Instead of worrying about floods, water managers will be looking to maximize storage of what could be a very low runoff year in some of Colorado’s river basins
By Bob Berwyn
SUMMIT COUNTY — Even though it feels like winter is just getting started in the high country, Colorado water managers are starting to think about spring runoff, flooding and water storage.
Denver Water will issue its first spring reservoir outlook early next month after the March 1 snowpack figures have been compiled, and the National Weather Service this week issued its first outlook for flood potential.
No surprise, the spring runoff flood potential is slightly below average in the South Platte Basin, the Upper Colorado Basin and the North Platte Basin, including the headwaters tributaries in Grand, Jackson and Summit counties.
“It should be noted that it’s still early in the snow accumulation season and conditions could change before the runoff begins,” hydrologist Treste Huse wrote in the bulletin.
Flooding is not likely because the snowpack in the Upper Colorado Basin and the North Platte Basin is only at 91 percent of average for this time of year — the second and third-lowest readings for those basins in the last 25 years.
The South Platte snowpack is at 82 percent of average, thanks to a powerful early February storm that blasted the Front Range. The highest snowpack readings are in the northern Front Range mountains, at 90 percent of average in the Cache la Poudre Basin.
Even with a lower-than-average snowpack, some localized flooding is possible under certain conditions, for example a combination of a sudden and prolonged early heat wave and heavy rains.
Despite a snowpack that’s tracking on par with the drought year of 2002, reservoir storage levels are high, at 109 percent of average for the entire state and 119 percent of average for the Upper Colorado, or about 77 percent of capacity in the Upper Colorado storage system.
Streamflows in the Upper Colorado Basin are below average, but near normal in the South Platte Basin, while rivers in the North Platte system are subject to ice jam flooding, especially in Jackson County.
While a few isolated locations reported slightly above average snowfall in January, the month on the whole was drier than average, and temperatures ran anywhere from 2 to 10 degrees above average. During the first half of February, temps remained above normal west of the Continental Divide but cooled to slightly below average east of the Divide.
As a result, the mountain regions of Summit and Grand counties are showing as being in moderate drought on the U.S. Drought Monitor. The outlook is calling for cooler than average temps and above-normal precipitation for the next two weeks, but a return to warmer and drier than average conditions for the 30- and 90-day outlooks.
The story is similar to the west, where the outlook for the Yampa/White river system, the Green, Gunnison and Dolores and San Juan river basins are all expected to deliver below-average runoff.
According to the outlook from the Grand Junction NWS office, areas north of I-70 saw less than 50 percent of average precipitation through mid-February (though those numbers will change dramatically with the current round of storms).