Date of Award

Spring 2023

Project Type

Thesis

Program or Major

Earth Sciences

Degree Name

Master of Science

First Advisor

Anne F Lightbody

Second Advisor

Michael Palace

Third Advisor

Brian P Colleran

Abstract

As floods increase in frequency and magnitude throughout New England, research on controls of erosion is necessary to help manage riverbank erosion and its implications on river system health and safety of infrastructure situated along the bank. Reynoutria japonica (Itadori knotweed) is an invasive species spreading throughout New Hampshire rivers which is suspected to cause riverbank erosion due to its unique root structure and winter die-back. To examine the impact of knotweed on riverbank erosion, paired knotweed and native species vegetation patches were selected as study sites along the Sugar and Lamprey Rivers, New Hampshire. Study sites were monitored over the course of a year using bank pins, remote sensing (LiDAR and Structure from Motion), and hydraulic modeling. Banks colonized by knotweed experienced 6.8 cm more erosion on average than similar banks with native vegetation. No statistically significant difference was recorded between modeled applied shear stress or estimated critical shear stress values between paired vegetation patches, apart from Sugar Site 6. Overall, the results of the bank erosion monitoring, estimated critical shear stress, and modeled applied shear stress results show that the only significant differences across paired vegetation patches were the presence of Itadori knotweed and an increase in erosion measured at knotweed patches. To minimize the impacts on river ecosystems by knotweed and damage to infrastructure by erosion, river corridor management should consider efforts to remove knotweed from river systems.

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