Statement	Evaluation	Explanation
Assertion	True	Check dams trap sediment in catchment areas by slowing water flow.
Reason	False	Check dams promote sediment deposition, not keep it in suspension. They do act as detention reservoirs.

Revision Table: Check Dams and Sediment Control

Feature	Description	Purpose related to Sediment
Check Dam Location	Across gullies or small tributaries in catchment areas.	Built upstream to control sediment close to its source.
Check Dam Height	Typically low height.	Designed to slow water and trap sediment without creating a large, deep reservoir.
Mechanism of Sediment Control	Reduces water velocity.	Allows suspended sediment and bedload to settle out of the water.
Sediment Outcome	Sediment is trapped/deposited behind the dam.	Reduces sediment load carried downstream, protecting larger rivers and reservoirs.

Additional Information on Check Dams and Catchment Management

Check dams are a key component of integrated watershed management and soil conservation efforts. Beyond trapping sediment, they offer several other benefits:

Soil Conservation: By slowing water and trapping sediment, they reduce soil erosion upstream and stabilize gully beds.
Water Infiltration: The temporary pooling of water behind the dam increases the time water has to infiltrate into the soil, helping to recharge groundwater.
Moisture Availability: Improved soil moisture in the area around the check dam benefits vegetation growth.
Runoff Management: They help regulate water flow, reducing peak flows during heavy rainfall and maintaining some flow during dry periods.

Different materials are used to construct check dams, including rocks, brushwood, logs, gabions (wire mesh cages filled with rocks), or concrete, depending on the site conditions and the desired lifespan of the structure. They are strategically placed at intervals along a watercourse to maximize their effectiveness in controlling erosion and managing sediment across the entire catchment area.