Discharge is the volume of water that passes a point during a given period of time. Discharge is calculated by multiplying the water's velocity times the channel's area. Most commonly, river discharge is reported in cubic feet per second.
We use a Marsh-McBirney Portable Flow Meter®, a Sontek Flowtracker Handheld - ADV®, a Sontek Agronaut® and a Rivercat Doppler Profiler® to measure stream velocities at our monitoring stations. During low flow, we typically use instruments attached to wading rods to measure velocities across the stream's cross section; during high flow events, we either set drag lines to pull instruments across the stream or suspend instruments from bridges to measure velocities across the stream's cross section.
To estimate discharge for long periods of time, we develop stage rating discharge curves at our monitoring stations. Two parameters are necessary to create the stage rating discharge curve.
First, it is necessary to continually measure stream depth (stage). We set out to measure stage every thirty minutes during our project periods.
Second, an adequate amount of velocity measurements and discharge calculations at numerous stream depths are needed.
We correlate discharge estimations to various stages, and develop a stage rating discharge curve. The model allows the extrapolation of discharge for long periods of time at many stages.
Equilibrium uses discharge measurements and water quality sample concentrations to aid in estimating parameter loadings.
