Predicting runoff, managing spill is not an exact science

Predicting runoff, managing spill is not an exact science, BuRec explains

May 26, 2001

By Jim Mimiaga
Journal Staff Writer

Fifty Dolores River users listened to a lecture Thursday night on the minutiae of how water officials determine whether a rafting release from McPhee reservoir is feasible.

The meeting was called in response to public inquiries on why no spill is scheduled this year on the lower Dolores River, despite a near-normal winter.

Because of a drought last summer and consequent heavy irrigation demand, this year McPhee is predicted to be short of filling; therefore, no rafting season is likely below the dam, reported managers of the Dolores Water Conservancy District.

"We wanted to get the information out to the public as to why, although it is not an exact science," said Vern Harrell of the Bureau of Reclamation, adding that, in the end, the results are contingent on the whims of Mother Nature.

Trying to predict snowpack, along with innumerable other variables such as soil conditions, wind, temperature and irrigation demand, is a constant challenge, said Roland Springer, a Dolores River analyst with the Bureau.

"It can be off substantially, because climate forecasting is a crapshoot," he said.

To improve accuracy, reservoir managers recently convinced the National Weather Service to predict conditions in the Dolores Valley twice per month, data that is then inserted into the runoff models. A separate, "unofficial" model was created by an independent contractor for the District and is compared to the "official" Bureau forecast as a back-up tool.

The constantly updated spill-prediction information is automatically e-mailed to river users by the DWCD.

Regression formulas, "spaghetti graphs," statistical models, forecast methodology and "The Rock" were explained in depth by analysts with the BOR, DWCD and the Bureau of Land Management.

"We do the best we can with the data collected, both current and historical," Harrell said. "It is not done in a vacuum or in secret; all of this data is available to the public."

Scientific information is also judged against visual aids in the high mountains. A rock outcropping on the snowfields in the La Plata Mountains helps to determine the amount of snowpack remaining when compared to previous years and those runoff results.

Data is then charted on a predicted operations plan indicating whether water will be left over after expected irrigation demand is factored in. If there is a spill, it is managed to occur sometime between April and June. Last year rafters enjoyed a 28-day season.

Rick Ryan, the BLM Dolores River ranger, explained that spills are managed at a minimum of 800 cubic feet per second, released for the longest period possible.

The level is the lowest amount that a raft, loaded with gear for the three- to five-day run from Slickrock to Bedrock, can reasonably negotiate.

Boaters expressed general appreciation for improved forecasting techniques and communication with the boating community, and they had suggestions.

If there was not enough spill for the 800 cfs, one boater suggested that a "low flow" release occur if possible for rafting benefit. Kayakers and canoers typically require between 300 and 400 cfs to run the river.

Tom Klema, a commercial river outfitter, said his business needs more advanced notice of spills in order to book clients wanting multi-day trips on the Dolores. He was critical of the district’s forecasting technique.

"There is too much effort to pinpoint exactly how much runoff will occur," he said. "What happens with that mentality is that there is no room for error, so like in 1999, it was predicted there would not be a spill, but then there was one."

The district is fond of pointing out that a cloud seeding program benefits rafters by coaxing moisture to fall from clouds during dry years. But audience member Kevin Craig, a hydro-ecologist, said cloud seeding results are unscientific because there is no way to prove that the snow would not have fallen without the technique, which uses silver iodide delivered from the ground as a catalyst.

It was also suggested that more sno-tels — devices relied on for measuring snowpack — be installed throughout the basin to account for variances in snowpack levels.

While the lower Dolores is not raftable, the upper reach of the river is a raging torrent of snowmelt moving at 1,970 cfs. Kayaking and rafting conditions are ideal beginning upstream from the Stapleton Bridge to McPhee reservoir at Dolores, with rapids rated at a class 2 or 3. A longer, more technical stretch from below Rico is also navigable for experts, officials said.

For more information on the Dolores call the Dolores Water Conservancy District at 565-7562, or check out their informative website at doloreswater.com.