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 ...

Granby inflow beats all-time record

If you're into runoff-related recordkeeping, here's another one for the books. As of yesterday the total virgin inflow to Lake Granby was 379,000 acre feet. We expect that by the end of the month that number will top 400,000 acre feet.

The previous record was in 1984, with 355,000 acre feet coming in between April 1 and July 31.

Inflows to Willow Creek Reservoir are still running above average for this time of year, although we are noticing that the diurnal (daily) fluctuations are nearly gone. This is a sign that melting snow is no longer dominating the streamflow hydrology.

Granby outflows to decrease, elevation will rise

Engineers and operators have determined that an adequate amount of water has been released from Lake Granby, so we'll get back to filling the reservoir. We've kept the reservoir at lower levels to leave room for the finale of our forecasted runoff and to prevent the need for sudden large releases downstream.

We are going to decrease releases gradually, which limits environmental disruptions. We will cut flows back 200 cfs per day until we reach an outflow of 1,000 cfs, which will be early next week. Then we'll determine whether outflows should be reduced more.

With this reduction in releases, Lake Granby's elevation should begin to rise noticeably in the next week.

Record inflow on North Fork of Colorado River

Yesterday's flow of 995 cfs on the North Fork of the Colorado River broke an all-time record, according to records kept by the USGS since 1953.

The previous record was 976 cfs on June 30, 1957. As it turns out, we've been comparing this year's snowpack to 1957 for some time.

Our models suggest there's still plenty of gas in the tank in terms of snowpack, so record-level flows are likely to continue for another day or two.

The North Fork of the Colorado River discharges into Shadow Mountain Reservoir.

Weekend forecast: Peaking rivers, some records

A cocktail of increased temperatures on top of big snowpack may swell area rivers over the weekend. 

The Colorado Basin River Forecast Center recently put out a forecast expecting peaks on all of the high-elevation watersheds in their area this weekend. The center based its forecast on current cool temperatures, which have prevented snowmelt, along with predicted upcoming high temperatures that would kickstart more runoff.

If you had a bird's eye view, the CBRFC's forecast would have you seeing simultaneous peaks in several Upper Colorado basin rivers: the Fraser, Williams Fork, Upper Colorado into Granby, and Blue into Dillion.

The Colorado River at the Cameo gage (between De Beque and Palisade) may have its second peak, possibly higher than the one we saw June 7.

The center is most concerned about Northern Utah, Northwestern Colorado and Southwestern Wyoming. A few streams in Utah and Wyoming, for example, are expected to hit record flows. The forecast also stated that flooding is occurring and will likely continue to occur along rivers where there's still high-elevation snow.

The CBRFC does not forecast Northern Water's East Slope tributaries, but we expect the climate to have similar effects on our snowpack.

Willow Creek inflow record shattered, with more to come

After 57 years of tracking Willow Creek Reservoir stats, we've now hit an amazing new inflow record.

Some background: in the Western U.S., April through July are considered the snowmelt months, so official streamflow forecasts (and thus runoff records) are based on that four-month period.


Willow Creek Reservoir

Until now, Willow Creek Reservoir's inflow record was in 1986, when the April through July runoff totaled 85,600 acre feet, which is 168 percent of the official average of 50,800 acre feet. That sounded like a lot until yesterday, when we tabulated the inflow since April 1 as 87,100 acre feet. And we still have six weeks to go! 

Our latest forecast anticipated a total of 110,000 acre feet of inflow to Willow Creek by July 31. If it materializes, this would be 216 percent of the official average. And the Colorado Basin River Forecast Center expects even more than we do. 

The peak inflow rate (in daily average) this year was 1,652 cfs on June 7. This wasn't quite a record, but anything more than 1,500 cfs is notable for Willow Creek. This date of peak inflow was about two weeks later than usual (about May 24); late peaks often come hand-in-hand with larger-than-normal snowpacks.

This staggering runoff quantity raises questions about what kind of runoff we should expect from neighboring watersheds - especially above Lake Granby. While we don't expect as high an inflow to Granby, our latest forecast anticipates 175 percent of average, which would be another one for the record books.

It's disconcerting to drive past Granby, which is 20 feet below full, and see the surrounding dry sagebrush - if you know how high snowpack is in Rocky Mountain National Park and along the Gore Range.

That snowpack may seem remote and unassuming, but looks are deceiving. Stay tuned.

Too soon to say that rivers have peaked

There has been much in the news this week about our rivers being past their peak flows for the season.

Not so fast!

The high elevation portions of our watersheds melted next to nothing during the month of May. They're just now getting started. While temperatures may continue to play nice, there's every chance that a couple of days of warmth could cause surprise surges in streamflow.

Don't believe us? Take a look at the 1957 hydrographs - a year with a giant snowpack (but not as big as this year's) and a cold May. That year, the peak runoff didn't happen until the very end of June. Here's Middle Boulder Creek at Nederland as an example.

BODMIDCO - this year (red) vs. 1957 (green)

Adams Tunnel diversions decreasing

When we expect gigantic runoff, we prefer to keep the Adams Tunnel running full blast, because every acre foot diverted to the East Slope creates room for another acre foot of runoff. With that, we lower the possibility of having to make higher releases out of Lake Granby.

But we have two things working against us. First, East Slope reservoirs are nearly full, and soon we won't have empty space available for Adams Tunnel diversions.

Second, the water rights system limits our options. Northern Water holds decrees for Big Thompson River water, and when those rights come into priority, we are obligated to use that water, not West Slope water, to fill our East Slope reservoirs and make water deliveries.

Yesterday our East Slope decree came into priority and operators reduced tunnel diversions by 40 cfs. Today, even more East Slope water became available and tunnel diversions went down an additional 125 cfs.

The amount of East Slope water available to our decree varies from day to day and depends on streamflow and other water users' demands. To keep up to date, you can monitor Adams Tunnel diversions as we move through the warm season.



Adams Tunnel diversions, last 10 days





Willow Creek backing off after three near-record peaks

The past several days have brought three peak events on Willow Creek: 1,748 cfs on May 30 and again on June 3, and 1,761 cfs on June 8.

But it's not over yet. The snowpack at the top of Willow Creek Pass normally peaks in late April, but it's the beginning of June and we still have more snow up there than the average peak, despite the fact it's been melting. The forecast calls for cooler weather, which means snowpack will continue to melt - but at a slower, much more manageable rate. Flows are retreating today and will likely hold steady or decline slightly in the next few days. But keep an eye on the skies and thermometers: We are still vulnerable to additional peaking events if there's a rainstorm or stretch of hot weather.

Our records show that the maximum observed inflow to Willow Creek Reservoir was a daily average of 1,857 cfs on May 24, 1984. In comparison, this year's three peak flow rates occurred for just a few minutes each; our maximum daily average for 2011 so far was yesterday at 1,652 cfs.

So while we don't have a flow rate that's going into the record books, we're still on track to smash the previous record for the total volume of runoff: 85,300 acre feet from April 1 to July 31 in 1957. This year's inflows are already 64,600 acre feet, and we still have seven weeks to go!

As the elevation in Willow Creek Reservoir continues to rise, we will pump water into Lake Granby if necessary to help keep Willow Creek Reservoir outflows at or below 1,300 cfs.



Inflows to Willow Creek Reservoir



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.

May 1 forecast brings increased runoff expectations

Northern Water released its May streamflow forecast last week. The May 1 snowpack breaks records for the Blue River, Upper Colorado, Willow Creek, Cache la Poudre and Big Thompson basins. And it's not just in our area - many SNOTEL sites across the Western U.S. broke records for snow water equivalent accumulation this year.

The first SNOTEL stations were established 30 years ago; hydrologically speaking, that's not a very long period of record. So although this year's record snowpack is notable, should we consider it exceptional?

We might want to consider it. A much longer-standing record has been smashed too: the Snow Course at Cameron Pass, which has been around since 1936. The chart here shows the May 1 snow water equivalent, which has 17 percent more water than the previous record (1986)!

However, a record-breaking snowpack doesn't necessarily translate into record-breaking runoff, especially in Northern Water's East Slope watersheds. We need precipitation on top of melting snow to break those records. Still, two of our West Slope basins, the Upper Colorado and Willow Creek, are expected to produce record-breaking runoff this year from snowmelt alone.

Warm weather triggers increased snowmelt

Warm weekend temperatures increased the inflow to Willow Creek Reservoir. Right now we are holding the reservoir's elevation steady at around 8,092 feet and passing inflows right through. The highest release so far this year was 782 cfs at 9:45 this morning.

Releases from Lake Granby are holding steady at about 400 cfs. Below the dam at Lake Granby there are small side tributaries that add to the flow of the river, so flows can be higher by the time they reach the "Y Gage" (listed as "Colorado River near Granby, CO" on the USGS website). Saturday evening was a good example: the flows were at 600 cfs, so the tributaries likely contributed about 200 cfs. The flow has not been as high since then.

The schematic shown with this post shows the various stream gages below Willow Creek Reservoir and Lake Granby. The releases from Granby and Willow Creek reservoirs, along with the flow of the Fraser River, all add to the Colorado River's flow as measured below Windy Gap Reservoir. Today, that flow went above 2,000 cfs for the first time this year. The flows are affected by Denver Water's diversions; they aren't diverting much Fraser River water right now because it has been so cold. 

News coverage: April 13 meeting, water year

The Sky-Hi Daily News ran an article about government agencies' preparation for the 2011 runoff season. Check out the article to learn more about what's going on the Grand County area.

The article mentions our April 13 meeting in Granby, which we highly encourage you to attend if you're interested in the forecast and related project operations. It's at 6 p.m. at the Granby Library, 55 Zero Street.

Join us: Runoff season meeting April 13 in Granby

Want to learn more about the 2011 runoff season? Join Northern Water and Reclamation at a public meeting, 6 p.m. Wednesday, April 13 at the Granby Library, 55 Zero Street, in the Community Meeting Room.

Granby Library, from gcld.org

We'll share forecasted runoff and streamflows for spring and summer, along with potential operational changes to the Colorado-Big Thompson and other projects. We'll also answer questions you may have about what to expect this season.

Although inflows are a moving target, we will be working to provide the public with as much information as we can, as soon as we can, during this meeting and throughout the season.

It could be an epic year

Northern Water published its April streamflow forecast today. We expect the flows to be even higher than what we projected a month ago - so high that some of us are using words like "epic" to describe the West Slope snowpack.

Many of our forecasting tools are struggling because of a lack of a key type of data: comparable years. Our forecasters look at similar water years to estimate what kind of runoff to expect, and for many of the basins Northern Water monitors, we have less than a handful of "comparables" available to analyze.

For example, Willow Creek only has one year on SNOTEL record that compares to this year: 1986. That year the seasonal runoff (April through July) on Willow Creek was 85,600 acre feet - 170 percent of average. This year we're not far behind with an anticipated runoff that's 160 percent of average.

The Colorado River Basin Forecast Center has a nice tool for following this year's snowpack and how it matches up to 1986. We're less than an inch away from a record snowpack for Willow Creek ... and the National Weather Service is calling for more snow later this week!

Willow Creek to stay steady for now

Operators cut back releases from Willow Creek Reservoir early yesterday and now the reservoir's elevation is at 8,117 feet.

For now we plan to adjust the release rate as needed to maintain this elevation, so you can expect to see it there until May, when runoff starts getting heavy.

And so we begin...

Many of our mountain-area stream gages are frozen or too hard to get to, which makes it difficult to spot the first signs of spring snowmelt.

However, one of our favorite year-round gages has started to show sure signs of melting snow: the gage on Middle Boulder Creek at Nederland.

You can see from the gage image here that the jagged, mostly flatlined trace gave way to a wave-like and up-trending pattern in recent days. Warm daytime temperatures and cold nighttime temperatures create the cyclical pattern. This is the unmistakable signature of snowmelt in the mountains.

And so we begin.

Last throes of winter

While college students enjoy spring break skiing, water resources managers are watching for the first signs of spring runoff.

Upper Colorado SnoWatch page

Runoff follows a predictable sequence. Our low-elevation SNOTEL sites reach their peak accumulation and start to melt during the last week of March, while our highest-elevation sites continue accumulating snow until the first week of May. Willow Creek Reservoir receives its highest inflow during the last week of May, but our other watersheds typically peak during the first week of June.

Our West Slope watersheds start to show snowmelt at least a couple of weeks before our East Slope watersheds. This is counterintuitive since the West Slope watersheds are at a higher elevation. But solar radiation is a big driver of snowmelt activity, and West Slope watersheds have more southerly and westerly exposures than the East Slope.

Examples of low-elevation sites to watch are Stillwater Creek and Phantom Valley, both located in watersheds tributary to Lake Granby. Our Upper Colorado SnoWatch page tracks the action if you want to see it for yourself.

Northern Water forecast: Above-average runoff

Northern Water issued its second 2011 streamflow forecast on March 7. It anticipates above-average seasonal runoff throughout our district collection and service areas. This is in stark contrast to the dry conditions on the eastern plains.

We compute forecasts for eight basins, all of which either directly supply the C-BT and/or Windy Gap projects or provide native water supplies for Northern Water constituents. Updated forecasts will be published in April and May.

We began developing our streamflow forecasting program in 1999. At first, our forecasting tools were used to provide estimates of supply and demand to the Board as they set the quota allocation in April each year. Now, using customized technologies and tools we developed in-house, we also compute short-term streamflow forecasts to support operational decision-making for our West Slope Collection System.