When filling a new reservoir, or filling a reservoir to a new height thanks to construction of a taller dam, a great deal of time and care is taken to ensure safety.
Elkhead Reservoir east of Craig, now bearing a dam that recently was raised 25 feet, is slowly filling with runoff water as part one of a six-phase plan, Craig Public Works Director Bill Earley said.
The project, which closed the area to the public for two years, is complete as far as dam construction. Now the inspections begin.
The reservoir is filling slowly, Earley said. "About 1 foot a week right now."
That's good news for city officials, who will monitor the process carefully in the months ahead.
The new dam contains 14 piezometers, a device that measures groundwater pressure in each of its buried locations throughout the dam.
The measurements can warn water department officials of high, or changing, levels of water in the dam structure.
Step two of the process involves bringing the water level up to the height of the old dam.
When the level of the old dam is reached, the filling process holds steady for one week while water levels settle and readings are allowed to stabilize.
During the early filling process, the water is allowed to rise 2 feet per day while undergoing weekly inspections and twice-weekly readings of the piezometers.
Step three of the process allows the fill rate to increase to three feet per day.
At that rate, the dam requires visual inspections twice daily, and meter readings are performed twice daily seven days a week.
All of the readings are reported to the engineering firm in Denver that designed the dam.
There also are a number of benchmarks set in concrete monuments on top of the dam that are surveyed at the end of each of the six steps involved with filling the reservoir. While the dam is expected to settle nearly a foot, any unusual or large changes in readings could show potential problems for the structure, Earley said.
"The vast majority of earthen dams that experience failures have them occur in the first year," he said. "We visually make sure there is no water around the dry side of the dam. We're watching how the rising water reacts to the dam and surrounding areas."
A 6-foot-wide drain in the center of the dam structure is constantly monitored during the filling process to note any increases in dirty water or increased flow rates.
When the reservoir is filled to capacity, the fourth step in the process, inspections continue twice daily for one week, and then once daily for the next week. Weekly inspections continue for the next 90 days, in the fifth step of the filling process.
Step six is normal operating procedures for the dam, with inspections as required in the operation and maintenance manual supplied to the city.
Having a new dam near the city of Craig also requires the implementation of a new Emergency Preparedness Plan. Escape and evacuation routes are mapped out on a document approved by the state of Colorado. Final touches are being added to the EPP and, when finished, it will be presented to city council for approval.
Dan Olsen can be reached at 824-7031, ext. 207, or firstname.lastname@example.org.