A snowy winter in Southwest Colorado has caused some concern among water managers about snow runoff inflow this spring and summer at Vallecito Reservoir. The Bureau of Reclamation and Pine River Irrigation District are taking precautions to mitigate the above-average runoff.
Last winter, a U.S. Department of Agriculture SNOTEL site above Vallecito Reservoir measured the snowpack at 170% and 180% of normal. The SNOTEL reported around 202 inches when the snowpack was at its peak with a snowpack of 34 inches as of Tuesday.
With a capacity of only 125,440 acre-feet, the Bureau of Reclamation expects an inflow of 255,000 acre feet from this year’s remaining snow runoff, which is around 144% above normal.
Bureau of Reclamation Hydraulic Engineer Susan Behery said the average runoff inflow as of late April was 950 cubic feet per second with it reaching 1,400 cfs on May 1.
In most years, the reservoir experiences a snow runoff inflow of around 177,000 acre feet which means normally the dam must release a little over 50,000 acre feet of water to accommodate the inflow. However, this year it will have to take on a much greater volume of runoff.
“We don’t want to go into high runoff and have a full reservoir. We want to kind of create enough space in the reservoir to be able to capture that and then release things downstream and not cause any concern about flooding and release at a manageable level,” said Reece Carpenter, resource division manager for the Bureau of Reclamation.
Based on the weather forecast and estimates made by hydrologists, the bureau of reclamation decides how much water to release to prevent overflow.
“Right now the dam is releasing 800 cfs and it is 31% full. There is 84,500 acre-feet of available space,” Behery said.
PRID has been releasing around 700 to 800 cfs per week since late March.
The Bureau of Reclamation does not monitor the yearly average of water released from reservoirs during the snow runoff season, Behery said.
“If the reservoir is full going into a season they’d have to make room in a poor snowpack year, just like they are doing now,” she said.
In an op-ed published in April by Writers on the Range, Pine River Irrigation District Superintendent and Reservoir Manager Ken Beck expressed concern about the runoff and the inability to use spillways because the dam was in need of repairs.
Beck declined to comment for this story.
Carpenter said the dam is not at risk of failing. He said during a routine inspection water was found seeping to the spillway floor.
A spillway is a structure used to provide controlled release of water downstream from a dam. Concerns over the spillway seepage has forced the bureau to take alternative measures and pass water through the outlet works to minimize use of the spillway.
“Reclamation is in the process of gathering more information about the cause of the seepage and determining the best course of action to ensure that dam’s risks are not outside Reclamation’s public protection guidelines,” Carpenter said.
Outlet works is a closed conduit under or through a dam, or through an abutment that controls discharge of the water behind a dam.
Reclamation has also taken temporary measures, such as sealing cracks in the spillway floor, but the dam is still under review for repairs.
Carpenter said it is not unusual to see this type of wear and tear on dams that are old.
The 82-year-old reservoir is known for its outdoor recreation use such as camping, fishing and boating. But more importantly, it stores water for Bayfield as well as providing supplemental irrigation for 65,000 acres of tribal and nontribal land to the south.
In addition to irrigation, the dam also prevents the flooding of crops, farmland and structures along the Pine River.
It is important that the dam doesn’t release too much water to accommodate the runoff because PRID must ensure it has enough water for the irrigation season. Behery said irrigation demands depend on the year but would typically be around 150,000 to 200,000 acre feet.
If spring rain showers come, measuring water inflow and release can fluctuate.
“Reclamation coordinates with the National Weather Service and the Colorado River Basin Forecast Center, which are both government agencies within NOAA (National Oceanic and Atmospheric Administration) on weather and streamflow forecasts and will advise PRID on making changes to their releases to avoid any problems,” Behery said.
National Weather Service Meteorologist Scott Stearns said nowhere near Durango or Bayfield is considered a flood hazard by NWS, and that the lower reaches of the Dolores River is the only place in Southwest Colorado currently being monitored for floods.
Lemon Reservoir is supposed to experience a snow runoff of around 160% of normal. Behery said this equates to about 76,000 acre-feet of inflow. The Florida Water Conservancy District has been releasing water from the dam at a rate of around 200 cubic feet per second.
“I think releases will be pretty normal,” Behery said. “It’s not going to be as dramatic as folks might see at Vallecito.”
The amount of water received this year has allowed the Florida Water Conservancy District to complete a flush on the reservoir, which hasn’t happened in a few years. Most reservoir operators conduct a flush at the beginning of the year to remove debris and sediment.
“Vallecito is a very small reservoir for the size of its basin, so it takes much less water to fill whereas Lemon is a very large reservoir for the size of its basin, so even in a big year, it’s not quite as dramatic of a situation typically,” Behery said.
tbrown@durangoherald.com
