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Reconstructing and relining Nottingham Lake high in the Rockies

February 1st, 2015 / By: / Feature, Geomembranes

Replacing a 32-year-old liner.

Introduction

Nottingham Lake is nestled high in the Rocky Mountains and has been the pride of Avon, Colo., for as long as anyone can remember. Tourists and residents use the lake for winter recreation and for boating, fishing, and swimming in the summer. It serves as the background for Avon’s City Hall and is the center of an extensive trails and park system maintained by the city.

This man-made lake was built more than 32 years ago. It was originally PVC-lined with an expected 20-year life span. The geomembrane liner worked longer than expected; however, by 2012 the city’s engineering department was struggling to keep the leaking lake full.

In the second decade of the 21st century, much of the West was immersed in an ongoing drought and the state of Colorado was no exception. The low flows at nearby Buck Creek and Eagle River did not allow town engineers to divert adequate water from those sources to make up for the amount of water leaking from the lake. But the town was eager to have its gem restored for the outdoor activities in the 48-acre park surrounding the lake.

The liner had been repaired twice and in the course of those repairs, it was discovered that the liner had significantly deteriorated. Other changes made to the lake during its 32-year history further degraded the geomembrane liner, including installation of irrigation piping and construction work for the pumphouse dock and fishing pier. During special events, buoys were placed in the lake. Sediment removal, soil erosion, and exposure to sunlight also contributed to the liner’s deterioration.

New liner?

Installing a new pond liner would not normally pose a challenge for experienced geomembrane contractors. On this project, however, the contractors were not allowed to use any park area surrounding the lake to stage equipment and materials.

The logistics were formidable from the start. There was limited access to the site and the storage pad was reduced to one small parking lot. All the soil moving was done within the lake’s perimeter. The project was further complicated by uncharacteristic amounts of rainfall during installation. The sequence for the geomembrane installation was different from a typical pond due to the restriction on staging outside of the lake’s footprint.

In 2012, the Avon Town Council budgeted $1.25 million for 2013 repair work on the lake. Justin Hildreth, Avon’s city engineer, noted “The city also added amenities such as a beach area for swimming and two wetland areas that previously did not exist.” The construction project was scheduled to start in spring 2013.

Construction was delayed until after the annual Salute to the USA celebration July 3 and a triathlon later that month. The pond could not be repaired and refilled in time for the July events so it was drained and work commenced at the end of July. Delaying the start of construction resulted in a compressed time period to complete the job. Reconstruction had to be finished before winter which, at 7,500 feet elevation, presented a challenge for a Rocky Mountain ski town.

City officials brought on board professional engineering, contractor, and installation assistance for the reconstruction and relining of the lake. The 2013 design called for a 30-mil PVC liner with an 8oz. geotextile protection layer.

The plan called for the fabrication of 58 custom panels for 731,061ft2 (approximately 16–17 acres) in September 2013. Installation of the geomembrane and geotextile occurred Sept. 27–Oct. 27, 2013, in two mobilizations. Once the original 20-mil liner was removed, the general contractor moved all the cover soil to the middle of the lake and set up a staging area around a large dirt pile. The entire panel construction and liner installation had to be planned around this unusual requirement.

“This type of staging is rare due to the amount of earth moving start to finish,” said geomembrane installer, Duff Simbeck. “The contractor did an extraordinary job working within the limitations required by the city, the rainy weather, and under a compressed time frame.”

To compound the challenges, this part of Colorado received considerable rainfall during the months of September and October 2013, extending the construction schedule by four weeks. Dewatering the lake was nearly a constant process.

City engineer Justin Hildreth commented, “[The contractor] had to contend with the rain and when it rained the water had nowhere to go, so it drained into the lake area and it would turn to mud.”

The geomembrane delivery to the job was held up because of issues with friction-angle testing. The job specification stated: “… demonstrated that selected nonwoven, needle-punched protective geotextile fabric placed in contact with 30-mil PVC geomembrane has an interface friction angle of at least 21 degrees.”

Because the lake is gently sloped with a maximum slope of 5.0:1, initially there was no concern with the interface friction test passing. But when it did not pass the first time, the team realized that no soil was sent from the jobsite to prepare the plates. Retesting using the native soil was successful. (This issue brings up an important topic for consideration during the design phase of a project: clearly spelling out who is responsible for conducting and paying for any testing.)

The grading, liner deployment, geotextile placement, and soil cover were accomplished using a circular pattern working out from the northeast dock counterclockwise, then inside-out to the boat ramp by the lake’s east-side playground. The key to getting this installation completed before winter was the use of fabricated geomembrane panels in the field. The fabricated panels arrived onsite with the majority of the quality control process already completed.

On average, about 53,000ft2 of geomembrane and geotextile was installed daily. Without the fabricated panels, finishing within four weeks could have taken a small army of technicians welding in 1- to 3-hour bursts of good welding conditions. With 75% fewer seams to heat-weld, large panels enabled crews to work steadily around the “shell” with subgrade protected from rain in large swaths 150 × 200ft.

The pond geomembrane was covered just in time for the winter freeze. The second phase to reconstruct the dam face was done whenever the frozen ground allowed equipment to operate. The dam area was lined but still needed rip-rap in place. Once the dam face was fully restored in December 2013, the state’s dam inspector came in for extensive analysis. That process was completed and the dam was ready.

This area of Colorado received 30% more snow than in an average year. Hildreth, the city engineer, expected “the lake will fill up from the spring snowmelt. State engineers won’t allow the lake to fill too quickly.”

Beautiful Nottingham Lake was ready for recreational activities just in time for the summer season.

Bart Ewing, owner of Ewing Trucking & Construction LLC since 1981, operates primarily out of Eagle County in Colorado, performing a variety of earthmoving and trucking needs including site development, utilities, and road construction.

Duff Simbeck, vice president of Simbeck and Associates Inc., Mancos, Colo., handles administration and contracts for the company, a family business since 1992.

Bart Ewing and Duff Simbeck visited the Mt. Elbert Forebay Reservoir
in 1981 where both of their fathers worked. In 1981, the Mt. Elbert Forebay Reservoir, located in Chaffee County, Colo., was the largest liner job in
the western United States.

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