2. 2. 1. Dug Well Irrigation

 

Dug Well Irrigation Design

Dug wells are one of the oldest methods of accessing groundwater for irrigation. They are typically shallow, with depths ranging from a few meters to about 15 meters. The design of a dug well involves several considerations, including the size of the well, the materials used for lining, the method of water extraction, and the potential yield.

Components of Dug Well Design

1. Diameter and Depth:

   • The diameter of a dug well typically ranges from 1 to 4 meters, depending on the required water volume and the water table's stability. The depth is determined based on the water table depth and the required water quantity.

2. Lining:

   • Lining is crucial to prevent the well walls from collapsing. Materials such as concrete, bricks, stone, or timber are commonly used.

3. Well Curb and Platform:

   • A curb or parapet is built around the well mouth to prevent contamination. A concrete platform is often constructed around the well to keep the surrounding area clean.

4. Water Extraction System:

   • A variety of water extraction methods can be used, including bucket and rope, hand pumps, or motorized pumps.

5. Water Storage and Distribution:

   • Storage tanks and pipelines may be used to distribute the water to fields.

Numerical Real-Life Example

Scenario: Designing a dug well for irrigation in a rural area with the following requirements and conditions:

• Daily water requirement for crops: 15,000 liters (15 m³)
• Depth to the water table: 5 meters
• Expected water yield: 0.5 liters/second (lps)
• Well diameter: 2 meters

Step 1: Calculate the Well Yield

The yield of the well is the amount of water it can supply per unit of time. It is calculated using the formula:

$Q=\frac{\mathrm{V/}}{T}$

Where:

• $Q$ = Yield (lps)
• $\mathrm{V =\; Volume\; of\; water\; (liters)}$
• $\mathrm{T=\; Time\; (seconds)}$

Given:

• Yield ($\mathrm{Q)\; =\; 0.5\; lps}$

The daily water requirement is 15,000 liters. To check if the well can meet this requirement:

Daily Water Yield:

$Q\times T=\mathrm{V<span\; class="base"><br></span>}$

Where:

• $\mathrm{Q =\; Yield\; (0.5\; lps)}$
• $\mathrm{T=\; Time\; (seconds\; per\; day)}$

There are 86,400 seconds in a day (24 hours × 60 minutes × 60 seconds).

$0.5\text{ lps}\times 86,400\text{ seconds}=43,200\text{ liters/day}$

$0.5 \text{ lps} \times 86,400 \text{ seconds} = 43,200 \text{ liters/day}$

0.5 lps×86,400 seconds=43,200 liters/day

The well can provide 43,200 liters/day, which exceeds the daily requirement of 15,000 liters. Thus, the well can adequately supply water for irrigation.

Step 2: Design Parameters

1. Well Diameter and Depth:

   • The chosen diameter is 2 meters, providing a sufficient water surface area.
   • The depth to the water table is 5 meters. The well should be dug deeper to provide a buffer above the water table to ensure adequate water supply.

2. Lining:

   • Concrete rings or bricks can be used for lining, ensuring stability and preventing collapse.

3. Water Extraction:

   • A submersible pump can be installed to efficiently draw water from the well. The pump's capacity should match the well's yield.

4. Storage and Distribution:

   • A storage tank with a capacity of at least 15,000 liters should be installed to meet daily requirements. Pipes can be laid to distribute water to the fields.

Step 3: Cost Estimation

• Excavation and Lining Costs:

  • These depend on local labor and material costs. For instance, if the cost is   ₹ 50 per cubic meter for excavation and lining, the cost for a well with a depth of 6 meters (adding 1 meter as a buffer) and a diameter of 2 meters would be:

  Volume = $\pi \times \left(\frac{2}{2}\right)^2 \times 6 = 18.85 \text{ m}^3$

  Cost = Volume x   ₹ 50 = ₹ 942.5

• Pump Installation:

  • A pump suitable for a 5-meter head and a flow rate of 0.5 lps might cost around ₹500.

• Storage and Distribution:

  • A tank and piping system might cost an additional ₹ 1,000.

Conclusion

Dug wells are a reliable source of water for irrigation, especially in areas with shallow water tables. This example demonstrates that with proper design and equipment, a dug well can meet the irrigation needs of a crop field. The design considerations ensure the well's efficiency and longevity while providing a sustainable water source.