Know Your Watershed: River Discharge as a Way of Describing Streamflow
Discharge… such an impersonal and flatly technical term for something so dynamic. It’s really just a description of water flowing in a channel, how much at any one moment to be precise. Flow expressed in cfs or cubic feet per second over a period of time can teach you a lot about a river from how it swells during spring runoff to how it shrinks during winter’s cold.
Why is discharge one of those things you as a river-lover should know about?
Boaters look at discharge to see if there’s enough water to float, fisherman look for lower calmer flows signaling clearer water. Irrigators look for adequate cfs to make their complex system of water rights, diversions, and head gates work the way they are supposed to. But beyond that, discharge tells the unique story of a river and how it changes as it flows downhill.
In this graph below, the red line shows the Uncompahgre’s flow in Ouray, revealing a smaller river with less flow that’s subject to sudden swings from daily snowmelt dynamics or summer rainstorms. By the time the river reaches Ridgway, the flow shown in green, has increased and moderated, with the addition of Cutler, Dexter, and Corbett Creeks and the effects of agricultural diversions and return flows. Below Ridgway Reservoir, the blue line reflects the dam operator’s control over when and how much water is released into the river, eliminating the daily ebbs and flows and replacing them with uniform flows that change abruptly. While the peak flow from spring runoff is in May or June, the summer monsoon season typically brings lesser peaks from late June to late July.
USGS stream gage data showing discharge for the 2022 water year along the Uncompahgre River measured in cubic feet per second. Red line: Ouray gage, green line: Ridgway gage, blue line: gage below Ridgway Reservoir. Link to gage data
