Examining drivers of ecomorphodynamic change in the Avon River Estuary

Abstract

The Avon River Estuary is a hypertidal, muddy estuary in the upper Bay of Fundy. The system has been in dynamic equilibrium since construction of the causeway in 1970, but recent construction activities and changes in tide gate management have caused an observable shift to disequilibrium. To assess the environmental consequences of these activities, we examine the relative influence of natural and anthropogenic drivers of ecomorphodynamic change within the Avon River, downstream of the Highway 101 causeway by comparing data from 2019-2023 to baseline conditions, 2007-2019. We hypothesize that system ecomorphodynamics will be strongly influenced by human activities. To evaluate changes in ecomorphodynamics occurring in the system we examined changes in channel cross-sectional profiles, cross-sectional area, changes in surface elevation, volumetric changes, sediment grain size, and vegetated area. These analyses were completed primarily through ArcGIS Pro and Microsoft Excel. We then compared these changes to tide gate manipulation information, construction activities, tidal cycles, and precipitation data to infer what may be influencing the change. Results indicate that there has been a quantifiable change in ecomorphodynamics between the baseline period and the study period. Additionally, most of the notable changes that occurred were concentrated around the Windsor Marsh and the Newport Bar, near the causeway. Based on patterns in natural and anthropogenic influences as well as the locations of changes, we believe that construction has had strong influence on the Avon River Estuary while the St. Croix River is mostly unaffected by anthropogenic interference and precipitation may be the dominant driver of change. While future studies need to be conducted and should be based closer to the causeway, these results provide insight from an environmental assessment perspective into how estuaries experiencing significant anthropogenic interference may respond and adjust.