Development and application of hydraulic geometry equations for tidal channel restoration in Atlantic Canada

Tidal wetlands play a key role in our environment, particularly in the face of climate change and rising sea levels. Successful restoration of these coastal habitats requires a good understanding of the hydrology and morphology of the site. In Atlantic Canada, restoration design must consider significant variation in tidal range (1 to 16 m), sediment supply (50-70,000 mg/L) and winter conditions. In 2012 ground surveys, aerial photos and digital terrain data were used to conduct a morphometric analysis of representative tidal channels and to establish regional hydraulic geometry relationships to aid in restoration design. Channel morphology was strongly related to freshwater discharge and channel order while drainage density, channel length, and sinuosity were related to site history and maturity. Five years after the initial study, two restored salt marshes have been analyzed to assess the validity of the equations. At both marshes, tidal channels were excavated and erosion/accretion tracked for five years following restoration. Channels were found to experience rapid erosion in the first 2 years following restoration but to stabilize with dimensions on par with those predicted. Furthermore, both sites rapidly developed hybrid creek networks beyond the primary excavated channels when allowed to self design. The methodology has been used to design tidal channels for 2 additional sites. Although these sites have not been restored at present, hydrodynamic modeling supported channel dimension predictions, with acceptable in-channel velocities and flood extents simulated in the model. The authors conclude that the use of regional hydraulic geometry equations have been effective in salt marsh restoration design in Atlantic Canada, particularly when used in conjunction with other techniques such as hydrodynamic modeling and analysis of historic conditions.