Quick Answer
To calculate water yield based on well depth, you'll need to know the well's diameter, static water level, and transmissivity of the aquifer. A commonly used formula is the Thiem equation, which requires these variables. By plugging in the numbers, you can estimate the well's potential daily yield.
Understanding the Basics
Calculating water yield from a well involves understanding the relationship between the well’s depth, diameter, and the aquifer’s properties. The Thiem equation is a widely accepted method for estimating yield, which is based on Darcy’s Law. This equation requires the following variables: well diameter (D), static water level (s), aquifer transmissivity (T), and the distance from the well to the water table (b).
Applying the Thiem Equation
The Thiem equation is given by the formula: Q = (2.303 * T * A * (H-s)) / (D log(b/r)). Here, Q is the well yield, T is the transmissivity of the aquifer, A is the well’s cross-sectional area, H is the total head, s is the static water level, D is the well diameter, b is the distance from the well to the water table, and r is the well’s radius. To estimate transmissivity, you can use the Cooper-Jacob method, which involves measuring drawdown and distance from the well.
Case Study Example
A well with a diameter of 10 inches (0.25 meters) has a static water level at 50 feet (15.24 meters) and a total head of 100 feet (30.48 meters). The distance from the well to the water table is 200 feet (60.96 meters), and the aquifer’s transmissivity is 1000 ft^2/day (107.63 m^2/day). Using the Thiem equation, we can estimate the well’s yield. Assuming a well radius of 5 inches (0.125 meters) and a well cross-sectional area of 0.7854 square inches (0.00506 square meters), we can plug in the numbers to get an estimate of the well’s potential daily yield.
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