Gauge rating is the process of measuring the water discharge or flow at a particular point on a stream or river. There are many reasons why someone might take gauging measurements, such as implementing a long term study for ecological reasons, establishing a baseline to compare future data to, and studying trends for future growth, to name a few. Stream gauging measurements can be made using portable equipment or permanent monitoring stations. The stream gauging instruments used by water professionals don’t actually measure the flow of the stream, because making a direct measurement of flow is challenging. Instead they measure water velocity or level as a substitute and use a rating curve to calculate the actual stream gauge measurement.