Issues of Meander Development: Land Degradation or Ecological Value? The Example of the Sajó River, Hungary

László Bertalan,Szilárd Szabó,Zoltán Németh,Jesús Rodrigo-Comino,Tibor Novák,Ádám Kertész

doi:10.3390/w10111613

Abstract

The extensive destruction of arable lands by the process of lateral bank erosion is a major issue for the alluvial meandering type of rivers all around the world. Nowadays, land managers, stakeholders, and scientists are discussing how this process affects the surrounding landscapes. Usually, due to a land mismanagement of agroforestry activities or urbanization plans, river regulations are designed to reduce anthropogenic impacts such as bank erosion, but many of these regulations resulted in a degradation of habitat diversity. Regardless, there is a lack of information about the possible positive effects of meandering from the ecological point of view. Therefore, the main aim of this study was to investigate a 2.12 km long meandering sub-reach of Sajó River, Hungary, in order to evaluate whether the process of meander development can be evaluated as a land degradation processes or whether it can enhance ecological conservation and sustainability. To achieve this goal, an archive of aerial imagery and UAV (Unmanned Aerial Vehicle)-surveys was used to provide a consistent database for a landscape metrics-based analysis to reveal changes in landscape ecological dynamics. Moreover, an ornithological survey was also carried out to assess the composition and diversity of the avifauna. The forest cover was developed in a remarkable pattern, finding a linear relationship between its rate and channel sinuosity. An increase in forest areas did not enhance the rate of landscape diversity since only its distribution became more compact. Eroding riverbanks provided important nesting sites for colonies of protected and regionally declining migratory bird species such as the sand martin. We revealed that almost 70 years were enough to gain a new habitat system along the river as the linear channel formed to a meandering and more natural state.

Highlights

Alluvial rivers represent dynamic landforms of the watersheds all over the world [1].Under minimal regulation, these rivers can generate diverse landscapes by shifting back and forth along their floodplain [2,3]
This study aims to develop a spatiotemporal analysis on the river channel development and the offer a valuable solution to produce high-resolution aerial imagery from a few km2 large areas [50,51]; ecological diversity based on a set of aerial imagery in 10 different time periods (Table 1)
Class Area of the forests (CA_F): we considered the forests’ area as the indicator of landscape change

Summary

Introduction

Alluvial rivers represent dynamic landforms of the watersheds all over the world [1].Under minimal regulation, these rivers can generate diverse landscapes by shifting back and forth along their floodplain [2,3]. The channel flow undercuts the outside banks resulting in seepage outflow or mass failure processes i.e., slab failures, rotational slides and sloughings or slump blocks eroding into the water body [4,5]. These materials can form point bar accretion at the inside banks downstream due to the lower current velocity at the inner side, as opposed to the outer side of the bends [6]. The maxima of lateral bank erosion rates are concentrated downstream of the point bar symmetry-axis [11] resulting elongated, skewed or compound meander bends [13]

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Conclusion