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Slope failure photo with blog title

Landslides: Prevention & Repair Through Slope Stabilization

In New England, March marks the last weeks of winter and the start of spring rains and snow melt.  Paying attention to erosion control during this time of year is always on the minds of municipal public works staff, state agencies, construction companies, and even homeowners, especially those fortunate enough (or perhaps not) to have water frontage. 

A 2018 study conducted by the USDA found that precipitation is increasing in the northeast more than any other region in the United States. The frequency of consecutive wet days is generally increasing in the northeast and precipitation extremes have also become more frequent. Given these trends, it is no surprise that peak flows in rivers and streams are also increasing and occurring earlier in the year which can result in a greater risk of flooding.

While it is difficult to prevent major erosion of stream and river banks due to extreme precipitation events, damage can be mitigated by inspections of at-risk areas combined with prioritization of these areas for repair. It is important to address slope failures quickly because bank degradation can cause significant damage including loss of property and infrastructure, sedimentation of the waterbody, water quality issues and damage to critical riparian buffer areas. As civil engineers, we can provide assistance with erosion control issues that range from preventative design practices, culvert replacements and stabilization of failed embankments.

Below is a list of some stabilization practices along with before and after photos of our recent embankment stabilization projects.

One such embankment failure occurred in Lancaster, New Hampshire, when high flow conditions in the Connecticut River resulted in severe washouts along an 800 foot long embankment causing loss of land and unstable soil conditions. Hoyle, Tanner designed and permitted solutions to repair and stabilize the slope using native riparian vegetation and rip rap armament. Live willow and dogwood stakes were planted in soil between the rip rap stones.

Terms to know:

  • Live willow & dogwood stakes: Living shrub cuttings that take root quickly in bank environments – provides natural habitat and additional erosion control
  • Rip rap: Large stones used for protection and dissipation of energy from high water flows
Washout along the Connecticut River in Lancaster
Lancaster Embankment after Stabilization

Hoyle, Tanner also designed and permitted repairs to a steep slope in Rochester, Vermont, when intense rainfall events undermined the toe of the bank, causing the slope and roadway above to fail and slide into Brandon Brook 90 feet below.  The repair solutions included installation of a blast rock toe detail and stone facing with grubbing material along the hillside to restore the slope. The roadway was reconstructed and a mid-slope underdrain was installed to intercept groundwater seepage. Debris from the slope failure was removed from Brandon Brook and the streambed was restored.

Terms to know:

  • Stone facing with grubbings: Combination of stone and native material to promote vegetation growth
  • Blast rock toe: Large rocks placed at the toe of the re-stabilized slope to combat undermining
Rochester Slope Failure at Brandon Brook
Brandon Brook Stabilized Slope Repair

Improving safety and combatting damage from growing peak flows and extreme storm events is an important part of our job. Hoyle, Tanner is excited to offer solutions to slope stability issues and challenging site conditions. For more information on how we can be of assistance, please contact me.

Marisa DiBiaso

About Marisa DiBiaso

Marisa DiBiaso, PE, is a Civil Engineer with the Municipal Engineering Team at Hoyle, Tanner where she manages and designs civil/site projects for municipalities, state agencies and private developers. She earned her Bachelor of Science and Master of Science degrees in civil engineering at the University of New Hampshire and is working toward a graduate certificate in Historic Preservation at Plymouth State University. She served as Vice President on the Board of Directors for the American Society of Civil Engineers, New Hampshire chapter (ASCE-NH). Marisa is licensed in NH, ME, MA and VT and has a strong design background focused on site, roadway, drainage, and utility projects. Outside of work, Marisa enjoys spending time with her family, snowboarding, hiking, reading, and researching her 1700s farmhouse.