Which term refers to the water level measurement in a stilling well?

The term that accurately refers to the water level measurement in a stilling well is depth measurement. A stilling well is a structure used to stabilize water levels for accurate measurement, ensuring that water movement from surface turbulence or external disturbances does not affect the readings.

In this setting, depth measurement specifically indicates how deep the water is within the stilling well, providing precise data about water level changes over time. This information is essential for various applications, including monitoring water quality, flow rates, and assessing the overall health of a water body.

The other terms mentioned refer to different concepts that do not align with the primary function of a stilling well. Surface tension measurement pertains to the forces acting at the surface of liquids, hydraulic head measurement indicates the potential energy of water in a certain point relative to a reference point, and flow velocity measurement assesses how fast the water is moving, which does not reflect the water level directly within a stilling well. Depth measurement is about determining how high water reaches within the stilling well itself, making it the correct term in this context.