Define drawdown and explain its significance for well yield testing.

• A. Drawdown is the rise in water level during pumping; it indicates aquifer response and helps determine sustainable yield.
• B. Drawdown is the dropping water level during pumping; it indicates aquifer response and helps determine sustainable yield.
• C. Drawdown is the total water pumped per day.
• D. Drawdown is the sediment loading in the pumped water.

Answer: (B)

Drawdown is the decline in the water level inside a well while pumping occurs. It is measured as the difference between the static water level (before pumping) and the pumped water level. This drop shows how the aquifer responds to withdrawal at a given rate: a larger drawdown means the aquifer is less able to replenish water quickly (lower transmissivity or storage effects), while a smaller drawdown indicates a more responsive aquifer. In well yield testing, the drawdown over time is used to infer aquifer properties such as transmissivity and storativity, to gauge sustainable yield, and to evaluate the well’s performance and any potential interference with nearby wells. Remember, drawdown is about the water level drop during pumping, not the total volume pumped or sediment in the water.