Operators reduced flooding in face of record-breaking year

As the sun sets on the runoff season, we have plenty of new entries for the record books.

One of the most impressive: The flows in the Colorado River above Lake Granby from April through July produced 429,000 acre feet, far surpassing the previous all-time record from 1984, which was 355,000 acre feet.

Lake Granby spillway releases on June 22

Although it's been a great year for rebuilding our reserves, we aren't always thinking about C-BT solely in terms of storage. We also know that huge runoff numbers raise huge concerns for people who live downstream of Lake Granby.

Although C-BT is not a flood control project, we were able to operate it this year in a way that prevented damaging flows. The pre-emptive releases operators made kept the releases downstream at or below about 2,300 cfs. If we hadn't tweaked operations to create these sustained lower flows, the downstream channel would have at times quickly risen to about 3,900 cfs.

For more details on how Northern Water and Reclamation worked together to reduce flooding, read the recent Sky-Hi Daily News guest column by Northern Water General Manager Eric Wilkinson.

You won't see too many entries to this online update for a while, but as always, we're keeping an eye on what to expect during the next runoff season. Given the bounty of this year's snowpack, we can tell you that we don't expect it to be a low-flow kind of year ...

Looking ahead to extreme runoff

Even though it's called "forecasting," predicting runoff doesn't come with a crystal ball, in part because we cannot know Mother Nature's next move.

We do know now that we have record-setting snowpack in the high country. But we don't know exactly how that snowpack will translate into streamflow. A sudden heat wave or another soggy spring storm can alter the picture in unexpected ways.

Northern Water has a suite of tools to forecast water supplies. However, most of those tools were designed to predict total streamflow volume, or the total amount of water runoff will add to stored supplies. These models were not explicitly designed to predict or analyze flood flows. Similarly, Northern Water does not own or operate any facilities designed for the sole purpose of flood protection.

However, there are some other good places to look for flood flow information:

• The National Weather Service maintains models that predict flood flows. Their Advanced Hydrologic Prediction Service provides real-time information and, for a few locations, expected flow forecasts.
• Across the country, designated basin forecast centers provide detailed information about river flows. For areas west of the Continental Divide, the Colorado Basin River Forecast Center has a comprehensive website that details short-term forecasts, water supply forecasts and estimates of peak flow magnitudes and dates.
• For areas east of the Continental Divide, the Missouri River Forecast Center has a website that mostly duplicates the Advanced Hydrologic Prediction Service material. This week, the map on their home page has been lit up with flooding problems across the northern plains.

This 2011 Runoff Update site originally focused on the unusual runoff expected in Northern Water's West Slope watersheds. As the snow has piled on, we will also use this site to communicate runoff conditions on the East Slope.

Historically, Colorado flood events causing property damage and loss of life were the result of torrential rains and cloudbursts, not snowmelt. But with a record-setting snowpack still in place this week - a time by which most of our snow has normally melted - we can't afford to discount the possibility of damaging floodwaters.

Staying informed is one way to stay safe.