Coastal, River, & Wetland Restoration
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- Emergency Riverbank Stabilization for Natural Gas Pipeline Protection
Manhan River, Easthampton, Massachusetts
the challengeRiverbank erosion threatened to expose a regional main natural gas pipeline at a bend of the Manhan River in western Massachusetts. This constituted a potential emergency which needed an immediate solution; however, because of the presence of five endangered species, regulators denied the initial proposal for rock armor and required an ecologically sensitive treatment.
the interdisciplinary approach The Bioengineering Group developed a bank restoration and stabilization design, using a combination of vegetation and structural materials designed to harness active geomorphic processes and to enhance stream habitat. Design innovations and sensitivity to regulatory agency concerns greatly expedited project permitting. At the apex of the meander bend, the closest point to the pipeline, the bank reconstruction included a rock toe cradled in high-strength coated wire mesh intended to remain functional even under scour conditions. Rock vanes further protected the banks by re-directing flows toward the channel center, but unlike riprap, do not lead to increased downstream erosion. A variety of pre-vegetated coir products and dormant cutting treatments were used to stabilize and vegetate the lower and upper banks. In combination with logistical support, material procurement, construction subcontractor co-ordination and construction supervision, this regulator-accepted solution addressed the client’s need for rapid response.
the resultsThe avoidance of in-stream excavation, the increase in plant cover, and the incorporation of boulders used as resting perches enhanced habitat conditions for the endangered fish, insect, and mussel species of concern. Additionally, the planting of a 50-foot riparian buffer of cottonwoods and other canopy species enhanced habitat linkage values. Working on a tight schedule, construction of the entire 600 linear foot project was completed in less than two weeks, just before the onset of frozen soil conditions, allowing the pipeline to serve the community without interruption.