# Investigation of a Gravel-Bed River's Pattern Changes: Insights from Satellite Images
## 2 Materials and Methods  
### Images and Data Detected  
The Tagliamento River, intensively studied and illustrated in the literature [8; 19; 34; 44], flows in northeastern Italy. It is only moderately impacted by anthropogenic intervention, and thus it is considered as the last morphologically intact river in the Alps and represents a model ecosystem for large European rivers [8]. The river bed is composed mainly of gravel-pebbles (with \(D_{50}\) > 50 mm), but large areas with gravel covered by sand and finer sediment can be also found [45]. In the present work, attention is devoted to the reach characterized by a braided dominant morphology, about 2700 m long, located between the Corino village and the Flagogna village (see Figure 1).  
The considered river reach was also the object of previous literature studies [32; 34; 43]. [PERSON] et al. [32] investigated, in a 1-km-long reach, the morphological changes induced by different flow and flood pulses. [PERSON] et al. [34] considered a 14 km long reach and explored, over long timescale, the existence of a threshold discharge above which erosion of vegetated patches occur. [PERSON] et al. [43] analyzed, over short timescale (i.e., from single floods to decades), the river's islands and vegetated patches development processes in a reach few kilometers long, based on the conceptual model proposed by [PERSON] et al. [19]. In the present work, the attention is focused on the stream pattern changes and the evolving morphological features in a decadal time scale. Satellite images available from Google Earth in a time period 13 years long (from June 2002 to December 2015), as shown in Figure 2, have been considered for the analysis. Field photos (by courtesy by [PERSON] and [PERSON]- IGB Berlin, Germany) have been also used to check the river's pattern and vegetation characteristics especially during periods of times when no satellite images were available.  
Figure 1: Localization of the study reach along the Tagliamento River (images obtained from Google Earth, Image ©2016 DigitalGlobe).  
By inspecting the sequences of images reported in Figure 2 it can be observed that: (i) passing from June 2002 to July 2002 (i.e., after one month) no evident variations of the braided stream pattern occur; (ii) from June 2002 to June 2003 (i.e., after one year) very little changes of the stream pattern can be observed; (iii) from July 2003 to September 2003 some flowing channels at the upstream end of the study reach become dry but not substantial stream pattern changes can be observed; (iv) from September 2003 to June 2005 (i.e., after almost two years) no significant stream pattern variations occur; (v) passing from June 2005 to May 2011 (i.e., after almost six years) an evident stream pattern change can be observed with the formation of a bend of high curvature; (vi) from May 2011 to February 2012 the stream pattern maintains almost the same; (vii) from February 2012 to December 2015 the stream pattern presents only slightly modifications. Thus, from Figure 2 it appears clear that, for the considered study reach, the changes in stream pattern can be especially observed in June 2003, in June 2005 and in February 2012. For this reason, in the  
Figure 2: Available images from Google Earth (images obtained from Google Earth, Image ©2015 DigitalGlobe).  
present work attention has been restricted to the time period 2003-2012 and, for simplicity of exposure, in the following often only the aforementioned three images are considered.  
Based on the aforementioned considerations, the images have been grouped into two classes: class I which includes the images (from June 2002 to June 2005) detected with time intervals equal or less than three years; class II which includes the images detected with time intervals greater than two years (from June 2005 to December 2015).