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
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
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.