To measure discharge, the stream's cross-sectional area must be determined as well as the average velocity. This can be challenging.

Fortunately, discharge can be estimated with a reasonable degree of accuracy from a stream's STAGE value. That's the elevation of the stream's surface above some permanent reference mark.

There are a number of different types of Gage Houses.

Some gage houses record the stream's stage using a "STILLING" well.

Here a "float" in the well below the gage house is attached to a recording device.

Another type of gage house uses a "pressure transducer" placed in the stream to estimate the water depth.

A gage house can be set up to automatically transmit a stream's stage to a place such as the United States Geological Survey via satellite.