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 releases decreasing starting today

Our “second spill” from Lake Granby will be drawing to a close in the coming days. Last week’s monsoonal storms created some significant inflows to the system, causing us to increase and prolong our spill from what had been expected.

The diurnal (daily) snowmelt patterns are fading away. Notice on the North Inlet gage that the cyclic pattern is starting to flatten out. That means that the snow is nearly gone.

We will hold Lake Granby at elevation 8278.50 feet (that’s one foot below the operational full level) for a few days longer, just to ensure that we have space to store another rain event. After all, the monsoon pattern could shift back to the west in the coming days and weeks.



2011 spill releases from Lake Granby



Increased releases from Lake Granby

A series of rain events this week has filled Lake Granby faster than we would have liked. Therefore, as of this morning, releases from Lake Granby have been increased from 1,900 cfs to 2,200 cfs.

We will stay at this release rate through the weekend and re-evaluate on Monday. More precipitation could change the plan, so we’ll be watching the skies. We still have space in the reservoir, but we want to preserve as much space as we can in the event that Mother Nature continues to pile on more precipitation.

Changes at WIllow Creek Reservoir and Lake Granby

Northern Water has determined it is time to initiate the second spill operation this season at Lake Granby. Outlet releases are being increased throughout today until outflows reach 1,500 cfs. We will maintain this release until at least next Monday. We are watching the skies this week – rainstorms are in the forecast and a significant rainfall event might prompt us to boost outflows even more.

At Willow Creek Reservoir, our West Slope operators will allow the reservoir elevation to rise to 8,129 feet this week. The high runoff this year generated a lot of debris which is now floating on the surface of the reservoir. The operators will adjust both the river outlet works and the gates on the pump canal. Prevailing winds should then help force the debris to move to the northeast corner of the reservoir where it can be removed. Once this operation is complete, the reservoir will be returned to its normal operating elevation of 8124 feet.

Granby Dam spillway water to taper off

We're continuing to reduce releases from Lake Granby this week. By Friday, water will no longer be going over the spillway; releases will only be coming out of the valves, which is where we normally make releases. We'll have 430 cfs coming out of the valves until re-evaluating the situation next week.

This spill was successful because it evacuated enough water so we could capture the peak inflow to the reservoir.

We expect to have a second spill as the reservoir approaches full capacity. It will be shorter and involve less water over the spillway. Operating the dam this way will allow us to gently fill the reservoir to the top while preventing the need to make large releases below the dam.

Willow Creek Reservoir elevation: Back to normal

After a couple of months of looking pretty low, Willow Creek Reservoir's elevation will start looking up.

The reservoir's elevation will start to rise in the next few days as we go back to more normal operations for this time of year. The elevation has been lower than the seasonal average because of releases, which since April 1 have equaled more than 106,300 acre feet - nearly two and a half times the amount that normally flows in.

In a typical year, Willow Creek's pump plant moves reservoir water to Lake Granby. But in this wet year, we knew Lake Granby wouldn't have room for that water, so we let it simply pass through Willow Creek Reservoir. There was so much Willow Creek water passing through that we had to keep the reservoir elevation much lower than usual so we could be prepared for heavier runoff peaks and help protect the channel downstream.

Now that the runoff is tapering, the risk of peaking events is significantly reduced and we feel comfortable letting Willow Creek Reservoir go back to its normal elevation. Over the next few days, it will gradually rise to 8,124 feet - about nine feet higher than it is today.

During this fill period, flows below the reservoir will be reduced, but once the reservoir reaches elevation, we will start passing inflows again.

This chart shows how Willow Creek inflows (red) compare to outflows (green) this year:



2011 Willow Creek Reservoir inflows (red) and outflows (green)



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.

Granby releases to increase today

Spillway at Lake Granby as seen from below

The elevation of Lake Granby is now above the spillway elevation of 8,260 feet. Currently, the radial gates at the top of the spillway are closed, preventing water from flowing down the spillway. This morning, Northern Water’s West Slope operators will open the gates and water will start flowing down the spillway for the first time in 11 years. At first, the outflows will be rather small, on the order of 100 cfs or less. But as Lake Granby continues to fill, more and more water will flow down the spillway.
The increases in outflows will be evident at the downstream USGS gage.

Note that releases from the outlet valves will continue at approximately 410 cfs. The combined release from the valves and from the spillway will be approximately 500 cfs.

Testing may increase Willow Creek releases

Willow Creek releases may be incrementally increased over the next few days for the purpose of testing safe channel capacity below the reservoir.

Northern Water is coordinating closely with area property owners. If you have questions, please contact Noble Underbrink at the Farr Pump Plant at 970-627-3406.

Make your own streamflow dashboard page

Would you like to be able to see all of your favorite streamflow gages on one page? Colorado's Division of Water Resources has a Web page that allows you to do just that.

Here are step-by-step instructions for creating your own Northern Water Gage Page.

1. Go to this link and click on the "My Stations" link at the bottom right.

2. Select stations of interest and, one by one, move them from the left side ("Available") box to the right side ("Current Station List") box. Here's a list of stations to get you started. This list will allow you to watch key canyon gages on the East Slope and key collection system flows on the West Slope:

ADATUNCO, ALVA B. ADAMS TUNNEL AT EAST PORTAL NEAR ESTES PARK
BOCOROCO, BOULDER CREEK NEAR ORODELL
SVCLYOCO, SAINT VRAIN CREEK AT LYONS, CO
BTABESCO, BIG THOMPSON RIVER ABOVE LAKE ESTES
BTCANYCO, BIG THOMPSON RIVER AT MOUTH OF CANYON NEAR DRAKE
CLAFTCCO, CACHE LA POUDRE AT CANYON MOUTH NEAR FORT COLLINS
CLANSECO, NORTH FORK CACHE LA POUDRE RIVER BELOW SEAMAN RESERVOIR
COLNGBCO, COLORADO RIVER NEAR GRANBY
COLBAKCO, COLORADO R BELOW BAKER GULCH, NR GRAND LAKE, CO
FRAGRACO, FRASER RIVER AT GRANBY, CO
COLAWICO, COLORADO RIVER AT WINDY GAP, NEAR GRANBY, CO
WILABVCO, WILLOW CREEK ABOVE WILLOW CREEK RESERVOIR
WILWCRCO, WILLOW CREEK BELOW WILLOW CREEK RESERVOIR

3. If you want the list to be in a particular order, use the arrow buttons to sort.

4. After you've populated your Current Station List and sorted it, enter a name in the box at the bottom of the screen (you can keep the name "My Stations" if you like) and click "Save."

5. After you save the list, a "Current Conditions" page appears. This is a list of all of your stations with the current values. Bookmark this page!

6. Click on the "Graph(s)" tab to see 10-day graphs for all of your gages.

7. Add or remove gages any time by going to the "Edit List" tab. Remember to save your changes.

Thank you, DWR - this is a great tool!

Morning spike in Willow Creek releases

Operators tested the outlet works at Willow Creek Reservoir this morning. They initially released 900 cfs and then went up to 1,200 cfs for a brief period. This was a test to check operations for the releases we anticipate making. It was successful, and we're back to passing inflows.

The graph here shows the spike in flow that occurred this morning.

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. 

Granby releases increase Friday

Beginning at 8 a.m. Friday, outflow from Lake Granby will increase by 50 cfs every two hours until outflow reaches 430 cfs in the late afternoon.

The flow of 430 cfs will be maintained indefinitely. It is the maximum that operators can release out of the valves that sit toward the bottom of Granby. If more water needs to be released, it will come down the spillway at the top of the reservoir, but only after the reservoir rises to the spillway's elevation.

The Colorado Basin River Forecast Center is predicting inflow to Lake Granby to be the largest on record. Northern Water's models agree.

Releases from Willow Creek Reservoir going up

Inflows to Willow Creek Reservoir are on the rise, which means runoff is underway. Reservoir operators determined that we need more empty space in the reservoir to capture and dampen the peaking flows.

To do this, operators started increasing releases out of Willow Creek Reservoir today, and by later this afternoon they will be at 230 cfs. They will continue increasing releases tomorrow until they reach a rate of 330 cfs.

Plans are to lower the reservoir, which is at 8,117 feet in elevation now, to 8,092 feet.

Lake Granby releases increase starting tonight

The April 1 forecasts (the latest available) are indicating a greater inflow to Lake Granby this year than forecasters previously expected. Accordingly, operators are going to make a pre-emptive release of stored water in Lake Granby. Pre-emptive releases help operators balance inflows into a reservoir with the flows going out, and they can curb the need to ramp up releases at faster rates.

Outflow from the reservoir will increase from the current 20 cfs to 80 cfs this evening. Additional increases are scheduled through this week until a rate of 200 cfs is reached; that rate will continue until further notice.