Aquifer Drawdown Calculator (Theis Equation)

Data Source and Methodology

All calculations are based on the Theis Equation, a fundamental formula in hydrogeology. For more details, refer to the US Geological Survey. All calculations are strictly based on the formulas and data provided by this source.

The Formula Explained

The Theis Equation is expressed as:

Where u = (r²S) / (4Tt) and W(u) is the well function.

Glossary of Variables

• Transmissivity (T): The ability of the aquifer to transmit water.
• Storativity (S): The amount of water an aquifer releases from storage per unit decline in hydraulic head.
• Pumping Rate (Q): The volume of water extracted from the aquifer per unit time.
• Time (t): The duration of pumping.
• Distance from Well (r): The distance from the pumping well to the point of interest.
• Drawdown (s): The decrease in hydraulic head observed in a well.

Practical Example: A Step-by-Step Guide

Consider a scenario where you need to determine the drawdown at a distance of 100 meters from a well, pumping at 500 m³/day, after 10 days. With a transmissivity of 200 m²/day and a storativity of 0.0001, the drawdown can be calculated as follows:

Given: Q = 500 m³/day, T = 200 m²/day, S = 0.0001, t = 10 days, r = 100 m

Calculate u = (r²S) / (4Tt), then use the W(u) function to find s.

Frequently Asked Questions (FAQ)