Murky Shadow indicates clarity problems
November 1, 2013
GRAND LAKE – This summer's six week stop-pump benefited clarity in Grand Lake, but had bad consequences for water quality in Shadow Mountain Reservoir.
Water quality managers have confirmed what locals and summer recreaters at Shadow Mountain reservoir suspected as they gazed at its murky green waters.
The Farr Pumping Plant's shutdown from July to early September created the worse algae bloom seen in years. It's a highly visible indicator of the looming challenges in finding a solution to Grand County's West Slope water collection system, which moves Colorado River Water through Lake Granby, Shadow Mountain and Grand Lake to the Front Range. This summer's algae growth was a result of the trade-off between clarity in Grand Lake and quality in its adjoining reservoir.
"If there's any take-home message from what we saw, it's that what was beneficial to Grand Lake was not beneficial to Shadow Mountain," said Esther Vincent, water quality manager with Northern Water Conservancy District.
According to Vincent, Shadow Mountain's algae bloom was even worse than the glop seen in 2007, which followed a drawdown of the reservoir after chronic aquatic weed issues. In 2006, water managers drained Shadow Mountain low enough to expose and freeze weeds. But once it refilled, organic material became suspended in the water column and became food for a massive bloom of the slimy green organisms.
"That was one of the water quality events that triggered lots of interest from local stakeholders in water quality in Three Lakes and in Grand Lake," Vincent said.
Starting in 2008, those stakeholders worked with the Bureau of Reclamation to experiment with pumping suspensions at Lake Granby. They then evaluated its effects on clarity in Shadow Mountain and Grand Lake. In 2008 and 2009, the stop-pumping lasted around two weeks. An unusually high runoff season and low Front Range demand resulted in a long shutdown of the pumps in 2011, lasting from late May to early September. In all cases, water clarity in Grand Lake noticeably improved. But in Shadow Mountain, results were mixed.
"That's typical of the unintended consequences," said Grand County Manager Lurline Underbrink-Curran. "Shadow Mountain is always algae and weed-laden, but the stop pump gives it more time to grow."
Grand County, local water managers and the Bureau of Reclamation have long explored options for improving Grand Lake's water clarity. The natural lake's water becomes compromised each summer as water moves up from Lake Granby, through Shadow Mountain, into Grand Lake and under the Continental Divide as part of the Colorado-Big Thompson water collection system.
A Bureau of Reclamation Grand Lake Water Clarity Technical Review and Work Plan, released Monday, Oct. 28, identified gaps in researchers' understanding about water quality issues in the Three Lakes system. The plan called water quality in Shadow Mountain an important secondary consideration in controlling clarity levels in Grand Lake. The two water bodies are linked, and there's a possibility poor water quality in the reservoir could outweigh clarity benefits in the lake.
Over the last few years, the Bureau of Reclamation, Grand County, Northern Water and other stakeholders have identified a gamut of options for addressing clarity issues in Grand Lake. Structural changes could include completely bypassing Grand Lake and Shadow Mountain with a new system, installing oxygenation equipment at Shadow Mountain or dredging the reservoir to make it deeper. Non-structural changes could involve a continuation of the stop-pumping process, pumping water at a more steady flow, or doing nothing at all.
Before any of these options can be put into action, the plan developed a 10-task timeline to fill informational holes and aid in the selection of a Grand Lake clarity solution. Each of the 10 tasks is staggering in scope.
"This provides a road map," said Carlie Ronca with the Bureau of Reclamation. "What we're going to do is review the scopes of alternatives and move into design work – if the budget is available."
Beyond design and budget, Ronca noted other daunting processes ahead, like obtaining environmental permitting.
Resumed pumping and heavy September rains have helped clear Shadow Mountain once again. Cold temperatures will quell any more organic growth, at least until next summer.
Late last August, just before the Farr Plant's pump fired up again, Vincent visited the reservoir with some stakeholders interested in its noxious aquatic weed growth.
"But when we got there, you could not even see aquatic weeds because (the reservoir) was so green," she said. "You couldn't see through the water."
For the near-term, it seems a solution to the Three Lakes' water clarity problems will also remain out of sight.
Leia Larsen can be reached at 970-887-3334 ext. 19603.