A GREENARMOR? ALTERNATIVE FOR RIVERBANK STABILIZATION

摘要

Watauga County, North Carolina implemented a riverbank stabilization project along the South Fork of the New River approximately 325 feet in length near Boone, North Carolina. Following hurricanes Frances and Ivan in September of 2004, channel banks along the river were severely eroded to near vertical slopes ranging in height from 10-20 feet. The river also migrated towards an asphalt-walking path, which bordered the local park adjacent to the river. The selected riverbank stabilization measures included repairing the failed channel banks back to their pre-disturbance location through fill placement and augmenting the repair with in-stream structures. The repair included the installation of toe stabilization measures along the river reach to prevent excessive scour. Based on the observed and measured conditions of the failed banks, and the amount of disturbance that occurred, it was determined that the bank repairs alone, without supplemental in-stream structure reinforcement, would likely be insufficient to withstand future flood flows. An In-stream single rock (boulder) vane structure was installed to reduce shear stresses along the repair reach at the head of the toe stabilization to protect the rebuilt riverbanks and toe protection. The new channel bank was graded to a slope no steeper than 1H:1V to the approximate elevations described for each repair cross-section. The repaired banks are within the "active channel," and were stabilized using the GreenArmor? System consisting of Enkamat~? 7020 Turf Reinforcement Mat (TRM) and Flexterra~? Flexible Growth Matrix (FGM). The banks were seeded with an appropriate native grass mixture and vegetated with natural vegetation consisting of live stakings and planted shrubs and trees. The GreenArmor? System was selected for its ability to withstand the high velocities and shear stresses of the river flows, and the ability to easily install live stakings as the primary form of woody vegetation. Also, due to the potential of high shear stresses, Terra-Shield?, a Prescriptive Agronomic Formulation (PAF), was added to the Flexterra~? for added ease of installation and long term bank protection. The specified riverbank stabilization measures have reduced near bank shear stresses and created a stable stream section along the South Fork of the New River. The successful methods for riverbank stabilization selected and used in this project will be described in this technical paper.