Confined Aquifer Discharge Given Drawdown At Well Calculator

Confined Aquifer Discharge Formula:

\[ Q = \frac{2\pi KWH \cdot bp \cdot Stw}{\ln\left(\frac{Rw}{r}\right)} \]

Coefficient of Permeability (KWH):

m/s

Aquifer Thickness During Pumping (bp):

Total Drawdown in Well (Stw):

Radius of Influence (Rw):

Radius of Well (r):

Discharge (Q):

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1. What is the Confined Aquifer Discharge Formula?

The confined aquifer discharge formula calculates the rate of groundwater flow from a well in a confined aquifer. It's derived from Thiem's equation and accounts for the aquifer's properties, well characteristics, and drawdown effects.

2. How Does the Calculator Work?

The calculator uses the confined aquifer discharge formula:

\[ Q = \frac{2\pi KWH \cdot bp \cdot Stw}{\ln\left(\frac{Rw}{r}\right)} \]

Where:

\( Q \) — Discharge rate (m³/s)
\( KWH \) — Coefficient of permeability (m/s)
\( bp \) — Aquifer thickness during pumping (m)
\( Stw \) — Total drawdown in well (m)
\( Rw \) — Radius of influence (m)
\( r \) — Radius of well (m)
\( \pi \) — Mathematical constant pi (≈3.1416)
\( \ln \) — Natural logarithm function

Explanation: The formula calculates groundwater discharge based on the aquifer's hydraulic properties and the geometry of the well and its influence zone.

3. Importance of Discharge Calculation

Details: Accurate discharge calculation is crucial for well design, groundwater resource management, environmental impact assessments, and determining sustainable pumping rates for confined aquifers.

4. Using the Calculator

Tips: Enter all values in consistent units (meters and meters/second). Ensure the radius of influence is greater than the well radius. All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is a confined aquifer?
A: A confined aquifer is an aquifer bounded above and below by impermeable layers, creating pressure that causes water to rise above the top of the aquifer when a well is drilled.

Q2: How is coefficient of permeability determined?
A: It's typically determined through pumping tests, where water is pumped from a well and the drawdown is measured in observation wells at various distances.

Q3: What is radius of influence?
A: The distance from the center of the well to the point where drawdown becomes negligible, essentially where the water table remains unaffected by pumping.

Q4: When is this formula applicable?
A: This formula applies to steady-state flow in homogeneous, isotropic confined aquifers with fully penetrating wells and negligible well losses.

Q5: What are the limitations of this equation?
A: It assumes ideal conditions: homogeneous aquifer, constant thickness, isotropic properties, and steady-state conditions. Real-world conditions may deviate from these assumptions.