Drawdown When Steady Flow Of Unconfined Aquifer Calculator

Formula Used:

\[ s_w = \frac{Q_u \cdot \ln\left(\frac{r}{R_w}\right)}{2 \pi T} \]

Steady Flow of an Unconfined Aquifer (Qu):

m³/s

Radius at the Edge of Zone of Influence (r):

Radius of the Pumping Well (Rw):

Transmissivity of an Unconfined Aquifer (T):

m²/s

Drawdown at the Pumping Well (sw):

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1. What is the Drawdown at the Pumping Well?

The Drawdown at the Pumping Well refers to the term applied to the maximum lowering of the groundwater table caused by pumping or artesian flow. It is a critical parameter in hydrogeology for assessing the impact of groundwater extraction.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ s_w = \frac{Q_u \cdot \ln\left(\frac{r}{R_w}\right)}{2 \pi T} \]

Where:

\( s_w \) — Drawdown at the Pumping Well (m)
\( Q_u \) — Steady Flow of an Unconfined Aquifer (m³/s)
\( r \) — Radius at the Edge of Zone of Influence (m)
\( R_w \) — Radius of the Pumping Well (m)
\( T \) — Transmissivity of an Unconfined Aquifer (m²/s)
\( \pi \) — Archimedes' constant (≈3.14159)
\( \ln \) — Natural logarithm function

Explanation: The formula calculates the maximum drawdown at a pumping well in an unconfined aquifer under steady-state conditions, considering the aquifer's transmissivity and the geometric relationship between the well radius and the zone of influence.

3. Importance of Drawdown Calculation

Details: Accurate drawdown calculation is crucial for designing well systems, assessing groundwater resource sustainability, predicting interference between wells, and managing aquifer depletion risks.

4. Using the Calculator

Tips: Enter all values in appropriate units (m³/s for flow, m for distances, m²/s for transmissivity). Ensure all values are positive and the radius at the edge of influence is greater than the well radius.

5. Frequently Asked Questions (FAQ)

Q1: What is the difference between confined and unconfined aquifers?
A: Unconfined aquifers have a water table that represents the upper boundary, while confined aquifers are bounded above and below by impermeable layers.

Q2: How is transmissivity different from hydraulic conductivity?
A: Transmissivity (T) is the product of hydraulic conductivity (K) and saturated thickness (b) of the aquifer (T = K × b).

Q3: What defines the "edge of zone of influence"?
A: The edge of zone of influence is the maximum distance from the pumping well where drawdown can be detected, typically where drawdown approaches zero.

Q4: When is the steady-state assumption valid?
A: Steady-state conditions apply when the pumping rate and water table elevation have stabilized over time, typically after prolonged pumping.

Q5: What are the limitations of this formula?
A: This formula assumes homogeneous, isotropic aquifer properties, constant pumping rate, and negligible well losses. It may not accurately represent complex geological conditions.