# Investigation of a Gravel-Bed River's Pattern Changes: Insights from Satellite Images
## 1 Introduction  
As it is well known, alluvial rivers develop different planform morphologies that extend between braided and meandering [1; 2; 3]. While a braided stream is formed by multiple threads channels with emerged bars separating the threads from each other, a meandering stream consists of one-thread channel. Especially braided rivers are characterized by a high dynamism [4; 5; 6; 7], with rapid and frequent changes in bed topography, plan-form shape and vegetated patches. The identification of river's islands and vegetated patches evolution is important for the evolution of the stream pattern changes and the habitat dynamism [8]. Stream pattern changes have been documented in the literature both in sand-bed rivers [3; 9; 10; 11; 12] and in gravel-bed rivers [3; 13; 14; 15]. In this work attention is restricted to gravel-bed rivers with the aim of contributing to clarify conditions that support meandering pattern. [PERSON] and [PERSON] [13], by conducting field investigations in the gravel-bed Bullin River in England, suggested that the stream pattern changes could be due either to river's intrinsic threshold conditions (termed as autogenic factors) or to anthropogenic actions or to combined effects related to temperature, runoff regime and vegetation pattern (termed as allogenic factors). [PERSON] and [PERSON] [3] analyzed a large amount of literature data of meandering and braided gravel-bed rivers and established that the stream pattern changes may be induced either by a change in the aspect ratio or by a change in sediment supply transported as bed-load. Other researchers [16; 17; 18] exalted the role of vegetation on river's dynamics: on one hand vegetation controls sediment dynamics (as an example vegetation traps, reinforces and aggrades landforms) driving the geometric variations within the river's active reaches, on the other hand it increases the stability of deposited sediments because of its roots system. Thus, vegetation is not a passive factor in the fluvial processes but an active one and could exert an important role in the stream pattern changes [6; 19; 20]. Field studies [21; 22; 23], flume experiments [24; 25; 26] and aerial images analyses [27; 28] have been carried out to explore the mutual feedbacks vegetation/morphodynamics and how the hydrological processes could influence them. Flooding events on one hand could induce the vegetation's mechanical damage [29; 30; 31] and on the other hand could facilitate the transport of seeds and sediments and their deposition [32]. In this context, while some researchers, among others [33], suggested that high-magnitude events exert the major role on the vegetation erosion, others [34] highlighted also the important role of low-magnitude events in determining significant vegetation erosion, especially in high energy systems. Furthermore, all studies indicate that the growth of vegetation and the extension of the vegetated areas can vary greatly in time depending on the tolerance of the species to frequent floods [32; 35; 36; 37]. Although several works have been conducted to investigate the river's dynamism, field studies are still scarce and further real cases documenting the aforementioned processes are needed [38; 39]. The difficulty is related to the fact that detailed and simultaneous information at different points and at different times are required. To overcome such a difficulty, in recent years remote sensing approaches have been also applied and radar technologies and advanced aquatic-terrestrial LIDAR (Light Detection and Ranging) techniques have been used both for measuring high resolution topographic data in a relatively short time [40] and for mapping the morphology of clear-water streams in fluvial environments [41; 42].