Modified Parshall Flume, 9 in

A modified Parshall flume was designed by the USGS and is virtually the same as the Parshall flume except that it does not have a diverging section and is used only under free-flow conditions.

The modified Parshall flume is recommended for general use because of its simplicity, light weight, and ease of installation. A flume has an accuracy of 2-3 percent under free-flow conditions.

The flume is installed by placing it in a hole dug in the channel and by filling in around it to prevent any water from bypassing it. A bubble level is used to set the floor of the converging section level. After the flume is in place, the streamflow is allowed to stabilize before reading the gages. The flume is equipped with an attached stilling well for float, hook/point gage or transducer use or can be supplied with a side mounted staff gage. Gage readings indicate flow conditions. The discharge is determined by means of the flume rating table provided.