Danika van Proosdij

Controls on suspended sediment deposition over single tidal cycles in a macrotidal saltmarsh, Bay of Fundy, Canada

Abstract A field study was conducted on a section of Allen Creek marsh in the Bay of Fundy to examine changes in suspended sediment circulation and deposition over single tidal cycles. Net flow velocity, suspended sediment concentration and sediment deposition were measured over 13 individual tidal cycles during the summer of 1998. A vertical array was deployed in the low marsh region, consisting of three pairs of electromagnetic current meters, OBStm probes and one pressure transducer. Sediment deposition was measured using full-cycle sediment traps. The temporal distribution of sediment deposition was monitored using sequential sediment traps exposed at different tidal stages. The data suggest that sediment deposition on the marsh surface is primarily controlled by the interaction of water flow, marsh morphology and vegetation. The highest amounts of sediment are deposited during conditions of high suspended sediment concentration and low wave activity, particularly when the relative roughness of the vegetation is the highest. Loss of suspended sediment from the water column was shown to be correlated with the sediment trap data; however, predictions of sediment deposition based on the variation in suspended sediment concentration were found to be valid only for conditions with less than 0.15 m high waves. For higher wave conditions, the use of suspended sediment loss calculations should be used primarily for estimating the relative rather than absolute values of deposition on the marsh surface.

Development of a relative coastal vulnerability index in a macro-tidal environment for climate change adaptation

Coastal vulnerability assessments to climate change impacts have been conducted in the past. However, few if any account for the highly variable risk associated with tidal stage in macro-tidal environments. The purpose of this research was to develop a geomatics tool which interactively determines the biophysical vulnerability of a macro-tidal estuary in the Bay of Fundy to varying levels of storm surge and tide state. A conceptual framework was designed to illustrate the relative interrelationships between exposure conditions (surge height, tidal stage), biophysical state (freeboard, exposure, width of foreshore, intertidal slope, observed erodibility, shore protection) and morphological resilience condition. This conceptual framework was then used to develop a dynamic, custom Python programming script within ArcGIS 9.3 to calculate coastal vulnerability for user determined combinations of surge height and tide state. The analysis was conducted for four coastlines, backshore, upper foreshore, middle foreshore and lower foreshore, to reflect varying biophysical states with varying tide levels. The results of the tool were compared with known areas of concern (high erosion, dyke overtopping), as determined by historical records, local expert knowledge and GIS analysis of aerial photography. The number of known locations of concern is lower than that of the results produced by the tool. This is most likely due to the results being analyzed at extreme water levels, greater than higher high water large tide. However, this estimation of vulnerability may limit negative impacts of climate change by highlighting vulnerable areas prior to an event, allowing coastal managers and planners to install measures to reduce the vulnerability and enhance the adaptive capacity of local communities.

Salt Marsh Tidal Restoration in Canada’s Maritime Provinces

Salt marshes form an important component of the coastal landscape of the Canadian Maritimes. The characteristics of salt marshes are determined by a wide range of physical and biological controls. The coastal zone of the Maritime Provinces (Nova Scotia, New Brunswick, and Prince Edward Island) exhibits a diverse geologic and sea level history, sediment supply, tidal amplitude (micro- to macrotidal), and varying exposure to wave energy. These factors contribute to the development of three distinct biophysical regions of salt marsh: Bay of Fundy, Atlantic Coastal, and Gulf of St. Lawrence/Northumberland Strait (fig. 13.1; Hatcher and Patriquin 1981; Roberts and Robertson 1986; Wells and Hirvonen 1988). Most recent estimates indicate that there are approximately 287 square kilometers of salt marsh in the Maritimes (table 13.1; Hanson and Calkins 1996; Mendelsohn and McKee 2000). The majority of this (54 percent) occurs along the coast of Nova Scotia.

Salt marsh geomorphology: Physical and ecological effects on landform

Salt marshes are among the most productive ecosystems on the planet, producing more organic matter per unit area than forests, grasslands, and cultivated fields. Marsh landscapes typically fringe low-energy coastal environments, but in places they may extend inland tens to hundreds of kilometers. As a consequence of their high productivity and interactions with the coastal ocean, salt marshes provide numerous benefits to society. For example, salt marshes are critical habitats for commercially harvested marine and estuarine biota; they filter nutrients and sediment from the water column; and they provide recreational opportunities. In addition, salt marshes help dissipate erosive tide and wave energy and they have intrinsic aesthetic values. All of these societal benefits have a quantifiable economic value, and salt marsh impairment and degradation have associated costs.

Development and Application of a Geo-temporal Atlas for Climate Change Adaptation in Bay of Fundy Dykelands

ABSTRACT van Proosdij, D; Perrott, B and Carroll, K., 2013. Development and Application of a Geo-temporal Atlas for Climate Change Adaptation in Bay of Fundy Dykelands. Globally, dykelands (former marsh areas protected by dykes) are of strategic importance for climate change adaptation. Many were originally designed to protect agricultural land, yet now protect valuable infrastructure. The purpose of this project was to develop a comprehensive digital atlas incorporating historical plans, shore protection, coastal geomorphology and LiDAR to serve as a basis for climate change adaptation planning in the Bay of Fundy. 110 paper plans were scanned, geo-referenced and features such as current and historical dykes, aboiteaux (tide gates), armouring, ditches, creeks, property boundaries, foreshore marsh, and geodetic elevations were digitized using ArcGIS. Attributes included age of structure, material, dimensions, and ownership. Dyke elevations were surveyed using an RTK GPS, and individual sections were identified as being vulnerable to storm surge and sea level rise. Erosion rates and width of foreshore marsh were calculated per dyke segment. At present, 55% of dykes within Nova Scotia are within 0.5 m of critical elevations established in the 1960s, 2% are more than 0.5 m below critical and all are below the predicted rates of SLR by 2055. There is also a strong relationship between the placement of armouring along the dyke toe and foreshore erosion. Conversely, timely placement of armouring along the foreshore marsh decreased rates of erosion. This was most effective in areas with the largest fetch; less effective where erosion was driven by tidal currents. All data were integrated into ArcReader for use by Agriculture personnel and have been essential for cost effective climate change adaptation planning including dyke topping, hazard mitigation and education.

Elevation-Dependent Multiscale Analysis of a Complex Intertidal Zone

ABSTRACT Horne, P.; Suteanu, C.; van Proosdij, D., and Baker, G., 2013. Elevation-dependent multiscale analysis of a complex intertidal zone. Coastal geomorphology is the result of many complex interacting processes operating over a range of scales in space, and multiscale analysis on relevant scale intervals can help link form with process. Numerous studies focus on lines resulting from the intersection of a plane at a certain elevation with the three-dimensional landscape. However, in most cases, the reason for the choice of the actual elevation is not mentioned, nor at times is the value of the selected elevation even specified. Such an approach relies on the assumption that one studies an isotropic, self-affine pattern for which the irregularity is independent from elevation. The present study questions this assumption by applying fractal analysis not to one, but rather to a series of different elevations relating to tidal stages. The research takes place in a macrotidal estuary, in the Upper Bay of Fundy, Canada, where diurnal tides exceed 14 m. The topography of Avon Estuary is influenced by complex interacting factors, including hydrodynamic and sedimentary processes, vegetation, and ice formations, as well as by anthropogenic structures. The area–perimeter analysis method was applied to 0.5-m contour intervals on a digital elevation model derived from a light detection and ranging survey conducted at low tide. The results show a pronounced and coherent dependence of the fractal dimension on elevation. Fractal dimensions between 1.2 and 1.17 are generally associated with sand sediment transport and bedform development at elevation ranges from −5 to −1 m Canadian Geodetic vertical datum of 1928. Between D values 1.7 and 1.12 at elevations from −0.5 to 2.5 m CGVD28, vertical accretion processes dominate with bank edge erosion. D values continue to increase above elevations greater than 3 m as vegetation becomes established and stabilizes the intricate tidal creek networks. We show that this approach supports a better understanding of the interacting processes that dominate the area on different ranges of scale.