What is Borewell Yield?

Borewell yield refers to the quantity of water that can be safely extracted from a borewell per unit time, typically measured in:

Liters per minute (LPM)

Cubic meters per hour (m³/hr)

Gallons per minute (GPM)

The yield depends on several factors:

Aquifer type (confined or unconfined)

Rock formation and fracture zones

Recharge rate

Borewell depth and diameter

Pump capacity

Seasonal groundwater fluctuation

Why Borewell Yield Estimation is Important?

Accurate yield estimation helps in:

Selecting the right pump capacity

Preventing borewell failure

Avoiding over-extraction

Designing irrigation systems

Planning industrial water requirements

Ensuring sustainable groundwater management

Improper estimation can result in dry borewells, excessive power consumption, and aquifer damage.

Major Borewell Yield Estimation Methods

1. Pumping Test Method (Constant Discharge Test)

Overview

The pumping test method is the most reliable and scientifically accepted method for borewell yield estimation.

Procedure

Install a submersible pump.

Pump water at a constant discharge rate.

Measure water level drawdown at regular intervals.

Continue pumping for 4–24 hours.

Record recovery after stopping pumping.

Key Parameters

Static Water Level (SWL)

Pumping Water Level (PWL)

Drawdown (s)

Discharge (Q)

Formula

Specific Capacity = Q / s

Where:

Q = Discharge rate

s = Drawdown

This method provides accurate sustainable yield estimation and aquifer characteristics.

2. Step Drawdown Test

Overview

The step drawdown test involves pumping at increasing discharge rates in steps.

Procedure

Pump at low discharge for 1 hour.

Increase discharge gradually in 3–5 steps.

Measure drawdown for each step.

Plot discharge vs drawdown graph.

Benefits

Identifies optimal pumping rate

Determines well efficiency

Prevents over-pumping

This method is widely used for agricultural and industrial borewell design.

3. Air Compressor Yield Estimation

Overview

In this method, compressed air is used to lift water from the borewell to estimate yield.

Advantages

Quick field estimation

Low cost

Suitable for rural areas

Limitations

Less accurate

Short-duration testing

Not suitable for final pump design

This method is mainly used during borewell drilling stage.

4. Recovery Test Method

Overview

The recovery test measures how quickly the water level recovers after pumping stops.

Procedure

Pump the borewell for a fixed duration.

Stop pumping.

Record water level recovery at regular intervals.

Analyze recovery rate.

Importance

Indicates aquifer recharge capacity

Helps determine sustainable yield

Useful in low-yield borewells

5. Specific Capacity Method

Specific Capacity = Discharge / Drawdown

This quick estimation method helps:

Compare borewell performance

Identify well clogging

Assess long-term efficiency

Though simple, it should be combined with pumping tests for accuracy.

Factors Affecting Borewell Yield

Geological formation (Hard rock, sedimentary rock)

Fracture density

Borewell depth

Recharge area

Rainfall pattern

Nearby borewell interference

Pump selection

In hard rock regions like many parts of South India, fracture zones play a critical role in yield estimation.

Sustainable Borewell Yield vs Maximum Yield

Maximum Yield: Highest discharge possible during pumping

Sustainable Yield: Safe discharge without aquifer depletion

Always design pump systems based on sustainable yield, not maximum yield.

Recommended Borewell Yield Testing Duration

Longer tests provide more reliable results.

Best Practices for Accurate Borewell Yield Estimation

Conduct geophysical survey before drilling

Maintain proper borewell casing

Use calibrated flow measurement devices

Record detailed test data

Consult certified hydrogeologists

Avoid over-extraction