To further understand bank undercutting processes that occur in the Petitcodiac River estuary (New Brunswick, Canada), the erosion of sediment cores obtained at the base of the estuary banks was studied by testing for the critical shear stress and erosion rates in a laboratory flume. It was found that there is variation in the erodibility of the sediment with depth horizontally into the bank over the depths tested. The bank cores were shown to erode in distinct layers, with the erosion of extremely weak layers occurring at rates that were an order of magnitude higher than the rates of adjacent resistant layers. Bed cores obtained at the toe of the bank were also tested and similar variability in sediment erodibility was found with vertical depth into the bed. Sediment properties of the cores, including particle size distribution, bulk density, water content, and organic content were compared to the erodibility of the sediment. Additional investigations included observations of the Petitcodiac River estuary bank movement through GPS surveys and erosion pin monitoring, as well as testing for the presence of biological sediment-stabilization factors, and changes in particle size and mineralogy on the river bank.