Shifts in hillslope-channel connectivity after land reclamation in a Mediterranean semi-humid badland landscape

Abstract

Badlands morphodynamics largely depends on shifts in hillslope-channel coupling and decoupling through time and space. In sub-humid badlands, the already complex pattern of connectivity change is further complicated by extrinsic variables, such as human induced land use changes, resulting in alteration of sediment source areas and cascades, but the impact that such interventions have had on the sediment dynamics at the catchment scale has had little attention.

This paper investigates the impact of human intervention on the hillslope-channel system morphodynamics of a badland landscape of the Upper Orcia Valley (southern Tuscany, Italy). Utilizing a multi-temporal approach, we analyzed the historical archive of the Land Reclamation Authority, aerial photographs, and LiDAR data to reconstruct land use changes and geomorphological evolution over the past century. Our analysis focused on identifying shifts in hillslope-channel coupling by mapping changes in sediment sources on the hillslopes as well as the main channel adjustments along the main river channels. The application of an index-based connectivity approach allowed to assess changes in structural connectivity under different land use scenarios.

Results demonstrate a significant decrease in sediment supply and hillslope-channel connectivity due to land reclamation works implemented in the 20th century. These interventions, aimed at stabilizing badlands and increasing land profitability, have led to substantial changes in river morphology.

This study highlights the importance of considering human interventions and their long-term impacts on sediment dynamics when developing catchment-based management plans for extremely dynamic environments like badlands.