In recent years, the City of Alma recognized the importance of the Pine River as a community asset and has successfully redeveloped the Pine River waterfront throughout the community. The restoration and redevelopment of the 180 acre parcel of land, where a decommissioned refinery once operated, is part of the city’s long-term plan.
Hamp, Mathews & Associates (HMA), an environmental engineering firm in the greater Lansing area, has been strategically involved with the site restoration for decades. HMA personnel were initially involved with the facility in the 1990s to evaluate on-site soils and groundwater contamination. Refinery operations ceased in 1965 and was demolished in the early 1970s. HMA continues to consult with the site owner and Michigan Department of Environmental Quality to create a long-term plan to protect the Pine River and wetlands, which run along the entire site.
HMA developed an environmental capping solution to protect both people and wildlife from on-site contaminated soils. The engineered cap included a geotextile, 6” of engineered fill material and 6” of topsoil, creating a system which prevents contaminants from migrating to the adjacent river.
To protect the engineered cap system and native soils, HMA introduced Contech Engineered Solution’s ArmorFlex® Hard Armor system. 13,050 square feet of ArmorFlex Class 50-S articulating concrete block mats were utilized to stabilize and protect the Pine River banks.
The ACB system was developed to manage a critical shear stress capacity of 6.2 psf and a critical velocity of 15 fps. The greater challenge was matching the ACB mat system with a fixed toe elevation to the natural riverbank without disturbing the underlying materials with significant over excavation. HMA completed an extensive field survey during the design phase then coordinated with Contech’s Engineering Team to model the final mat layout. Standard mat sizes were used where possible, while custom mats were provided to meet specific bank contours and radius.
"The ArmorFlex system provided the bank protection needed to eliminate erosion of the riverbank without the look of everyday riprap materials," concluded Abby Varner, P.E., Project Engineer with HMA. "As vegetation fills in the gaps, the riverbank will have a more natural look and feel. It was very impressive how smoothly the installation went.”