Disentangling the Main Components of Hydromorphological Modifications at Reach Scale in Rivers of Greece

Abstract

The Water Framework Directive (WFD) requires from member states to monitor hydromorphological features of rivers in order to assess their ecological quality. Thus, numerous hydromorphological assessment methods have been developed with most of them focusing on the dynamics of hydrology, geomorphology and riparian zone extent. Within the scope of this study, we assessed the hydromorphological features of 106 river reaches distributed among thirteen WFD River Basin Districts (RBDs) to identify the main drivers of hydromorphological perturbation at a national scale. The studied reaches reflect a wide range of natural variability as they include various types of watercourses extending from lowlands to mid-altitude and mountainous systems. We employed the River Habitat Survey (RHS), and we recorded hydromorphological features and modifications in both banks and the channel bed along 500 m for each reach. Then, the Habitat Modification Score (HMS) and the individual sub-scores that indicate the extent of specific modifications (e.g., bridges, fords, weirs, bank reprofiling, bank reinforcement, etc.) were calculated in order to a) assess the severity of the total artificial modification and b) to highlight the most common and severe causes of overall alteration. The results showed that alterations such as reprofiling and reinforcement of banks contributed the most to the total HMS followed by the presence of fords and bridges. Particularly, the bank alterations indicate a serious deterioration of the longitudinal profile of the reaches, while the occurrence of many fords and bridges is the main cause for perturbations that affect locally the stream cross-sectional profile. Overall, these results compile a first nationwide assessment of the hydromorphological status of Greek rivers in line with the WFD and set the basis for further research that will focus on the diversity of stream habitat features as a measure for the overall ecological quality.

Pressures and Status of the Riparian Vegetation in Greek Rivers: Overview and Preliminary Assessment

“…The construction of dams and barriers are among the most important factors for the decrease of the riparian vegetation, due to the hydrological regime's alterations. Recently, a study by Stefanidis et al [5] showed that bank and channel modifications (i.e., resectioning, reinforcement) were a common hydromorphologic modification in Greek rivers. These modifications are used as a flood defense management practice.…”

“…As a result, dams, bridges, weirs, channelization, embankments, deepening, resectioning, and many others are some examples of the modifications that threaten the river connectivity, the riparian corridor's naturalness, and the overall ecosystem health. Identifying these pressures at reach scale is often accomplished through monitoring activities in accordance with the implementation of the WFD [5].…”

“…The Directive recommends that the structure of riparian zones should be analyzed systematically and that their restoration and conservation should be included within the programmes of measures that form part of the Integrated Basin Management Plans [4]. As the Directive (WFD) requires from member states to monitor hydromorphological features of rivers in order to assess their ecological quality, numerous hydromorphological assessment methods have been developed with most of them focusing on the dynamics of hydrology, geomorphology, and riparian zone extent [5]. The riparian zones consist of a wide variety of structures.…”

A comparative assessment of the riparian vegetation status using two different indices: Results from a large-scale study in Greece.

“…Agricultural activity in particular is considered a major driver of hydromorphological modifications in Mediterranean rivers [15][16][17]. For instance, bank and channel resectioning is used as a practice of flood defense management to protect neighboring agricultural land from flood events.…”

“…In addtion, bank reinforcement that uses hard materials (concrete, bricks, rip-rap, etc.) aims to mitigate bank erossion [17]. These changes inevitably are associated with significant alterations in the riparian zone affecting the structure and cover of the vegetation.…”