When a river adjusts its shape over longer timescales, it is no longer in equilibrium with its environment. These ‘disequilibrium trends’ can affect projects that are designed in or around rivers. To capture these trends in river behaviour, two surveys of the river that show its shape at two points in time can be compared, and what we call the ‘net morphological displacement’ or NMD can be calculated. NMD easily identifies whether a river is in equilibrium with its environment, which can help determine whether a project designed in or around that river will be successful.
We calculated both the NMD and the amount of sediment supplied in different reaches of a small gravel-bed creek from annual surveys over 15 years. While performing these calculations, we introduced a new way to ensure that the changes in the river shape are actually real changes, because sometimes when the changes are small, it can be difficult to determine if the changes were due to the river actually changing or due to the measurement and interpolation errors of the surveys.
We found that during the same hydrological events different reaches of the creek behaved uniquely because they had different amounts of sediment supplied to their sections of the stream. We also found that reach-scale morphological trends were not necessarily revealed over shorter measurement periods; instead the further apart in time the two surveys are, the more likely it is that the changes in the river shape infer the equilibrium or disequilibrium trends of the river. Therefore, longer-term monitoring programs are important for helping to determine if a project designed in or around a river would be successful.
Acknowledgments. The research was funded by NSERC Discovery and Canada Foundation for Innovation. This study would not be possible without the help from the numerous field assistants that assisted over the 15-year period, including Dave Reid, Joshua Caulkins, Marcelino Secaira Ziegler, Ryan Matheson, Caitlin Tatham, Carina Helm, Luke Terhart, David Waine, Ilana Klinghoffer, Andre Zimmermann, Tony Lagemaat, Sam Robinson, Michael More, and Tim Reid. Other contributors to the dataset include Conor McDowell and Elli Papangelakis. Discharge data was collected and shared by John Richardson.
Citation: Wlodarczyk, K., Hassan, M. A., & Church, M. (2023). Annual and decadal net morphological displacement of a small gravel‐bed channel. Earth Surface Processes and Landforms.