Let the river erode! Enabling lateral migration increases geomorphic unit diversity.

Area of Science:

• River geomorphology and restoration ecology.
• Fluvial geomorphology and landscape dynamics.

Background:

• Traditional river restoration often uses static designs, neglecting the dynamic nature of resilient river systems.
• Resilient rivers naturally adjust their morphology in response to environmental changes, creating diverse habitats.

Purpose of the Study:

• To investigate if restoring lateral migration in a channelized river enhances in-channel geomorphological diversity.
• To quantify the morphodynamic changes and geomorphic unit distribution post-restoration.

Main Methods:

• Acquired pre- and post-restoration topographic surveys of the Allt Lorgy, Scotland.
• Utilized Geomorphic Unit Tool (GUT) software to map geomorphic units based on a 3-tiered classification system.
• Quantified morphodynamics and geomorphic unit diversity using the Shannon Diversity Index.

Main Results:

• Geomorphic unit diversity increased significantly, with the Shannon Diversity Index rising from 1.40 to 2.04 post-restoration.
• Channel widening due to bank erosion increased the aerial coverage of in-channel geomorphic units by 23% initially and 6% over two years.
• Restoration facilitated the formation of lateral and point bars, riffles, and diagonal bar complexes, with instream wood creating pools and riffles.

Conclusions:

• Restoring lateral migration and allowing natural bank erosion significantly increases geomorphic unit diversity in channelized rivers.
• This approach leads to more diverse and productive habitats, supporting self-sustaining river ecosystems.
• The methodology provides a framework for testing restoration hypotheses and appraising post-project outcomes.