on ours,” he said. “We worked together to accomplish multiple goals.”
Best-Laid Plans
The East Side Detention Facility (ESDF) high-hazard dam in northern Colorado
is aimed at reducing flood-related damage. In 2012, Ayres conducted the site
investigation for the dam, analyzing 14 locations. The site and design had to
meet requirements of the Federal Emergency Management Agency and State
Engineer. Groundwater testing and soils logs helped pinpoint the location,
and Ayres civil engineer Chris Pletcher said groundwater was so far below the
proposed construction site that it was eliminated as an issue.
But when excavation started in 2014, water seeped into the site. New testing
found that groundwater levels were 8 to 10 feet higher than during the pre-
construction testing.
“Back in 2013 we had all that flooding here,” said Stan Myers, manager of the
Boxelder Basin Regional Stormwater Authority. “We had a week of solid rain,
which just never happens out here. A few months after those rains, people
started reporting that groundwater was at record levels.”
Pletcher noted the original permitting didn’t miss anything: “It wasn’t there to
be caught. There was a different condition when construction began that was
going to be a long-term problem.”
Because the underlying issues had changed, Ayres had to restart the
permitting process during construction. And because changes during
construction cost money, “we added to our permitting effort on the fly to
keep the project moving,” Pletcher said. The project needed dewatering
permits from the Colorado Division of Water Resources (CDWR) as well
as augmentation permits to replace water lost to evaporation during
construction.
Despite the groundwater issues, construction moved forward, and the
30-foot-tall ESDF is complete and ready to contain floodwaters. Ayres
continues to monitor groundwater levels at the site.
The high groundwater levels also led to concerns related to Colorado water
rights law. It’s a complicated law involving who gets to use water first and how
much. Myers noted that water rights in the Boxelder Basin revolve around
Colorado-Big Thompson water transfer shares. Water that evaporates from
the ESDF must be replaced, potentially requiring a formal augmentation plan
to be submitted to CDWR.
“Our hope is that when hot weather hits, groundwater levels will drop,
and we may not have to augment at all,” Myers said. “Another thing we’re
contemplating is to narrow up the channel to keep the flows from spreading
out so much and losing water to evaporation.”
The Ayres team will work with the Authority to keep the project and any
future permits on track. “Chris has always been a proactive team member and
really takes ownership of things,” Myers said.
6│ TRENDS