How does hydrometry measure precipitation and streamflow?

In hydrologic sciences, hydrometry is the discipline dedicated to the measurement of surface water, specifically precipitation and streamflow.1

Measuring Precipitation

Direct measurements are primarily conducted using various rain gauges, which use funnels to direct water into storage containers.2
* Storage gauges collect total precipitation over set intervals.2
* Recording gauges allow for the determination of precipitation rates.2
* Ground-level gauges are considered the most accurate, as they minimize wind and splash effects.2

For snowfall, techniques include measuring depth with stakes, weighing samples to determine density, using snow pillows to record weight, or employing heated gauges. Indirectly, radar scattering is used to estimate spatial distribution and intensity, often calibrated against gauge data.2

Measuring Streamflow

Streamflow, or discharge, is typically measured at a gauging station. Common methods include:3
* Velocity-Area Method: Multiplying flow velocity (measured via current meters or ultrasonic sounding) by the cross-sectional area.4
* Tracer Dilution: Estimating total discharge based on the dilution of a tracer.4
* Weirs: Using structures that create a unique relationship between upstream water level and discharge.4

Continuous records of water levels are often maintained using float recorders to construct a stream hydrograph.4