KNOW YOUR STREAMFLOW: River discharge

Discharge… such an impersonal and flatly technical term for something so dynamic. It’s really just a description of how much water flows in a channel. 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 something that you as a river lover should know about?

Boaters look at discharge to see if there’s enough water to float, anglers 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 as expected. Beyond that, discharge tells the unique story of a river and how it changes as it flows downhill.

In the graph above, 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 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 Uncompahgre 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. Source: USGS